通过URL读取网页内容
    1通过URL对象的openStream（）方法能够得到指定资源的输入流。
    2通过输入流能够读取、訪问网络上的数据。

    案例：

   import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.MalformedURLException;

import java.net.URL;

public class UrlTest {

       public static void main(String[] args) {

		try {

			URL url = new URL("http://www.baidu.com");

		    InputStream is = url.openStream();

		    InputStreamReader isr = new InputStreamReader(is,"utf-8");

		    BufferedReader br = new BufferedReader(isr);

		    String data = br.readLine();

		    while(data != null){

		    	System.out.println(data);

		    	data = br.readLine();

		    }

		    br.close();

		    isr.close();

		    is.close();

		} catch (MalformedURLException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

	}

}

Socket通信实现步骤
   1 创建ServerSocekt和Socket
   2 打开连接到Socket的输入/输出流
   3 依照协议对Socket进行读写操作
   4关闭输入输出流、关闭Socket

   基于TCP的Socket通信
   client能够对应，
    服务端：

 import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.PrintWriter;

import java.net.ServerSocket;

import java.net.Socket;

public class Server {

       public static void main(String[] args) {

		try {

			ServerSocket serverSocket = new ServerSocket(8888);

			System.out.println("server端即将启动！！");

			Socket socket = serverSocket.accept();

			InputStream is = socket.getInputStream();

			InputStreamReader isr = new InputStreamReader(is);

			BufferedReader br = new BufferedReader(isr);

			String info = null;

			while((info = br.readLine()) != null){

				System.out.println("我是server，client说：" + info);

			}

			socket.shutdownInput();

			OutputStream os = socket.getOutputStream();

			PrintWriter pw = new PrintWriter(os);

			pw.write("欢迎您！！");

			pw.flush();

			pw.close();

			os.close();

			br.close();

			isr.close();

			is.close();

			socket.close();

			serverSocket.close();

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

	}

}

client：

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.PrintWriter;

import java.net.Socket;

import java.net.UnknownHostException;

public class Client {

        public static void main(String[] args) {

			try {

				Socket socket = new Socket("localhost",8888);

				OutputStream os = socket.getOutputStream();

				PrintWriter pw = new PrintWriter(os);

				pw.write("username：admin;password:123");

				pw.flush();

				socket.shutdownOutput();

				InputStream is = socket.getInputStream();

				BufferedReader br = new BufferedReader(new InputStreamReader(is));

				String info = null;

				while((info = br.readLine()) != null){

					System.out.println("我是client。server说：" + info);

				}

				br.close();

				is.close();

				pw.close();

				os.close();

				socket.close();

			} catch (UnknownHostException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (IOException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

}

多线程server与多client通信：
   基本实现步骤：
        1 server端创建ServerSocket，循环调用accept（）等待client连接
2 client创建一个socket并请求和服务端连接
3 服务端接受client请求，创建socket与客户建立专线连接
4 建立连接的两个socket在一个单独的线程对话
5 server端继续等待新的连接
案例：

 import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.PrintWriter;

import java.net.Socket;

public class ServerThread extends Thread{

	Socket socket = null;

	public ServerThread(Socket socket){

		this.socket = socket;

	}

	public void run(){

		InputStream is= null;

		InputStreamReader isr = null;

		BufferedReader br = null;

		OutputStream os = null;

		PrintWriter pw = null;

		try {

			is = socket.getInputStream();

			isr = new InputStreamReader(is);

			br = new BufferedReader(isr);

			String info = null;

			while((info = br.readLine()) != null){

				System.out.println("我是server。client说：" + info);

			}

			socket.shutdownInput();

			os = socket.getOutputStream();

			pw = new PrintWriter(os);

			pw.write("欢迎您！

。");

			pw.flush();

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}finally{

				try {

					if(pw!= null)

						pw.close();

					if(os != null)

						os.close();

					if(br != null)

						br.close();

					if(isr != null)

						isr.close();

					if(is != null)

						is.close();

					if(socket != null)

						socket.close();

				} catch (IOException e) {

					e.printStackTrace();

				}

		}

//		serverSocket.close();

	}

}

服务端：

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.PrintWriter;

import java.net.InetAddress;

import java.net.ServerSocket;

import java.net.Socket;

public class Server {

       public static void main(String[] args) {

		try {

			ServerSocket serverSocket = new ServerSocket(8888);

			Socket socket = null;

			int count = 0;

			System.out.println("server端即将启动！！

");

            while(true){

            	socket = serverSocket.accept();

            	ServerThread serverThread = new ServerThread(socket);

            	serverThread.start();

            	count++;

            	System.out.println("client连接数量：" + count);

               InetAddress address = socket.getInetAddress();

               System.out.println("当前client的IP：" + address);

            }

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

	}

}

client同上。

UDP
     DatagramPacket:表示数据报包
     DatagramSocket：进行端到端通信的类
基于UDP的Socket编程
   服务端：

 package com.hpu.lianxi;

import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;

public class UDPServer {

      public static void main(String[] args) throws IOException {

		DatagramSocket socket = new DatagramSocket(8800);

		byte[] data = new byte[1024];

		System.out.println("server已经启动，等待client发送数据****");

		DatagramPacket packet = new DatagramPacket(data,data.length);

	    socket.receive(packet);

	    String info = new String(data,0,packet.getLength());

	    System.out.println("这是服务端，client说：" + info);

	    InetAddress address = packet.getAddress();

	    int port = packet.getPort();

	    byte[] data2 = "欢迎您！

。".getBytes();

	    DatagramPacket packet2 = new DatagramPacket(data2, data2.length,address,port);

	    socket.send(packet2);

	    socket.close();

      }

} 

client：

 package com.hpu.lianxi;

import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;

import java.net.UnknownHostException;

public class UDPClient {

         public static void main(String[] args) throws IOException {

			InetAddress address = InetAddress.getByName("localhost");

			int port = 8800;

			byte[] data = "username:admin;password：123".getBytes();

			DatagramPacket packet = new DatagramPacket(data, data.length,address,port);

			DatagramSocket socket = new DatagramSocket();

			socket.send(packet);

			byte[] data2 = new byte[1024];

			DatagramPacket packet2 = new DatagramPacket(data2, data2.length,address,port);

			socket.receive(packet2);

			String reply = new String(data2,0,packet2.getLength());

			System.out.println("我是client，server说：" + reply);

			socket.close();

		}

}

 多线程的优先级
    假设不设置优先级可能会导致执行时速度很慢，可减少优先级
    输入流与输出流的关闭
    对于同一个socket，假设关闭了输出流。则与该输出流关联的socket也会被关闭，所以一般不用
    关闭流，直接关闭socket就可以

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