Web开发基础_Servlet学习_0011_Servlet中的多线程安全问题与Servlet运行原理

Servlet中的多线程安全问题

Servlet运行原理

Servlet中的多线程安全问题演示

案例演示：

工程案例目录结构

pom.xml:

<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>com.study</groupId>
  <artifactId>Servlet03</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>war</packaging>
  <dependencies>
  	<dependency>
  		<groupId>javaee</groupId>
  		<artifactId>javaee-api</artifactId>
  		<version>5</version>
  	</dependency>
  </dependencies>
</project>

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
  <display-name>Servlet04</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  

  <servlet>
  	<servlet-name>suibian</servlet-name>
  	<servlet-class>web.SuibianServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>suibian</servlet-name>
  	<url-pattern>/suibian</url-pattern>
  </servlet-mapping>

</web-app>

SuibianServlet.java

package web;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SuibianServlet extends HttpServlet{
	
	private double sal = 3000;

	@Override
	protected void service(HttpServletRequest req, 
			HttpServletResponse res) throws ServletException, IOException {
		
		
		//涨工资
		sal += 100;
		
		//模拟网络延迟
		try{
			Thread.sleep(8000);
		}catch(InterruptedException e){
			e.printStackTrace();
		}
		
		//输出最新工资
		res.setContentType("text/html;charset=utf-8");
		PrintWriter pw	= res.getWriter();
		pw.println("<h1>工资："+sal+"</h1>");
		pw.close();
	}
	
	

}

同时使用两个浏览器请求同一路径：http://localhost:8080/Servlet04/suibian；会发现最终显示效果如下：

与我们希望的3100，3200不符。

IE:

Chrome：

添加线程锁后：

package web;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SuibianServlet extends HttpServlet{
	
	private double sal = 3000;

	@Override
	protected void service(HttpServletRequest req, 
			HttpServletResponse res) throws ServletException, IOException {
		
		synchronized(this){
			//涨工资
			sal += 100;
			
			//模拟网络延迟
			try{
				Thread.sleep(8000);
			}catch(InterruptedException e){
				e.printStackTrace();
			}
			
			//输出最新工资
			res.setContentType("text/html;charset=utf-8");
			PrintWriter pw	= res.getWriter();
			pw.println("<h1>工资："+sal+"</h1>");
			pw.close();
		}
		
	}
	
	

}

同时使用两个浏览器请求同一路径：http://localhost:8080/Servlet04/suibian；会发现最终显示效果如下：

与我们希望的3100，3200相符合。线程安全解决。

IE:

Chrome：

Web开发基础_Servlet学习_0011_Servlet中的多线程安全问题与Servlet运行原理

Servlet中的多线程安全问题

Servlet运行原理

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