为了解决同步阻塞I/O一个链路需要一个线程处理问题，对BIO模型做了优化——后端通过一个线程池处理多个客户端的请求接入，设置线程最大值，防止线程并发接入导致的线程耗尽。
当有新的客户端接入时，将客户端Socket封装成一个Task（该任务实现java.lang.Runnable接口）投递到后端的线程池中进行处理，JDK的线程池维护一个消息队列和N个活跃线程，对消息队列中的任务进行处理。由于线程池可以设置消息队列的大小和最大线程数，因此资源占用是可控的，无论多少客户端并发访问都不会导致资源耗尽和宕机。
伪异步I/O通信框架采用了线程池实现，避免了每次请求创建一个独立的线程造成的资源耗尽问题，底层通信依然采用BIO同步阻塞模型，无法从根本上解决问题。当对方发送请求或者应答消息比较缓慢（如数据大），或者网路传输较慢时（网速差）读取输入流一方的通信线程将被长时间阻塞，阻塞期间，其他接入消息只能在消息队列中排队。阻塞结束情况：1）有数据可读，2）可用数据已经读取完毕，3）发生空指针或IO异常
package com.hjp.netty.pseudoasynio; import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit; public class TimeServerHandlerExecutePool { private ExecutorService executor; public TimeServerHandlerExecutePool(int maxPoolSize, int queueSize) {
executor = new ThreadPoolExecutor(Runtime.getRuntime().availableProcessors(), maxPoolSize, 120L, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(queueSize));
} public void execute(Runnable task) {
executor.execute(task);
} }
线程池处理类
package com.hjp.netty.pseudoasynio; import sun.awt.windows.ThemeReader; import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket; public class TimeServer { public static void main(String[] args) throws IOException {
int port = 8080;
if (args != null && args.length > 0) {
try {
port = Integer.valueOf(port);
} catch (NumberFormatException e) {
e.printStackTrace();
}
}
ServerSocket server = null;
try {
server = new ServerSocket(port);
System.out.println("The time server is start in port : " + port);
Socket socket = null;
TimeServerHandlerExecutePool singleExecutor = new TimeServerHandlerExecutePool(50, 10000);
while (true) {
socket = server.accept();
singleExecutor.execute(new TimeServerHandler(socket));
}
} finally {
if (server != null) {
System.out.println("The time server close");
server.close();
server = null;
}
}
} }
TimeServer
package com.hjp.netty.pseudoasynio; import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Date; public class TimeServerHandler implements Runnable { private Socket socket; public TimeServerHandler(Socket socket) {
this.socket = socket;
} @Override
public void run() {
BufferedReader in = null;
PrintWriter out = null;
try {
in = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
out = new PrintWriter(this.socket.getOutputStream(), true);
String currentTime = null;
String body = null;
while (true) {
body = in.readLine();
if (body == null) {
break;
}
System.out.println("The time server receive order : " + body);
currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
out.println(currentTime);
}
} catch (Exception e) {
if (in != null) {
try {
in.close();
} catch (IOException e1) {
e1.printStackTrace();
}
}
if (out != null) {
out.close();
out = null;
}
if (this.socket != null) {
try {
this.socket.close();
} catch (IOException e1) {
e1.printStackTrace();
}
this.socket = null;
}
}
}
}
TimeServerHandler
客户端代码和BIO客户端代码一样