从JDBCUtils看代码简洁之道

从JDBCUtils看代码简介之道

使用PreparedStatement实现增删改查

import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.util.Properties;
import java.util.Scanner;

public class TestPreparedStatement1 {
        public static void main(String[] args) throws Exception {
             Scanner input = new Scanner(System.in);
             System.out.println("请输入待修改的客户编号：");
             int id = input.nextInt();
             System.out.println("请输入新的客户姓名：");
             String name = input.next();

  //------------------------连接数据库的步骤------------------------

             Properties info = new Properties();
             info.load(new FileInputStream("src\\jdbc1.properties"));

             String user = info.getProperty("user");
             String password = info.getProperty("password");
             String url = info.getProperty("url");
             String driver = info.getProperty("driver");

             //1.注册驱动
             Class.forName(driver);
             //2.获取连接
             Connection connection = DriverManager.getConnection(url, user, password);

             //3.执行修改
             String sql = "UPDATE customers SET name = ? WHERE id = ?";
             PreparedStatement statement = connection.prepareStatement(sql);
             statement.setString(1, name);
             statement.setInt(2, id);
             int i = statement.executeUpdate();//执行增删改，返回受影响的行数
             System.out.println(i > 0 ? "修改成功！" : "修改失败！");

             //4.关闭
             statement.close();
             connection.close();
        }
}

工具类JDBCUtils

由于每次都要加载配置文件，读取配置信息，注册驱动，获取连接，想到封装成工具类JDBCUtils。功能：

• 1、获取连接
• 2、释放资源

public class JDBCUtils {
    /**
     * 功能：获取可用的连接对象
     * @return 连接
     * @throws Exception
     */
    public static Connection getConnection() throws Exception{
        Properties info = new Properties();
        info.load(new FileInputStream("src\\jdbc1.properties"));

        String user = info.getProperty("user");
        String password = info.getProperty("password");
        String url = info.getProperty("url");
        String driver = info.getProperty("driver");

        //1.注册驱动
        Class.forName(driver);
        //2.获取连接
        Connection connection = DriverManager.getConnection(url, user, password);
        return connection;
    }
    /**
      * 功能：释放资源
      *
      */
    public static void close(ResultSet set, Statement statement,Connection connection) throws Exception {
        if(set != null) set.close();
        if(statement != null) statement.close();
        if(connection != null) connection.close();
    }
}

在getConnection()方法中仍有可以提出的部分，使用静态代码块只执行一次加载配置文件，读取配置信息，注册驱动的步骤，使代码更加简洁，效率更高。注意：提出的步骤需要处理异常。将user\url。

public class JDBCUtils {
    static String user;
    static String password;
    static String url ;
    static String driver;
    
    static{
        try {
        Properties info = new Properties();
        info.load(new FileInputStream("src\\jdbc1.properties"));

        user = info.getProperty("user");
        password = info.getProperty("password");
        url = info.getProperty("url");
        driver = info.getProperty("driver");

        //1.注册驱动

            Class.forName(driver);
        } catch (Exception e) {
            throw new RuntimeException(e);//编译时异常转为运行时异常
        }
    }
    
    /**
     * 功能：获取可用的连接对象
     * @return 连接
     * @throws Exception
     */
    public static Connection getConnection() throws Exception{
        
        //2.获取连接
        return DriverManager.getConnection(url, user, password);
    }
    /**
      * 功能：释放资源
      *
      */
    public static void close(ResultSet set, Statement statement,Connection connection) throws Exception {
        if(set != null) set.close();
        if(statement != null) statement.close();
        if(connection != null) connection.close();
    }
}

改进之后

有了JDBCUtils工具类，再看改进后的代码

public class TestPrepasredStatementByUtils {
    public static void main(String[] args) throws Exception{
        Scanner input = new Scanner(System.in);
        System.out.println("请输入待修改的客户编号：");
        int id = input.nextInt();
        System.out.println("请输入新的客户姓名：");
        String name = input.next();

        //----------------------连接数据库的步骤----------------
        //1.获取连接
        Connection connection = JDBCUtils.getConnection();
        //2.执行修改
        String sql = "UPDATE customers SET name = ? WHERE id = ?";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setString(1, name);
        statement.setInt(2, id);
        int i = statement.executeUpdate();//执行增删改，返回受影响的行数
        System.out.println(i > 0 ? "修改成功！" : "修改失败！");

        //3.关闭
        JDBCUtils.close(null,statement,connection);
    }
}

直接调用工具类中的方法就简洁多啦！

再体会一下编译时异常变为运行时异常：

如果不抛异常，会报错

对JDBCUtils工具类中的getConnection()方法进行try-catch处理，将编译时异常转为运行时异常

public static Connection getConnection() {

        //2.获取连接
        try {
            return DriverManager.getConnection(url, user, password);
        }
        catch (Exception e){
            throw new RuntimeException(e);
        }

    }

此时将不会报编译时错误

对另一个close方法的处理也一样

public static void close(ResultSet set, Statement statement,Connection connection){
        try {
            if (set != null) set.close();
            if (statement != null) statement.close();
            if (connection != null) connection.close();
        }
        catch (SQLException e){
            throw new RuntimeException(e);
        }
    }

最终代码为：

public class TestPrepasredStatementByUtils {
    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        System.out.println("请输入待修改的客户编号：");
        int id = input.nextInt();
        System.out.println("请输入新的客户姓名：");
        String name = input.next();

        //----------------------连接数据库的步骤----------------
        Connection connection = null;
        PreparedStatement statement = null;
        try {
            //1.获取连接
            connection = JDBCUtils.getConnection();
            //2.执行修改
            String sql = "UPDATE customers SET name = ? WHERE id = ?";
            statement = connection.prepareStatement(sql);
            statement.setString(1, name);
            statement.setInt(2, id);
            int i = statement.executeUpdate();//执行增删改，返回受影响的行数
            System.out.println(i > 0 ? "修改成功！" : "修改失败！");
        }
        catch(Exception e){
            e.printStackTrace();
        }
        finally {
            //3.关闭
            JDBCUtils.close(null, statement, connection);
        }
    }
}