该实例来源于Apache项目源代码，源程序有800余行，功能比较全 面，而且是非常完善的，并且运行于诸多服务器如tomcat上，就是分析起来有点繁琐。如果开发人员直接把这段程序拿来修改后使用到自己的开发项目中，不失为拿来主义的上策。
本文对该源程序进行了修改和简化，对其中核 心部分进行分析，然后创建测试类进行测试。读者学习之后可以直接模仿和套用，而不需要花费大量时间自己亲自再去写线程池程序了。
关键的程序有2个:线程池类(ThreadPool)和线程池接口(ThreadPoolRunnable)。
首先看较复杂的线程池类程序，文件名为ThreadPool.java，有200余行，需要读者有耐心，内容如下：
---------------------------------------------------------------------------------------
import java.util.Vector;
public class ThreadPool {
public static final int MAX_THREADS = 100;
public static final int MAX_SPARE_THREADS = 50;
public static final int MIN_SPARE_THREADS = 10;
public static final int WORK_WAIT_TIMEOUT = 60 * 1000;
protected Vector pool;
protected MonitorRunnable monitor;
protected int maxThreads;
protected int minSpareThreads;
protected int maxSpareThreads;
protected int currentThreadCount;
protected int currentThreadsBusy;
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protected boolean stopThePool;
public ThreadPool() {
maxThreads = MAX_THREADS;
maxSpareThreads = MAX_SPARE_THREADS;
minSpareThreads = MIN_SPARE_THREADS;
currentThreadCount = 0;
currentThreadsBusy = 0;
stopThePool = false;
}
public synchronized void start() {
adjustLimits();
openThreads(minSpareThreads);
monitor = new MonitorRunnable(this);
}
public void setMaxThreads(int maxThreads) {
this.maxThreads = maxThreads;
}
public int getMaxThreads() {
return maxThreads;
}
public void setMinSpareThreads(int minSpareThreads) {
this.minSpareThreads = minSpareThreads;
}
public int getMinSpareThreads() {
return minSpareThreads;
}
public void setMaxSpareThreads(int maxSpareThreads) {
this.maxSpareThreads = maxSpareThreads;
}
public int getMaxSpareThreads() {
return maxSpareThreads;
}
public void runIt(ThreadPoolRunnable r) {
if (null == r) {
throw new NullPointerException();
}
if (0 == currentThreadCount || stopThePool) {
throw new IllegalStateException();
}
ControlRunnable c = null;
synchronized (this) {
if (currentThreadsBusy == currentThreadCount) {
if (currentThreadCount < maxThreads) {
int toOpen = currentThreadCount + minSpareThreads;
openThreads(toOpen);
} else {
while (currentThreadsBusy == currentThreadCount) {
try {
this.wait();
}catch (InterruptedException e) {
}
if (0 == currentThreadCount || stopThePool) {
throw new IllegalStateException();
}
}
}
}
c = (ControlRunnable) pool.lastElement();
pool.removeElement(c);
currentThreadsBusy++;
}
c.runIt(r);
}
public synchronized void shutdown() {
if (!stopThePool) {
stopThePool = true;
monitor.terminate();
monitor = null;
for (int i = 0; i < (currentThreadCount - currentThreadsBusy); i++) {
try {
((ControlRunnable) (pool.elementAt(i))).terminate();
} catch (Throwable t) {
}
}
currentThreadsBusy = currentThreadCount = 0;
pool = null;
notifyAll();
}
}
protected synchronized void checkSpareControllers() {
if (stopThePool) {
return;
}
if ((currentThreadCount - currentThreadsBusy) > maxSpareThreads) {
int toFree = currentThreadCount - currentThreadsBusy - maxSpareThreads;
for (int i = 0; i < toFree; i++) {
ControlRunnable c = (ControlRunnable) pool.firstElement();
pool.removeElement(c);
c.terminate();
currentThreadCount--;
}
}
}
protected synchronized void returnController(ControlRunnable c) {
if (0 == currentThreadCount || stopThePool) {
c.terminate();
return;
}
currentThreadsBusy--;
pool.addElement(c);
notify();
}
protected synchronized void notifyThreadEnd() {
currentThreadsBusy--;
currentThreadCount--;
notify();
openThreads(minSpareThreads);
}
protected void adjustLimits() {
if (maxThreads <= 0) {
maxThreads = MAX_THREADS;
}
if (maxSpareThreads >= maxThreads) {
maxSpareThreads = maxThreads;
}
if (maxSpareThreads <= 0) {
if (1 == maxThreads) {
maxSpareThreads = 1;
} else {
maxSpareThreads = maxThreads / 2;
}
}
if (minSpareThreads > maxSpareThreads) {
minSpareThreads = maxSpareThreads;
}
if (minSpareThreads <= 0) {
if (1 == maxSpareThreads) {
minSpareThreads = 1;
} else {
minSpareThreads = maxSpareThreads / 2;
}
}
}
protected void openThreads(int toOpen) {
if (toOpen > maxThreads) {
toOpen = maxThreads;
}
if (0 == currentThreadCount) {
pool = new Vector(toOpen);
}
for (int i = currentThreadCount; i < toOpen; i++) {
pool.addElement(new ControlRunnable(this));
}
currentThreadCount = toOpen;
}
class MonitorRunnable implements Runnable {
ThreadPool p;
Thread t;
boolean shouldTerminate;
MonitorRunnable(ThreadPool p) {
shouldTerminate = false;
this.p = p;
t = new Thread(this);
t.start();
}
public void run() {
while (true) {
try {
synchronized (this) {
this.wait(WORK_WAIT_TIMEOUT);
}
if (shouldTerminate) {
break;
}
p.checkSpareControllers();
} catch (Throwable t) {
t.printStackTrace();
}
}
}
public synchronized void terminate() {
shouldTerminate = true;
this.notify();
}
}
class ControlRunnable implements Runnable {
ThreadPool p;
Thread t;
ThreadPoolRunnable toRun;
boolean shouldTerminate;
boolean shouldRun;
boolean noThData;
Object thData[] = null;
ControlRunnable(ThreadPool p) {
toRun = null;
shouldTerminate = false;
shouldRun = false;
this.p = p;
t = new Thread(this);
t.start();
noThData = true;
thData = null;
}
public void run() {
while (true) {
try {
synchronized (this) {
if (!shouldRun && !shouldTerminate) {
this.wait();
}
}
if (shouldTerminate) {
break;
}
try {
if (noThData) {
thData = toRun.getInitData();
noThData = false;
}
if (shouldRun) {
toRun.runIt(thData);
}
} catch (Throwable t) {
System.err.println("ControlRunnable Throwable: ");
t.printStackTrace();
shouldTerminate = true;
shouldRun = false;
p.notifyThreadEnd();
} finally {
if (shouldRun) {
shouldRun = false;
p.returnController(this);
}
}
if (shouldTerminate) {
break;
}
} catch (InterruptedException ie) {
}
}
}
public synchronized void runIt(ThreadPoolRunnable toRun) {
if (toRun == null) {
throw new NullPointerException("No Runnable");
}
this.toRun = toRun;
shouldRun = true;
this.notify();
}
public synchronized void terminate() {
shouldTerminate = true;
this.notify();
}
}
}
---------------------------------------------------------------------------------------
以上程序中，关键的是openThreads方法、runIt方法以及2个内部类：MonitorRunnable和ControlRunnable。
刚开始运行的时候，线程池会往Vector对象里装入minSpareThreads个元素，每个元素都是ControlRunnable线程 类，ControlRunnable类在其构造方法中启动线程。如果shouldRun和shouldTerminate都是false的话，线程就等 待。如果shouldRun为true，就调用ThreadPoolRunnable的runIt(Object[])方法，该接口的方法就是我们需要在 自己的任务类中覆盖的方法。
如果minSpareThreads个线程都处于Busy后，线程池会再创建出minSpareThreads个线程。MonitorRunnable是 用来监视线程池运行情况的，其线程间隔60秒(WORK_WAIT_TIMEOUT)调用一次线程池类的checkSpareControllers方 法，如果发现(currentThreadCount - currentThreadsBusy) > maxSpareThreads，就会调用ControlRunnable类的terminate方法删除空闲线程，准备删除的线程是否空闲是通过 shouldTerminate参数来判断的。
线程池接口ThreadPoolRunnable有2个空方法getInitData和runIt，我们一般自己创建一个任务类实现这个线程池接口就可以了，把具体的任务内容放在任务类的runIt方法中。如果不想用getInitData，就让它返回null值。
线程池接口程序很简单，文件名为ThreadPoolRunnable.java，就几行，内容如下：
---------------------------------------------------------------------------------------------
public interface ThreadPoolRunnable {
public Object[] getInitData();
public void runIt(Object thData[]);
}
---------------------------------------------------------------------------------------------
线程池类和线程池接口都已经说完，下面就举个例子说说怎么使用它们了。
我们的任务还是扫描端口(请参考我的“多线程程序模型研究”)，文件名为TestThreadPool.java，内容如下：
---------------------------------------------------------------------------------------------
import java.net.InetAddress;
import java.net.Socket;
public class TestThreadPool {
public static void main(String[] args) {
String host = null; //第一个参数，目标主机。
int beginport = 1; //第二个参数，开始端口。
int endport = 65535; //第三个参数，结束端口。
try{
host = args[0];
beginport = Integer.parseInt(args[1]);
endport = Integer.parseInt(args[2]);
if(beginport <= 0 || endport >= 65536 || beginport > endport){
throw new Exception("Port is illegal");
}
}catch(Exception e){
System.out.println("Usage: java PortScannerSingleThread host beginport endport");
System.exit(0);
}
ThreadPool tp = new ThreadPool();
tp.setMaxThreads(100);
tp.setMaxSpareThreads(50);
tp.setMinSpareThreads(10);
tp.start();
for(int i = beginport; i <= endport; i++){
Task task = new Task(host,i);
tp.runIt(task);
}
}
}
class Task implements ThreadPoolRunnable{
String host;
int port;
Task(String host, int port){
this.host = host;
this.port = port;
}
public Object[] getInitData(){
return null;
}
public void runIt(Object thData[]){
Socket s = null;
try{
s = new Socket(InetAddress.getByName(host),port);
System.out.println("The port " + port + " at " + host + " is open.");
}catch(Exception e){
}finally{
try{
if(s != null) s.close();
}catch(Exception e){
}
}
}
}
-----------------------------------------------------------------------------------------------
在TestThreadPool类的main方法中定义了三个参数，分别是目标主机IP地址，开始端口和结束端口。然后通过new ThreadPool()创建线程池类，并通过setMaxThreads、setMaxSpareThreads和 setMinSpareThreads设置线程池的maxThreads、maxSpareThreads和minSpareThreads参数。 Task类通过实现ThreadPoolRunnable接口，在runIt中定义了具体内容(创建Socket对象达到扫描端口的目的)。
以上程序都在JDK1.4.2的环境下编译并运行通过，输入 java TestThreadPool 10.1.1.182 1 10000 运行得出如下结果：
The port 25 at 10.1.1.182 is open.
The port 110 at 10.1.1.182 is open.
The port 135 at 10.1.1.182 is open.
...
通过以上的线程池类、线程池接口的分析和介绍，读者可以在理解的基础上，直接把这个线程池类和接口拿来，应用到自己的开发项目中。
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