第ThreadLocal工作原理及用法案例關于InheritableThreadLocal

InheritableThreadLocal類是ThreadLocal類的子類。ThreadLocal中每個線程擁有它自己的值，與ThreadLocal不同的是，InheritableThreadLocal允許一個線程以及該線程創(chuàng)建的所有子線程都可以訪問它保存的值。

代碼示例

ThreadLocal使用

publicclassThreadLocalTest{

//第一種初始化方式

*聲明為static是讓ThreadLocal實例隨著程序的結束才結束，這樣才不會讓GC回收了

*聲明為final是讓ThreadLocal實例引用不會被替換，這樣子也不會因為被替換導致被GC回收

*這兩個聲明都是為了避免作為key的ThreadLocal對象沒有外部強引用而導致被GC回收，從而導致內存泄漏的問題，因為ThreadLocalMapThreadLocal,Object中的ThreadLocal

*對象作為key是弱引用，會被GC回收。

privatestaticfinalThreadLocalStringthreadLocalStr=ThreadLocal.withInitial(()-"fresh");

privatestaticAtomicIntegerintGen=newAtomicInteger(0);

//第二種初始化方式

privatestaticfinalThreadLocalIntegerthreadLocalInt=newThreadLocalInteger(){

@Override

publicIntegerinitialValue(){

returnintGen.incrementAndGet();

publicstaticvoidmain(String[]args)throwsInterruptedException{

ArrayListThreadthreads=newArrayList();

for(inti=0;ii++){

Threadt=newThread(()-{

try{

System.out.println(Thread.currentThread().getName()+""+threadLocalInt.get());

System.out.println(Thread.currentThread().getName()+""+threadLocalStr.get());

TimeUnit.SECONDS.sleep(5);

threadLocalStr.set("bojackhorseman"+threadLocalInt.get());

System.out.println(Thread.currentThread().getName()+""+threadLocalInt.get());

System.out.println(Thread.currentThread().getName()+""+threadLocalStr.get());

}catch(InterruptedExceptione){

e.printStackTrace();

}finally{

threadLocalInt.remove();

threadLocalStr.remove();

t.start();

threads.add(t);

TimeUnit.SECONDS.sleep(2);

System.out.println(threads);

System.out.println(threadLocalStr);

System.out.println(threadLocalInt);

*Thread-01

*Thread-12

*Thread-0fresh

*Thread-1fresh

*[Thread[Thread-0,5,main],Thread[Thread-1,5,main]]

*java.lang.ThreadLocal$SuppliedThreadLocal@1ef7fe8e

*cn.vv.schedule.test.ThreadLocalTest$1@6f79caec

*Thread-12

*Thread-1bojackhorseman2

*Thread-01

*Thread-0bojackhorseman1

}

InheritableThreadLocal使用

publicclassInheritableThreadLocalTest{

//第一種初始化方式

privatestaticfinalInheritableThreadLocalStringthreadLocalStr=newInheritableThreadLocalString(){

@Override

publicStringinitialValue(){

return"fresh";

privatestaticAtomicIntegerintGen=newAtomicInteger(0);

//第二種初始化方式

privatestaticfinalThreadLocalIntegerthreadLocalInt=newThreadLocalInteger(){

@Override

publicIntegerinitialValue(){

returnintGen.incrementAndGet();

publicstaticvoidmain(String[]args)throwsInterruptedException{

//如果是InheritableThreadLocal，則父線程創(chuàng)建的所有子線程都會復制一份父線程的線程變量，而不是去初始化一份線程變量

threadLocalStr.set("main");

ArrayListThreadthreads=newArrayList();

for(inti=0;ii++){

Threadt=newThread(()-{

try{

System.out.println(Thread.currentThread().getName()+""+threadLocalInt.get());

System.out.println(Thread.currentThread().getName()+""+threadLocalStr.get());

TimeUnit.SECONDS.sleep(5);

//子線程可以自由地改變自己的本地變量

threadLocalStr.set("bojackhorseman"+threadLocalInt.get());

System.out.println(Thread.currentThread().getName()+""+threadLocalInt.get());

System.out.println(Thread.currentThread().getName()+""+threadLocalStr.get());

}catch(InterruptedExceptione){

e.printStackTrace();

}finally{

threadLocalInt.remove();

threadLocalStr.remove();

t.start();

threads.add(t);

TimeUnit.SECONDS.sleep(2);

System.out.println(Thread.currentThread().getName()+""+threadLocalStr.get());

*Thread-02