TypeHandler lost information of actualTypeArguments when class is ParameterizedType

[DavidTangWei]

MyBatis version

3.4.5

Database vendor and version

mysql 5.7+

Test case or example project

deserialize data in table test to POJO Test using mybatis mapper.xml.

create table test {
    `id` bigint pk,
    `names` json
}

//POJO Test    
class Test {
    private long id;
    public void setId(long id) {
        this.id = id;
    }
    private List<String> names;
    public void setNames(List<String> names) {
        this.names = names;
    }
}

// typehandler use jackson for deserialization 
// the clazz in constructor lost actualTypeArguments when real class is ParameterizedType
class JsonTypeHandler<T>(private var clazz: Class<T>) : BaseTypeHandler<T>() {
    
    protected val objectMapper = ObjectMapper()
   
    override fun setNonNullParameter(ps: PreparedStatement?, i: Int, parameter: T, jdbcType: JdbcType?) {
        ps?.setString(i, this.toJson(parameter))
    }

    private fun toJson(obj: T): String {
        try {
            return this.objectMapper.writeValueAsString(obj)
        } catch (e: Exception) {
            throw RuntimeException(e);
        }
    }

    <resultMap id="testMapper" type="Test">
        <result property="id" column="id" />
        <result property="names" column="names" 
                typeHandler="JsonTypeHandler"/>
    </resultMap>

After debug the source code of mybatis, the class in the constructor of TypeHandler is get from org.apache.ibatis.reflection.Reflector#setTypes. But when the type is ParameterizedType to be added, ignore the actualTypeArguments and only add rawType.

//org.apache.ibatis.reflection.Reflector
 private void addSetMethod(String name, Method method) {
   if (isValidPropertyName(name)) {
     setMethods.put(name, new MethodInvoker(method));
     Type[] paramTypes = TypeParameterResolver.resolveParamTypes(method, type);
     setTypes.put(name, typeToClass(paramTypes[0]));
   }
 }

 private Class<?> typeToClass(Type src) {
   Class<?> result = null;
   if (src instanceof Class) {
     result = (Class<?>) src;
   } else if (src instanceof ParameterizedType) {
     // ignore the `actualTypeArguments` and only add `rawType`.
     result = (Class<?>) ((ParameterizedType) src).getRawType();
   } 
   ...
   }
   return result;
 }

Expected result

TypeHandler need to get the real ParameterizedType. Otherwise, I need to write many useless code to create many class inherit TypeHandler to pass the ParameterizedType manual.

Actual result

TypeHandler lost information of actualTypeArguments when class is ParameterizedType

[DavidTangWei]

@harawata hi.
Why do TypeHandler ignore the actualTypeArguments when the type is ParameterizedType ? Do you have plan to give us another method to get the actualTypeArguments.
I need your help! Please reply, thanks!

[harawata]

Hello @DavidTangWei ,

It is a known limitation.
I have been working on a patch, but it requires a lot of changes and I don't have much free time recently.

[wyl0706]

@harawata
I am experiencing the same problem, is there a plan to complete it?
My problem link: https://stackoverflow.com/questions/69140073/how-to-use-generics-in-mybatis-jsontypehandler

[harawata]

@wyl0706 There will be a new comment when/if there is any news. :)

[half-dead]

@harawata any update on this issue?

[FlyInWind1]

I am trying to work on this https://github.com/FlyInWind1/mybatis-3

[FlyInWind1]

I have impl ListTypeHandler. I pass ResolvedType (wrap jackson JavaType) to TypeHandler, instead of Class.
link https://github.com/FlyInWind1/mybatis-3
And this is my mybatis-plus https://github.com/FlyInWind1/mybatis-plus

[bunnyblueair]

any update on this issue?

[gr0l]

Any updates on this issue?

[la3rence]

Any update on this?

[Jasonyou-boy]

Is there any update？I had the same problem

[Vzhangs]

Any updates on this? I want to create a common List TypeHandler for a PostgreSQL composite type array column. But it might not be possible to implement it without getting the actualTypeArguments.

[harawata]

Hi all,

I have submitted #3379 .
It's still "draft", but I would appreciate if you could test your own usage against #3379 .
If you found a problem, please create/share a test case.