同步阻塞I/O

TimeServer:

package netty.chapter2;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * @ClassName TimeServer
 * @Description 同步阻塞I/O的TimeServer
 * @author lihk
 * @Date Jul 18, 2017 10:47:42 AM
 * @version 1.0.0
 */
public class TimeServer {

    public static void main(String[] args) {

        int port = 8090;
        ServerSocket server = null;
        try {
            server = new ServerSocket(port);
            System.out.println("The time server is started in port:" + port);
            Socket socket = null;
            while (true) {
                socket = server.accept();
                System.out.println("Accept message.");
                new Thread(new TimeServerHandler(socket)).start();

            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (server != null) {
                System.out.println("The time server close");
                try {
                    server.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                server = null;
            }
        }

    }

}

TimeServerHandler:

package netty.chapter2;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Date;
/**
 * @ClassName TimeServerHandler
 * @Description 同步阻塞I/O的TimeServerHandler
 * @author lihk
 * @Date Jul 18, 2017 10:38:56 AM
 * @version 1.0.0
 */
public class TimeServerHandler implements Runnable {

    private Socket socket;

    public TimeServerHandler(Socket socket) {
        this.socket = socket;
    }

    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;
            }

        }

    }

}

TimeClient:

package netty.chapter2;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

/**
 * @ClassName TimeClient
 * @Description 同步阻塞I/O的TimeClient
 * @author lihk
 * @Date Jul 18, 2017 10:58:49 AM
 * @version 1.0.0
 */
public class TimeClient {
    
    public static void main(String[] args) {
        int port = 8090;
        Socket socket = null;
        BufferedReader in = null;
        PrintWriter out = null;
        try {
            socket = new Socket("127.0.0.1", port);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(),true);
            out.println("QUERY TIME ORDER");
            System.out.println("Send order 2 server succeed.");
            String resp = in.readLine();
            System.out.println("Now is:"+resp);
            
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(out != null){
                out.close();
                out = null;
            }
            if(in != null){
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                in = null;
            }
            if(socket != null){
                try {
                    socket.close();
                } catch (Exception e2) {
                    e2.printStackTrace();
                }
                socket = null;
            }
        }
    }

}

BIO主要的問題在於每當一個新的客戶端請求鏈接時，服務器必須建立一個新的線程處理新接入的客戶端鏈路，一個線程只能處理一個客戶端鏈接。在高性能服務器應用領域，每每須要面向成千上萬個客戶端的併發鏈接，這種模型顯然沒法知足高性能、高併發的接入場景。爲了改進一線程一鏈接模型，後來又演進出了一種經過線程池或者消息隊列實現１個或者多個線程處理Ｎ個客戶端的模型，因爲它的底層通訊機制依然使用同步阻塞的I/O(read(),write()方法)，因此被稱爲「僞異步」。