[网络协议]TCP、UDP网络协议（文件传输、消息聊天）

TCP、UDP协议

1.1、网络通信要素

1.网络编程中两个主要问题

• 如何准确定位到网络上的一台主机或者多台主机
• 找到主机之后如何进行通信

2.网络编程中的要素

• IP和端口号
• 网络通信协议 UDP、TCP

1.2、IP

含义：

ip（InetAdsress）唯一定位一台网络上计算机

本机地址：127.0.0.1，localhost

import java.net.InetAddress;
import java.net.UnknownHostException;
//测试IP
public class TestInetAddress {
    public static void main(String[] args) throws UnknownHostException {
        InetAddress inetAddress =InetAddress.getByName("127.0.0.1");
        System.out.println(inetAddress);
        InetAddress inetAddress2 = InetAddress.getByName("www.baidu.com");
        System.out.println(inetAddress2);
        //常用方法
        System.out.println(inetAddress2.getAddress());
        System.out.println(inetAddress2.getCanonicalHostName());
        System.out.println(inetAddress2.getHostAddress());
    }
}

1.3、端口

端口表示计算机上的一个程序的进程；

不同的进程有不同的端口号（范围被规定为0-65535）

#查看所有端口
netstat -ano

#查看指定的端口
netstat -ano findstr “3306”

# 查看指定端口的进程
Ctrl+shift+ESC（打开任务管理器）

1.4、通信协议

协议：约定

网络通信协议：速率、传输码率、代码结构、传输控制。。

TCP/IP协议簇：实际上是一组协议

TCP:用户传输协议

UDP：用户数据报协议

IP：网络互联协议

TCP-UDP对比

TCP ：

• 连接、稳定
• 三次握手、四次挥手
• 客户端、服务端
• 传输完成、释放连接、效率低

UDP：

• 不连接，不稳定
• 客户端、服务端：没有明确的界限
• 不管有没有准备好都可以发给你

1.5、TCP

客户端、服务端通信

• 客户端

// 客户端
public class TcpClient {
    public static void main(String[] args) {
        Socket socket = null;
        OutputStream os = null;
        try {
            //1.创建Socket对象，指明服务器端的ip和端口号
            InetAddress inet = InetAddress.getByName("127.0.0.1");
            socket = new Socket(inet, 8899);
            //2.获取一个输出流，用于输出数据
            os = socket.getOutputStream();
            //3.写出数据的操作
            os.write("你好，我是客户端mm".getBytes());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //4.资源的关闭
            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

// 服务端
public class TcpServer {
    public static void main(String[] args) {
        ServerSocket ss = null;
        Socket socket = null;
        InputStream is = null;
        ByteArrayOutputStream baos = null;
        try {
            //1.创建服务器端的ServerSocket，指明自己的端口号
            ss = new ServerSocket(8899);
            //2.调用accept()表示接收来自于客户端的socket
            socket = ss.accept();
            //3.获取输入流
            is = socket.getInputStream();

            //不建议这样写，可能会乱码
//        byte[] buffer = new byte[1024];
//        int len;
//        while((len = is.read(buffer)) != -1){
//            String str = new String(buffer,0,len);
//            System.out.print(str);
//        }
            //4.读取输入流中的数据
            baos = new ByteArrayOutputStream();
            byte[] buffer = new byte[5];
            int len;
            while ((len = is.read(buffer)) != -1) {
                baos.write(buffer, 0, len);
            }

            System.out.println(baos.toString());

            System.out.println("收到了来自于：" + socket.getInetAddress().getHostAddress() + "的数据");

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (baos != null) {
                //5.关闭资源
                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 (ss != null) {
                try {
                    ss.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

文件上传、文件下载

• 客户端

/*
  这里涉及到的异常，应该使用try-catch-finally处理
*/
@Test
public void client() throws IOException {
    //1.
    Socket socket = new Socket(InetAddress.getByName("127.0.0.1"),9090);
    //2.
    OutputStream os = socket.getOutputStream();
    //3.
    FileInputStream fis = new FileInputStream(new File("beauty.jpg"));
    //4.
    byte[] buffer = new byte[1024];
    int len;
    while((len = fis.read(buffer)) != -1){
        os.write(buffer,0,len);
    }
    //关闭数据的输出
    socket.shutdownOutput();
    //5.接收来自于服务器端的数据，并显示到控制台上
    InputStream is = socket.getInputStream();
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    byte[] bufferr = new byte[20];
    int len1;
    while((len1 = is.read(buffer)) != -1){
        baos.write(buffer,0,len1);
    }
    System.out.println(baos.toString());
    //6.
    fis.close();
    os.close();
    socket.close();
    baos.close();
}

• 服务端

/*
这里涉及到的异常，应该使用try-catch-finally处理
 */
@Test
public void server() throws IOException {
    //1.
    ServerSocket ss = new ServerSocket(9090);
    //2.
    Socket socket = ss.accept();
    //3.
    InputStream is = socket.getInputStream();
    //4.
    FileOutputStream fos = new FileOutputStream(new File("beauty2.jpg"));
    //5.
    byte[] buffer = new byte[1024];
    int len;
    while((len = is.read(buffer)) != -1){
        fos.write(buffer,0,len);
    }
    System.out.println("图片传输完成");
    //6.服务器端给予客户端反馈
    OutputStream os = socket.getOutputStream();
    os.write("你好，美女，照片我已收到，非常漂亮！".getBytes());

    //7.
    fos.close();
    is.close();
    socket.close();
    ss.close();
    os.close();

}

1.6、UDP

UDP实现消息发送

• 发送端

import java.io.IOException;
import java.net.*;
//不需要连接服务器
public class UdpClient {
    public static void main(String[] args) throws IOException {
        //1.建立一个socket
        DatagramSocket socket = new DatagramSocket();
        //2.建立包
        String msg = "你好呀，服务器！";
        //发送给谁
        InetAddress localhost = InetAddress.getByName("localhost");
        int port= 9999;
        //数据，数据的长度起始
        DatagramPacket packet = new DatagramPacket(msg.getBytes(), 0, msg.getBytes().length, localhost, port);
        //3.发送包
        socket.send(packet);
        //4.关闭
        socket.close();
    }
}

• 接收端

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
public class UdpServer {
    public static void main(String[] args) throws IOException {
        //开放端口
        DatagramSocket socket = new DatagramSocket(9999);
        //接受数据包
        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);
        socket.receive(packet);
        System.out.println(packet.getAddress().getHostAddress());
        System.out.println(new String(packet.getData(),0,packet.getLength()));
        //关闭
        socket.close();
    }
}

UDP实现聊天功能

• 发送端

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.*;
public class UdpSender {
    public static void main(String[] args) throws IOException {
        DatagramSocket socket = new DatagramSocket(8888);
        //准备数据
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String data = reader.readLine();
        byte[] datas = data.getBytes();
        DatagramPacket packet = new DatagramPacket(datas,0,datas.length,new InetSocketAddress("localhost",999));
        socket.send(packet);
        socket.close();
    }
}

• 接收端

import org.omg.CORBA.DATA_CONVERSION;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
public class UdpReceiver {
    public static void main(String[] args) throws IOException {
        DatagramSocket socket = new DatagramSocket(9999);
        while (true){
            //准备接收包裹
            byte[] container = new byte[1024];
            DatagramPacket packet = new DatagramPacket(container,0,container.length);
            socket.receive(packet); //阻塞式接收包裹
            //断开连接 bye
            byte [] data =  packet.getData();
            String recreiveData = new String(data,0,data.length);
            System.out.println(recreiveData);
            if (recreiveData.equals("bye")){
                break;
            }
        }
        socket.close();
    }
}

1.7 URL编程

URL(Uniform Resource Locator)的理解：

统一资源定位符，对应着互联网的某一资源地址。

URL的5个基本结构：

http://localhost:8080/examples/beauty.jpg?username=Tom

协议 主机名 端口号 资源地址 参数列表

如何实例化:

URL url = new URL("http://localhost:8080/examples/beauty.jpg?username=Tom");

public class URLTest {
    public static void main(String[] args) {

        HttpURLConnection urlConnection = null;
        InputStream is = null;
        FileOutputStream fos = null;
        try {
            URL url = new URL("http://icweiliimg1.pstatp.com/weili/l/913146374019088384.webp");
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.connect();
            is = urlConnection.getInputStream();
            fos = new FileOutputStream("hello.jpg");

            byte[] buffer = new byte[1024];
            int len;
            while ((len = is.read(buffer)) != -1) {
                fos.write(buffer, 0, len);
            }

            System.out.println("下载完成");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭资源
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
        }
    }
}