synchronizeOnSession

boolean synchronizeOnSession = false：表示该控制器是否在执行时同步session，从而保证该会话的用户串行访问该控制器。一个正在执行，另一个则等待。参考最下方实例：

关于 synchronizeOnSession

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2019.01.30 14:52:23字数 363阅读 556

本文为[原创]文章，转载请标明出处。
原文链接：https://weyunx.com/2019/01/22/gitlab-install/
原文出自微云的技术博客

最近在维护一个老项目，发现了一个问题。我们新增了一个耗时较久的复杂查询的功能，页面采用了ajax异步请求数据，但是请求未返回之前，点击页面其他功能都只能打开空白页，必须等待之前的数据返回后才能开始加载，整个过程是串行等待，调试过程中发现服务器仅分配了一个线程给该用户。故查看了一下原始代码，发现web.xml中配置了如下参数：

<init-param>
    <param-name>synchronizeOnSession</param-name>
    <param-value>true</param-value>
</init-param>

看了一下spring mvc 的说明文档，仅找到一处说明：

Enforces the presence of a session. As a consequence, such an argument is never null. Note that session access is not thread-safe. Consider setting the RequestMappingHandlerAdapter instance’s synchronizeOnSession flag to true if multiple requests are allowed to concurrently access a session.

因为 session 是非线程安全的，如果需要保证用户能够在多次请求中正确的访问同一个 session ，就要将 synchronizeOnSession 设置为 TRUE 。

所以此处把synchronizeOnSession 改为 false 后，问题随之解决，调试中可以看到服务器为用户分配了多个线程。

参考最下方实例：

==========================

https://qiita.com/siumennel/items/f7d0973a0b6acbfd94b4

spring synchronizeOnSession example

JavaspringexamplesynchronizeOnSessionMappingHandler

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to run this synchronizeOnSession example:

• set adapter.setSynchronizeOnSession(true) in MyPostProcessor
• run http://localhost:8080/sleep
• run http://localhost:8080/xxx
• then xxx will wait for sleep wake up!

or test the synchronizeOnSession = false

• set adapter.setSynchronizeOnSession(false) in MyPostProcessor
• run http://localhost:8080/sleep
• run http://localhost:8080/xxx
• then xxx will NOT wait for sleep wake up!

DemoApplication.java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ImportResource;

@SpringBootApplication
@Configuration
@ImportResource("servlet-context.xml")
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

HelloWorldController.java

package com.example.demo;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.apache.tomcat.util.http.parser.Cookie;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 *  * Spring Boot HelloWorld.  synchronizeOnSession example
 */
@RestController
public class HelloWorldController {
    @RequestMapping(value = "/{param}")
    public String sayHello(@PathVariable String param, HttpServletRequest request, HttpSession session) {
        System.out.println("param=" + param);

        Object id = session.getId();
        if (id == null) {
            System.out.println("session not exist " + id);
            //session.setAttribute("p", p);
        } else {
            System.out.println("session existed ，id=" + id);
            if (param.equals("sleep")) {
                try {
                    Thread.sleep(15000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                System.out.println("wake up!");
            }
        }
        return "Hello,World! " + param;
    }
}

MyPostProcessor.java

package com.example.demo;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;

@Component
public class MyPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {
        if (bean instanceof RequestMappingHandlerAdapter) {
            RequestMappingHandlerAdapter adapter = (RequestMappingHandlerAdapter) bean;
            adapter.setSynchronizeOnSession(true);
        }

        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

servlet-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <context:property-placeholder
        location="classpath:*.properties" />
    <context:component-scan
        base-package="com.example.demo.MyPostProcessor" />

</beans>

details ref: https://github.com/siumennel/demo
https://dzone.com/articles/creating-a-spring-boot-project-with-eclipse-and-ma