理解ThreadLocal的涵义
import java.util.HashMap;import java.util.Map;public class CustomThreadLocal { private static Map threadMap = new HashMap(); public static void add(Object object) { threadMap.put(Thread.currentThread(), object); } public static void remove(Object object) { threadMap.remove(Thread.currentThread()); } public static Object get() { return threadMap.get(Thread.currentThread()); }}
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public class ThreadContext { private String userId; private Long transactionId; public String getUserId() { return userId; } public void setUserId(String userId) { this.userId = userId; } public Long getTransactionId() { return transactionId; } public void setTransactionId(Long transactionId) { this.transactionId = transactionId; } public String toString() { return 'userId:' + userId + ',transactionId:' + transactionId; }}?
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public class ThreadLocalMainSampleEx1 { public static void main(String[] args) { new Thread(new Runnable() { public void run() { ThreadContext threadContext = new ThreadContext(); threadContext.setTransactionId(1l); threadContext.setUserId('User 1'); CustomThreadLocal.add(threadContext); //here we call a method where the thread context is not passed as parameter PrintThreadContextValues.printThreadContextValues(); } }).start(); new Thread(new Runnable() { public void run() { ThreadContext threadContext = new ThreadContext(); threadContext.setTransactionId(2l); threadContext.setUserId('User 2'); CustomThreadLocal.add(threadContext); //here we call a method where the thread context is not passed as parameter PrintThreadContextValues.printThreadContextValues(); } }).start(); }}?当我CustomThreadLocal.get()时候，它使用通过内部map去寻找到它自身独有Context上下文信息。
那如果采纳使用ThreadLocal呢？
public class ThreadContext { private String userId; private Long transactionId; private static ThreadLocal threadLocal = new ThreadLocal(){ @Override protected ThreadContext initialValue() { return new ThreadContext(); } }; public static ThreadContext get() { return threadLocal.get(); } public String getUserId() { return userId; } public void setUserId(String userId) { this.userId = userId; } public Long getTransactionId() { return transactionId; } public void setTransactionId(Long transactionId) { this.transactionId = transactionId; } public String toString() { return 'userId:' + userId + ',transactionId:' + transactionId; }}?是不是挺简单的使用的呢？如果配置上Pool，是不是挺完美的，在N多框架中都基本上采用上述方式，ibatis、BoneCP等都是携带
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ThreadLocal另外用处是对于非线程安全的实例，通过ThreadLocal的包装同样能够保证并发下的安全。
package ccs.progest.javacodesamples.threadlocal.ex4;import java.text.SimpleDateFormat;import java.util.Date;public class ThreadLocalDateFormat { // SimpleDateFormat is not thread-safe, so each thread will have one private static final ThreadLocal formatter = new ThreadLocal() { @Override protected SimpleDateFormat initialValue() { return new SimpleDateFormat('MM/dd/yyyy'); } }; public String formatIt(Date date) { return formatter.get().format(date); }}?ThreadLocal的应用场景
1.类似于userId、tractionId、以及session等
2.为了保证每个线程更好独享自己实例信息