Socket：一個Socket由一個IP地址和一個埠號唯一確定 

ServerSocket：伺服器端套接字，接收請求

TCP：傳輸控制協議，是可靠協議，必須先建立連線

UDP：使用者資料報協議

Socket

java在包java.net中提供了兩個類 Socket和ServerSocket，分別用來表示雙向連線的客戶端和服務端，其建構函式：

Socket（String host，int port）；

Socket（String host，int port，boolean stream）；

Socket（InetAddress address，int port）；

Socket（InetAddress address，int port，boolean stream）；

其中address，host和port分別是雙向連線中另一方的IP地址，主機名和埠號，stream指明socket是流socket還是資料報socket。

在選擇埠時，要選大於1023的數，因為0~1023是系統保留的埠號

package socketDemo;

import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketAddress;

public class ServerSocketDemo {

	public static void main(String[] args) {

		try {
			ServerSocket ss = new ServerSocket(1234);
			while (true) {
				Socket socket = ss.accept();
				InetAddress sa = socket.getInetAddress();
				System.out.println("sa.getHostAddress()" + ":" + sa.getHostAddress());
				System.out.println("sa.getHostName()" + ":" + sa.getHostName());
				System.out.println("sa.getAddress()" + ":" + sa.getAddress());
				System.out.println("socket.getPort()" + ":" + socket.getPort());
				System.out.println(sa.toString() + "連線成功了");
				System.out.println("正在接收");
			}

		} catch (IOException e) {
			e.printStackTrace();
		}

	}

}
 

package socketDemo;

import java.net.Socket;

public class SocketDemo {

	public static void main(String[] args) {
		try {
			Socket socket = new Socket("localhost", 1234);
			System.out.println("socket");
		} catch (Exception e) {
			e.printStackTrace();
		}
		


	}

}

用Socket實現文字傳輸

package socketDemo;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerSocketDemo {

	public static void main(String[] args) {

		try {
			ServerSocket ss = new ServerSocket(1234);
			while (true) {
				Socket socket = ss.accept();
				InputStream is = socket.getInputStream();
				OutputStream os = socket.getOutputStream();
				BufferedReader br = new BufferedReader(new InputStreamReader(is,"gbk"));
				BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os,"gbk"));
				String line = null;
				while((line = br.readLine()) != null){
					System.out.println("收到資料" + line);
					String send = "hello ," + line + "\r\n" ;
					bw.write(send);
					bw.flush();
					System.out.println("傳送了" + send);
				}
				
				
			}

		} catch (IOException e) {
			e.printStackTrace();
		}

	}

}
 

package socketDemo;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.Socket;

public class SocketDemo {

	public static void main(String[] args) {
		try {
			Socket socket = new Socket("localhost", 1234);
			InputStream is = socket.getInputStream();
			OutputStream os = socket.getOutputStream();
			BufferedReader br = new BufferedReader(new InputStreamReader(is,"gbk"));
			BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os,"gbk"));
			bw.write("abc\r\n");
			bw.flush();
			System.out.println(br.readLine());
			bw.close();
			
		}
		catch (Exception e) {
			e.printStackTrace();
		}

	}

}