网络编程

入门

c/s：Client/Server结构，客户端和服务器
B/S：Browser/Server结构，浏览器和服务器

java.net包中提供了两种常见的网络协议的支持：

• UDP：用户数据报协议。无连接，数据限制在64kb以内
• TCP：传输控制协议。有连接，三次握手

网络编程三要素

• 协议
• IP
• 端口

狂神说

计算机网络

网络编程的目的：传播、交流信息

IP、端口、通信协议

IP

InetAddress

public class App {
    public static void main(String[] args) {
        try {
            InetAddress address = InetAddress.getByName("127.0.0.1");
            System.out.println(address);
            InetAddress address2 = InetAddress.getByName("localhost");
            System.out.println(address2);
            InetAddress address3 = InetAddress.getLocalHost();
            System.out.println(address3);
            InetAddress address4 = InetAddress.getByName("www.baidu.com");
            System.out.println(address4);

            //常用方法
            System.out.println(address4.getAddress());
            System.out.println(address4.getCanonicalHostName());//规范的名字
            System.out.println(address4.getHostAddress());//ip
            System.out.println(address4.getHostName());//域名，或者自己电脑的名字
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }
}

端口

一个端口对应一个程序的进程

• 范围0-65535
• TCP和UDP各有0-65535
• 端口分类
  • 共有端口0-1023
    • HTTP:80
    • HTTS:443
    • FTP:21
    • Telent：23
  • 程序注册端口：1024-49151，分配用户或者程序
    • Tomcat:8080
    • mysql:3306
    • Oracle:1521
  • 动态、私有：49152-65535

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

public class PortDemo {
    public static void main(String[] args) {
        InetSocketAddress socketAddress = new InetSocketAddress("127.0.0.1", 8080);
        InetSocketAddress socketAddress2 = new InetSocketAddress("localhost", 8080);
        System.out.println(socketAddress);
        System.out.println(socketAddress2);

        System.out.println(socketAddress.getAddress());
        System.out.println(socketAddress.getHostName());
        System.out.println(socketAddress.getPort());
    }
}

通信协议

网络通信：速率、传输码率、代码结构、传输控制……

重要：

• TCP：用户传输协议——打电话
  • 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：用户数据协议——发短信
  • 不连接、不稳定
  • 客户端、服务器没有明确的界限
  • 不管有没有准备好，都可以发给你
  • DDOS：洪水攻击

TCP实现聊天

服务器

1. 建立服务的端口 ServerSocket
2. 等待用户的连接 Socket.accept()
3. 接收客户端消息

客户端

1. 连接服务器Socket
2. 发送消息

//服务端
public class ServerDemo1 {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket socket = null;
        InputStream inputStream = null;
        ByteArrayOutputStream baos = null;
        try {
            //1、一个地址
            serverSocket = new ServerSocket(9999);
            //2、等待客户端连接过来
            socket = serverSocket.accept();
            //3、读取客户端消息
            inputStream = socket.getInputStream();
            //管道流
            baos = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int len;
            while((len=inputStream.read(buffer))!=-1){
                baos.write(buffer,0,len);
            }
            System.out.println(baos.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //关闭资源
            if(baos!=null){
                try {
                    baos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(inputStream!=null){
                try {
                    inputStream.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();
                }
            }
        }
    }
}

//客户端
public class ClientDemo1 {
    public static void main(String[] args) {
        Socket socket = null;
        OutputStream outputStream = null;
        try {
            //1、知道服务器的地址，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
            outputStream = socket.getOutputStream();
            outputStream.write("你好,欢迎来到未来世界".getBytes());
       } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(outputStream!=null){
                try {
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(socket!=null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

TCP文件上传

//客户端
public class ClientDemo2 {
    public static void main(String[] args) throws IOException {
        //1、创建一个Socket连接
        Socket socket = new Socket(InetAddress.getByName("127.0.0.1"),9999);
        //2、创建一个输出流
        OutputStream os = socket.getOutputStream();
        //3、读取文件
        FileInputStream fileInputStream = new FileInputStream(new File("F:\1.png"));
        //4、写出文件
        byte[] buffer = new byte[1024];
        int len;
        while((len=fileInputStream.read(buffer))!=-1){
            os.write(buffer,0,len);
        }
        //通知服务器，我已经结束了
        socket.shutdownOutput();
        //确定服务器接收完毕，才能断开连接
        InputStream inputStream = socket.getInputStream();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte[] buffer2 = new byte[1024];
        int len2;
        while((len=inputStream.read(buffer2))!=-1){
            baos.write(buffer2,0,len);
        }
        System.out.println(baos.toString());
        //5、关闭资源
        baos.close();
        inputStream.close();
        fileInputStream.close();
        os.close();
        socket.close();
    }
}

//服务端
public class ServerDemo2 {
    public static void main(String[] args) throws IOException {
        //1、创建服务
        ServerSocket serverSocket = new ServerSocket(9999);
        //2、监听客户端的连接
        Socket socket = serverSocket.accept();//阻塞式监听
        //3、获取输入流
        InputStream inputStream = socket.getInputStream();
        //4、文件输出
        FileOutputStream fileOutputStream = new FileOutputStream(new File("receive.png"));
        byte[] buffer = new byte[1024];
        int len;
        while((len=inputStream.read(buffer))!=-1){
            fileOutputStream.write(buffer,0,len);
        }
        //通知客户端我接收完毕了
        OutputStream outputStream = socket.getOutputStream();
        outputStream.write("我接收完毕了，你可以断开了".getBytes());
        //5、关闭资源
        fileOutputStream.close();
        inputStream.close();
        socket.close();
        serverSocket.close();
    }
}

Tomcat

UDP消息发送

public class UdpClient1 {
    public static void main(String[] args) throws Exception {
        //1、建立一个Socket
        DatagramSocket socket = new DatagramSocket();
        //2、建个包
        String msg = "你好阿,服务器";
        //发送给谁
        InetAddress localhost = InetAddress.getByName("localhost");
        int port = 9999;
        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();
    }

public class UdpServer1 {
    public static void main(String[] args) throws IOException {
        //开放端口
        DatagramSocket socket = new DatagramSocket(9999);
        //接收数据包
        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);
        socket.receive(packet);
        System.out.println(new String(packet.getData(),0,packet.getLength()));
        //关闭连接
        socket.close();
    }
}

UDP聊天实现

UDP多线程在线咨询

URL下载网络资源