Get请求

HttpGet请求响应的一般步骤：
1). 创建HttpClient对象,可以使用HttpClients.createDefault()；
2).
如果是无参数的GET请求：
直接使用构造方法HttpGet(String url)创建HttpGet对象即可；
如果是带参数GET请求：
先使用URIBuilder(String url)创建对象，
再调用addParameter(String param, String value)，或setParameter(String param, String value)来设置请求参数，
并调用build()方法构建一个URI对象。

只有构造方法HttpGet(URI uri)来创建HttpGet对象。

3). 创建HttpResponse：
调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。
调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头；
调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。
程序可通过该对象获取服务器的响应内容，通过调用getStatusLine().getStatusCode()可以获取响应状态码。
4). 释放连接。

无参

例：

先从​​https://mvnrepository.com/​​maven资源站上提取httpclient相关源码，编辑.xml文件。

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>cn.itcast</groupId>
    <artifactId>itcast-crawler-first</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>4.5.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
        </dependency>

    </dependencies>

</project>

再创建个.Java测试类

package cn.csdn.crawlar.test;

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;

public class HttpGetTest {

    public static void main(String[] args) {
        //创建HttpClient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();

        //创建HttpGet对象，设置url访问地址
        String uri = 
        HttpGet httpGet = new HttpGet(uri);

        //try/catch/finally : Ctrl+Alt+T
        CloseableHttpResponse response = null;
        try {
            //使用HttpClient发起请求，获取response
            response = httpClient.execute(httpGet);

            //解析响应
            if (response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity(), "utf8");
                System.out.println(content.length());
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭response
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

在运行后的控制面上，将会找出如图所示的一些内容：
首行是Get请求，接着会发现下面有 HTTP/1.1 200 OK[\r][\n] ，200则表示请求成功。

java爬虫.HttpClient.Get请求_java

含参

package cn.csdn.crawlar.test;

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;

public class HttpGetTest含参 {

    public static void main(String[] args) throws Exception {
        //创建HttpClient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();

        //设置请求地址是：https://www.icourse163.org/search.htm?search=java#/
        //创建URI地址
        String string="https://www.icourse163.org/search.htm";
        URIBuilder uriBuilder = new URIBuilder( string );

        //设置参数
        String param="search",value="java";
        uriBuilder.setParameter(param,value );

        //创建HttpGet对象，设置url访问地址
        HttpGet httpGet = new HttpGet(uriBuilder.build());

        //发起请求
        System.out.println("发起请求的信息"+httpGet);

        //try/catch/finally : Ctrl+Alt+T
        CloseableHttpResponse response = null;
        try {
            //使用HttpClient发起请求，获取response
            response = httpClient.execute(httpGet);

            //解析响应
            if (response.getStatusLine().getStatusCode() == 200) {
                String content = EntityUtils.toString(response.getEntity(), "utf8");
                System.out.println(content.length());
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭response
            try {
                response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

结果也会显示出有一些基础的设置，以及访问网站的相关链接

java爬虫.HttpClient.Get请求_maven_02