java json转实体 java json转换工具

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数码悟透 2023-08-15 14:37:54

文章标签 java json转实体字符串 java gson xml 文章分类 Java 后端开发

java对象和json转换三种工具类汇总

说明:

去年的时候就像总结json工具类的,不然每次用到都需要百度,好麻烦,这次总结了三种工具类详细的用法

准备工作

1.准备springboot工程

2.引入依赖

jackson是springboot默认json转换方式的工具类

Gson,是google的json工具类,我们需要自己引入

FastJson是阿里的json工具类,需要问哦们手动引入

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <spring-boot.version>2.3.7.RELEASE</spring-boot.version>
    </properties>

    <dependencies>
        <!--springfox swagger官方Starter-->
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-boot-starter</artifactId>
            <version>3.0.0</version>
        </dependency>
        <!--引入开源工具库hutool-->
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.6.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.72</version>
        </dependency>
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.8.5</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.6</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.1</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring-boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.3.7.RELEASE</version>
                <configuration>
                    <mainClass>com.example.demo.DemoApplication</mainClass>
                </configuration>
                <executions>
                    <execution>
                        <id>repackage</id>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

3.准备测试的java bean

@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class Demo {
    private Integer id;
    private String userName;
    @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
    @DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    private Date bir;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class DemoOne {
    private Integer id;
    private String userName;
    @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
    @DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    private Date bir;
    private Double salary;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class DemoThree {
    private Integer id;
    private String userName;
    @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
    @DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    private Date bir;
    private Double salary;
    private List<Demo> demoList;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class DemoTwo {
    private Integer id;
    private String userName;
    @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
    @DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    private Date bir;
    private Double salary;
    private Demo demo;
}

Jackson测试

import cn.hutool.core.bean.BeanUtil;
import com.example.demo.model.Demo;
import com.example.demo.model.DemoOne;
import com.example.demo.model.DemoThree;
import com.example.demo.model.DemoTwo;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.*;

/**
 * 测试jackson工具类ObjectMapper的api
 * json和java对象互相转换
 */
@SpringBootTest
public class JacksonTest {
    /**
     * 获取jackson进行java和json转换的工具类ObjectMapper
     */
    public ObjectMapper getObjMapper() {
        return new ObjectMapper();
    }

    public List<DemoOne> getList() {
        List<DemoOne> demoOneList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            DemoOne demoOne =
                    new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("userName--" + i);
            demoOneList.add(demoOne);
        }
        return demoOneList;
    }

    public Map<String, Object> getMap() {
        HashMap<String, Object> map = new HashMap<>();
        DemoOne demoOne = new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("张三");
        BeanUtil.copyProperties(demoOne, map);
        return map;
    }

    public List<Map<String, Object>> getListMap() {
        List<Map<String, Object>> listMap = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            DemoOne demoOne =
                    new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("zhangsan--" + i);
            HashMap<String, Object> map = new HashMap<>();
            BeanUtil.copyProperties(demoOne, map);
            listMap.add(map);
        }
        return listMap;
    }

    /**
     * 获取测试java bean , 并且这个java bean属性有java bean
     *
     * @return
     */
    public DemoTwo getJavaBeanFiledJavaBean() {
        Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfJavaBeanUserName");
        DemoTwo demoTwo = new DemoTwo().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                "javabeanOfNae").setDemo(demo);
        return demoTwo;
    }

    /**
     * 获取测试java bean , 并且这个java bean属性有 list
     *
     * @return
     */
    public DemoThree getJavaBeanFiledList() {
        List<Demo> demoList = new ArrayList<Demo>();
        for (int i = 0; i < 5; i++) {
            Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfListName-----" + i);
            demoList.add(demo);
        }
        DemoThree demoThree = new DemoThree().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                "javabeanOfNae").setDemoList(demoList);
        return demoThree;
    }

    /**
     * 获取测试list , 并且这个list属性有 list
     *
     * @return
     */
    public List<DemoThree> getListFiledList() {
        List<Demo> demoList = new ArrayList<Demo>();
        List<DemoThree> demoThreeList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfListName-----" + i);
            demoList.add(demo);
        }

        for (int i = 0; i < 5; i++) {
            DemoThree demoThree = new DemoThree().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                    "javabeanOfNae").setDemoList(demoList);
            demoThreeList.add(demoThree);
        }
        return demoThreeList;
    }

    /**
     * java bean 转为json格式字符窜
     *
     * @throws JsonProcessingException
     */
    @Test
    public void testJavaBeanToJson() throws JsonProcessingException {
        ObjectMapper objMapper = getObjMapper();
        DemoOne demoOne = new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("张三");
        String demoOneToJsonString = objMapper.writeValueAsString(demoOne);
        System.out.println(demoOneToJsonString);
    }

    /**
     * json格式字符窜转为 java bean
     */
    @Test
    public void testJsonToJavaBean() throws JsonProcessingException {
        String jsonString = "{\"id\":1,\"userName\":\"张三\",\"bir\":\"2021-04-25 09:58:53\",\"salary\":10000.0}";
        ObjectMapper objMapper = getObjMapper();
        DemoOne demoOne = objMapper.readValue(jsonString, DemoOne.class);
        System.out.println(demoOne);
    }

    /**
     * java中list<T> T为基础数据类型 转为json
     */
    @Test
    public void testListBaseDataToJsonString() throws JsonProcessingException {
        List<String> listString = new ArrayList<>();
        listString.add("AAAA");
        listString.add("BBBB");
        listString.add("CCCC");
        ObjectMapper objMapper = getObjMapper();
        String stringToJsonString = objMapper.writeValueAsString(listString);
        System.out.println(stringToJsonString);
    }

    /**
     * java中list<T> T为基础数据类型 转为json
     */
    @Test
    public void testJsonStringToListString() throws JsonProcessingException {
        ObjectMapper objMapper = getObjMapper();
        String stringJsonString = "[\"AAAA\",\"BBBB\",\"CCCC\"]";
        List list = objMapper.readValue(stringJsonString, List.class);
        System.out.println("打印list<String>集合的数据");
        System.out.println(list);
        String strIndex1 = (String) list.get(1);
        System.out.println("List<String>中索引为1的值");
        System.out.println(strIndex1);
    }

    /**
     * java中list集合转为json格式字符窜
     */
    @Test
    public void testListToJson() throws JsonProcessingException {
        List<DemoOne> demoOneList = getList();
        ObjectMapper objMapper = getObjMapper();
        String listJsonString = objMapper.writeValueAsString(demoOneList);
        System.out.println(listJsonString);
    }

    /**
     * json格式字符窜转换为java list<T> T为自定义实体类
     * 报错
     * java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.demo.model.DemoOne
     */
    @Test
    public void testJsonToListWrong() throws JsonProcessingException {
        String listJsonString = "[{\"id\":1,\"userName\":\"userName--0\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--1\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--2\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--3\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--4\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0}]\n";
        ObjectMapper objMapper = getObjMapper();
        List list = objMapper.readValue(listJsonString, List.class);
        System.out.println("打印出List<DemoOne>数据");
        DemoOne demoOne = (DemoOne) list.get(1);
        System.out.println("打印出List<DemoOne>集合索引为1的数据");
        System.out.println(demoOne);
    }

    /**
     * json格式字符窜转换为java list<T> T为自定义实体类
     */
    @Test
    public void testJsonToList() throws JsonProcessingException {
        String listJsonString = "[{\"id\":1,\"userName\":\"userName--0\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--1\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--2\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--3\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--4\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0}]\n";
        ObjectMapper objMapper = getObjMapper();
        /**
         * 注意此处引入的是
         * import com.fasterxml.jackson.core.type.TypeReference;
         */
        /**
         * 使用匿名内部类方式声明TypeReference
         */
        TypeReference<List<DemoOne>> listDemoTypeReference = new TypeReference<List<DemoOne>>() {
        };
        /**
         * 使用自定义TypeReference方式指明json字符窜转换后的数据类型
         */
        ListDemoOneTypeReference mylistDemoOneTypeReference = new ListDemoOneTypeReference();
        List<DemoOne> list = objMapper.readValue(listJsonString, listDemoTypeReference);
        List<DemoOne> mylist = objMapper.readValue(listJsonString, mylistDemoOneTypeReference);
        System.out.println("方式一:打印出List<DemoOne>数据");
        System.out.println(list);
        System.out.println("方式二:打印出List<DemoOne>数据");
        System.out.println(mylist);
        DemoOne demoOne = list.get(1);
        DemoOne mydemoOne = mylist.get(1);
        System.out.println("方式一:打印出List<DemoOne>集合索引为1的数据");
        System.out.println(demoOne);
        System.out.println("方式二:打印出List<DemoOne>集合索引为1的数据");
        System.out.println(mydemoOne);
    }

    /**
     * java bean中属性有java bean ,转为json格式的字符窜
     */
    @Test
    public void testJavaBeanFiledJavaBeanToJsonString() throws JsonProcessingException {
        DemoTwo demoTwo = getJavaBeanFiledJavaBean();
        System.out.println("javabean信息");
        System.out.println(demoTwo);
        System.out.println("转为json后的数据");
        ObjectMapper objMapper = getObjMapper();
        String jsonString = objMapper.writeValueAsString(demoTwo);
        System.out.println(jsonString);
    }

    /**
     * json格式的字符窜 转为  java bean中属性有java bean
     */
    @Test
    public void testJsonStringToJavaBeanFiledJavaBean() throws JsonProcessingException {
        String jsonString = "{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 10:43:55\"," +
                "\"salary\":10000.0,\"demo\":{\"id\":1,\"userName\":\"filedOfJavaBeanUserName\",\"bir\":\"2021-04-25 " +
                "10:43:55\"}}\n";
        ObjectMapper objMapper = getObjMapper();
        DemoTwo demoTwo = objMapper.readValue(jsonString, new TypeReference<DemoTwo>() {
        });
        System.out.println("json格式字符窜转为java对象的数据:");
        System.out.println(demoTwo);
        System.out.println("json格式字符窜转为java对象中属性为javabean属性的数据:");
        System.out.println(demoTwo.getDemo());
    }

    /**
     * java bean中属性有List<T> t为自定义java bean ,转为json格式的字符窜
     */
    @Test
    public void testJavaBeanFiledListToJsonString() throws JsonProcessingException {
        DemoThree demoThree = getJavaBeanFiledList();
        ObjectMapper objMapper = getObjMapper();
        String jsonString = objMapper.writeValueAsString(demoThree);
        System.out.println("javabean信息");
        System.out.println(demoThree);
        System.out.println("转为json后的数据");
        System.out.println(jsonString);
    }

    /**
     * json格式的字符窜 转为 java bean中属性有List<T> t为自定义java bean
     */
    @Test
    public void testJsonStringToJavaBeanFiledList() throws JsonProcessingException {
        String jsonString = "{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 10:51:48\"," +
                "\"salary\":10000" +
                ".0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\",\"bir\":\"2021-04-25 10:51:48\"}," +
                "{\"id\":1,\"userName\":\"filedOfListName-----1\",\"bir\":\"2021-04-25 10:51:48\"},{\"id\":1," +
                "\"userName\":\"filedOfListName-----2\",\"bir\":\"2021-04-25 10:51:48\"},{\"id\":1," +
                "\"userName\":\"filedOfListName-----3\",\"bir\":\"2021-04-25 10:51:48\"},{\"id\":1," +
                "\"userName\":\"filedOfListName-----4\",\"bir\":\"2021-04-25 10:51:48\"}]}\n";
        ObjectMapper objMapper = getObjMapper();
        DemoThree demoThree = objMapper.readValue(jsonString, new TypeReference<DemoThree>() {
        });
        System.out.println("转换后的javabean信息");
        System.out.println(demoThree);
        System.out.println("转换后的javabean中list中信息");
        System.out.println(demoThree.getDemoList());
        System.out.println("转换后的javabean中list中索引为2的javabean信息");
        System.out.println(demoThree.getDemoList().get(2));
    }

    /**
     * list属性有 list 转为 json格式字符窜
     */
    @Test
    public void testlistFiledListToJsonString() throws JsonProcessingException {
        List<DemoThree> listFiledList = getListFiledList();
        ObjectMapper objMapper = getObjMapper();
        String stringJson = objMapper.writeValueAsString(listFiledList);
        System.out.println("list信息");
        System.out.println(listFiledList);
        System.out.println("转为json后的数据");
        System.out.println(stringJson);
    }

    /**
     * json字符窜 转为  list 属性 中有list
     */
    @Test
    public void testJsonStringTolistFiledList() throws JsonProcessingException {
        String jsonString = "[{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 11:22:26\"," +
                "\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]}]\n";
        ObjectMapper objMapper = getObjMapper();
        List<DemoThree> demoThreeList = objMapper.readValue(jsonString, new TypeReference<List<DemoThree>>() {
        });
        System.out.println("转换后的list信息");
        System.out.println(demoThreeList);
        System.out.println("转换后的list索引为2信息");
        System.out.println(demoThreeList.get(2));
        System.out.println("转换后的list索引为2属性中list中信息");
        System.out.println(demoThreeList.get(2).getDemoList());
        System.out.println("转换后的list索引为2属性中list索引为2信息");
        System.out.println(demoThreeList.get(2).getDemoList().get(2));
    }
    /**
     * map 转换为 json格式字符窜
     */
    @Test
    public void testMapToJsonString() throws JsonProcessingException {
        Map<String, Object> map = getMap();
        ObjectMapper objMapper = getObjMapper();
        String jsonString = objMapper.writeValueAsString(map);
        System.out.println("map信息");
        System.out.println(map);
        System.out.println("map转为json格式后:");
        System.out.println(jsonString);
    }
    /**
     * json 格式转map
     */
    @Test
    public void testJsonStringToMap() throws JsonProcessingException {
        String jsonString = "{\"bir\":1619328801393,\"id\":1,\"userName\":\"张三\",\"salary\":10000.0}";
        ObjectMapper objMapper = getObjMapper();
        HashMap map = objMapper.readValue(jsonString, HashMap.class);
        System.out.println("json格式字符串转map对象");
        System.out.println(map);
    }

    /**
     *list<map> 转为 json格式的字符窜
     */
    @Test
    public void testListMapToJsonString() throws JsonProcessingException {
        List<Map<String, Object>> listMap = getListMap();
        ObjectMapper objMapper = getObjMapper();
        String jsonString = objMapper.writeValueAsString(listMap);
        System.out.println("list<map>的数据:");
        System.out.println(listMap);
        System.out.println("list<map>转为json字符窜的数据:");
        System.out.println(jsonString);
    }
    /**
     * json格式字符窜 转为 list<map>
     */
    @Test
    public void testJsonStringToListMap() throws JsonProcessingException {
        String jsonString = "[{\"bir\":1619329384863,\"id\":1,\"userName\":\"zhangsan--0\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--1\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--2\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--3\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--4\",\"salary\":10000.0}]\n";
        ObjectMapper objMapper = getObjMapper();
        List<Map> listMap = objMapper.readValue(jsonString, new TypeReference<List<Map>>() {
        });
        System.out.println("json格式字符窜转为list<map>");
        System.out.println(listMap);
    }
}

需要的别的辅助类

/**
 * @author shaoming
 * @Date: 2021/4/25 09:24
 * @Description:
 * Jackson声明自定义TypeReference指明json转为java对象的数据类型
 */
public class ListDemoOneTypeReference extends TypeReference<List<DemoOne>> {
}

FastJson测试

import cn.hutool.core.bean.BeanUtil;
import com.alibaba.fastjson.JSON;
import com.example.demo.model.Demo;
import com.example.demo.model.DemoOne;
import com.example.demo.model.DemoThree;
import com.example.demo.model.DemoTwo;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.jupiter.api.Test;
import java.util.*;

/**
 * 测试fastjson工具类JSON的api
 * json和java对象互相转换
 */
public class FastJsonTest {

    public List<DemoOne> getList() {
        List<DemoOne> demoOneList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            DemoOne demoOne =
                    new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("userName--" + i);
            demoOneList.add(demoOne);
        }
        return demoOneList;
    }

    public Map<String, Object> getMap() {
        HashMap<String, Object> map = new HashMap<>();
        DemoOne demoOne = new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("张三");
        BeanUtil.copyProperties(demoOne, map);
        return map;
    }

    public List<Map<String, Object>> getListMap() {
        List<Map<String, Object>> listMap = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            DemoOne demoOne =
                    new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("zhangsan--" + i);
            HashMap<String, Object> map = new HashMap<>();
            BeanUtil.copyProperties(demoOne, map);
            listMap.add(map);
        }
        return listMap;
    }

    /**
     * 获取测试java bean , 并且这个java bean属性有java bean
     *
     * @return
     */
    public DemoTwo getJavaBeanFiledJavaBean() {
        Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfJavaBeanUserName");
        DemoTwo demoTwo = new DemoTwo().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                "javabeanOfNae").setDemo(demo);
        return demoTwo;
    }

    /**
     * 获取测试java bean , 并且这个java bean属性有 list
     *
     * @return
     */
    public DemoThree getJavaBeanFiledList() {
        List<Demo> demoList = new ArrayList<Demo>();
        for (int i = 0; i < 5; i++) {
            Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfListName-----" + i);
            demoList.add(demo);
        }
        DemoThree demoThree = new DemoThree().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                "javabeanOfNae").setDemoList(demoList);
        return demoThree;
    }

    /**
     * 获取测试list , 并且这个list属性有 list
     *
     * @return
     */
    public List<DemoThree> getListFiledList() {
        List<Demo> demoList = new ArrayList<Demo>();
        List<DemoThree> demoThreeList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfListName-----" + i);
            demoList.add(demo);
        }

        for (int i = 0; i < 5; i++) {
            DemoThree demoThree = new DemoThree().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                    "javabeanOfNae").setDemoList(demoList);
            demoThreeList.add(demoThree);
        }
        return demoThreeList;
    }

    /**
     * java bean 转为json格式字符窜
     *
     * @throws JsonProcessingException
     */
    @Test
    public void testJavaBeanToJson()  {
        DemoOne demoOne = new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("张三");
        System.out.println("java bean转为json格式字符窜");
        String JsonString = JSON.toJSONString(demoOne);
        System.out.println(JsonString);
        System.out.println("java bean转为json格式字符窜,使用PrettyFormat(true表示格式化json格式)");
        String jsonStringPrettyFormat = JSON.toJSONString(demoOne, true);
        System.out.println(jsonStringPrettyFormat);
    }

    /**
     * json格式字符窜转为 java bean
     */
    @Test
    public void testJsonToJavaBean() throws JsonProcessingException {
        String jsonString = "{\"bir\":1619329956814,\"id\":1,\"salary\":10000.0,\"userName\":\"张三\"}";
        DemoOne demoOne = JSON.parseObject(jsonString, DemoOne.class);
        System.out.println("json字符窜转为java bean");
        System.out.println(demoOne);
    }

    /**
     * java中list<T> T为基础数据类型 转为json
     */
    @Test
    public void testListBaseDataToJsonString() throws JsonProcessingException {
        List<String> listString = new ArrayList<>();
        listString.add("AAAA");
        listString.add("BBBB");
        listString.add("CCCC");
        String jsonString = JSON.toJSONString(listString, true);
        System.out.println("list<string>转为json格式字符窜,使用PrettyFormat(true表示格式化json格式)");
        System.out.println(jsonString);
    }

    /**
     * java中list<T> T为基础数据类型 转为json
     */
    @Test
    public void testJsonStringToListString() throws JsonProcessingException {
        String jsonString = "[\"AAAA\",\"BBBB\",\"CCCC\"]";
        List<String> stringList
                = JSON.parseArray(jsonString, String.class);
        System.out.println("打印list<String>集合的数据");
        System.out.println(stringList);
        String strIndex1 = (String) stringList.get(1);
        System.out.println("List<String>中索引为1的值");
        System.out.println(strIndex1);
    }

    /**
     * List<T> T为java bean 转为json格式字符窜
     */
    @Test
    public void testListToJson() throws JsonProcessingException {
        List<DemoOne> demoOneList = getList();
        String jsonString = JSON.toJSONString(demoOneList);
        System.out.println("List<T> T为javabean 转 json格式字符窜");
        System.out.println(jsonString);
    }

    /**
     * json格式字符窜转换为java list<T> T为自定义实体类
     * 报错
     * java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.demo.model.DemoOne
     * 如果json数据为集合形式,那么我们需要调用JSON.ParaseArray(String , class)这个api
     * 而不是JSON.ParseObject(String,class)这个api
     */
    @Test
    public void testJsonToListWrong() throws JsonProcessingException {
        String jsonString = "[{\"bir\":1619330606019,\"id\":1,\"salary\":10000.0,\"userName\":\"userName--0\"}," +
                "{\"bir\":1619330606019,\"id\":1,\"salary\":10000.0,\"userName\":\"userName--1\"}," +
                "{\"bir\":1619330606019,\"id\":1,\"salary\":10000.0,\"userName\":\"userName--2\"}," +
                "{\"bir\":1619330606019,\"id\":1,\"salary\":10000.0,\"userName\":\"userName--3\"}," +
                "{\"bir\":1619330606019,\"id\":1,\"salary\":10000.0,\"userName\":\"userName--4\"}]\n";
        List list = JSON.parseObject(jsonString, List.class);
        System.out.println("打印出List<DemoOne>数据");
        DemoOne demoOne = (DemoOne) list.get(1);
        System.out.println("打印出List<DemoOne>集合索引为1的数据");
        System.out.println(demoOne);
    }

    /**
     * json格式字符窜转换为java list<T> T为自定义实体类
     * 说明:
     * 如果json字符窜是集合形式,我们需要使用JSON.ParseArray(String jsonString,Class)这个api
     */
    @Test
    public void testJsonToList() {
        String jsonString = "[{\"id\":1,\"userName\":\"userName--0\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--1\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--2\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--3\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--4\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0}]\n";
        List<DemoOne> demoOneList = JSON.parseArray(jsonString, DemoOne.class);
        System.out.println("json格式字符窜转为List<T> T为java bean");
        System.out.println(demoOneList);
    }

    /**
     * java bean中属性有java bean ,转为json格式的字符窜
     */
    @Test
    public void testJavaBeanFiledJavaBeanToJsonString() throws JsonProcessingException {
        DemoTwo demoTwo = getJavaBeanFiledJavaBean();
        System.out.println("javabean信息");
        System.out.println(demoTwo);
        System.out.println("转为json后的数据");
        String jsonString = JSON.toJSONString(demoTwo);
        System.out.println(jsonString);
    }

    /**
     * json格式的字符窜 转为  java bean中属性有java bean
     */
    @Test
    public void testJsonStringToJavaBeanFiledJavaBean() throws JsonProcessingException {
        String jsonString = "{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 10:43:55\"," +
                "\"salary\":10000.0,\"demo\":{\"id\":1,\"userName\":\"filedOfJavaBeanUserName\",\"bir\":\"2021-04-25 " +
                "10:43:55\"}}\n";
        System.out.println("json格式字符窜转为java对象的数据:");
        DemoTwo demoTwo = JSON.parseObject(jsonString, DemoTwo.class);
        System.out.println(demoTwo);
        System.out.println("json格式字符窜转为java对象中属性为javabean属性的数据:");
        System.out.println(demoTwo.getDemo());
    }

    /**
     * java bean中属性有List<T> t为自定义java bean ,转为json格式的字符窜
     */
    @Test
    public void testJavaBeanFiledListToJsonString() throws JsonProcessingException {
        DemoThree demoThree = getJavaBeanFiledList();
        String jsonString = JSON.toJSONString(demoThree);
        System.out.println("javabean信息");
        System.out.println(demoThree);
        System.out.println("转为json后的数据");
        System.out.println(jsonString);
    }

    /**
     * json格式的字符窜 转为 java bean中属性有List<T> t为自定义java bean
     */
    @Test
    public void testJsonStringToJavaBeanFiledList() throws JsonProcessingException {
        String jsonString = "{\"bir\":1619331360905,\"demoList\":[{\"bir\":1619331360905,\"id\":1," +
                "\"userName\":\"filedOfListName-----0\"},{\"bir\":1619331360905,\"id\":1," +
                "\"userName\":\"filedOfListName-----1\"},{\"bir\":1619331360905,\"id\":1," +
                "\"userName\":\"filedOfListName-----2\"},{\"bir\":1619331360905,\"id\":1," +
                "\"userName\":\"filedOfListName-----3\"},{\"bir\":1619331360905,\"id\":1," +
                "\"userName\":\"filedOfListName-----4\"}],\"id\":1,\"salary\":10000.0,\"userName\":\"javabeanOfNae\"}\n";
        DemoThree demoThree = JSON.parseObject(jsonString, DemoThree.class);
        System.out.println("转换后的javabean信息");
        System.out.println(demoThree);
        System.out.println("转换后的javabean中list中信息");
        System.out.println(demoThree.getDemoList());
        System.out.println("转换后的javabean中list中索引为2的javabean信息");
        System.out.println(demoThree.getDemoList().get(2));
    }

    /**
     * list属性有 list 转为 json格式字符窜
     */
    @Test
    public void testlistFiledListToJsonString()  {
        List<DemoThree> listFiledList = getListFiledList();
        String jsonString = JSON.toJSONString(listFiledList);
        System.out.println("list信息");
        System.out.println(listFiledList);
        System.out.println("转为json后的数据");
        System.out.println(jsonString);
    }

    /**
     * json字符窜 转为  list 属性 中有list
     */
    @Test
    public void testJsonStringTolistFiledList()  {
        String jsonString = "[{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 11:22:26\"," +
                "\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]}]\n";
        List<DemoThree> demoThreeList = JSON.parseArray(jsonString, DemoThree.class);
        System.out.println("转换后的list信息");
        System.out.println(demoThreeList);
        System.out.println("转换后的list索引为2信息");
        System.out.println(demoThreeList.get(2));
        System.out.println("转换后的list索引为2属性中list中信息");
        System.out.println(demoThreeList.get(2).getDemoList());
        System.out.println("转换后的list索引为2属性中list索引为2信息");
        System.out.println(demoThreeList.get(2).getDemoList().get(2));
    }

    /**
     * map 转换为 json格式字符窜
     */
    @Test
    public void testMapToJsonString() {
        Map<String, Object> map = getMap();
        String jsonString = JSON.toJSONString(map);
        System.out.println("map信息");
        System.out.println(map);
        System.out.println("map转为json格式后:");
        System.out.println(jsonString);
    }

    /**
     * json 格式转map
     */
    @Test
    public void testJsonStringToMap() throws JsonProcessingException {
        String jsonString = "{\"bir\":1619328801393,\"id\":1,\"userName\":\"张三\",\"salary\":10000.0}";
        Map map = JSON.parseObject(jsonString, Map.class);
        System.out.println("json格式字符串转map对象");
        System.out.println(map);
    }

    /**
     * list<map> 转为 json格式的字符窜
     */
    @Test
    public void testListMapToJsonString() throws JsonProcessingException {
        List<Map<String, Object>> listMap = getListMap();
        String jsonString = JSON.toJSONString(listMap);
        System.out.println("list<map>的数据:");
        System.out.println(listMap);
        System.out.println("list<map>转为json字符窜的数据:");
        System.out.println(jsonString);
    }

    /**
     * json格式字符窜 转为 list<map>
     */
    @Test
    public void testJsonStringToListMap() {
        String jsonString = "[{\"bir\":1619329384863,\"id\":1,\"userName\":\"zhangsan--0\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--1\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--2\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--3\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--4\",\"salary\":10000.0}]\n";
        List<Map> listMap = JSON.parseArray(jsonString, Map.class);
        System.out.println("json格式字符窜转为list<map>");
        System.out.println(listMap);
        System.out.println("获取list集合第一个元素的map,再map中key为id的value的值");
        Map map = (Map) listMap.get(1);
        System.out.println(map);
        Object id = map.get("id");
        System.out.println(id);
    }
}

Gson测试

package com.example.demo.json;

import cn.hutool.core.bean.BeanUtil;
import com.alibaba.fastjson.JSON;
import com.example.demo.model.Demo;
import com.example.demo.model.DemoOne;
import com.example.demo.model.DemoThree;
import com.example.demo.model.DemoTwo;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.*;

/**
 * 测试GSON工具类GSON的api
 * json和java对象互相转换
 */
@SpringBootTest
public class GsonTest {
    public Gson getGson() {
        return new Gson();
    }

    public Gson getDateFormatGson() {
        Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm:ss").create(); //按照 yyyy-MM-dd HH:mm:ss格式化。
        return gson;
    }

    public List<DemoOne> getList() {
        List<DemoOne> demoOneList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            DemoOne demoOne =
                    new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("userName--" + i);
            demoOneList.add(demoOne);
        }
        return demoOneList;
    }

    public Map<String, Object> getMap() {
        HashMap<String, Object> map = new HashMap<>();
        DemoOne demoOne = new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("张三");
        BeanUtil.copyProperties(demoOne, map);
        return map;
    }

    public List<Map<String, Object>> getListMap() {
        List<Map<String, Object>> listMap = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            DemoOne demoOne =
                    new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("zhangsan--" + i);
            HashMap<String, Object> map = new HashMap<>();
            BeanUtil.copyProperties(demoOne, map);
            listMap.add(map);
        }
        return listMap;
    }

    /**
     * 获取测试java bean , 并且这个java bean属性有java bean
     *
     * @return
     */
    public DemoTwo getJavaBeanFiledJavaBean() {
        Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfJavaBeanUserName");
        DemoTwo demoTwo = new DemoTwo().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                "javabeanOfNae").setDemo(demo);
        return demoTwo;
    }

    /**
     * 获取测试java bean , 并且这个java bean属性有 list
     *
     * @return
     */
    public DemoThree getJavaBeanFiledList() {
        List<Demo> demoList = new ArrayList<Demo>();
        for (int i = 0; i < 5; i++) {
            Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfListName-----" + i);
            demoList.add(demo);
        }
        DemoThree demoThree = new DemoThree().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                "javabeanOfNae").setDemoList(demoList);
        return demoThree;
    }

    /**
     * 获取测试list , 并且这个list属性有 list
     *
     * @return
     */
    public List<DemoThree> getListFiledList() {
        List<Demo> demoList = new ArrayList<Demo>();
        List<DemoThree> demoThreeList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            Demo demo = new Demo().setBir(new Date()).setId(1).setUserName("filedOfListName-----" + i);
            demoList.add(demo);
        }

        for (int i = 0; i < 5; i++) {
            DemoThree demoThree = new DemoThree().setId(1).setBir(new Date()).setSalary(10000.0).setUserName(
                    "javabeanOfNae").setDemoList(demoList);
            demoThreeList.add(demoThree);
        }
        return demoThreeList;
    }

    /**
     * java bean 转为json格式字符窜
     *
     * @throws JsonProcessingException
     */
    @Test
    public void testJavaBeanToJson() {
        DemoOne demoOne = new DemoOne().setBir(new Date()).setId(1).setSalary(10000.0).setUserName("张三");
        Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm:ss").create(); //按照 yyyy-MM-dd HH:mm:ss格式化。Gson
        /**
         * 如果gson不进行时间格式化处理可能会报错
         * com.google.gson.JsonSyntaxException
         */
//        Gson gson = new Gson();
        String jsonString = gson.toJson(demoOne);
        System.out.println("java bean转为json格式字符窜");
        System.out.println(jsonString);
    }
    /*
    控制台打印:
     java bean转为json格式字符窜
{"id":1,"userName":"张三","bir":"2021-04-25 15:40:31","salary":10000.0}
     */

    /**
     * json格式字符窜转为 java bean
     */
    @Test
    public void testJsonToJavaBean() {
        String jsonString = "{\"id\":1,\"userName\":\"张三\",\"bir\":\"2021-04-25 15:36:49\",\"salary\":10000.0}";
        Gson gson = getGson();
        DemoOne demoOne = gson.fromJson(jsonString, DemoOne.class);
        System.out.println("json字符窜转为java bean");
        System.out.println(demoOne);
    }
/*
json字符窜转为java bean
DemoOne(id=1, userName=张三, bir=Sun Apr 25 15:36:49 CST 2021, salary=10000.0)
 */

    /**
     * java中list<T> T为基础数据类型 转为json
     */
    @Test
    public void testListBaseDataToJsonString() throws JsonProcessingException {
        List<String> listString = new ArrayList<>();
        listString.add("AAAA");
        listString.add("BBBB");
        listString.add("CCCC");
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(listString);
        System.out.println("list<string>转为json格式字符窜,使用PrettyFormat(true表示格式化json格式)");
        System.out.println(jsonString);
    }

    /**
     * java中list<T> T为基础数据类型 转为json
     */
    @Test
    public void testJsonStringToListString() throws JsonProcessingException {
        String jsonString = "[\"AAAA\",\"BBBB\",\"CCCC\"]";
        Gson gson = getDateFormatGson();
        List stringList = gson.fromJson(jsonString, List.class);
        System.out.println("打印list<String>集合的数据");
        System.out.println(stringList);
        String strIndex1 = (String) stringList.get(1);
        System.out.println("List<String>中索引为1的值");
        System.out.println(strIndex1);
    }

    /**
     * List<T> T为java bean 转为json格式字符窜
     */
    @Test
    public void testListToJson() {
        List<DemoOne> demoOneList = getList();
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(demoOneList);
        System.out.println("List<T> T为javabean 转 json格式字符窜");
        System.out.println(jsonString);
    }

    /**
     * json格式字符窜转换为java list<T> T为自定义实体类
     */
    @Test
    public void testJsonToList() {
        String jsonString = "[{\"id\":1,\"userName\":\"userName--0\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--1\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--2\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--3\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0},{\"id\":1,\"userName\":\"userName--4\",\"bir\":\"2021-04-25 09:15:00\"," +
                "\"salary\":10000.0}]\n";
        Gson gson = getDateFormatGson();
        List<DemoOne> demoOneList = gson.fromJson(jsonString, List.class);
        System.out.println("json格式字符窜转为List<T> T为java bean");
        System.out.println(demoOneList);
        System.out.println("json格式字符窜转为List<T> T为java bean  其中索引为2的javabean的数据:");
        System.out.println(demoOneList.get(2));
    }

    /**
     * java bean中属性有java bean ,转为json格式的字符窜
     */
    @Test
    public void testJavaBeanFiledJavaBeanToJsonString() {
        DemoTwo demoTwo = getJavaBeanFiledJavaBean();
        System.out.println("javabean信息");
        System.out.println(demoTwo);
        System.out.println("转为json后的数据");
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(demoTwo);
        System.out.println(jsonString);
    }

    /**
     * json格式的字符窜 转为  java bean中属性有java bean
     */
    @Test
    public void testJsonStringToJavaBeanFiledJavaBean() {
        String jsonString = "{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 10:43:55\"," +
                "\"salary\":10000.0,\"demo\":{\"id\":1,\"userName\":\"filedOfJavaBeanUserName\",\"bir\":\"2021-04-25 " +
                "10:43:55\"}}\n";
        System.out.println("json格式字符窜转为java对象的数据:");
        Gson gson = getDateFormatGson();
        DemoTwo demoTwo = gson.fromJson(jsonString, DemoTwo.class);
        System.out.println(demoTwo);
        System.out.println("json格式字符窜转为java对象中属性为javabean属性的数据:");
        System.out.println(demoTwo.getDemo());
    }

    /**
     * java bean中属性有List<T> t为自定义java bean ,转为json格式的字符窜
     */
    @Test
    public void testJavaBeanFiledListToJsonString() {
        DemoThree demoThree = getJavaBeanFiledList();
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(demoThree);
        System.out.println("javabean信息");
        System.out.println(demoThree);
        System.out.println("转为json后的数据");
        System.out.println(jsonString);
    }

    /**
     * json格式的字符窜 转为 java bean中属性有List<T> t为自定义java bean
     */
    @Test
    public void testJsonStringToJavaBeanFiledList() throws JsonProcessingException {
        String jsonString = "{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 16:01:25\"," +
                "\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 16:01:25\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 16:01:25\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 16:01:25\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 16:01:25\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 16:01:25\"}]}";
        Gson gson = getDateFormatGson();
        DemoThree demoThree = gson.fromJson(jsonString, DemoThree.class);
        System.out.println("转换后的javabean信息");
        System.out.println(demoThree);
        System.out.println("转换后的javabean中list中信息");
        System.out.println(demoThree.getDemoList());
        System.out.println("转换后的javabean中list中索引为2的javabean信息");
        System.out.println(demoThree.getDemoList().get(2));
    }

    /**
     * list属性有 list 转为 json格式字符窜
     */
    @Test
    public void testlistFiledListToJsonString() {
        List<DemoThree> listFiledList = getListFiledList();
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(listFiledList);
        System.out.println("list信息");
        System.out.println(listFiledList);
        System.out.println("转为json后的数据");
        System.out.println(jsonString);
    }

    /**
     * json字符窜 转为  list 属性 中有list
     * 报错:
     * java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.example.demo.model
     * .DemoThree
     */
    @Test
    public void testJsonStringTolistFiledList() {
        String jsonString = "[{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 11:22:26\"," +
                "\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]},{\"id\":1,\"userName\":\"javabeanOfNae\",\"bir\":\"2021-04-25 " +
                "11:22:26\",\"salary\":10000.0,\"demoList\":[{\"id\":1,\"userName\":\"filedOfListName-----0\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----1\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----2\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----3\"," +
                "\"bir\":\"2021-04-25 11:22:26\"},{\"id\":1,\"userName\":\"filedOfListName-----4\"," +
                "\"bir\":\"2021-04-25 11:22:26\"}]}]\n";
        Gson gson = getDateFormatGson();
        /**
         * 这种情况会报错,因为没有明确指定json字符窜转换后数据的类型
         */
//        List<DemoThree> demoThreeList = gson.fromJson(jsonString, List.class);
        /**
         * 第一种方式指定json字符窜转换为java对象的数据类型
         * 指定使用的是匿名内部类的方式
         */
//        List<DemoThree> demoThreeList = gson.fromJson(jsonString, new TypeToken<List<DemoThree>>() {
//        }.getType());
        /**
         * 第一种方式指定json字符窜转换为java对象的数据类型
         * 指定使用的是匿名内部类的方式
         */
        List<DemoThree> demoThreeList = gson.fromJson(jsonString, new MyTypeToken().getType());
        System.out.println("转换后的list信息");
        System.out.println(demoThreeList);
        System.out.println("转换后的list索引为2信息");
        System.out.println(demoThreeList.get(2));
        System.out.println("转换后的list索引为2属性中list中信息");
        System.out.println(demoThreeList.get(2).getDemoList());
        System.out.println("转换后的list索引为2属性中list索引为2信息");
        System.out.println(demoThreeList.get(2).getDemoList().get(2));
    }

    /**
     * map 转换为 json格式字符窜
     */
    @Test
    public void testMapToJsonString() {
        Map<String, Object> map = getMap();
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(map);
        System.out.println("map信息");
        System.out.println(map);
        System.out.println("map转为json格式后:");
        System.out.println(jsonString);
    }

    /**
     * json 格式转map
     */
    @Test
    public void testJsonStringToMap() {
        String jsonString = "{\"bir\":1619328801393,\"id\":1,\"userName\":\"张三\",\"salary\":10000.0}";
//        String jsonString = "{bir=Sun Apr 25 16:14:45 CST 2021, id=1, userName=张三, salary=10000.0}";
        Gson gson = getDateFormatGson();
        Map map = gson.fromJson(jsonString, Map.class);
        System.out.println("json格式字符串转map对象");
        System.out.println(map);
    }

    /**
     * list<map> 转为 json格式的字符窜
     */
    @Test
    public void testListMapToJsonString() {
        List<Map<String, Object>> listMap = getListMap();
        Gson gson = getDateFormatGson();
        String jsonString = gson.toJson(listMap);
        System.out.println("list<map>的数据:");
        System.out.println(listMap);
        System.out.println("list<map>转为json字符窜的数据:");
        System.out.println(jsonString);
    }

    /**
     * json格式字符窜 转为 list<map>
     */
    @Test
    public void testJsonStringToListMap() {
        String jsonString = "[{\"bir\":1619329384863,\"id\":1,\"userName\":\"zhangsan--0\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--1\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--2\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--3\",\"salary\":10000.0}," +
                "{\"bir\":1619329384902,\"id\":1,\"userName\":\"zhangsan--4\",\"salary\":10000.0}]\n";
        Gson gson = getDateFormatGson();
        List listMap = gson.fromJson(jsonString, List.class);
        System.out.println("json格式字符窜转为list<map>");
        System.out.println(listMap);
        System.out.println("获取list集合第一个元素的map,再map中key为id的value的值");
        Map map = (Map) listMap.get(1);
        System.out.println(map);
        Object id = map.get("id");
        System.out.println(id);
    }
}

需要辅助的工具类

import com.example.demo.model.DemoThree;
import com.google.gson.reflect.TypeToken;
import java.util.Collection;
import java.util.List;

/**
 * @author shaoming
 * @Date: 2021/4/25 16:07
 * @Description:
 * Gson中定义的接口
 *用于指定json字符窜转为java对象的类型
 * 不使用这个接口报错:
 *
* java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.example.demo.model
 */
public  class MyTypeToken extends TypeToken<List<DemoThree>> {

}

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