TCP和UDP用Java实现

查询进程

netstat -ano #查看所有的端口
netstat -ano|findstr "5900" # 查看指定端口
tasklist|findstr "8696 #查看指定端口进程

TCP和UDP的区别

TCP相当于打电话

• 连接稳定
• 三次握手、四次挥手

三次握手：
A：你瞅啥？
B：瞅你咋滴？
A：干一场（连接建立成功，信息开始传输）

四次挥手：

A：我要走了！
B：你真的要走了吗？
B：你真的真的要走了吗？
A：我真的要走了！

• 客户端、服务端分开
• 传输完成，释放连接、效率低

UDP

• 相当于发短信
• 不进行连接，不稳定
• 客户端、服务端没有明确的界线
• 不管是否准备好，都可以进行连接

TCP通信实战

这里分为客户端和服务端
客户端：

1. 连接服务端Socket
2. 发送消息

//TCP客户端
public class TCPClientDemo01 {public static void main(String[] args) {OutputStream os = null;Socket socket = null;//连接服务器try {//1.要知道服务端的地址，端口号InetAddress serverIP = InetAddress.getByName("127.0.0.1");int port = 9999;//2.创建一个socket连接socket = new Socket(serverIP, port);//3.发送消息IO流os = socket.getOutputStream();os.write("您好Java".getBytes());} catch (Exception e) {e.printStackTrace();}finally {//注意关闭流的顺序和打开流的顺序要相反//判断null避免空指针异常if(os != null){try {os.close();} catch (IOException e) {e.printStackTrace();}}if(socket != null){try {socket.close();} catch (IOException e) {e.printStackTrace();}}}}
}

服务端：

1. 建立服务的端口 ServerSocket
2. 等待用户的连接 accept
3. 接收用的消息

//TCP服务端
public class TcpServerDemo01 {public static void main(String[] args) {ServerSocket serverSocket = null;;Socket socket = null;InputStream is = null;;ByteArrayOutputStream baos = null;try {//1.得现有一个服务端地址serverSocket = new ServerSocket(9999);//这里一直循环可以一直接收客户端的请求while(true){//2.等待客户端进行连接socket = serverSocket.accept();//3.读取客户端的消息is = socket.getInputStream();//管道流来处理消息baos = new ByteArrayOutputStream();byte[] buffer = new byte[1024];int len;while((len=is.read(buffer))!=-1){baos.write(buffer,0,len);}System.out.println(baos);}} catch (IOException e) {e.printStackTrace();}finally {if(baos != null){try {baos.close();} catch (IOException e) {e.printStackTrace();}}if(is != null){try {is.close();} catch (IOException e) {e.printStackTrace();}}if(socket != null){try {socket.close();} catch (IOException e) {e.printStackTrace();}}if(serverSocket != null){try {serverSocket.close();} catch (IOException e) {e.printStackTrace();}}}}
}

文件上传

public class TcpClientDemo02 {public static void main(String[] args) throws IOException {//1.创建Socket连接Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 9000);//2.创建一个输出流OutputStream os = socket.getOutputStream();//3.读取文件FileInputStream fis = new FileInputStream(new File("upLoadImager.png"));//4.写出文件byte[] buffer = new byte[1024];int len;while ((len=fis.read(buffer))!=-1){os.write(buffer,0,len);}//通知服务器，我已经上传结束了socket.shutdownOutput();    //我已经传输完成//确定服务端接收完毕，断开连接InputStream inputStream = socket.getInputStream();ByteArrayOutputStream baos = new ByteArrayOutputStream();byte[] buffer2 = new byte[1024];int len2;while((len2=inputStream.read(buffer2))!=-1){baos.write(buffer2,0,len2);}System.out.println(baos);//5.关闭资源baos.close();inputStream.close();fis.close();os.close();socket.close();}
}

public class TcpServerDemo02 {public static void main(String[] args) throws IOException {//1.创建服务ServerSocket serverSocket = new ServerSocket(9000);//2.监听客户端连接Socket socket = serverSocket.accept();//3.获取输入流InputStream is = socket.getInputStream();//4.文件输出FileOutputStream fos = new FileOutputStream(new File("receive.png"));byte[] buffer = new byte[1024];int len;while((len=is.read(buffer))!=-1){fos.write(buffer,0,len);}//通知客户端服务端接收完毕了——对应TCP的握手与挥手OutputStream os = socket.getOutputStream();os.write("接收完毕，可以断开".getBytes());//关闭资源os.close();fos.close();is.close();socket.close();serverSocket.close();}
}

UDP进行通信

发送端

public class UdpSendDemo01 {public static void main(String[] args) throws IOException {//1.建立Socket连接DatagramSocket socket = new DatagramSocket();//2.建个包String msg = "您好Java";InetAddress localhost = InetAddress.getByName("localhost");int port = 9090;//数据，数据长度起始，发给谁DatagramPacket packet = new DatagramPacket(msg.getBytes(), 0, msg.getBytes().length, localhost, port);//3.发送包socket.send(packet);//4.关闭流socket.close();}
}

接收端

public class UdpReceiveDemo01 {public static void main(String[] args) throws IOException {//开放端口DatagramSocket socket = new DatagramSocket(9090);//接受数据包byte[] buffer = new byte[1024];DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);//阻塞接收socket.receive(packet);System.out.println(packet.getAddress().getHostAddress());System.out.println(new String(packet.getData(),0,packet.getLength()));socket.close();}
}

UDP实现聊天框

因为聊天框需要同时一起进行发送消息，所以在这里使用多线程进行实现。
消息类都实现了Runnable类。

发送类

public class TalkSend implements Runnable{DatagramSocket socket = null;BufferedReader reader = null;private int fromPort;private String toIP;private int toPort;public TalkSend(int fromPort, String toIP, int toPort) {this.fromPort = fromPort;this.toIP = toIP;this.toPort = toPort;try {socket = new DatagramSocket(fromPort);reader = new BufferedReader(new InputStreamReader(System.in));} catch (SocketException e) {e.printStackTrace();}}@Overridepublic void run() {while(true){String data = null;try {data = reader.readLine();byte[] datas = data.getBytes();DatagramPacket pakcet = new DatagramPacket(datas, 0, datas.length, new InetSocketAddress(this.toIP, this.toPort));socket.send(pakcet);if(data.equals("bye")){break;}}catch (IOException e) {e.printStackTrace();}}socket.close();}
}

接收类

public class TalkReceive implements Runnable{DatagramSocket socket = null;private int port;private String receiver;public TalkReceive(int port,String receiver) {this.receiver =receiver;this.port = port;try {socket = new DatagramSocket(port);} catch (SocketException e) {e.printStackTrace();}}@Overridepublic void run() {while(true){//接受包byte[] container = new byte[1024];DatagramPacket packet = new DatagramPacket(container, 0, container.length);try {socket.receive(packet);//断开连接  byebyte[] data = packet.getData();String receiveData = new String(data, 0, data.length);System.out.println(receiver+receiveData);//发送bye时，跳出循环，即断开连接if(receiveData.equals("bye")){break;}} catch (IOException e) {e.printStackTrace();}}socket.close();}
}

学生类

public class TalkStu {public static void main(String[] args) {new Thread(new TalkSend(7777,"localhost",9999)).start();new Thread(new TalkReceive(8888,"老师")).start();}
}

老师类

public class TalkTeacher {public static void main(String[] args) {new Thread(new TalkSend(5555,"localhost",8888)).start();new Thread(new TalkReceive(9999,"学生")).start();}
}

使用URL下载资源

只要知道某一个资源的所在位置（URL，统一资源定位符）
那么就可以给它下载下来。

public class URLTest {public static void main(String[] args) throws IOException {//1.下载地址（该地址是从网上随便找的一个图片的所在路径）URL url = new URL("https://i1.hdslb.com/bfs/face/e3637ff7fa559e53a6bd4a8521b9446619f00cad.jpg@160w_160h_1c_1s.webp");//下载什么格式的文件，则文件后缀名需要对应上String fileName = "46619f00cad.jpg";//2.连接到该资源 HTTPHttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();InputStream inputStream = urlConnection.getInputStream();FileOutputStream fos = new FileOutputStream(fileName);byte[] buffer = new byte[1024];int len;while((len=inputStream.read(buffer))!=-1){fos.write(buffer,0,len);}//关闭资源fos.close();inputStream.close();urlConnection.disconnect();}
}