逆向学习 SDK 篇：通过封装来简化代码编写，提高代码复用性

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class DatabaseHelper {
    private String url;
    private String user;
    private String password;
    public DatabaseHelper(String url, String user, String password) {
        this.url = url;
        this.user = user;
        this.password = password;
    }
    private Connection connect() throws SQLException {
        return DriverManager.getConnection(url, user, password);
    }
    public ResultSet executeQuery(String query) throws SQLException {
        Connection conn = connect();
        PreparedStatement stmt = conn.prepareStatement(query);
        return stmt.executeQuery();
    }
    public int executeUpdate(String query) throws SQLException {
        Connection conn = connect();
        PreparedStatement stmt = conn.prepareStatement(query);
        return stmt.executeUpdate();
    }
    // 关闭连接
    public void closeConnection(Connection conn) {
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String[] args) {
        DatabaseHelper dbHelper = new DatabaseHelper("jdbc:mysql://localhost:3306/testdb", "user", "password");
        try {
            ResultSet rs = dbHelper.executeQuery("SELECT * FROM users");
            while (rs.next()) {
                System.out.println("User: " + rs.getString("username"));
            }
            int rowsAffected = dbHelper.executeUpdate("UPDATE users SET password = 'newpassword' WHERE username = 'john'");
            System.out.println("Rows affected: " + rowsAffected);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
public class HttpHelper {
    private static final String USER_AGENT = "Mozilla/5.0";
    public static String sendGet(String url) throws Exception {
        URL obj = new URL(url);
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        con.setRequestMethod("GET");
        con.setRequestProperty("User-Agent", USER_AGENT);
        int responseCode = con.getResponseCode();
        System.out.println("GET Response Code :: " + responseCode);
        if (responseCode == HttpURLConnection.HTTP_OK) {
            BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
            String inputLine;
            StringBuilder response = new StringBuilder();
            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();
            return response.toString();
        } else {
            return "GET request not worked";
        }
    }
    public static String sendPost(String url, String urlParameters) throws Exception {
        URL obj = new URL(url);
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        con.setRequestMethod("POST");
        con.setRequestProperty("User-Agent", USER_AGENT);
        con.setDoOutput(true);
        con.getOutputStream().write(urlParameters.getBytes());
        int responseCode = con.getResponseCode();
        System.out.println("POST Response Code :: " + responseCode);
        if (responseCode == HttpURLConnection.HTTP_OK) {
            BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
            String inputLine;
            StringBuilder response = new StringBuilder();
            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();
            return response.toString();
        } else {
            return "POST request not worked";
        }
    }
    public static void main(String[] args) {
        try {
            String url = "https://jsonplaceholder.typicode.com/posts";
            String response = HttpHelper.sendGet(url);
            System.out.println("GET Response: " + response);
            String urlParameters = "userId=1&title=foo&body=bar";
            response = HttpHelper.sendPost(url, urlParameters);
            System.out.println("POST Response: " + response);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Logger {
    private String logFile;
    public Logger(String logFile) {
        this.logFile = logFile;
    }
    public void log(String message) {
        try (PrintWriter out = new PrintWriter(new FileWriter(logFile, true))) {
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String timestamp = sdf.format(new Date());
            out.println(timestamp + " - " + message);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        Logger logger = new Logger("app.log");
        logger.log("Application started");
        logger.log("An example log message");
        logger.log("Application ended");
    }
}