网络编程

概述

网络编程目的：传播交流信息，数据交换，通信

网络编程中的两个主要问题：

• 如何准确定位到网络上的一台或多态主机
• 找到主机之后如何进行通信

网络编程中的要素：

• IP 和端口号
• 网络通信协议

IP

ip 地址

• 唯一定位一台网络上的计算机

• 127.0.0.1：本机地址（localhost）

• ip地址分类

  • ipv4 / ipv6
    • ipv4：127.0.0.1，四个字节组成
    • ipv6：128位，8个无符号整数
  • 公网（互联网）-私网（局域网）
    • A、B、C、D类地址

• 域名：解决IP记忆问题

InetAddress类

InetAddress 类：此类表示Internet协议（IP）地址

//查询本机地址
InetAddress inetAddress = InetAddress.getByName("127.0.0.1");
System.out.println(inetAddress);
InetAddress inetAddress1 = InetAddress.getByName("localhost");
System.out.println(inetAddress1);
InetAddress inetAddress2 = InetAddress.getLocalHost();
System.out.println(inetAddress2);

//查询网站ip地址
InetAddress inetAddress3 = InetAddress.getByName("www.baidu.com");
System.out.println(inetAddress3);

//常用方法
System.out.println(inetAddress3.getAddress());
System.out.println(inetAddress3.getCanonicalHostName());  //规范名字
System.out.println(inetAddress3.getHostAddress());  //ip
System.out.println(inetAddress3.getHostName());  //域名，或者自己电脑的名字

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，可以用来区分不同的软件
• 端口号规定0~65535
• 端口分为TCP端口和UDP端口，单个协议下，端口号不能冲突
• 端口分类
  • 公有端口：0~1023
    • HTTP：80
    • HTTPS：443
    • FTP：21
    • Telent：23
  • 程序注册端口：1024~49151，分配给用户或者程序
    • Tomcat：8080
    • MySQL：3306
    • Oracle：1521
  • 动态，私有的端口：49152~65535

#常用Dos命令
netstat -ano #查看所有的端口
netstat -ano|findstr "3306" #查看指定的窗口
tasklist|findstr "9760" #查看指定端口的进程
Ctrl + shift + ESC #任务管理器

InetSocketAddress 类：

InetSocketAddress 类：该类实现IP套接字地址（IP地址+端口号）它也可以是一对（主机名+端口号），在这种情况下将尝试解析主机名。

InetSocketAddress socketAddress = new InetSocketAddress("127.0.0.1",8080);
        InetSocketAddress socketAddress1 = new InetSocketAddress("localhost",8080);
        System.out.println(socketAddress);
        System.out.println(socketAddress1);

        System.out.println(socketAddress.getAddress());
        System.out.println(socketAddress.getHostName());  //地址
        System.out.println(socketAddress.getPort());  //端口

通信协议

TCP/IP 协议簇

TCP：用户传输协议

UDP：用户数据报协议

IP：网络互连协议

TCP 与 UDP 对比

TCP：

• 需要连接，稳定传输
• 连接时：三次握手。断开时：四次挥手
• 分为客户端和服务端
• 传输完成，释放连接，效率低

UDP：

• 不需要连接，不稳定
• 客户端与服务端没有明确的界限
• 不用管对方是否准备好，都可以发过去

TCP

TCP连接

客户端

1. 连接服务器，通过Socket
2. 发送消息

public class TcpClientDemo01 {
    public static void main(String[] args) {

        Socket socket = null;
        OutputStream os = null;
        try {
            //1.我得知道服务器地址，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IO流
            os = socket.getOutputStream();
            os.write("歪歪歪".getBytes());

        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(socket!=null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(os!=null){
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

服务器

1. 建立服务端口，通过ServerSocket
2. 等待用户连接，通过accept
3. 接收用户的消息

public class TcpServerDemo01 {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket socket = null;
        InputStream is = null;
        ByteArrayOutputStream baos = null;
        try {
            //1.我得有一个地址
            serverSocket = new ServerSocket(9999);
            //2.等待客户端连接
            socket = serverSocket.accept();
            //3.读取客户端消息
            is = socket.getInputStream();
            
            //管道流
            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.toString());

        } 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();
                }
            }

        }
    }
}

文件传输

客户端

public class TcpClient {
    public static void main(String[] args) throws Exception {
        //1.创建一个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("Practice/src/com/hui/pic/01.jpg"));

        //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，传输完成
        socket.shutdownOutput();

        //确定服务器接受完毕，才能断开连接
        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.toString());

        //5.关闭资源
        baos.close();
        inputStream.close();
        fis.close();
        os.close();
        socket.close();
    }
}

服务器

public class TcpServer {
    public static void main(String[] args) throws Exception {
        //1.创建服务
        ServerSocket serverSocket = new ServerSocket(9000);

        //2.监听客户端的连接
        Socket socket = serverSocket.accept();//阻塞式监听，会一直等待客户端连接

        //3.获取输入流
        InputStream is = socket.getInputStream();

        //4.文件输出
        FileOutputStream fos = new FileOutputStream(new File("1.jpg"));
        byte[] buffer = new byte[1024];
        int len;
        while ((len=is.read(buffer))!=-1){
            fos.write(buffer,0,len);
        }

        //通知客户端接受完毕了
        OutputStream os = socket.getOutputStream();
        os.write("接收完毕，可以断开".getBytes());

        //5.关闭资源
        os.close();
        fos.close();
        is.close();
        socket.close();
        serverSocket.close();
    }
}

Tomcat

服务端

• 自定义 S
• Tomcat服务器 S

客户端

• 自定义 C
• 浏览器 B

UDP

UDP发送接收

发送端

public class UdpDemo01 {
    public static void main(String[] args) throws Exception {
        //1.建立一个Socket
        DatagramSocket socket = new DatagramSocket(8080);

        //2.建一个包
        String msg = "好好学习，天天向上";
        InetAddress localhost = InetAddress.getByName("localhost");
        int port = 9090;
        //数据，数据的起始长度，发送给谁
        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 UdpDemo02 {
    public static void main(String[] args) throws Exception {
        //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);

        socket.receive(packet);//阻塞接收
        System.out.println(packet.getAddress().getHostAddress());
        System.out.println(new String(packet.getData(),0,packet.getLength()));

        //关闭
        socket.close();
    }
}

UDP聊天实现

发送端

public class UdpDemo03 {
    public static void main(String[] args) throws Exception {

        DatagramSocket socket = new DatagramSocket(8888);

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        while (true){
            String data = reader.readLine();
            DatagramPacket packet = new DatagramPacket(data.getBytes(), 0, data.getBytes().length, new InetSocketAddress("localhost", 6666));

            socket.send(packet);

            if (data.equals("bye")){
                break;
            }
        }
        socket.close();
    }
}

接收端

public class UdpDemo04 {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(6666);

        while (true){
            //准备接受包
            byte[] container = new byte[1024];
            DatagramPacket packet = new DatagramPacket(container,0,container.length);
            socket.receive(packet);
            
            //断开连接
            byte[] data = packet.getData();
            String s = new String(data, 0, data.length);
            System.out.println(s);
            if (s.equals("bye")){
                break;
            }
        }
    }
}

UDP多线程聊天

发送线程

public class TalkDemo01 implements Runnable{

    DatagramSocket socket = null;
    BufferedReader reader = null;
    private int fromPort;
    private String toIP;
    private int toPort;

    public TalkDemo01(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();
        }
    }

    @Override
    public void run() {
        while (true){
            try {
                String data = reader.readLine();
                DatagramPacket packet = new DatagramPacket(data.getBytes(), 0, data.getBytes().length, new InetSocketAddress(this.toIP, this.toPort));
                socket.send(packet);

                if (data.equals("bye")){
                    break;
                }

            }catch (Exception e){
                e.printStackTrace();
            }
        }
        socket.close();
    }
}

接收线程

public class TalkDemo02 implements Runnable{

    DatagramSocket socket = null;
    private int port;
    private String msgFrom;

    public TalkDemo02(int port,String msgFrom) {
        this.port = port;
        this.msgFrom = msgFrom;

        try {
            socket = new DatagramSocket(port);
        } catch (SocketException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {

        while (true){
            try {
                //准备接受包
                byte[] container = new byte[1024];
                DatagramPacket packet = new DatagramPacket(container,0,container.length);
                socket.receive(packet);

                //断开连接
                byte[] data = packet.getData();
                String s = new String(data, 0, data.length);
                System.out.println(msgFrom+":"+s);
                if (s.equals("bye")){
                    break;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        socket.close();
    }
}

用户一

public class TalkTeacher {
    public static void main(String[] args) {
        //开启两个线程
        new Thread(new TalkDemo01(5555, "localhost", 8888)).start();
        new Thread(new TalkDemo02(6666, "学生")).start();
    }
}

用户二

public class TalkStudent {
    public static void main(String[] args) {
        //开启两个线程
        new Thread(new TalkDemo01(7777, "localhost", 6666)).start();
        new Thread(new TalkDemo02(8888, "老师")).start();
    }
}

URL

URL：统一资源定位符，定位互联网上的某一个资源

协议://ip地址:端口/项目名、资源

public class Demo02 {
    public static void main(String[] args) throws Exception{

        //1.下载地址
        URL url = new URL("https://webfs.yun.kugou.com/202103181852/432f218656152a7d71aa66fcce8cac11/part/0/972998/G187/M01/11/15/m5QEAF5ehrOAU8M5AEMdldbXbfg325.mp3");

        //2.连接到这个资源
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
        InputStream inputStream = urlConnection.getInputStream();
        FileOutputStream fos = new FileOutputStream("5.mp3");

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