七、网络编程
7.1．IP协议
最重要的贡献是IP地址
7.2．TCP和UDP协议
TCP（快）可靠传输，发送时必须建立连接（三次握手协议 ）
UDP（慢）不可靠传输，发送时无须建立连接
7.3．TCP 的TCP Server和TCP Client
注意，要首先启动Server，再启动Client
端口号是应用的入口，有两个字节，所以每个服务器最多能运行65536个应用程序，而TCP的端口和UDP的端口不一样，定义端口时，尽量定义1024以上的。
特别典型的端口号，http 80；
//TCP Server
import java.net.*;
import java.io.*;
public class TCPServer {
public static void main(String[] args) throws Exception {
ServerSocket ss = new ServerSocket(6666);
while(true) {
Socket s = ss.accept();//阻塞函数，一直在这等，直到有访问，才会继续执行
System.out.println("a client connect!");
DataInputStream dis = new DataInputStream(s.getInputStream());
System.out.println(dis.readUTF());
dis.close();
s.close();
}
}
}
//TCP Client
import java.net.*;
import java.io.*;
public class TCPClient {
public static void main(String[] args) throws Exception {
Socket s = new Socket("127.0.0.1", 6666);
OutputStream os = s.getOutputStream();
DataOutputStream dos = new DataOutputStream(os);
Thread.sleep(3000);
dos.writeUTF("hello server!");
dos.flush();
dos.close();
s.close();
}
}
7.4．UDP Server和Client（UDP只能传送字节数组）
//UDP Server
import java.net.*;
public class TestUDPServer
{
public static void main(String args[]) throws Exception
{
byte buf[] = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, buf.length);
DatagramSocket ds = new DatagramSocket(5678);
while(true)
{
ds.receive(dp);
System.out.println(new String(buf,0,dp.getLength()));//String的构造函数
}
}
}
//UDP Client
import java.net.*;
public class TestUDPClient
{
public static void main(String args[]) throws Exception
{
byte[] buf = (new String("Hello")).getBytes();
DatagramPacket dp = new DatagramPacket(buf, buf.length,
new InetSocketAddress("127.0.0.1", 5678)
);
DatagramSocket ds = new DatagramSocket(9999);//client自己的端口，因为UDP不是面向连接的
ds.send(dp);
ds.close();
}
}
//TestUDP Client
import java.net.*;
import java.io.*;
public class TestUDPClient
{
public static void main(String args[]) throws Exception
{
long n = 10000L;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
dos.writeLong(n);
byte[] buf = baos.toByteArray();//将long型数据转化成字符数组的形式，进行输入
System.out.println(buf.length);
DatagramPacket dp = new DatagramPacket(buf, buf.length,
new InetSocketAddress("127.0.0.1", 5678)
);
DatagramSocket ds = new DatagramSocket(9999);
ds.send(dp);
ds.close();
}
}
//TestUDP Server
import java.net.*;
import java.io.*;
public class TestUDPServer
{
public static void main(String args[]) throws Exception
{
byte buf[] = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, buf.length);
DatagramSocket ds = new DatagramSocket(5678);
while(true)
{
ds.receive(dp);
ByteArrayInputStream bais = new ByteArrayInputStream(buf);
DataInputStream dis = new DataInputStream(bais);
System.out.println(dis.readLong());//将字符数组读成long型
}
}
}