PreparedStatement的增删改操作

1.首先我们要知道Statement是干什么的

create a statement object for senting SQL statement to the databases

意思就是：创建一个语句对象，用于向数据库发送SQL语句

简单来说就是用这个类来对数据库进行增删改查

2.为什么不用statement用preparedstatement,

主要有两点：

一：拼接串过于麻烦

二：SQL注入问题（可以自行百度）

所以我们用他的子接口来实现这个方法

3.什么是preparedstatement

an object that represents a precompiled SQL statement

大致意思为：表示预编译SQL语句的对象

4.我会根据讲三种方法来演示（我直接写函数，具体的自己在类中加载就行，以及customers这个表我已经插入进去了）

4.1

// 向customers表中添加一条记录
    @Test
    public void testInsert() {
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            // 1.读取配置文件中的4个基本信息
            InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");
 
            Properties pros = new Properties();
            pros.load(is);
 
            String user = pros.getProperty("user");
            String password = pros.getProperty("password");
            String url = pros.getProperty("url");
            String driverClass = pros.getProperty("driverClass");
 
            // 2.加载驱动
            Class.forName(driverClass);
 
            // 3.获取连接
            conn = DriverManager.getConnection(url, user, password);
             
//      System.out.println(conn);
             
            //4.预编译sql语句，返回PreparedStatement的实例
            String sql = "insert into customers(name,email,birth)values(?,?,?)";//?:占位符
            ps = conn.prepareStatement(sql);
            //5.填充占位符
            ps.setString(1, "哪吒");
            ps.setString(2, "nezha@gmail.com");
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            java.util.Date date = sdf.parse("1000-01-01");
            ps.setDate(3, new Date(date.getTime()));
             
            //6.执行操作
            ps.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            //7.资源的关闭
            try {
                if(ps != null)
                    ps.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            try {
                if(conn != null)
                    conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
             
        }
         
    }

这个里面我要说明一个点

就是ps.setDate这个方法他是在Java.util.Date不是SQL语句下的Date，所以要进行转换

4.2因为增删改的操作无非就是SQL语句的不同

链接数据库，关闭啥的方法都重复，所以我们考虑用一个类来封装

类中直接用两个方法，一个链接方法，一个关闭方法，直接调用方法就可

package com.atguigu3.util;
 
import com.atguigu1.connection.ConnectionTest;
 
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
 
/**
 *
 *
 *
 */
public class JDBCUtils {
    public static Connection getConnection() throws ClassNotFoundException, IOException, SQLException {
        //1.读取配置文件中的4个基本信息
        InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");
 
        Properties pros = new Properties();
 
        pros.load(is);
 
        String user = pros.getProperty("user");
        String password = pros.getProperty("password");
        String url = pros.getProperty("url");
        String driverClass = pros.getProperty("driver");
 
        //2.加载驱动
        Class.forName(driverClass);
 
        //3.获取连接
        Connection conn = DriverManager.getConnection(url, user, password);
        System.out.println(conn);
        return conn;
    }
 
    public static void closeResource(Connection conn, Statement ps){
        try {
            if(ps != null)
                ps.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if(conn != null)
                conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

　　利用方法改良版增删改来啦！

    //修改customers表的一条记录
    @Test
    public void testUpdate(){
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            //1.获取数据库的连接
            conn = JDBCUtils.getConnection();
            //2.预编译sql语句，返回PreparedStatement的实例
            String sql = "update customers set name = ? where id = ?";
            ps = conn.prepareStatement(sql);
            //3.填充占位符
            ps.setObject(1,"莫扎特");
            ps.setObject(2, 18);
            //4.执行
            ps.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            //5.资源的关闭
            JDBCUtils.closeResource(conn, ps);
            
        }
    }

这不就少了很多，但是还可以减少！！

4.3 不清楚需要几个占位符？，所以可以用一个args直接代替即可，到时候一个for循环就可以解决

@Test
    public void TestCommonUpdate()
    {
        String sql = "delete from customers where id = ?";
        update(sql,3);
    }

 public void update(String sql,Object...args) {
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = JDBCUtils.getConnection();

            ps = conn.prepareStatement(sql);

            for (int i = 0; i < args.length;i++)
            {
                ps.setObject(i+1,args[i]);
            }

            ps.execute();
        } catch (ClassNotFoundException | SQLException | IOException e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(conn,ps);
        }