import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
class UDPClient
{
public static void main(String[] args) throws IOException
{
// 构造数据报套接字并将其绑定到本地主机上任何可用的端口
DatagramSocket client = new DatagramSocket();
// 在给定主机名的情况下确定主机的 IP 地址
InetAddress addr = InetAddress.getByName("127.0.0.1");
int port = 10021;
for (int i = 0; i < 5; i++)
{
String sendStr = "Hello! I‘m Client" + i;
byte[] sendBuf = sendStr.getBytes();
// 构造数据报包，用来将长度为 length 的包发送到指定主机上的指定端口号。length 参数必须小于等于 buf.length。
// buf - 包数据 length - 包长度 address - 目的地址 port - 目的端口号
DatagramPacket sendPacket = new DatagramPacket(sendBuf, sendBuf.length, addr, port);
// 从此套接字发送数据报包。DatagramPacket 包含的信息指示：将要发送的数据、其长度、远程主机的 IP
// 地址和远程主机的端口号。
client.send(sendPacket);
byte[] recvBuf = new byte[100];
// 构造 DatagramPacket，用来接收长度为 length 的数据包。 length 参数必须小于等于
// buf.length。
DatagramPacket recvPacket = new DatagramPacket(recvBuf, recvBuf.length);
// 从此套接字接收数据报包。
client.receive(recvPacket);
String recvStr = new String(recvPacket.getData(), 0, recvPacket.getLength());
System.out.println("recvMsg =" + recvStr +"; remotePort =" + recvPacket.getPort());
}
client.close();
}
}
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
class UDPServer
{
public static void main(String[] args) throws IOException
{
DatagramSocket server = new DatagramSocket(10021);
byte[] recvBuf = new byte[100];
for (int i = 0; i < 5; i++)
{
DatagramPacket recvPacket = new DatagramPacket(recvBuf, recvBuf.length);
server.receive(recvPacket);
String recvStr = new String(recvPacket.getData(), 0, recvPacket.getLength());
int port = recvPacket.getPort();
System.out.println("reveMsg = "+ recvStr + "; remote port =" + port);
InetAddress addr = recvPacket.getAddress();
String sendStr = "Hello ! I‘m Server" + i;
byte[] sendBuf = sendStr.getBytes();
DatagramPacket sendPacket = new DatagramPacket(sendBuf, sendBuf.length, addr, port);
server.send(sendPacket);
}
server.close();
}
}
client端输出：
recvMsg =Hello ! I‘m Server0; remotePort =10021
recvMsg =Hello ! I‘m Server1; remotePort =10021
recvMsg =Hello ! I‘m Server2; remotePort =10021
recvMsg =Hello ! I‘m Server3; remotePort =10021
recvMsg =Hello ! I‘m Server4; remotePort =10021
server端输出：
reveMsg = Hello! I‘m Client0; remote port =61226
reveMsg = Hello! I‘m Client1; remote port =61226
reveMsg = Hello! I‘m Client2; remote port =61226
reveMsg = Hello! I‘m Client3; remote port =61226
reveMsg = Hello! I‘m Client4; remote port =61226
UDP运输层协议：
（1）UDP是一种无连接的服务，即在两个进程间没有创建管道时的初始握手阶段。
（2）因为UDP没有管道，所以当一个进程需要向另一个进程发送一批字节时，该发送进程需要为这批字节附上目的进程地址（IP和port），并且，该过程对于每批由发送进程所发送的字节都必须重复做，见循环中五次发送UDP报文的操作。
由于UDP当中没有流与套接字相关联，事实上UDP也不是将字节送入与Socket相关的流，而是将一个个分组通过DataGramSocket对象直接发送出去。
而在TCP运输层协议中：
（1）TCP在客户机进程和服务机进程之间提供了可靠的字节流服务，一旦建立连接，两端就可以通过与Socket对象相关联的输入输出流来进行数据交互，而不用像UDP那样每次都要通过DataGramSocket对象指明远端IP和port来发送和接收
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
class TCPClient
{
public static void main(String[] args) throws IOException
{
// 构造数据报套接字并将其绑定到本地主机上任何可用的端口
Socket client = new Socket();
// 在给定主机名的情况下确定主机的 IP 地址
InetAddress addr = InetAddress.getByName("127.0.0.1");
int port = 10021;
client.connect(new InetSocketAddress(addr, port));
OutputStream output = client.getOutputStream();
InputStream input = client.getInputStream();
for (int i = 0; i < 5; i++)
{
String sendStr = "Hello! I‘m Client" + i;
output.write(sendStr.getBytes());
byte[] recvBuf = new byte[100];
int length = input.read(recvBuf);
String str = new String(recvBuf);
System.out.println("recvMsg =" + str.substring(0,length));
}
client.close();
}
}
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
class TCPServer
{
public static void main(String[] args) throws IOException
{
ServerSocket server = new ServerSocket(10021);
Socket socket = server.accept();
OutputStream output = socket.getOutputStream();
InputStream input = socket.getInputStream();
byte[] recvBuf = new byte[100];
for (int i = 0; i < 5; i++)
{
int len = input.read(recvBuf);
String str = new String(recvBuf);
System.out.println("reveMsg = "+ str.substring(0,len) + "; remote port =" + socket.getRemoteSocketAddress());
String sendStr = "Hello ! I‘m Server" + i;
output.write(sendStr.getBytes());
}
server.close();
}
}
client端输出：
recvMsg =Hello ! I‘m Server0
recvMsg =Hello ! I‘m Server1
recvMsg =Hello ! I‘m Server2
recvMsg =Hello ! I‘m Server3
recvMsg =Hello ! I‘m Server4
server端输出：
reveMsg = Hello! I‘m Client0; remote port =/127.0.0.1:54233
reveMsg = Hello! I‘m Client1; remote port =/127.0.0.1:54233
reveMsg = Hello! I‘m Client2; remote port =/127.0.0.1:54233
reveMsg = Hello! I‘m Client3; remote port =/127.0.0.1:54233
reveMsg = Hello! I‘m Client4; remote port =/127.0.0.1:54233