Mybatis枚举类型转换源码分析

public final class TypeHandlerRegistry {
  ....
  public TypeHandlerRegistry(Configuration configuration) {
    this.unknownTypeHandler = new UnknownTypeHandler(configuration);
    register(Boolean.class, new BooleanTypeHandler());
    register(boolean.class, new BooleanTypeHandler());
    register(JdbcType.BOOLEAN, new BooleanTypeHandler());
    register(JdbcType.BIT, new BooleanTypeHandler());
    ...

public EnumTypeHandler(Class<E> type) {
    if (type == null) {
      throw new IllegalArgumentException("Type argument cannot be null");
    }
    this.type = type;
  }
  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
    if (jdbcType == null) {
      ps.setString(i, parameter.name());
    } else {
      ps.setObject(i, parameter.name(), jdbcType.TYPE_CODE); // see r3589
    }
  }
  @Override
  public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
    String s = rs.getString(columnName);
    return s == null ? null : Enum.valueOf(type, s);
    ...

public <T> TypeHandler<T> getInstance(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
    if (javaTypeClass != null) {
      try {
        Constructor<?> c = typeHandlerClass.getConstructor(Class.class);
        return (TypeHandler<T>) c.newInstance(javaTypeClass);
      } catch (NoSuchMethodException ignored) {
        // ignored
      } catch (Exception e) {
        throw new TypeException("Failed invoking constructor for handler " + typeHandlerClass, e);
      }
    }
    try {
      Constructor<?> c = typeHandlerClass.getConstructor();
      return (TypeHandler<T>) c.newInstance();
    } catch (Exception e) {
      throw new TypeException("Unable to find a usable constructor for " + typeHandlerClass, e);
    }
  }

public interface BaseEnum {
    Integer getValue();
}

@AllArgsConstructor
@Getter
public enum GroupStatusEnum implements BaseEnum {
    DISBANDED("已解散", 0),
    NORMAL("正常", 1);
    private final String desc;
    private final Integer value;
}

public class GenericEnumHandler<E extends BaseEnum> implements TypeHandler<E> {
    private final Map<Integer, E> map = new HashMap<>();
    public GenericEnumHandler(Class<E> clazz) {
        E[] constants = clazz.getEnumConstants();
        for (E constant : constants) {
            map.put(constant.getValue(), constant);
        }
    }
    @Override
    public void setParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
        ps.setInt(i, parameter.getValue());
    }
    @Override
    public E getResult(ResultSet rs, String columnName) throws SQLException {
        return map.get(rs.getInt(columnName));
    }
    @Override
    public E getResult(ResultSet rs, int columnIndex) throws SQLException {
        return map.get(rs.getInt(columnIndex));
    }
    @Override
    public E getResult(CallableStatement cs, int columnIndex) throws SQLException {
        return map.get(cs.getInt(columnIndex));
    }
}

mybatis:
  configuration:
    local-cache-scope: statement
    jdbc-type-for-null: null
    use-generated-keys: true
    cache-enabled: false
    map-underscore-to-camel-case: true
    default-enum-type-handler: com.windcf.easychatjava.typehandler.GenericEnumHandler
  mapper-locations: classpath:/mappers/**/*.xml
#  type-handlers-package: com.windcf.easychatjava.typehandler