Mybatis-3: Maybe it is a bug. Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'id' in 'class java.lang.Integer'

[letiantian]

I used Mybatis 3.2.5 in a simple project. The structure of th project is :

The content of mybatis-config.xml is

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/blog_db?useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="123"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="letian/mybatis/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

The table user in blog_db has 2 records.

mysql> select * from user;
+----+--------+----------------+----------+
| id | name   | email          | password |
+----+--------+----------------+----------+
|  1 | letian | [email protected] | 123      |
|  2 | xiaosi | [email protected] | 123      |
+----+--------+----------------+----------+
2 rows in set (0.00 sec)

The source code of letian.mybatis.bean.User is

package letian.mybatis.bean;

public class User {

    private int id;
    private String name;
    private String email;
    private String password;

    // ......
    // getters and setters
    // ......

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", email='" + email + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

The source code of letian.mybatis.dao.UserMapper is

package letian.mybatis.dao;

import letian.mybatis.bean.User;

public interface UserMapper {

    User findById(int id);
}

The source code of letian/mybatis/mapper/UserMapper.xml is

<?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="letian.mybatis.dao.UserMapper">
    <select id="findById" parameterType="HashMap" resultType="letian.mybatis.bean.User">
        select
        * from blog_db.user where id=#{id}
    </select>
</mapper>

The source code of Main.java is

import java.io.IOException;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import letian.mybatis.bean.User;
import letian.mybatis.dao.UserMapper;


public class Main {

    public static void main(String[] args) throws IOException {

        SqlSessionFactory sessionFactory;
        sessionFactory = new SqlSessionFactoryBuilder()
                .build(Resources.getResourceAsReader("mybatis-config.xml"));

        SqlSession sqlSession = sessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        User user = userMapper.findById(1);
        System.out.println(user);

    }
}

Main.java could be executed correctly. If the value of parameterType in <select id="findById">...</select> in letian/mybatis/mapper/UserMapper.xml is set to int or Integer, Main.java could be executed correctly as well.

However, if the content of letian/mybatis/mapper/UserMapper.xml is changed to

<?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="letian.mybatis.dao.UserMapper">

    <select id="findById" parameterType="HashMap" resultType="letian.mybatis.bean.User">
        select * from
        blog_db.user where
        <choose>
            <when test="id &lt; 0">
                id = 0-#{id}
            </when>
            <otherwise>
                id = #{id}
            </otherwise>
        </choose>
    </select>

</mapper>

Main.java cannot be executed and I got the error as follows:

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'id' in 'class java.lang.Integer'
### Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'id' in 'class java.lang.Integer'
......

If the value of parameterType in <select id="findById">...</select> in letian/mybatis/mapper/UserMapper.xml is set to int or Integer, Main.java cannot be executed as well.

Though this problem was solved in a different way, I think it's an unreasonable implementation for MyBatis.

[Condor70]

Are you sure that parameterType="int" (or "java.lang.Integer") doesn't work?

"Integer" isn't a type or an alias, so that won't work.

[legend0702]

Recommend use Integer instead of int,if you can.
And @harawata is true,plz check your param. :)

[harawata]

• As documented, parameterType is optional and it is usually better to let MyBatis detect it.
• As your statement has one simple type parameter without @Param annotation, you need to use the implicit name _parameter to reference it in the OGNL expression or ${}.

[letiantian]

@Condor70 @legend0702 I am sure. When I use dynamic SQL, parameterType="int", or "java.lang.Integer", or "Integer", or "HashMap", it doesn't work. I know how to solve it, but just think it is strange that Mybatis can not work in the situation I mentioned above.

[harawata]

Java does not allow us to obtain the parameter name at runtime, unfortunately.
Please search 'java parameter name' for more detailed explanation.

So, as I explained, you may have to 1) modify the xml mapper as follows:

<when test="_parameter &lt; 0">
  id = 0-#{id}
</when>

Or 2) add @Param("id") to the method parameter.

User findById(@Param("id")int id);

[qq291462491]

• 1，good！

[trohovsky]

549

[fushenshen]

5楼说的对 顶起

[crystalcyw]

i got this too,and i added annotation @Param and problem solved.