MyBatis中如何使用${}和#{}

2024-12-12 技术教程

这篇文章主要为大家展示了MyBatis中如何使用${}和#{}，内容简而易懂，希望大家可以学习一下，学习完之后肯定会有收获的，下面让小编带大家一起来看看吧。

1、#{}是预编译处理，MyBatis在处理#{ }时，它会将sql中的#{ }替换为？，然后调用PreparedStatement的set方法来赋值，传入字符串后，会在值两边加上单引号，如上面的值 “4,44,514”就会变成“ ‘4,44,514' ”；

2、是字符串替换，在处理是字符串替换，MyBatis在处理时,它会将sql中的{}是字符串替换，在处理{ }是字符串替换， MyBatis在处理{ }时,它会将sql中的是字符串替换，在处理是字符串替换，MyBatis在处理时,它会将sql中的{ }替换为变量的值，传入的数据不会加两边加上单引号。

注意：使用${ }会导致sql注入，不利于系统的安全性！SQL注入：就是通过把SQL命令插入到Web表单提交或输入域名或页面请求的查询字符串，最终达到欺骗服务器执行恶意的SQL命令。常见的有匿名登录（在登录框输入恶意的字符串）、借助异常获取数据库信息等

package com.xiaobu.mapper;import com.xiaobu.base.mapper.MyMapper;import com.xiaobu.entity.Country;import java.util.List;/** * @author xiaobu * @version JDK1.8.0_171 * @date on 2018/11/27 19:21 * @description V1.0 */public interface CountryMapper extends MyMapper<Country> { /** * 功能描述:通过#{}来进行查询 * * @param ids id * @return java.util.List<com.xiaobu.entity.Country> * @author xiaobu * @date 2019/7/26 11:53 * @version 1.0 */ List<Country> findList(String ids); /** * 功能描述:通过${}来进行查询 * * @param ids id * @return java.util.List<com.xiaobu.entity.Country> * @author xiaobu * @date 2019/7/26 11:53 * @version 1.0 */ List<Country> findList2(String ids); /** * 功能描述: 通过foreach来进行查询 * * @param ids id * @return java.util.List<com.xiaobu.entity.Country> * @author xiaobu * @date 2019/7/26 11:53 * @version 1.0 */ List<Country> findListByForEach(List<Integer> ids);}

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" ><mapper namespace="com.xiaobu.mapper.CountryMapper"> <select id="findList" resultType="com.xiaobu.entity.Country"> select * from country where id in (#{ids} ) </select> <select id="findList2" resultType="com.xiaobu.entity.Country"> select * from country where id in (${ids} ) </select> <select id="findListByForEach" parameterType="List" resultType="com.xiaobu.entity.Country"> select * from country where id in <foreach collection="list" index="index" item="item" open="(" separator="," close=")"> #{item} </foreach> </select></mapper>

@Test public void countTotal(){ //统计总数 SELECT COUNT(Id) FROM country Example example = new Example(City.class); int count =countryMapper.selectCountByExample(example); System.out.println("count = " + count); //按条件查询 SELECT COUNT(Id) FROM country Country country = new Country(); //country.setCountryname("1234"); int conunt2 = countryMapper.selectCount(country); System.out.println("conunt2 = " + conunt2); } @Test public void findList(){ //Preparing: select * from country where id in ( '1,2,3') List<Country> countries = countryMapper.findList("1,2,3"); //countries = [Country(countryname=Angola, countrycode=AO)] System.out.println("countries = " + countries); //报错 There is no getter for property named 'ids' in 'class java.lang.String List<Country> countries2 = countryMapper.findList2("1,2,3"); System.out.println("countries2 = " + countries2); } @Test public void findListByForeach(){ //Preparing: select * from country where id in ( ? , ? , ? ) //Parameters: 1(Integer), 2(Integer), 3(Integer) List<Integer> list = new ArrayList<>(3); list.add(1); list.add(2); list.add(3); List<Country> countries2 = countryMapper.findListByForEach(list); System.out.println("countries2 = " + countries2); }