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
${compare}
#{age}
</if>
<if test="name != null and name != ''">
and name like '%#{name}%'
</if>
<if test="address != null and address != ''">
and address like '%#{address}%'
</if>
</where>
order by id
</select>
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写完后自我感觉良好，很开心的就去跑程序了，结果当然是报错了：
经百度得知，这么写经mybatis转换后(‘%#{name}%')会变为(‘%?%'),而(‘%?%')会被看作是一个字符串，所以java代码在执行找不到用于匹配参数的 ‘?' ,然后就报错了。
解决方法
1.用${…}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 '%${address}%'
</if>
</where>
order by id
</select>
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查询结果如下图：
注：使用${…}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>
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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>
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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>
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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();
}
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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