Netty权威指南之BIO（Block Input/Output，同步阻塞I/O通信）通信模型

网络编程的基本模型是Client/Server模型，也就是两个进程之间进行相互通信，其中服务端提供位置信息（绑定的IP地址和监听端口），客户端通过连接操作向服务端监听的地址发起连接请求，通过三次握手建立连接，如果连接建立成功，双方就可以通过网络套接字（Socket）进行通信。

采用BIO通信模型的服务端，通常由一个独立的Acceptor线程负责监听客户端的连接，它接收到客户端连接请求之后为每个客户端创建一个新的线程进行链路处理，处理完成之后，通过输出流返回应答给客户，线程销毁。

该模型下，服务端的线程个数和客户端并发访问数呈1:1正比关系，线程是Java虚拟机宝贵资源，线程数膨胀后，系统性能下降，线程并发访问了继续增大，会导致进程宕机或僵死。

TimeServer和TimeClient案例如下

package com.hjp.netty.bio;

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

/**
 * Created by JiaPeng on 2017/2/1.
 */
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) {

            }
        }
        ServerSocket server = null;
        try {
            server = new ServerSocket(port);
            System.out.println("The time server is start in port : " + port);
            Socket socket = null;
            while (true) {
                socket = server.accept();
                new Thread(new TimeServerHandler(socket)).start();
            }
        } finally {
            if (server != null) {
                System.out.println("The time server close");
                server.close();
                server = null;
            }
        }
    }

}

package com.hjp.netty.bio;

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

/**
 * Created by JiaPeng on 2017/2/1.
 */
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;
            }
        }
    }
}

package com.hjp.netty.bio;

import javax.management.Query;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

/**
 * Created by JiaPeng on 2017/2/2.
 */
public class TimeClient {

    public static void main(String[] args) {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(port);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        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) {

        } 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 (IOException e) {
                    e.printStackTrace();
                }
                socket = null;
            }
        }
    }

}