Java多线程系列--ThreadLocal的用法(有实例)

青旅半醒 2023-10-02 13:48 24阅读 0赞

原文网址：[Java多线程系列--ThreadLocal的用法(有实例)\_IT利刃出鞘的博客-CSDN博客][Java_--ThreadLocal_IT_-CSDN]

## 简介 ##

本文用示例来介绍Java中ThreadLocal的用法。

## **方法** ##

<table style="width:491.25pt;"> 
 <tbody> 
 <tr> 
 <td style="width:95.2pt;"> 方法 </td> 
 <td style="width:62.2pt;"> 作用 </td> 
 <td style="width:312pt;"> 说明 </td> 
 </tr> 
 <tr> 
 <td style="width:95.2pt;"> void set(T value) </td> 
 <td style="width:62.2pt;"> 设置值 </td> 
 <td style="width:312pt;"> 设置线程中本地变量xxx的值 </td> 
 </tr> 
 <tr> 
 <td style="width:95.2pt;"> T get() </td> 
 <td style="width:62.2pt;"> 获取值 </td> 
 <td style="width:312pt;"> 获取线程中本地变量xxx的值 </td> 
 </tr> 
 <tr> 
 <td style="width:95.2pt;"> void remove() </td> 
 <td style="width:62.2pt;"> 删除 </td> 
 <td style="width:312pt;"> 用完ThreadLocal后要调用此方法，不然可能导致<a href="https://so.csdn.net/so/search?q=%E5%86%85%E5%AD%98&amp;spm=1001.2101.3001.7020" title="内存" rel="nofollow">内存</a>泄露。 </td> 
 </tr> 
 </tbody> 
</table>

## 实例 ##

### **单个变量** ###

package com.example.a;
 
 public class Demo {
 private static ThreadLocal<String> threadLocal = new ThreadLocal<>();
 
 static void print(String str){
 System.out.println(str + ":" + threadLocal.get());
 }
 
 public static void main(String[] args) {
 Thread thread1 = new Thread(new Runnable() {
 @Override
 public void run() {
 threadLocal.set("abc");
 print("thread1 variable");
 
 // 必须要清除，否则可能导致内存泄露
 threadLocal.remove();
 }
 });
 
 Thread thread2 = new Thread(new Runnable() {
 @Override
 public void run() {
 threadLocal.set("def");
 print("thread2 variable");
 
 // 必须要清除，否则可能导致内存泄露
 threadLocal.remove();
 }
 });
 
 thread1.start();
 thread2.start();
 }
 }

运行结果

thread1 variable:abc
    thread2 variable:def

### **多个变量** ###

package com.example.a;
 
 public class Demo {
 private static ThreadLocal<String> threadLocal = new ThreadLocal<>();
 private static ThreadLocal<String> threadLocal2 = new ThreadLocal<>();
 
 static void print(String str){
 System.out.println(str + ":" + threadLocal.get());
 System.out.println(str + ":" + threadLocal2.get());
 }
 
 public static void main(String[] args) {
 Thread thread1 = new Thread(new Runnable() {
 @Override
 public void run() {
 threadLocal.set("abc");
 threadLocal2.set("abc2");
 print("thread1 variable");
 
 // 必须要清除，否则可能导致内存泄露
 threadLocal.remove();
 threadLocal2.remove();
 }
 });
 
 Thread thread2 = new Thread(new Runnable() {
 @Override
 public void run() {
 threadLocal.set("def");
 threadLocal2.set("def2");
 print("thread2 variable");
 
 // 必须要清除，否则可能导致内存泄露
 threadLocal.remove();
 threadLocal2.remove();
 }
 });
 
 thread1.start();
 thread2.start();
 }
 }

运行结果

thread1 variable:abc
    thread1 variable:abc2
    thread2 variable:def
    thread2 variable:def2

## 实际场景 ##

**Web项目当前请求的用户信息**

见：[SpringBoot--使用ThreadLocal保存每次请求的用户信息\_springboot threadlocal保存用户信息\_IT利刃出鞘的博客-CSDN博客][SpringBoot--_ThreadLocal_springboot threadlocal_IT_-CSDN]

**数据库连接**

public Connection initialValue() {
        return DriverManager.getConnection(DB_URL);
    }
    
    public static Connection getConnection() {  
        return connectionHolder.get();
    }

**Session管理**

public static Session getSession() throws InfrastructureException {  
        Session s = (Session) threadSession.get();
        try {
            if (s == null) {
                s = getSessionFactory().openSession();
                threadSession.set(s);
            }
        } catch (HibernateException ex) {
            throw new InfrastructureException(ex);
        }
        return s;
    }

[Java_--ThreadLocal_IT_-CSDN]: https://knife.blog.csdn.net/article/details/121110511
[SpringBoot--_ThreadLocal_springboot threadlocal_IT_-CSDN]: https://knife.blog.csdn.net/article/details/126617648