多线程06_张孝祥-ThreadLocal类及应用技巧

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多线程06_张孝祥-ThreadLocal类及应用技巧

2024-08-08 17:16:51 216人阅读

使用ThreadLocal类实现线程范围内的共享数据：

确保每个线程都有自己私有的变量和取到自己的变量。下面用ThreadLocal类实现，替代上节课中的map用法

代码：

package org.yla.thread;

import java.util.Random;

/**
 * 使用ThreadLocal类实现线程范围内的私有数据
 * 替代上节课map的作用
 * @author huo_chai_gun
 * 2014年12月18日下午3:25:35
 */
public class ThreadLocalTest {

	private static ThreadLocal<Integer> threadLocal = new ThreadLocal<Integer>();
	public static void main(String[] args) {
		
		//启动两个线程
		for (int i = 0; i < 2; i++) {
			new Thread(new Runnable() {
				@Override
				public void run() {
					//创建每个线程私有的变量
					int data = new Random().nextInt(100);
					System.out.println(Thread.currentThread().getName()+" has put data: "+data);
					//往local里面设置值
					threadLocal.set(data);
					new A().get();
					new B().get();
				}
			}).start();
		}
	}
	
	static class A{
		public void get(){
			int data =threadLocal.get();
			System.out.println("A from "+Thread.currentThread().getName()+" has get data: "+data);
		}
	}
	
	
	static class B{
		public void get(){
			int data =threadLocal.get();
			System.out.println("B from "+Thread.currentThread().getName()+" has get data: "+data);
		}
	}
}

运行结果：

Thread-0 has put data: 48
Thread-1 has put data: 95
A from Thread-1 has get data: 95
A from Thread-0 has get data: 48
B from Thread-0 has get data: 48
B from Thread-1 has get data: 95

假设我们有多个线程需要范围内的共享数据，那么我们的代码就得改成下面的形式了：思路是把其他属性的值打包成一个类

package org.yla.thread;

import java.util.Random;

/**
 * 使用ThreadLocal类实现线程范围内的私有数据
 * 替代上节课map的作用
 * @author huo_chai_gun
 * 2014年12月18日下午3:25:35
 */
public class ThreadLocalTest {

	private static ThreadLocal<Integer> threadLocal = new ThreadLocal<Integer>();
	private static ThreadLocal<MyThreadLocalScopeDate> myLocalScopeData = new ThreadLocal<MyThreadLocalScopeDate>();
	public static void main(String[] args) {
		
		//启动两个线程
		for (int i = 0; i < 2; i++) {
			new Thread(new Runnable() {
				@Override
				public void run() {
					//创建每个线程私有的变量
					int data = new Random().nextInt(100);
					System.out.println(Thread.currentThread().getName()+" has put data: "+data);
					//往local里面设置值
					threadLocal.set(data);
					MyThreadLocalScopeDate scopeDate = new MyThreadLocalScopeDate();
					scopeDate.setName("name "+data);
					scopeDate.setAge(data);
					myLocalScopeData.set(scopeDate);
					new A().get();
					new B().get();
				}
			}).start();
		}
	}
	
	static class A{
		public void get(){
			int data =threadLocal.get();
			System.out.println("A from "+Thread.currentThread().getName()+" has get data: "+data);
			MyThreadLocalScopeDate scopeDate=myLocalScopeData.get();
			System.out.println("A from "+Thread.currentThread().getName()+" has get MyThreadLocalScopeDate name: "+scopeDate.getName()+" , age: "+scopeDate.getAge());
		}
	}
	
	
	static class B{
		public void get(){
			int data =threadLocal.get();
			System.out.println("B from "+Thread.currentThread().getName()+" has get data: "+data);
			MyThreadLocalScopeDate scopeDate=myLocalScopeData.get();
			System.out.println("B from "+Thread.currentThread().getName()+" has get MyThreadLocalScopeDate name: "+scopeDate.getName()+" , age: "+scopeDate.getAge());
		}
	}
}

class MyThreadLocalScopeDate{
	private String name;
	private int age;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	
}

运行结果:

Thread-0 has put data: 2
Thread-1 has put data: 94
A from Thread-1 has get data: 94
A from Thread-0 has get data: 2
A from Thread-1 has get MyThreadLocalScopeDate name: name 94 , age: 94
A from Thread-0 has get MyThreadLocalScopeDate name: name 2 , age: 2
B from Thread-1 has get data: 94
B from Thread-0 has get data: 2
B from Thread-1 has get MyThreadLocalScopeDate name: name 94 , age: 94
B from Thread-0 has get MyThreadLocalScopeDate name: name 2 , age: 2

上面的代码虽然实现了功能，但是代码实现是很垃圾，一个线程有一个实例，那么多个线程就有多个实例，所以我们还要对代码进行修改：

思路：利用单例模式实现线程范围内的共享数据这样子就永远只有一个对象但是每个线程拿这个对象的时后我们让他显示互斥效果这样子就节省了内容的消耗并且外部调用的时候还看不见ThreadLocal对这个对象进行了封装

真正开发中应该这么设计比较好【注意】

代码：

package org.yla.thread;

import java.util.Random;

/**
 * 使用ThreadLocal类实现线程范围内的私有数据
 * @author huo_chai_gun
 * 2014年12月18日下午3:25:35
 */
public class ThreadLocalTest {

	private static ThreadLocal<Integer> threadLocal = new ThreadLocal<Integer>();
	public static void main(String[] args) {
		
		//启动两个线程
		for (int i = 0; i < 2; i++) {
			new Thread(new Runnable() {
				@Override
				public void run() {
					//创建每个线程私有的变量
					int data = new Random().nextInt(100);
					System.out.println(Thread.currentThread().getName()+" has put data: "+data);
					//往local里面设置值
					threadLocal.set(data);
					//获取自己线程的MyThreadLocalScopeDate实例对象
					MyThreadLocalScopeDate myData = MyThreadLocalScopeDate.getThreadInstance();
					myData.setName("name"+data);
					myData.setAge(data);
					new A().get();
					new B().get();
				}
			}).start();
		}
	}
	
	static class A{
		public void get(){
			int data =threadLocal.get();
			System.out.println("A from "+Thread.currentThread().getName()+" has get data: "+data);
			MyThreadLocalScopeDate myData = MyThreadLocalScopeDate.getThreadInstance();
			System.out.println("A from "+Thread.currentThread().getName()+" has get MyThreadLocalScopeDate name: "+myData.getName()+" , age: "+myData.getAge());
		}
	}
	
	
	static class B{
		public void get(){
			int data =threadLocal.get();
			System.out.println("B from "+Thread.currentThread().getName()+" has get data: "+data);
			MyThreadLocalScopeDate myData = MyThreadLocalScopeDate.getThreadInstance();
			System.out.println("B from "+Thread.currentThread().getName()+" has get MyThreadLocalScopeDate name: "+myData.getName()+" , age: "+myData.getAge());
		}
	}
}

class MyThreadLocalScopeDate{//单例模式
	
	private MyThreadLocalScopeDate(){};//构造方法私有化
	private static ThreadLocal<MyThreadLocalScopeDate> map = new ThreadLocal<MyThreadLocalScopeDate>();//封装MyThreadLocalScopeDate是线程实现范围内共享
	
	//思考AB两个线程过来的情况 自己分析 AB都需要的自己的对象 没有关系 所以不需要同步 如果有关系就需要同步了
	public static /*synchronized*/MyThreadLocalScopeDate getThreadInstance(){
		MyThreadLocalScopeDate instance =map.get();
		if(instance==null){
			instance = new MyThreadLocalScopeDate();
			map.set(instance);
		}
		return instance;
	}

	private String name;
	private int age;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	
}

运行结果:

Thread-0 has put data: 24
Thread-1 has put data: 13
A from Thread-1 has get data: 13
A from Thread-1 has get MyThreadLocalScopeDate name: name13 , age: 13
A from Thread-0 has get data: 24
A from Thread-0 has get MyThreadLocalScopeDate name: name24 , age: 24
B from Thread-1 has get data: 13
B from Thread-1 has get MyThreadLocalScopeDate name: name13 , age: 13
B from Thread-0 has get data: 24
B from Thread-0 has get MyThreadLocalScopeDate name: name24 , age: 24

多线程06_张孝祥-ThreadLocal类及应用技巧

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