在学习mybatis过程中想实现模糊查询，可惜失败了。后来上百度上查了一下，算是解决了。记录一下mybatis实现模糊查询的几种方式。
数据库表名为test_student,初始化了几条记录，如图：
起初我在mybatis的mapper文件中是这样写的：
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<select id="searchstudents" resulttype="com.example.entity.studententity" parametertype="com.example.entity.studententity"> select * from test_student <where> <if test="age != null and age != '' and compare != null and compare != ''"> age ${compare} #{age} </if> <if test="name != null and name != ''"> and name like '%#{name}%' </if> <if test="address != null and address != ''"> and address like '%#{address}%' </if> </where> order by id</select> |
写完后自我感觉良好，很开心的就去跑程序了，结果当然是报错了：
经百度得知，这么写经mybatis转换后(‘%#{name}%')会变为(‘%?%'),而(‘%?%')会被看作是一个字符串，所以java代码在执行找不到用于匹配参数的 ‘?' ,然后就报错了。
解决方法
1.用${…}代替#{…}
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<select id="searchstudents" resulttype="com.example.entity.studententity" parametertype="com.example.entity.studententity"> select * from test_student <where> <if test="age != null and age != '' and compare != null and compare != ''"> age ${compare} #{age} </if> <if test="name != null and name != ''"> and name like '%${name}%' </if> <if test="address != null and address != ''"> and address like '%${address}%' </if> </where> order by id </select> |
查询结果如下图：
注：使用${…}不能有效防止sql注入，所以这种方式虽然简单但是不推荐使用！！！
2.把'%#{name}%'改为”%”#{name}”%”
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<select id="searchstudents" resulttype="com.example.entity.studententity" parametertype="com.example.entity.studententity"> select * from test_student <where> <if test="age != null and age != '' and compare != null and compare != ''"> age ${compare} #{age} </if> <if test="name != null and name != ''"> and name like "%"#{name}"%" </if> <if test="address != null and address != ''"> and address like "%"#{address}"%" </if> </where> order by id</select> |
查询结果：
3.使用sql中的字符串拼接函数
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<select id="searchstudents" resulttype="com.example.entity.studententity" parametertype="com.example.entity.studententity"> select * from test_student <where> <if test="age != null and age != '' and compare != null and compare != ''"> age ${compare} #{age} </if> <if test="name != null and name != ''"> and name like concat(concat('%',#{name},'%')) </if> <if test="address != null and address != ''"> and address like concat(concat('%',#{address},'%')) </if> </where> order by id </select> |
查询结果：
4.使用标签
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<select id="searchstudents" resulttype="com.example.entity.studententity" parametertype="com.example.entity.studententity"> <bind name="pattern1" value="'%' + _parameter.name + '%'" /> <bind name="pattern2" value="'%' + _parameter.address + '%'" /> select * from test_student <where> <if test="age != null and age != '' and compare != null and compare != ''"> age ${compare} #{age} </if> <if test="name != null and name != ''"> and name like #{pattern1} </if> <if test="address != null and address != ''"> and address like #{pattern2} </if> </where> order by id </select> |
查询结果：
5.在java代码中拼接字符串
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public static void main(string[] args) { try { int count = 500; long begin = system.currenttimemillis(); teststring(count); long end = system.currenttimemillis(); long time = end - begin; system.out.println("string 方法拼接"+count+"次消耗时间：" + time + "毫秒"); begin = system.currenttimemillis(); teststringbuilder(count); end = system.currenttimemillis(); time = end - begin; system.out.println("stringbuilder 方法拼接"+count+"次消耗时间：" + time + "毫秒"); } catch (exception e) { e.printstacktrace(); } } private static string teststring(int count) { string result = ""; for (int i = 0; i < count; i++) { result += "hello "; } return result; } private static string teststringbuilder(int count) { stringbuilder sb = new stringbuilder(); for (int i = 0; i < count; i++) { sb.append("hello"); } return sb.tostring(); } |
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/lonely_dog/article/details/74171314
