MyBatis批量操作报错：Parameter 'xxxList' not found. Available parameters are [list]

问题背景：

在Dao中使用MyBatis进行查询操作，参数是传的一个List：studentNameList，但是在执行查询的时候报错，具体日志如下：

com.chenzhou.base.mybatis.IbatisSystemException: SqlSession operation; nested exception is org.apache.ibatis.exceptions.PersistenceException:
### Error querying database.  Cause: org.apache.ibatis.binding.BindingException: Parameter 'studentNameList' not found. Available parameters are [list]
### Cause: org.apache.ibatis.binding.BindingException: Parameter 'studentNameList' not found. Available parameters are [list]
    at com.chenzhou.base.mybatis.SqlSessionTemplate.wrapException(SqlSessionTemplate.java:341)
    at com.chenzhou.base.mybatis.SqlSessionTemplate.execute(SqlSessionTemplate.java:127)
    at com.chenzhou.base.mybatis.SqlSessionTemplate.execute(SqlSessionTemplate.java:106)
    at com.chenzhou.base.mybatis.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:138)
    at com.chenzhou.dao.GenericMybatisDao.count(GenericMybatisDao.java:306)
    at com.chenzhou.cds.ps.dao.impl.StudentDao.getStudentCount(StudentDao.java:42)
    at com.chenzhou.cds.ps.dao.impl.StudentDao$$FastClassByCGLIB$$8819e766.invoke(<generated>)
    at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:191)
    at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:689)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
    at com.chenzhou.util.LogUtil.doMethodInfo(LogUtil.java:85)
    at com.chenzhou.util.LogUtil.doDebugMethodLog(LogUtil.java:36)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:55)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:622)
    at com.chenzhou.cds.ps.dao.impl.StudentDao$$EnhancerByCGLIB$$d4fcf513.getStudentCount(<generated>)
    at com.chenzhou.ps.dao.StudentDaoTest.testgetStudentCount(StudentDaoTest.java:44)
……

单元测试用例代码如下：

@Test
public void testgetStudentCount(){
    List<String> studentNameList = new ArrayList<String>();
    studentNameList.add("chenzhou");
    studentNameList.add("zhangsan");
    studentNameList.add("lisi");
    int count = studentDao.getStudentCount(studentNameList);
    System.out.println(count);
}

studentDao中的getStudentCount方法代码如下：

public int getStudentCount(List<String> studentNameList){
    return super.count("getStudentCount", studentNameList);
}

MyBatis mapper.xml定义如下：

<!-- 查询学生数量  -->
<select id="Student.getStudentCount" parameterType="java.util.List" resultType="java.lang.Integer">
    <![CDATA[
    SELECT
        COUNT(*)
    FROM
        t_student WHERE 1=1
    ]]>
    <if test="studentNameList != null">
        AND student_name in
        <foreach collection="studentNameList" item="item" open="(" separator="," close=")">
            #{item}
        </foreach>
    </if>
</select>

根据报错日志分析，是MyBatis在解析xml时找不到其中声明的studentNameList，但是在Dao中明明传的参数就是studentNameList，怎么会报错呢?

查询了一下MyBatis官方的说明文档，终于找到了原因，在http://mybatis.github.io/mybatis-3/zh/dynamic-sql.html#foreach里有一段说明：

写道

注意 你可以传递一个 List 实例或者数组作为参数对象传给 MyBatis。当你这么做的时 候,MyBatis 会自动将它包装在一个 Map 中,用名称在作为键。List 实例将会以“list” 作为键,而数组实例将会以“array”作为键。

因为我传的参数只有一个，而且传入的是一个List集合，所以mybatis会自动封装成Map<"list",studentNameList>。在解析的时候会通过“list”作为Map的key值去寻找。但是我在xml中却声明成studentNameList了，所以自然会报错找不到。

解决办法：

第一种就是修改mapper.xml中foreach标签内容，把studentNameList修改为list

<if test="list != null">
    AND student_name in
    <foreach collection="list" item="item" open="(" separator="," close=")">
        #{item}
    </foreach>
</if>

不过这种方式我个人不太建议，因为以后如果要扩展该方法，增加集合参数的时候，还得修改xml中的内容。

第二种方式，修改dao中的参数传入方式，手动封装成map，然后把map当参数传进去

Dao方法修改为：

public int getStudentCount(List<String> studentNameList){
    //把参数手动封装在Map中
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("studentNameList", studentNameList);
    return super.count("getStudentCount", map);
}

然后修改mapper.xml中的parameterType类型为Map

<!--注意下面的parameterType类型必须修改为Map类型,foreach中引用的List名称不用改变-->
<select id="Student.getStudentCount" parameterType="java.util.Map" resultType="java.lang.Integer">
    <![CDATA[
    SELECT
        COUNT(*)
    FROM
        t_student WHERE 1=1
    ]]>
    <if test="studentNameList != null">
        AND student_name in
        <foreach collection="studentNameList" item="item" open="(" separator="," close=")">
            #{item}
        </foreach>
    </if>
</select>

修改完后，重新执行了一下测试用例，测试通过。