预编译语句是一种用于执行参数化SQL查问的技术，它能够进步性能并缩小SQL注入的危险。预编译语句次要有以下劣势：
- 防止SQL注入攻打。
- 进步性能，因为预编译语句只编译一次，而后能够屡次执行。
在Java中，应用java.sql.PreparedStatement接口实现预编译语句。以下是几个示例，展现了如何应用预编译语句进行各种数据库操作。
7.3.1. 插入数据
以下示例展现了如何应用预编译语句插入数据：
import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;public class PreparedStatementInsertExample { public static void main(String[] args) { try { Class.forName("com.mysql.cj.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=utf-8&useSSL=false&allowPublicKeyRetrieval=true"; String username = "root"; String password = "mypassword"; Connection connection = DriverManager.getConnection(url, username, password); String sql = "INSERT INTO users (name, age) VALUES (?, ?)"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1, "User 7"); preparedStatement.setInt(2, 30); preparedStatement.executeUpdate(); preparedStatement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } }}7.3.2. 查问数据
以下示例展现了如何应用预编译语句查问数据：
import java.sql.*;public class PreparedStatementSelectExample { public static void main(String[] args) { try { Class.forName("com.mysql.cj.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=utf-8&useSSL=false&allowPublicKeyRetrieval=true"; String username = "root"; String password = "mypassword"; Connection connection = DriverManager.getConnection(url, username, password); String sql = "SELECT * FROM users WHERE age > ?"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setInt(1, 30); ResultSet resultSet = preparedStatement.executeQuery(); while (resultSet.next()) { System.out.println("ID: " + resultSet.getInt("id") + ", Name: " + resultSet.getString("name") + ", Age: " + resultSet.getInt("age")); } resultSet.close(); preparedStatement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } }}7.3.3. 更新数据
以下示例展现了如何应用预编译语句更新数据：
import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;public class PreparedStatementUpdateExample { public static void main(String[] args) { try { Class.forName("com.mysql.cj.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=utf-8&useSSL=false&allowPublicKeyRetrieval=true"; String username = "root"; String password = "mypassword"; Connection connection = DriverManager.getConnection(url, username, password); String sql = "UPDATE users SET age = ? WHERE name = ?"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setInt(1, 31); preparedStatement.setString(2, "User 7"); preparedStatement.executeUpdate(); preparedStatement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } }}7.3.4. 删除数据
以下示例展现了如何应用预编译语句删除数据：
import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;public class PreparedStatementDeleteExample { public static void main(String[] args) { try { Class.forName("com.mysql.cj.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=utf-8&useSSL=false&allowPublicKeyRetrieval=true"; String username = "root"; String password = "mypassword"; Connection connection = DriverManager.getConnection(url, username, password); String sql = "DELETE FROMusers WHERE age > ?"; PreparedStatement preparedStatement = connection.prepareStatement(sql); preparedStatement.setInt(1, 60); preparedStatement.executeUpdate(); preparedStatement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } }}通过这些示例，你应该对如何应用预编译语句有了更清晰的理解。预编译语句使得你可能在查问中应用参数，进步了性能并缩小了SQL注入的危险。在理论我的项目中，尽量应用预编译语句来执行SQL查问。
举荐浏览：
https://mp.weixin.qq.com/s/dV2JzXfgjDdCmWRmE0glDA
https://mp.weixin.qq.com/s/an83QZOWXHqll3SGPYTL5g