目录结构

WebServlet 4.0_javaweb


package com.aaa.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
* Created by 张晨光 on 2020/3/20 16:01
*注解,来实现get请求 post请求的输出...
*/
@WebServlet("/login")
public class HelloServet extends HttpServlet {
//上次课的时候,重写的是service方法
//重写doGet()/doPost()方法
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// super.doGet(req, resp);
//哪个地方传过来的,是地址栏url传过来的,get请求...
System.out.println("get请求");
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// super.doPost(req, resp);
System.out.println("post请求...");
}
}

1.属性列表:

属性名

类型

描述

name

String

servlet-name,如果没有显示指定,该Servlet的取值为全限定名

value

String[]

等价于 urlPatterns 属性,与该属性不能同时使用

urlPatterns

String[]

指定Servlet url的匹配模式,等价于<url-parttern>

loadOnStartup

int

指定Servlet的加载顺序

initParams

webInitParam[]

指定初始化参数

asyncSupported

boolean

是否支持异步操作

description

String

描述

displayName

String

servlet显示名













二属性说明

1.initParams:

      initParams={@WebInitParam(paramName="zsms",paramValue="醉生梦死")//在服务器初始化的时候会打印,因为调用Init方法}

package com.kenny.servlet;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
* asyncSupported = true 是否支持异步请求
*/
@WebServlet(value = "/hello",asyncSupported = true,initParams = {
@WebInitParam(name="name",value = "Kenny"),
@WebInitParam(name="age",value = "20")
}
)
public class HelloServlet extends HttpServlet {

String name;
String age;

@Override
public void init(ServletConfig config) throws ServletException {
name = config.getInitParameter("name");
age = config.getInitParameter("age");

System.out.println("init--------- name: "+ name +" ,---------- age: "+age);

super.init(config);
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("doGet--------- name: "+ name +" ,---------- age: "+age);

resp.getWriter().write("hello,thank you "+ name+" ,and you age is "+ age);
}
}

servlet initParams 事例

2.urlPatterns/value(不可以同时使用):

      Servlet 2.5开始,一个servlet可以使用多个url-pattern规则,因此 urlPatterns 属性也支持数组配置;web.xml 配置下,是采用 servlet-mapping 和当servlet容器接收到浏览器发起的一个url请求后,容器会用url减去当前应用的上下文路径,以剩余的字符串作为servlet映射,假如url是http://localhost:8080/ServletTest/index.do,其应用上下文(context)是ServletTest。http://localhost:8080/ServletTest去掉,用剩下的/index.do部分拿来做servlet的映射匹配;url-pattern映射匹配过程是有优先顺序的(精确匹配>路径匹配>扩展名匹配>缺省匹配)而且当有一个servlet匹配成功以后,就不会去访问剩下的servlet了。

     可以使用数组方式:urlPatterns={"/servlet/url1","/servlet/url2"}

3.asyncSupported

模拟代码,可以打开多个浏览器查看

//Servlet
package com.kenny.servlet;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

@WebServlet(urlPatterns = "/async",asyncSupported = true)
public class AsyncServlet extends HttpServlet {

@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException, ServletException {
resp.setContentType("text/html;charset=UTF-8");
PrintWriter out = resp.getWriter();
out.println("进入Servlet的时间:" + new Date() + ".");
out.flush();

//在子线程中执行业务调用,并由其负责输出响应,主线程退出
AsyncContext ctx = req.startAsync();
new Thread(new Executor(ctx)).start();

out.println("结束Servlet的时间:" + new Date() + ".");
out.flush();
}
}

//模拟多线程
package com.kenny.servlet;

import javax.servlet.AsyncContext;
import java.io.PrintWriter;
import java.util.Date;

public class Executor implements Runnable {
private AsyncContext ctx = null;
public Executor(AsyncContext ctx){
this.ctx = ctx;
}

public void run(){
try {
//等待十秒钟,以模拟业务方法的执行
Thread.sleep(10000);
PrintWriter out = ctx.getResponse().getWriter();
out.println(Thread.currentThread().getId()+"----业务处理完毕的时间:" + new Date() + ".");
out.flush();
ctx.complete();
} catch (Exception e) {
e.printStackTrace();
}
}
}

支持多线程



注解源码:

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface WebServlet {
String name() default "";

String[] value() default {};

String[] urlPatterns() default {};

int loadOnStartup() default -1;

WebInitParam[] initParams() default {};

boolean asyncSupported() default false;

String smallIcon() default "";

String largeIcon() default "";

String description() default "";

String displayName() default "";
}

WebServlet 代码

@WebServlet注解用于标注在一个继承了HttpServlet类之上,属于类级别的注解。

用法形如:

@WebServlet("/DisplayHeader1")



// 扩展 HttpServlet 类

public class DisplayHeader extends HttpServlet {



// 处理 GET 方法请求的方法

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


其中 /DisplayHeader1 表示访问该servlet的 url 映射(地址)(此处为相对路径,即 “项目名称/DisplayHeader1” )。


该注解的作用等价于 在web.xml中配置的该servlet的<servlet-mapping>元素中<url-pattern>的配置,比如:

<servlet>

<!-- 类名 -->

<servlet-name>DisplayHeader</servlet-name>

<!-- 所在的包 -->

<servlet-class>test.DisplayHeader</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>DisplayHeader</servlet-name>

<!-- 访问的网址 -->

<url-pattern>/DisplayHeader2</url-pattern>

</servlet-mapping>

此时,访问如下两个路径的效果是一样的,不互斥:

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