Error with interface TypeHandler for enum with interface

Hi, I think I found an issue for a rather specific case. I’m not sure if this issue belongs to this repo, Spring integration, or MyBatis core. I put it here for now, because the demo is using TypeHandler’s component scanning.

When trying to map an enum with an interface using the interface’s TypeHandler Spring bean, there are cases which throws the following exception:

...
Caused by: org.apache.ibatis.type.TypeException: Unable to find a usable constructor for class com.example.demo.mybatis.TheInterfaceTypeHandler
	at org.apache.ibatis.type.TypeHandlerRegistry.getInstance(TypeHandlerRegistry.java:457) ~[mybatis-3.5.5.jar:3.5.5]
	at org.apache.ibatis.type.TypeHandlerRegistry.getJdbcHandlerMapForEnumInterfaces(TypeHandlerRegistry.java:286) ~[mybatis-3.5.5.jar:3.5.5]
	at org.apache.ibatis.type.TypeHandlerRegistry.getJdbcHandlerMap(TypeHandlerRegistry.java:262) ~[mybatis-3.5.5.jar:3.5.5]
	at org.apache.ibatis.type.TypeHandlerRegistry.getTypeHandler(TypeHandlerRegistry.java:237) ~[mybatis-3.5.5.jar:3.5.5]
	...
Caused by: java.lang.NoSuchMethodException: com.example.demo.mybatis.TheInterfaceTypeHandler.<init>()
	at java.lang.Class.getConstructor0(Class.java:3082) ~[na:1.8.0_265]
	at java.lang.Class.getConstructor(Class.java:1825) ~[na:1.8.0_265]

As I understand it, MyBatis is trying to instantiate a new TypeHandler instead of using the one registered as Spring bean, which it failed because the type handler class requires another Spring bean (therefore no no-arg constructor).

---

Here’s the sample code for demonstrating the case: https://github.com/KniveX/bugreport-springboot-mybatis-200816

• Java 8 (OpenJDK 1.8.0_265-8u265-b01-0ubuntu2~18.04-b01)
• Spring Boot (2.3.3.RELEASE)
• mybatis-spring-boot-starter (2.1.3)

Thank you, and I apologize if my english is not clear.

[kazuki43zoo]

I think you don’t need to use the spring bean in this case. I’ve modified as follow, it work fine. WDYT?

package com.example.demo.mybatis;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

import com.example.demo.obj.TheInterface;
import com.example.demo.obj.TheRequiredBean;

public class TheInterfaceTypeHandler extends BaseTypeHandler<TheInterface> {

	@Override
	public void setNonNullParameter(PreparedStatement ps, int i, TheInterface parameter, JdbcType jdbcType)
			throws SQLException {
		ps.setString(i, parameter.name());
	}

	@Override
	public TheInterface getNullableResult(ResultSet rs, String columnName) throws SQLException {
		return TheRequiredBean.findByName( rs.getString(columnName) );
	}

	@Override
	public TheInterface getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
		return TheRequiredBean.findByName( rs.getString(columnIndex) );
	}

	@Override
	public TheInterface getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
		return TheRequiredBean.findByName( cs.getString(columnIndex) );
	}

}

package com.example.demo.obj;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

import org.apache.ibatis.io.ResolverUtil;

public class TheRequiredBean {

  private static final Map<String, TheInterface> mapping;

  private TheRequiredBean() {
    // NOP
  }

  static {
    mapping = new ResolverUtil<>().find(new ResolverUtil.IsA(TheInterface.class), "com.example.demo")
        .getClasses().stream()
        .filter(Class::isEnum)
        .map(x -> ((Class<? extends Enum<?>>) x))
        .flatMap(x -> Arrays.stream(x.getEnumConstants()))
        .collect(Collectors.toUnmodifiableMap(Enum::name, x -> (TheInterface) x));
  }

  public static TheInterface findByName(String enumName) {
    return mapping.get(enumName);
  }

}

• application.properties

mybatis.type-handlers-package=com.example.demo.mybatis

[KniveX]

Your solution works great! I guess this issue can be safely closed.

Thanks a lot for your help @kazuki43zoo. Cheers