目前大多浏览器都支持多线程访问，但是如果Web服务器是单线程的话，多线程的浏览器也无用武之地，因为服务端只能一个请求一个请求的顺序处理。因此，Web服务器很有必要支持并发访问。下面通过使用线程池构造一个简单的Web服务器，这个服务器可以处理HTTP请求，并处理简单的文本和jpg格式图片内容。当客户端不断请求Socket连接，Web服务器将该连接以及请求提交线程池处理，使得Web服务器能够同时处理多个客户端的请求。
/**
SimpleHttpServer.java
*/
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class SimpleHttpServer {
// 处理HttpRequest的线程池
static ThreadPool<HttpRequestHandler> threadPool = new DefaultThreadPool<HttpRequestHandler>(11);
// SimpleHttpServer的根路径
static String basePath;
static ServerSocket serverSocket;
// 服务监听端口
static int port = 8080;
public static void setPort(int port) {
if (port > 0) {
SimpleHttpServer.port = port;
}
}
public static void setBasePath(String basePath) {
if (basePath != null && new File(basePath).exists() && new File(basePath).isDirectory()) {
SimpleHttpServer.basePath = basePath;
}
}
// 启动SimpleHttpServer
public static void start() throws Exception {
serverSocket = new ServerSocket(port);
Socket socket = null;
while ((socket = serverSocket.accept()) != null) {
// 接收一个客户端Socket，生成一个HttpRequestHandler，放入线程池执行
threadPool.execute(new HttpRequestHandler(socket));
}
serverSocket.close();
}
static class HttpRequestHandler implements Runnable {
private Socket socket;
public HttpRequestHandler(Socket socket) {
this.socket = socket;
}
@Override
public void run() {
String line = null;
BufferedReader br = null;
BufferedReader reader = null;
PrintWriter out = null;
InputStream in = null;
try {
reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String header = reader.readLine();
// 由相对路径计算出绝对路径
String filePath = basePath + header.split(" ")[1];
out = new PrintWriter(socket.getOutputStream());
// 如果请求资源的后缀为jpg或者ico，则读取资源并输出
if (filePath.endsWith("jpg") || filePath.endsWith("ico")) {
in = new FileInputStream(filePath);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int i = 0;
while ((i = in.read()) != -1) {
baos.write(i);
}
byte[] array = baos.toByteArray();
out.println("HTTP/1.1 200 OK");
out.println("Content-Type: image/jpeg");
out.println("Content-Length: " + array.length);
out.println("");
socket.getOutputStream().write(array, 0, array.length);
} else {
br = new BufferedReader(new InputStreamReader(new FileInputStream(filePath)));
out = new PrintWriter(socket.getOutputStream());
out.println("HTTP/1.1 200 OK");
out.println("Content-Type: text/html; charset=UTF-8");
out.println("");
while ((line = br.readLine()) != null) {
out.println(line);
}
}
out.flush();
} catch (Exception ex) {
out.println("HTTP/1.1 500");
out.println("");
out.flush();
} finally {
close(br, in, reader, out, socket);
}
}
}
// 关闭流或者Socket
private static void close(Closeable... closeables) {
if (closeables != null) {
for (Closeable closeable : closeables) {
try {
closeable.close();
} catch (Exception ex) {
// 忽略
}
}
}
}
public static void main(String[] args) {
basePath = "C:/Users/lenovo/Desktop";
SimpleHttpServer.setBasePath(basePath);
try{
start();
}catch(Exception e){
e.printStackTrace();
}
}
}/**
ThreadPool.java
*/
public interface ThreadPool<Job extends Runnable> {
// 执行一个Job，这个Job需要实现Runnable
void execute(Job job);
void shutdown();// 关闭线程池
void addWorkers(int num);// 增加工作者线程
void removeWorker(int num);// 减少工作者线程
int getJobSize();// 得到正在等待执行的任务数量
}
/**
DefaultThreadPool.java
*/
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;
public class DefaultThreadPool<Job extends Runnable> implements ThreadPool<Job> {
// 线程池最大限制数
private static final int MAX_WORKER_NUMBERS = 10;
// 线程池默认的数量
private static final int DEFAULT_WORKER_NUMBERS = 5;
// 线程池最小的数量
private static final int MIN_WORKER_NUMBERS = 1;
// 这是一个工作列表，将会向里面插入工作
private final LinkedList<Job> jobs = new LinkedList<Job>();
// 工作者列表
private final List<Worker> workers = Collections.synchronizedList(new ArrayList<Worker>());
// 工作者线程的数量
private int workerNum = DEFAULT_WORKER_NUMBERS;
// 线程编号生成
private AtomicLong threadNum = new AtomicLong();
public DefaultThreadPool() {
initializeWokers(DEFAULT_WORKER_NUMBERS);
}
public DefaultThreadPool(int num) {
workerNum = num > MAX_WORKER_NUMBERS ? MAX_WORKER_NUMBERS : num < MIN_WORKER_NUMBERS ? MIN_WORKER_NUMBERS : num;
initializeWokers(workerNum);
}
public void execute(Job job) {
if (job != null) {
// 添加一个工作，然后进行通知
synchronized (jobs) {
jobs.addLast(job);
jobs.notify();
}
}
}
public void shutdown() {
for (Worker worker : workers) {
worker.shutdown();
}
}
public void addWorkers(int num) {
synchronized (jobs) {
// 限制新增的Worker数量不能超过最大值
if (num + this.workerNum > MAX_WORKER_NUMBERS) {
num = MAX_WORKER_NUMBERS - this.workerNum;
}
initializeWokers(num);
this.workerNum += num;
}
}
public void removeWorker(int num) {
synchronized (jobs) {
if (num >= this.workerNum) {
throw new IllegalArgumentException("beyond workNum");
}
// 按照给定的数量停止Worker
int count = 0;
while (count < num) {
workers.get(count).shutdown();
count++;
}
this.workerNum -= count;
}
}
public int getJobSize() {
return jobs.size();
}
// 初始化线程工作者
private void initializeWokers(int num) {
for (int i = 0; i < num; i++) {
Worker worker = new Worker();
workers.add(worker);
Thread thread = new Thread(worker, "ThreadPool-Worker-" + threadNum.incrementAndGet());
thread.start();
}
}
// 工作者，负责消费任务
class Worker implements Runnable {
// 是否工作
private volatile boolean running = true;
public void run() {
while (running) {
Job job = null;
synchronized (jobs) {
// 如果工作者列表是空的，那么就wait
while (jobs.isEmpty()) {
try {
jobs.wait();
} catch (InterruptedException ex) {
// 感知到外部对WorkerThread的中断操作，返回
Thread.currentThread().interrupt();
return;
}
}
// 取出一个Job
job = jobs.removeFirst();
}
if (job != null) {
try {
job.run();
} catch (Exception ex) {
// 忽略Job执行中的Exception
}
}
}
}
public void shutdown() {
running = false;
}
}
}
将上面三段代码保存为java文件并放在同一个文件夹中，打开cmd命令窗口并指向该文件夹，依次执行javac SimpleHttpServer.java和java SimpleHttpServer，如下图所示：
然后建立一个简单的HTML测试页面：
<!--Index.html-->
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<html>
<head>
<title>测试页面</title>
</head>
<body align="center">
<h1>第一张图片</h1>
<img src="1.jpg" align="middle" width="50" height="50">
<h1>第二张图片</h1>
<img src="2.jpg" align="middle" />
<h1>第三张图片</h1>
<img src="3.jpg" align="middle" />
</body>
</html>注意到第一段代码（SimpleHttpServer.java）中main函数里的basePath = "C:/Users/lenovo/Desktop"，basePath的路径可以自由设置，这里设置的桌面Desktop，我们就将上面的Index.html保存在桌面（在桌面随意保存三张图片：1.jpg、2.jpg、3.jpg）。最后在浏览器中输入http://localhost:8080/Index.html即可访问Index.html页面。
此外，我们可以通过Apache HTTP server benchmarking tool（版本2.4，Windows下载地址： http://www.apachehaus.com/cgi-bin/download.plx）来测试不同线程数下SimpleHttpServer的吞吐量表现。
注意第一段代码（SimpleHttpServer.java）中的static ThreadPool<HttpRequestHandler> threadPool = new DefaultThreadPool<HttpRequestHandler>(11)表示建立线程数量为11的线程池，我们可以修改不同的线程池线程数，然后利用上面的Apache HTTP server benchmarking tool测试：
注：ab -n 1000 -c 10 http://localhost:8080/Index.html表示每次并发10个请求，总共请求1000次。