如何异步调用一个java方法，

定义一个类，实现 Runnable 接口，将任务实现代码放在 run 方法中，然后启动该线程。

如果该任务完成后要通知主线程，使用回调函数。

====

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.security.DigestInputStream;

/**

* 求文件的信息摘要码（MD5）

*

* @author leizhimin 2008-9-11 22:53:39

*/

public class InstanceCallbackDigest
implements Runnable {

private File inputFile;
//目标文件

//每个线程绑定一个回调对象

private InstanceCallbackDigestUserInterface instanceCallback;

/**

* 构件时一次注入回调对象

*

* @param instanceCallback

* @param inputFile

*/

public InstanceCallbackDigest(InstanceCallbackDigestUserInterface instanceCallback, File inputFile) {

this.instanceCallback = instanceCallback;

this.inputFile = inputFile;

}

public void run() {

try {

FileInputStream in = new FileInputStream(inputFile);

MessageDigest sha = MessageDigest.getInstance("MD5");

DigestInputStream din = new DigestInputStream(in, sha);

int b;

while ((b = din.read()) != -1) ;

din.close();

byte[] digest = sha.digest();
//摘要码

//完成后，回调主线程静态方法，将文件名-摘要码结果传递给住线程

instanceCallback.receiveDigest(digest);

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (NoSuchAlgorithmException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

}

import java.io.File;

/**

* 静态非同步回调

*

* @author leizhimin 2008-9-11 23:00:12

*/

public class InstanceCallbackDigestUserInterface {

private File inputFile;
//回调与每个文件绑定

private byte digest[]; //文件的消息摘要码

public InstanceCallbackDigestUserInterface(File inputFile) {

this.inputFile = inputFile;

}

/**

* 计算某个文件的消息摘要码

*/

public void calculateDigest() {

InstanceCallbackDigest callback = new InstanceCallbackDigest(this, inputFile);

Thread t = new Thread(callback);

t.start();

}

/**

* 接收消息摘要码

*

* @param digest

*/

public void receiveDigest(byte[] digest) {

this.digest = digest;

//将消息摘要码输出到控制台实际上执行的是this.toString()方法

System.out.println(this);

}

/**

* 显示结果

*

* @return 结果

*/

public String toString() {

String result = inputFile.getName() + ": ";

if (digest !=
null) {

for (byte b : digest) {

result += b + " ";

}

} else {

result += "digest 不可用！";

}

return result;

}

public static
void main(String[] args) {

String arr[] = {"C:\\xcopy.txt",
"C:\\x.txt", "C:\\xb.txt",
"C:\\bf2.txt"};

args = arr;

for (int i = 0; i < args.length; i++) {

File f = new File(args[i]);

InstanceCallbackDigestUserInterface cb =
new InstanceCallbackDigestUserInterface(f);

cb.calculateDigest();

}

}

}

结果：

xcopy.txt: 123 -91 90 -16 -116 -94 -29 -5 -73 25 -57 12 71 23 -8 -47

x.txt: 123 -91 90 -16 -116 -94 -29 -5 -73 25 -57 12 71 23 -8 -47

xb.txt: 112 -81 113 94 -65 -101 46 -24 -83 -55 -115 18 -1 91 -97 98

bf2.txt: 31 -37 46 -53 -26 -45 36 -105 -89 124 119 111 28 72 74 112

Process finished with exit code 0