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：
<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#{…}
<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}”%”
<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
<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
<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
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脚本之家。
