Allow registering a type handler for a common interface of enums.

[harawata]

It is common for multiple enums to have a common interface along with a corresponding type handler.
Up to version 3.4.2, to use this type handler, users had to list all the enum implementations in the @MappedType or <typeHandlers />.

This PR allows users to register the type handler against the common interface.
Please see the attached test case for how it works.

Cc-ing @gaohanghbut @liyuj @yxc023 @charlesluo2014 @Hubbitus @fengdh @fayou @sskeater @jlkm2010
Thought you guys might be interested.

[gaohanghbut]

@harawata thanks for your attribution

[kazuki43zoo]

Hi @harawata, I have one question.
I don't know how to convert to enum instance from result set value using this solution. I think that it need to set enum type to cutom TypeHandler for converting a enum instance. Could you tell me how to do it ?

[harawata]

@kazuki43zoo ,
I re-checked the code and you are right. This fix is incomplete :(
I'll create another PR soon.
Thank you for the review!

[mahengyang]

the constractor of custom typehandler has some error

public HasValueEnumTypeHandler(Class<E> type) {
   if (type == null)
     throw new IllegalArgumentException("Type argument cannot be null");
   this.type = type;
   this.enums = type.getEnumConstants();

this.enums is aways null becase the parameter type is a interface

[harawata]

@mahengyang

type is supposed to be an enum that implements HasValue interface, not the interface itself.

[mahengyang]

@harawata if there is many enum,we need write every enum type handler in mybatis-config.xml, like this, Witch makes me feel a little verbose

<typeHandlers>
    <typeHandler javaType="com.qbike.eum.LeipaiOrderStatus" handler="com.qbike.mybatis.EnumTypeHandler"/>
    <typeHandler javaType="com.qbike.eum.TestStatus" handler="com.qbike.mybatis.EnumTypeHandler"/>
</typeHandlers>

the handler EnumTypeHandler

public class EnumTypeHandler<E extends Enum<E> & EnumCode> extends BaseTypeHandler<E> {
    private Class<E> type;
    private EnumCode[] enums;

    public EnumTypeHandler(Class<E> type) {
        this.type = type;
        this.enums = type.getEnumConstants();
    }

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
        ps.setInt(i, parameter.getCode());
    }

    @Override
    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
        return find(rs.getInt(columnName));
    }

    @Override
    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        return find(rs.getInt(columnIndex));
    }

    @Override
    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        return find(cs.getInt(columnIndex));
    }

    private E find(int status) {
        for (EnumCode enumCode : enums) {
            if (enumCode.getCode() == status) {
                return (E) enumCode;
            }
        }
        return null;
    }
}

[harawata]

@mahengyang ,
Are you actually having a problem, or just reading the code?
this.enums being null should not be a problem because the instance registered against HasValue interface is not used when converting enums (a new instance is created and registered for each enum).

There is a working test case, so if you found a bug, please create a failing test case.
Thanks!

Note that there is a bug in 3.4.4 and you need to use 3.4.5-SNAPSHOT for now (I assumed you knew it seeing your comment on #976 ).

[michaelplavnik]

Implementation of the feature is still incomplete.
When used with XMLConfigBuilder.parse, eager instantiation of the defined handlers happens and each enum type need to be explicitly listed.

XMLConfigBuilder.parse is called by mybatis-spring project for example.

[kazuki43zoo]

@michaelplavnik This PR is already merged. Please create a new issue as related this.