Netty--通信模型演化之传统的BIO（同步阻塞式）

传统的BIO（同步阻塞式）

网络编程的基本模型是client/service模型，也就是说两个进程之间进行的相互通信，服务器提供位置服务（绑定ip地址和监听端口），客户端通过连接操作向服务器发起连接请求，通过三次握手建立连接，如果连接成功，双方就进行网络套接字进行通信。

在基于传统同步阻塞模型开发中，servicesocket负责绑定ip地址启动监听端口，socket负责连接操作。连接成功后双方通过输入输出流进行同步阻塞式通信。

BIO通信模型图

该模型最大的问题就是缺乏弹性伸缩能力，当客户端并发访问量增大，服务端线程高=个数和客户端并发数量成1:1正比关系线性增长。线程通胀之后，系统的性能将急剧下降，随着并发访问量继续增大，系统发生内存溢出，最后不能对外提供服务。

下面就以经典的时间服务器，通过代码进行熟悉回顾，

public class TimeServer {

    /**
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
	int port = 8080;
	if (args != null && args.length > 0) {

	    try {
		port = Integer.valueOf(args[0]);
	    } catch (NumberFormatException e) {
		// 采用默认值
	    }

	}
	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;
	    }
	}
    }
}

public class TimeServerHandler implements Runnable {

    private Socket socket;

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

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Runnable#run()
     */
    @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 java.util.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;
	    }
	}
    }
}

public class TimeClient {

    /**
     * @param args
     */
    public static void main(String[] args) {

	int port = 8080;
	if (args != null && args.length > 0) {

	    try {
		port = Integer.valueOf(args[0]);
	    } catch (NumberFormatException e) {
		// 采用默认值
	    }

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