Java网络编程入门

1.进程之间的通信

 　　运行EchoPlayer就启动一个进程，就启动了JVM进程，该进程（EchoPlayer类）执行main方法 ，echo负责生成响应结果，若想要将响应结果移动到一个远程主机上，那么此进程是无法完成的，这种情况需要创建两个程序：客户程序EchoClient和服务器程序EchoServer

　　客户程序EchoClient负责与用户交互，从本地获取标准输入和标准输出，和远程服务器程序EchoServer通信，发送用户输入的信息，接收返回的信息并将结果输出到标准输出。

　　服务器程序EchoServer负责接收客户程序EchoClient发送的信息，然后把响应结果发送给客户程序EchoClient。

public class EchoPlayer {
    
    //负责生成相应结果
    public String echo(String msg){
        return "echo : "+msg;
    }
    
    public void talk() throws IOException{
        System.out.println("please input String :");
        BufferedReader bt =new BufferedReader(new InputStreamReader(System.in));
        String msg=null;
        while((msg=bt.readLine())!=null){
            if(msg.equals("bye")){
                System.out.println(echo(msg));
                break;
            }else{
                System.out.println(echo(msg));
                System.out.println("please input String :");
            }
        }
    }
    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        new EchoPlayer().talk();
    }

}

 2.用Java编写客户/服务器程序

　　Java网络程序都建立在TCP/IP协议的基础上，致力于实现应用层。传输层向应用层提供了套接字Socket接口，Socket封装了下层数据传输细节，应用层的程序通过Socket来建立于远程主机的连接，以及进行数据传输。

　　Java中有3种套接字类：Socket、ServerSocket、DatagrameSocket，其中前两种为TCP协议基础上的，后一种为UDP协议基础上

服务器代码：

public class EchoServer {
    
    private int port = 8000;
    private ServerSocket serverSocket;
    
    //利用构造器初始化服务器
    public EchoServer() throws IOException{
        serverSocket = new ServerSocket(port);
        System.out.println("服务器启动");
    }
    
    //响应输出信息
    public String echo(String msg){
        return "Server echo : "+msg;
    }
    
    private PrintWriter getWriter(Socket socket) throws IOException{
        OutputStream socketOut = socket.getOutputStream();
        return new PrintWriter(socketOut,true);
    }
    
    private BufferedReader getReader(Socket socket)throws IOException{
        InputStream socketIn = socket.getInputStream();
        return new BufferedReader(new InputStreamReader(socketIn));
    }
    
    public void service(){
        while(true){
            Socket socket=null;
            try {
                //等待客户连接
                socket = serverSocket.accept();
                System.out.println("new connection accepted "+socket.getInetAddress()+":"+socket.getPort());
                BufferedReader  br= getReader(socket);
                PrintWriter pw = getWriter(socket);
                String msg = null;
                while((msg=br.readLine())!=null){
                    System.out.println(msg);
                    pw.println(echo(msg));
                    if(msg.equals("bye")){
                        break;
                    }
                }
                
                
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void main(String[] args) throws IOException {
        new EchoServer().service();
    }
}

客户端代码

public class EchoClient {
    
    private int port=8000;
    private String host = "localhost";
    private Socket socket;
    
    public EchoClient() throws IOException{
        socket = new Socket(host, port);
    }
    
    private PrintWriter getWriter(Socket socket) throws IOException{
        OutputStream socketOut = socket.getOutputStream();
        return new PrintWriter(socketOut, true);
    }
    
    private BufferedReader getReader(Socket socket) throws IOException{
        InputStream socketIn = socket.getInputStream();
        return new BufferedReader(new InputStreamReader(socketIn));
    }
    
    public void talk(){
        try {
            BufferedReader br = getReader(socket);
            PrintWriter pw = getWriter(socket);
            BufferedReader localReader = new BufferedReader(new InputStreamReader(System.in));
            String msg=null;
            while((msg = localReader.readLine())!=null){
                pw.println(msg);
                System.out.println(br.readLine());
                if(msg.equals("bye")){
                    break;
                }
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        new EchoClient().talk();
    }

}