初尝Java异步编程
最近从头了解了一下java的异步编程，通过一些例子去展现不同java版本下怎么去实现任务的并行。
（一）Java 1.0的通过Thread 类 和 Runnable接口
Thread类实现了Runnable接口。
一般用法：
1）创建一个类SendToCUPD，实现Runnable接口，重写run()方法去实现任务
2）创建一个类SendToCUPD的实例， 作为参数去新建一个Thread并调用Thread.start 方法。 然后系统去新建一个线程去执行这个任务
public class JThread {
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("get request from TC thread id="+Thread.currentThread().getId());
Runnable createRM = new CreateRichMedia("Thread RM");
new Thread(createRM).start();
Runnable tCUPD=new SendToCUPD("Thread CUPD");
new Thread(tCUPD).start();
System.out.println("End main method");
}
}
class SendToCUPD implements Runnable{
public String TName;
public SendToCUPD(String TName) {
// TODO Auto-generated constructor stub
this.TName=TName;
}
@Override
public void run() {
System.out.println("b4 send to cupd");
try {
System.out.println(" sending to cupd, thread id="+Thread.currentThread().getId());
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("end send to cupd");
}
}
class CreateRichMedia implements Runnable{
public String TName;
public CreateRichMedia(String TName) {
// TODO Auto-generated constructor stub
this.TName=TName;
}
@Override
public void run() {
System.out.println("start response Rich media");
try {
System.out.println("creating response Rich media, thread id="+Thread.currentThread().getId());
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("End response Rich media");
}
}（二）Java5， Callable, Future, FutureTask
通过Runable和Thread， 无法获取子线程的运行结果。Java5 引入了 java.util.concurrent， 可以获取到子线程的运行结果。
Future接口可以理解成一个任务， Future.get()方法可以获取任务的运行结果
例子步骤：
1）创建一个RMTask和CUPDTask， 实现Callable接口。 重写call（）方法去实现任务
2）通过Executors类去创建一个线程池
3）通过Executors.submit()去创建子线程去执行任务。
public class J5Thread {
public static void main(String[] args) {
// ES
System.out.println("Get request from TC, thread id="+Thread.currentThread().getId());
ExecutorService ES=Executors.newCachedThreadPool();
//task
Callable rmTask= new RMTask();
Callable cupdTask = new CUPDTask();
//ES submit task,
//param is callable
//return result
Future rmResult=ES.submit(rmTask);
Future cupdResult= ES.submit(cupdTask);
ES.shutdown();
System.out.println("ES shutdown, thread id="+Thread.currentThread().getId());
//ES shutdown
try {
Integer result = rmResult.get();
System.out.println("process rmResult, thread id="+Thread.currentThread().getId());
System.out.println("process rmResult="+result);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
//define task
class RMTask implements Callable{
@Override
public Integer call() throws Exception {
// TODO Auto-generated method stub
System.out.println("creating response Rich media, thread id="+Thread.currentThread().getId());
Thread.sleep(3000);
System.out.println("end response Rich media, thread id="+Thread.currentThread().getId());
return new Integer(3);
}
}
class CUPDTask implements Callable{
@Override
public Integer call() throws Exception {
System.out.println("creating CUPD msg, thread id="+Thread.currentThread().getId());
Thread.sleep(8000);
System.out.println("end response Rich media, thread id="+Thread.currentThread().getId());
return new Integer(10);
}
（三）Java7， fork/join
Java 7在java.util.concurrent包下加入了支持fork/join框架的RecursiveTask，forkjoinpool
例子，去计算从start到end的连续数字的和：
1）执行任务的类要继承RecursiveTask类
2）定义一个compute方法，将要算的数分成两组，再分别调用compute方法去算。 运用了递归算法
3）定义一个ForkJoinPool去执行任务， submit方法返还一个Future类， 通过future.get()去获取任务结果
public class J7ForkJoin extends RecursiveTask{
private static final int THRESHOLD=5;
private int beginning;
private int ending;
public J7ForkJoin(int beginning, int ending) {
super();
this.beginning = beginning;
this.ending = ending;
}
//override compute
@Override
protected Integer compute() {
// TODO Auto-generated method stub
//check if still need fork
int sum=0;
boolean canCompute = (ending-beginning)<=THRESHOLD;
if(canCompute){
//no need
System.out.println("no need fork, ThreadID="+Thread.currentThread().getId());
System.out.println("no need fork, beginning="+this.beginning);
System.out.println("no need fork, ending="+this.ending);
for(int i=beginning; i<=ending;++i){
sum+=i;
}
return sum;
}else{
//need
int interim=(this.ending+this.beginning)/2;
//5+1 /2 =3 1-3
//6+1 /2 =3 1-3
System.out.println("need fork, ThreadID="+Thread.currentThread().getId());
System.out.println("need fork, interim="+interim);
J7ForkJoin leftTask=new J7ForkJoin(this.beginning , interim);
J7ForkJoin rightTask=new J7ForkJoin(interim+1, this.ending);
//.fork
leftTask.fork();
rightTask.fork();
//get reuslt
int leftResult=leftTask.join();
int rightResult=rightTask.join();
sum =leftResult+rightResult;
return sum;
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
ForkJoinPool FJPool=new ForkJoinPool();
J7ForkJoin task=new J7ForkJoin(1, 20);
Future result=FJPool.submit(task);
try {
System.out.println("main result="+result.get());
} catch (InterruptedException | ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
（ 四 ） Java8 CompletableFuture
可以定义回调函数， 子线程执行完后，会触发回调函数
步骤：
1）CompletableFuture.supplyAsync（），定义要执行的异步任务
2）cupdResult.thenAccept(new Consumer
public class J8ComFuture3 {
public static void main(String[] args) {
ExecutorService executor = Executors.newFixedThreadPool(10);
// get msg from tc
System.out.println("Got reqeust from TC");
// prepare RM
System.out.println("prepare RM msg");
// trigger cupd
CompletableFuture cupdResult = CompletableFuture.supplyAsync(new Supplier() {
@Override
public String get() {
// TODO Auto-generated method stub
try {
System.out.println("sleep b4");
TimeUnit.SECONDS.sleep(1);
System.out.println("sleep after");
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "msg from CUPD";
}
}, executor);
// return cupd
cupdResult.thenAccept(new Consumer() {
// callback method
public void accept(String arg0) {
System.out.println("return msg to TC=" + arg0);
}
});
// return RM
System.out.println("return RM msg to customer");
}
}