java增删改查

Java中的增删改查通常是指对数据库中的数据进行操作，以下是一个简单的示例：

1. 建立数据库连接：

import java.sql.*;

public class DatabaseConnection {
    private static final String URL = "jdbc:mysql://localhost:3306/database_name?useSSL=false&serverTimezone=UTC";
    private static final String USERNAME = "username";
    private static final String PASSWORD = "password";

    public static Connection getConnection() {
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }
}

2. 插入数据：

import java.sql.*;

public class InsertData {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = DatabaseConnection.getConnection();
            String sql = "INSERT INTO table_name (col1, col2) VALUES (?, ?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "value1");
            pstmt.setString(2, "value2");
            int result = pstmt.executeUpdate();
            if (result > 0) {
                System.out.println("Insert data successfully.");
            } else {
                System.out.println("Insert data failed.");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

3. 查询数据：

import java.sql.*;

public class QueryData {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = DatabaseConnection.getConnection();
            String sql = "SELECT * FROM table_name WHERE col1=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "value1");
            rs = pstmt.executeQuery();
            while (rs.next()) {
                System.out.println(rs.getString("col1") + "\t" + rs.getString("col2"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

4. 更新数据：

import java.sql.*;

public class UpdateData {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = DatabaseConnection.getConnection();
            String sql = "UPDATE table_name SET col2=? WHERE col1=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "new_value");
            pstmt.setString(2, "value1");
            int result = pstmt.executeUpdate();
            if (result > 0) {
                System.out.println("Update data successfully.");
            } else {
                System.out.println("Update data failed.");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

5. 删除数据：

import java.sql.*;

public class DeleteData {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = DatabaseConnection.getConnection();
            String sql = "DELETE FROM table_name WHERE col1=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "value1");
            int result = pstmt.executeUpdate();
            if (result > 0) {
                System.out.println("Delete data successfully.");
            } else {
                System.out.println("Delete data failed.");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

注意：以上仅仅是一个简单的示例，实际应用中可能需要根据具体情况进行更改和优化。同时，为了防止 SQL 注入攻击，建议使用 PreparedStatement 来构建 SQL 语句。