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Java网络通信及Servlet常见场景实现

作者：木道寻08 | 2024-06-19 05:13:16

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Java网络通信及Servlet常见场景实现

UDP

UDPServer

  1. import java.io.IOException;
  2. import java.net.DatagramPacket;
  3. import java.net.DatagramSocket;
  4.  
  5. public class UDPServer {
  6.     public static void main(String[] args) throws IOException {
  7.         System.out.println("UdpServer启动");
  8.         // 创建upd套接字
  9.         DatagramSocket socket = new DatagramSocket(8080);
  10.         // 获取客户端连接
  11.         byte[] buffer = new byte[1024];
  12.         while (true) {
  13.             // 获取客户端请求
  14.             DatagramPacket client = new DatagramPacket(buffer, buffer.length);
  15.             socket.receive(client);
  16.             String request = new String(client.getData(), 0, client.getLength());
  17.             // 回显客户端
  18.             String response = request;
  19.             socket.send(new DatagramPacket(response.getBytes(), response.getBytes().length,
  20.                     client.getAddress(), client.getPort()));
  21.             // 打印交互日志
  22.             System.out.printf("客户端[%s:%d] receive-> %s send-> %s\n", client.getAddress().toString(),
  23.                     client.getPort(), request, response);
  24.         }
  25.     }
  26. }

UDPClient

  1. import java.io.IOException;
  2. import java.net.DatagramPacket;
  3. import java.net.DatagramSocket;
  4. import java.net.InetAddress;
  5. import java.util.Scanner;
  6.  
  7. public class UDPClient {
  8.     public static void main(String[] args) throws IOException {
  9.         System.out.println("UdpClient启动");
  10.         // 创建客户端套接字
  11.         DatagramSocket socket = new DatagramSocket();
  12.         // 创建数据报
  13.         byte[] buffer = new byte[1024];
  14.         DatagramPacket client = new DatagramPacket(buffer, buffer.length,
  15.                 InetAddress.getByName("127.0.0.1"), 8080);
  16.         while (true) {
  17.             // 获取发送数据
  18.             System.out.print("send -> ");
  19.             Scanner scanner = new Scanner(System.in);
  20.             String request = scanner.next();
  21.             client.setData(request.getBytes());
  22.             // 发送数据
  23.             socket.send(client);
  24.             // 获取服务器回显数据
  25.             DatagramPacket server = new DatagramPacket(buffer, buffer.length);
  26.             socket.receive(server);
  27.             // 打印交互日志
  28.             System.out.printf("receive ->[%s:%d] %s\n", server.getAddress().toString(), server.getPort(),
  29.                     new String(server.getData(), 0, server.getLength()));
  30.         }
  31.     }
  32. }

测试结果

TCP

TCPServer

  1. import java.io.IOException;
  2. import java.io.PrintStream;
  3. import java.net.InetAddress;
  4. import java.net.ServerSocket;
  5. import java.net.Socket;
  6. import java.util.Scanner;
  7. import java.util.concurrent.ExecutorService;
  8. import java.util.concurrent.Executors;
  9.  
  10. public class TCPServer {
  11.     public static void main(String[] args) throws IOException {
  12.         System.out.println("TCPServer启动");
  13.         // 创建监听套接字
  14.         ServerSocket listenSocket = new ServerSocket(8080, 20, InetAddress.getByName("127.0.0.1"));
  15.         // 创建线程池处理客户端数据
  16.         ExecutorService clientPool = Executors.newCachedThreadPool();
  17.         while (true) {
  18.             // 获取客户端连接
  19.             Socket client = listenSocket.accept();
  20.             // 客户端处理
  21.             clientPool.submit(() -> {
  22.                 try {
  23.                     clientProcess(client);
  24.                 } catch (IOException e) {
  25.                     e.printStackTrace();
  26.                 }
  27.             });
  28.         }
  29.     }
  30.  
  31.     public static void clientProcess(Socket client) throws IOException {
  32.         System.out.printf("client[%s:%d] connect success\n",
  33.                 client.getInetAddress().toString(), client.getPort());
  34.         // 处理客户端数据
  35.         try (Scanner input = new Scanner(client.getInputStream());
  36.              PrintStream output = new PrintStream(client.getOutputStream())) {
  37.             while (true) {
  38.                 if (!input.hasNext()) {
  39.                     System.out.printf("client[%s:%d] disconnect\n",
  40.                             client.getInetAddress().toString(), client.getPort());
  41.                 } else {
  42.                     // 约定以\n为一个完整报文
  43.                     String request = input.nextLine();
  44.                     // 回显客户端
  45.                     String response = request;
  46.                     output.println(response);
  47.                     output.flush();
  48.                     // 打印交互日志
  49.                     System.out.printf("client[%s:%d] receive -> %s send -> %s\n",
  50.                             client.getInetAddress().toString(), client.getPort(), request, response);
  51.                 }
  52.             }
  53.         }
  54.     }
  55. }

TCPClient

  1. import java.io.IOException;
  2. import java.io.PrintStream;
  3. import java.net.Socket;
  4. import java.util.Scanner;
  5.  
  6. public class TCPClient {
  7.     public static void main(String[] args) throws IOException {
  8.         System.out.println("TCPClient启动");
  9.         // 创建客户端连接
  10.         Socket socket = new Socket("127.0.0.1", 8080);
  11.         Scanner scanner = new Scanner(System.in);
  12.         try (Scanner input = new Scanner(socket.getInputStream());
  13.              PrintStream output = new PrintStream(socket.getOutputStream())) {
  14.             while (true) {
  15.                 System.out.print("send -> ");
  16.                 String request = scanner.nextLine();
  17.                 // 发送请求数据
  18.                 output.println(request);
  19.                 // 获取服务器回显数据
  20.                 String response = input.nextLine();
  21.                 // 打印交互日志
  22.                 System.out.printf("receive -> server[%s:%d] %s\n",
  23.                         socket.getInetAddress().toString(), socket.getPort(), response);
  24.             }
  25.  
  26.         }
  27.     }
  28. }

测试结果

Servlet 

项目搭建

pom文件引入依赖与打包配置

  1. <dependencies>
  2.         <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
  3.         <dependency>
  4.             <groupId>javax.servlet</groupId>
  5.             <artifactId>javax.servlet-api</artifactId>
  6.             <version>3.1.0</version>
  7.             <scope>provided</scope>
  8.         </dependency>
  9.         <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
  10.         <dependency>
  11.             <groupId>com.fasterxml.jackson.core</groupId>
  12.             <artifactId>jackson-databind</artifactId>
  13.             <version>2.16.2</version>
  14.         </dependency>
  15.  
  16.     </dependencies>
  17.  
  18.     <packaging>war</packaging>
  19.     <build>
  20.         <finalName>hello</finalName>
  21.     </build>

目录结构创建

web.xml写入配置

  1. <!DOCTYPE web-app PUBLIC
  2.         "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
  3.         "http://java.sun.com/dtd/web-app_2_3.dtd" >
  4. <web-app></web-app>

idea配置tomcat

普通接口

  1. import com.fasterxml.jackson.databind.json.JsonMapper;
  2.  
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  9.  
  10. @WebServlet("/test")
  11. public class HelloServlet extends HttpServlet {
  12.     long count = 0;
  13.  
  14.     @Override
  15.     public void init() throws ServletException {
  16.         new Thread(() -> {
  17.             while (true) {
  18.                 count++;
  19.                 try {
  20.                     Thread.sleep(1000);
  21.                 } catch (InterruptedException e) {
  22.                     e.printStackTrace();
  23.                 }
  24.             }
  25.         }).start();
  26.     }
  27.  
  28.     @Override
  29.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  30.         String username = req.getParameter("username");
  31.         String password = req.getParameter("password");
  32.         System.out.println("username = " + username + ", password = " + password);
  33.         resp.setContentType("text/html; charset=utf8");
  34.         resp.setStatus(200);
  35.         resp.setHeader("refresh", "1");
  36.         resp.getWriter().write("success " + count);
  37.     }
  38.  
  39.     static class Customer {
  40.         public String username;
  41.         public String password;
  42.     }
  43.  
  44.     static class ResponseMessage {
  45.         public Integer status;
  46.     }
  47.  
  48.     @Override
  49.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  50.         JsonMapper jsonMapper = new JsonMapper();
  51.         // 入参映射转换
  52. //        Customer customer = jsonMapper.readValue(req.getInputStream(), Customer.class);
  53.         // 读取入参报文
  54.         StringBuilder request = new StringBuilder();
  55.         // 读取方式一
  56. //        String line;
  57. //        while ((line = req.getReader().readLine()) != null) {
  58. //            request.append(line);
  59. //        }
  60.         // 读取方式二
  61.         byte[] requestBuffer = new byte[1024];
  62.         int length;
  63.         while ((length = req.getInputStream().read(requestBuffer, 0, requestBuffer.length)) > 0) {
  64.             request.append(new String(requestBuffer, 0, length));
  65.         }
  66.         // 组织出参报文，需要注意body的write一定要放在最后一行，否则resp上面设置的会失效(Servlet bug)
  67.         resp.setContentType("application/json; charset=utf8");
  68.         resp.setStatus(200);
  69.         ResponseMessage responseMessage = new ResponseMessage();
  70.         responseMessage.status = 200;
  71.         String response = jsonMapper.writeValueAsString(responseMessage);
  72.         resp.getWriter().write(response);
  73.         System.out.println("request: " + request + "\n" + "response: " + response);
  74.     }
  75. }

JDBC接口

引入JDBC依赖

  1. <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
  2. <dependency>
  3.     <groupId>mysql</groupId>
  4.     <artifactId>mysql-connector-java</artifactId>
  5.     <version>5.1.49</version>
  6. </dependency>

代码示例

  1. import com.fasterxml.jackson.databind.json.JsonMapper;
  2. import com.mysql.jdbc.StringUtils;
  3. import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
  4.  
  5. import javax.servlet.ServletException;
  6. import javax.servlet.annotation.WebServlet;
  7. import javax.servlet.http.HttpServlet;
  8. import javax.servlet.http.HttpServletRequest;
  9. import javax.servlet.http.HttpServletResponse;
  10. import javax.sql.DataSource;
  11. import java.io.IOException;
  12. import java.sql.Connection;
  13. import java.sql.PreparedStatement;
  14. import java.sql.ResultSet;
  15. import java.sql.SQLException;
  16. import java.util.ArrayList;
  17. import java.util.List;
  18.  
  19. @WebServlet("/jdbc")
  20. public class JDBCServlet extends HttpServlet {
  21.     DataSource dataSource;
  22.  
  23.     @Override
  24.     public void init() throws ServletException {
  25.         dataSource = new MysqlDataSource();
  26.         ((MysqlDataSource) dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/test?characterEncoding=utf8&useSSL=false");
  27.         ((MysqlDataSource) dataSource).setUser("root");
  28.         ((MysqlDataSource) dataSource).setPassword("root");
  29.     }
  30.  
  31.     static class User {
  32.         public String username;
  33.         public String password;
  34.     }
  35.  
  36.     @Override
  37.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  38.         List<User> userList = new ArrayList<>();
  39.         try (Connection connection = dataSource.getConnection();
  40.              PreparedStatement statement = connection.prepareStatement("select * from user");
  41.              ResultSet resultSet = statement.executeQuery()) {
  42.             while (resultSet.next()) {
  43.                 User user = new User();
  44.                 user.username = resultSet.getString("username");
  45.                 user.password = resultSet.getString("password");
  46.                 userList.add(user);
  47.             }
  48.         } catch (SQLException | NullPointerException e) {
  49.             e.printStackTrace();
  50.         }
  51.         JsonMapper jsonMapper = new JsonMapper();
  52.         String response = jsonMapper.writeValueAsString(userList);
  53.         resp.getWriter().write(response);
  54.     }
  55.  
  56.     @Override
  57.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  58.         JsonMapper jsonMapper = new JsonMapper();
  59.         User user = jsonMapper.readValue(req.getInputStream(), User.class);
  60.         if (StringUtils.isEmptyOrWhitespaceOnly(user.username) || StringUtils.isEmptyOrWhitespaceOnly(user.password)) {
  61.             resp.getWriter().write("body invalid");
  62.             return;
  63.         }
  64.         String message = "fail";
  65.         try (Connection connection = dataSource.getConnection();
  66.              PreparedStatement statement = connection.prepareStatement("insert into user values(null,?,?)")) {
  67.             statement.setString(1, user.username);
  68.             statement.setString(2, user.password);
  69.             int resultCount = statement.executeUpdate();
  70.             if (resultCount > 0) {
  71.                 message = "success";
  72.             }
  73.         } catch (SQLException e) {
  74.             e.printStackTrace();
  75.         }
  76.         resp.getWriter().write(message);
  77.     }
  78. }

Cookie及Session接口

Servlet已默认实现及提供了相关接口，直接使用即可。

代码示例

  1. import com.mysql.jdbc.StringUtils;
  2.  
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import javax.servlet.http.HttpSession;
  10. import java.io.IOException;
  11.  
  12.  
  13. @WebServlet("/session")
  14. public class SessionServlet extends HttpServlet {
  15.     @Override
  16.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  17.         String username = req.getParameter("username");
  18.         String password = req.getParameter("password");
  19.         resp.setContentType("text/html; charset=utf8");
  20.         if (StringUtils.isEmptyOrWhitespaceOnly(username) || StringUtils.isEmptyOrWhitespaceOnly(password)) {
  21.             resp.getWriter().write("parameter invalid");
  22.             return;
  23.         }
  24.         // 创建Session,这个方法会无论session是否存在都会自动创建session对象，并且会把sessionId设置到响应头中
  25.         HttpSession session = req.getSession(true);
  26.         session.setAttribute("username", username);
  27.         session.setAttribute("password", password);
  28.         // 添加一个cookie
  29.         resp.addCookie(new Cookie("test", "111"));
  30.         resp.sendRedirect("login");
  31.     }
  32. }

响应返回头中设置了两个Cookie。

 重定向的请求头中多了Cookie的两个参数。

重定向代码示例

  1. import javax.servlet.ServletException;
  2. import javax.servlet.annotation.WebServlet;
  3. import javax.servlet.http.Cookie;
  4. import javax.servlet.http.HttpServlet;
  5. import javax.servlet.http.HttpServletRequest;
  6. import javax.servlet.http.HttpServletResponse;
  7. import javax.servlet.http.HttpSession;
  8. import java.io.IOException;
  9.  
  10. @WebServlet("/login")
  11. public class LoginServlet extends HttpServlet {
  12.     @Override
  13.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  14.         HttpSession session = req.getSession(false);
  15.         resp.setContentType("text/html; charset=utf8");
  16.         if (session == null) {
  17.             resp.getWriter().write("access invalid");
  18.             return;
  19.         }
  20.         String username = (String) session.getAttribute("username");
  21.         String password = (String) session.getAttribute("password");
  22.         for (Cookie cookie : req.getCookies()) {
  23.             System.out.println(cookie.getName() + ":" + cookie.getValue());
  24.         }
  25.         resp.getWriter().write(username + "&" + password + " login success");
  26.     }
  27. }

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