为什么需要伪异步？

socket编程中每一个socket客户端去连接服务端的时候就需要开启一个线程进行处理，如果客户端过多服务端开启线程数也会过多，导致服务端资源耗尽崩溃

实现伪异步io的方法

通过线程池进行解决，这是比较老的解决方法，在jdk1.5之后java提供了nio，可以解决这个问题
实现代码如下：

客户端代码

public class Client {

    final static String ADDRESS = "127.0.0.1";
    final static int PORT =8765;

    public static void main(String[] args) {
        Socket socket = null;
        BufferedReader in = null;
        PrintWriter out = null;
        try {
            socket = new Socket(ADDRESS, PORT);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);

            out.println("Client request");

            String response = in.readLine();
            System.out.println("Client:" + response);


        }  catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if(in != null){
                try {
                    in.close();
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            }
            if(out != null){
                try {
                    out.close();
                } catch (Exception e2) {
                    e2.printStackTrace();
                }
            }
            if(socket != null){
                try {
                    socket.close();
                } catch (Exception e3) {
                    e3.printStackTrace();
                }
            }
            socket = null;                
        }



    }

}

服务端处理代码

public class ServerHandler implements Runnable {

    private Socket socket;
    public ServerHandler (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 body = null;
            while(true){
                body = in.readLine();
                if(body == null) break;
                System.out.println("Server:" + body);
                out.println("Server response");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if(in != null){
                try {
                    in.close();
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            }
            if(out != null){
                try {
                    out.close();
                } catch (Exception e2) {
                    e2.printStackTrace();
                }
            }
            if(socket != null){
                try {
                    socket.close();
                } catch (Exception e3) {
                    e3.printStackTrace();
                }
            }
            socket = null;            
        }


    }

}

服务端代码

public class Server {

    final static int PORT = 8765;

    public static void main(String[] args) {
        ServerSocket server = null;
        BufferedReader in = null;
        PrintWriter out = null;
        try {
            server = new ServerSocket(PORT);
            System.out.println("server start");
            Socket socket = null;
            HandlerExecutorPool executorPool = new HandlerExecutorPool(50, 1000);
            while(true){
                socket = server.accept();
                executorPool.execute(new ServerHandler(socket));
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if(in != null){
                try {
                    in.close();
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            }
            if(out != null){
                try {
                    out.close();
                } catch (Exception e2) {
                    e2.printStackTrace();
                }
            }
            if(server != null){
                try {
                    server.close();
                } catch (Exception e3) {
                    e3.printStackTrace();
                }
            }
            server = null;                
        }
    }    
}

自定义线程池

public class HandlerExecutorPool {

    private ExecutorService executor;
    public HandlerExecutorPool(int maxPoolSize, int queueSize){
        this.executor = new ThreadPoolExecutor(
                Runtime.getRuntime().availableProcessors(),
                maxPoolSize, 
                120L, 
                TimeUnit.SECONDS,
                new ArrayBlockingQueue<Runnable>(queueSize));
    }

    public void execute(Runnable task){
        this.executor.execute(task);
    }



}