TCP与UDP协议详解

一、TCP

TCP建立连接后，通信双方都可以进行数据的传输；在保证可靠性上，采用超时重传和捎带确认机制；在流量控制上，采用滑动窗口协议，协议中规定，对于窗口内未经确认的分组需要重传；在拥塞控制上，采用慢启动算法。
TCP服务端工作代码

private static final int TCP_SERVER_PORT = 2321;
    //创建一个ServerSocket对象
    ServerSocket serverSocket = null;
    private void initDataServer(){
        try{
            //TCP_SERVER_PORT为指定的绑定端口，为int类型
            serverSocket = new ServerSocket(TCP_SERVER_PORT);
            //监听连接请求
            Socket socket = serverSocket.accept();
            //写入读Buffer中、获取输入流
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            //放入写buffer中、获取输出流
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
            //读取接收信息转换为字符串
            String ingoingMsg = in.readLine() + System.getProperty("line.separator");
            //生成发送字符串
            String outgoingMsg = "goodbye from port" + TCP_SERVER_PORT +     System.getProperty("line.separator");
            //将发送字符串写入上面定义的BufferWriter中
            out.write(outgoingMsg);
            //刷新，发送
            out.flush();
            //关闭
            socket.close();
        } catch (InterruptedIOException e) {
            //超时错误
            e.printStackTrace();
            //IO异常
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(serverSocket != null){
                try{
                    serverSocket.close();
                }catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

TCP客户端代码

public void initDataClient(){
        try{
            //初始化Socket，TCP_SERVER_PORT为指定端口，int类型
            Socket socket = new Socket("localhost", TCP_SERVER_PORT);
            //获取输入流
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            //获取输出流
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
            //读取接收信息转换为字符串
            String ingoingMsg = in.readLine() + System.getProperty("line.separator");
            //生成输出内容
            String outMsg = "TCP connecting to" + TCP_SERVER_PORT +     System.getProperty("line.separator");
            //写入
            out.write(outMsg);
            //刷新，发送
            out.flush();
            //获取输入流
            String inMsg = in.readLine() + System.getProperty("line.separator");
            //关闭连接
            socket.close();
        }catch (UnknownHostException e){
            e.printStackTrace();
        }catch (IOException e) {
            e.printStackTrace();
        }
    }

二、UDP通信

UDP不提供数据报分组、组装和数据报排序的特点，当报文发送之后是无法得知其是否安全完整到达。
UDP服务端代码

//接收的字节的大小，客户端发送的数据不能超过MAX_UDP_DATAGRAM_LEN
byte[] IMsg = new byte[MAX_UDP_DATAGRAM_LEN];
//实例化一个DatagramPacket类
DatagramPacket dp = new DatagramPacket(IMsg, IMsg.length);
//新建一个DatagramPacket类
DatagramPacket ds = null;
try{
  //UDP服务器监听的端口
  ds = new DatagramPacket(UDP_SERVER_PORT);
  //准备接收数据
  ds.receive(dp);
} catch (SocketException e){
  e.printStackTrace();
} catch (IOException e){
  e.printStackTrace();
} finally {
  //如果ds对象不为空，则关闭ds对象
  if (da != null){
    ds.close();
  }
}

UDP客户端代码

//定义需要发送的信息
String udpMsg = "hello world from UDP client" + UDP_SERVER_PORT;
//新建一个DatagramPacket类
DatagramPacket ds = null;
try{
  //初始化DatagramPacket对象
  ds = new DatagramPacket();
  InetAddress serverAddr = InetAddress.getByName("127.0.0.1");
  DatagramPacket dp;
  //初始化DatagramPacket对象
  dp = new DatagramPacket(udpMsg.getBytes(), udpMsg.length(), serverAddr, UDP_SERVER_PORT);
  //发送
  ds.send(dp);
//Socket连接异常
} catch (SocketException e){
  e.printStackTrace();
//不能连接到主机
} catch (UnknownHostException e){
  e.printStackTrace();
//数据流异常
} catch (IOException e){
  e.printStackTrace();
//其他异常
} catch (Exception e){
  e.printStackTrace();
} finally {
  //如果ds对象不为空，则关闭ds对象
  if (ds != null){
    ds.close();
  }
}