1.UDP定义

????? UDP也叫用户数据协议【无连接的协议】

????? 优点：不能保证数据的安全与可靠

????? 缺点：消耗小，效率高

2.基于UDP的网络通讯程序需要的类和方法

????? 基于UDP的网络通讯程序是不区分客户端和服务器。

（1）java.net.DatagramPacket【只负责创建用来发送的包和用来接收用的包】

该类表示数据报包。【打包被发送的数据/接收发来的数据】

构造方法：用来打包

DatagramPacket(byte[]?buf, int?length) 构造一个 DatagramPacket用于接收长度的数据包length。【接收发来的数据的数据包】

DatagramPacket(byte[]?buf, int?length, InetAddress?address, int?port【接收方的端口号】) 构造用于发送长度的分组的数据报包 length指定主机上到指定的端口号。【打包被发送的数据】???

实例方法：用来解析

byte[]??? getData() 返回数据缓冲区。

int? getLength() 返回要发送的数据的长度或接收到的数据的长度。

InetAddress getAddress() 返回该数据报发送或接收数据报的计算机的IP地址。

int? getPort() 返回发送数据报的远程主机上的端口号，或从中接收数据报的端口号。【得到发送方的端口号】

（2）java.net.DatagramSocket【负责包的发送和包的接收】

此类表示用于发送和接收数据报数据包的套接字。

????? 构造方法：

????? DatagramSocket() 构造数据报套接字并将其绑定到本地主机上的任何可用端口。【发包】

????? DatagramSocket(int?port) 构造数据报套接字并将其绑定到本地主机上的指定端口。【收包】

????? 实例方法：

????? void???? send(DatagramPacket?p) 从此套接字发送数据报包。

????? void???? receive(DatagramPacket?p) 从此套接字接收数据报包。

????? void???? close() 关闭此数据报套接字。

3. 基于UDP协议的通信程序创建步骤

????? （1）发送方：

将需要发送的数据通过DatagramPacket(byte[]?buf, int?length, InetAddress?address, int?port) 构造方法打包好。
通过DatagramSocket()的构造方法创建DatagramSocket对象。
DatagramSocket对象的send方法将打包好的数据报包，发送。
关闭DatagramSocket。

????? （2）接收方：

通过DatagramSocket(int?port)创建接收数据的DatagramSocket对象。
通过DatagramPacket(byte[]?buf, int?length) 创建一个空的数据报包。
通过调用接收数据的DatagramSocket对象的receive方法接收数据报包到空的数据报包。
解析数据报包。
关闭DatagramSocket。

4.代码演示

4.1客户端发，服务器收

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;



public class ClientSendMain {??

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

????? //定义数据报包

????? DatagramPacket sendpacket=null;

????? InetAddress receiveaddress=null;

????? int port=3000;

????? BufferedReader buff=null;

????? DatagramSocket sendsocket=null;

????? /*

????? ?* 创建发送的包---数据打包----发送

????? ?*/

????? //键盘输入数据----准备发送的数据

????? System.out.println("请输入需要发送的数据：");

????? buff=new BufferedReader(new InputStreamReader(System.in));

????? String info = buff.readLine();

????? byte[] bytes = info.getBytes();

????? int length=bytes.length;

????? //本机地址

????? receiveaddress=InetAddress.getLocalHost();

????? //创建带有服务器地址和端口号的发送包

????? sendpacket=new DatagramPacket(bytes, length, receiveaddress, port);

????? //创建DatagramSocket对象

????? sendsocket=new DatagramSocket();

????? sendsocket.send(sendpacket);

????? sendsocket.close();

?? }

}

import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.SocketException;



public class ServerMain {

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

????? /*

????? ?* 创建接收对象---创建接收用的空的数据报包-----解析

????? ?*/

???
????? //创建接收包的对象

????? int port=3000;

????? DatagramSocket receivesocket = new DatagramSocket(port);

????? //创建空的数据报包??

????? byte buff[]=new byte[1024];

????? DatagramPacket receivepacket = new DatagramPacket(buff, buff.length);

????? //接收数据

????? receivesocket.receive(receivepacket);

????? //解析数据

????? byte data[] = receivepacket.getData();

????? int len=receivepacket.getLength();

????? String msg=new String(data,0,len);

????? String clientip = receivepacket.getAddress().getHostAddress();

????? int clientsendport = receivepacket.getPort();

????? System.out.println("接收到来自"+clientip+":"+clientsendport+"的消息:"+msg);

????? receivesocket.close();

?? }

}

4.2 客户端持续发，服务器持续收

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;



public class ClientSendMain {

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

????? BufferedReader buff = null;

????? InetAddress receiveaddress = null;

????? int serverport = 3000;

????? DatagramPacket sendpacket = null;

????? DatagramSocket sendsocket = null;



????? buff = new BufferedReader(new InputStreamReader(System.in));

????? sendsocket = new DatagramSocket();

????? receiveaddress = InetAddress.getLocalHost();

????? boolean flag = true;



????? while (flag) {

????????? System.out.println("请输入需要发送的数据：");

????????? String sendinfo = buff.readLine();??????

????????? sendpacket = new DatagramPacket(sendinfo.getBytes(), sendinfo.getBytes().length, receiveaddress,

??????????????? serverport);

????????? sendsocket.send(sendpacket);

????????? if (sendinfo.equals("exit")) {

???????????? flag=false;

????????? }

????? }

????? sendsocket.close();

?? }

}

import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.SocketException;



public class ServerMain {



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

????? DatagramSocket receivesocket = null;

????? DatagramPacket receivepacket = null;

????? String receivemsg = null;

????? int serverport = 3000;

????? String clientip = null;

????? int clientsendport = 0;

????? boolean flag = true;

?????

????? receivesocket = new DatagramSocket(serverport);

????? byte buff[] = new byte[1024];

????? receivepacket = new DatagramPacket(buff, buff.length);

?????

????? while (flag) {?

????????? receivesocket.receive(receivepacket);

????????? byte data[] = receivepacket.getData();

????????? int len = receivepacket.getLength();

????????? receivemsg = new String(data, 0, len);

????????? clientip = receivepacket.getAddress().getHostAddress();

????????? clientsendport = receivepacket.getPort();

????????? System.out.println("服务器接收到来自" + clientip + ":" + clientsendport + "的消息:" + receivemsg);

????????? if(receivemsg.equals("exit")){

???????????? flag=false;

????????? }

????? }

????? receivesocket.close();

?? }

}

4.3双向-客户端持续发和收，服务器持续收和发

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;



public class ClientSendMain {

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

????? //客户端发，需要的变量和对象

????? BufferedReader buff = null;

????? InetAddress receiveaddress = null;

????? int serverport = 3000;

????? DatagramPacket sendpacket = null;

????? DatagramSocket sendsocket = null;????

????? buff = new BufferedReader(new InputStreamReader(System.in));

????? sendsocket = new DatagramSocket();

????? receiveaddress = InetAddress.getLocalHost();

?????

????? //客户端收，需要的变量和对象

????? DatagramPacket receivepacket=null;

????? DatagramSocket receivesocket=null;

????? int receiveport=2000;

????? receivesocket=new DatagramSocket(receiveport);

????? byte bys[]=new byte[1024];

????? receivepacket=new DatagramPacket(bys,bys.length);

?????

????? boolean flag = true;

????? while (flag) {

????????? //发

????????? System.out.println("请输入需要发送的数据：");

????????? String sendinfo = buff.readLine();??????

????????? sendpacket = new DatagramPacket(sendinfo.getBytes(), sendinfo.getBytes().length, receiveaddress,

??????????????? serverport);

????????? sendsocket.send(sendpacket);

?????????

????????? //收

????????? receivesocket.receive(receivepacket);???????

????????? String receivemsg = new String( receivepacket.getData(), 0, receivepacket.getLength());

????????? System.out.println("收到来自服务器返回的数据---"+receivemsg);

?????????????
????????? if (receivemsg.equals("exit")) {

???????????? flag=false;

????????? }

????? }

????? sendsocket.close();

????? receivesocket.close();

?? }


}

import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;



public class ServerMain {



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

????? System.out.println("服务器已启动....");

?????

????? //服务器收

????? DatagramSocket receivesocket = null;

????? DatagramPacket receivepacket = null;

????? int serverport = 3000;



????? receivesocket = new DatagramSocket(serverport);

????? byte buff[] = new byte[1024];

????? receivepacket = new DatagramPacket(buff, buff.length);

?????

????? //服务器发

????? DatagramPacket sendpacket = null;

????? DatagramSocket sendsocket = null;

????? int sendport=2000;

????? InetAddress receiveaddress = InetAddress.getLocalHost();

????? sendsocket=new DatagramSocket();

?????

????? boolean flag = true;

????? while (flag) {?

????????? //收

????????? receivesocket.receive(receivepacket);

????????? byte data[] = receivepacket.getData();

????????? int len = receivepacket.getLength();

????????? String receivemsg = new String(data, 0, len);

????????? String clientip = receivepacket.getAddress().getHostAddress();

????????? int clientsendport = receivepacket.getPort();

????????? System.out.println("服务器接收到来自" + clientip + ":" + clientsendport + "的消息:" + receivemsg);

?????????

????????? //发

????????? sendpacket=new DatagramPacket(receivemsg.getBytes(),receivemsg.getBytes().length,receiveaddress,sendport);

????????? sendsocket.send(sendpacket);

?????????

?????????

????????? if(receivemsg.equals("exit")){

???????????? flag=false;

????????? }

????? }

????? sendsocket.close();

????? receivesocket.close();

?????

?? }



}

4.4 多个客户端持续发和收，服务器持续发和收

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;

import java.util.Scanner;



/**

?* 发送数据的客户端

?*/

public class Client {

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

????? BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));

?? ?? //绑定一个指定的端口用于接收数据和发送数据

????? DatagramSocket server=new DatagramSocket();

????? //定义接收数据的空包

????? byte[] sbyte=new byte[1024];

?????? DatagramPacket spack=new DatagramPacket(sbyte, sbyte.length);

????? //定义持续控制发送的循环变量

????? boolean flag=true;

????? while (flag) {

????????? System.out.println("请输入要发送的数据：");

????????? String info=buff.readLine();

????????? //打包数据

????????? byte[] fbyte=info.getBytes();

????????? DatagramPacket fpack=new DatagramPacket(fbyte, fbyte.length, InetAddress.getLocalHost(), 3000);????????

????????? //发送数据

????????? server.send(fpack);

????????? //判断退出

????????? if (info.equals("886")) {

???????????? flag=false;

???????????? System.out.println("关闭客户端！");

????????? }else{

???????????? //接收数据

???????????? server.receive(spack);

???????????? //拆包

???????????? byte data[]=spack.getData();

???????????? String msg=new String(data,0,spack.getLength());

???????????? System.out.println("接收到服务器返回的数据是："+msg);
????????? }
????? }????
????? server.close();
?? }

}

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;



/**

?* 接收数据的服务器端

?*/

public class Server {

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

???????????? //绑定接收数据的端口

???????????? DatagramSocket server=new DatagramSocket(3000);

???????????? System.out.println("----》服务器端已经启动，等待客户端发送数据");

???????????? byte[] bytes = new byte[1024];

???????????? while(true){

???????????? DatagramPacket packet = new DatagramPacket(bytes, bytes.length);
??????????
???????????? server.receive(packet);

???????????? ClientThread clientThread=new ClientThread(server,packet);

???????????? Thread th=new Thread(clientThread);????????????

???????????? th.start();

?????????????????? }

??????????????? }
}

/**

?* 用户发送数据线程类

?*/

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;


public class ClientThread implements Runnable{

????? private DatagramSocket server;

????? private DatagramPacket datagramPacket;

????? private? boolean falg=true;

????? public ClientThread(DatagramSocket server,DatagramPacket datagramPacket ) {

????????? this.server=server;

????????? this.datagramPacket=datagramPacket;

????? }

?????
???????? public void run() {
????????? ?
????         try{

????????    ? while(falg){????????????

???????????? //拆包

???????????? byte data[]=datagramPacket.getData();

???????????? int len=datagramPacket.getLength();

???????????? String info=new String(data,0,len);

???????????? String clientip = datagramPacket.getAddress().getHostAddress();

???????????? int clientsendport = datagramPacket.getPort();

???????????? System.out.println("服务器接收到来自" + clientip + ":" + clientsendport + "的消息:" + info);

???????????? //判断退出

???????????? if (info.equals("886")) {

??????????????? falg=false;

??????????????? //server.close();

??????????????? System.out.println("客户端退出");

???????????? }else{

??????????????? //发送数据

??????????????? info="server："+info;

??????????????? byte fbyte[]=info.getBytes();

??????????????? DatagramPacket fPacket=new DatagramPacket(fbyte, fbyte.length,datagramPacket.getAddress(),datagramPacket.getPort());

??????????????? server.send(fPacket);

??????????????? falg=false;

???????????? }???????????

????????? }

????????? //关闭

????????? }catch(Exception e){

???????????? e.printStackTrace();

????????? }?????????

????? }

}