MyBatis的类型处理器TypeHandler与自定义实现

private Object getPropertyMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)
    throws SQLException {
  if (propertyMapping.getNestedQueryId() != null) {
    return getNestedQueryMappingValue(rs, metaResultObject, propertyMapping, lazyLoader, columnPrefix);
  } else if (propertyMapping.getResultSet() != null) {
    addPendingChildRelation(rs, metaResultObject, propertyMapping);   // TODO is that OK?
    return DEFERED;
  } else {
    final TypeHandler<?> typeHandler = propertyMapping.getTypeHandler();
    final String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
    return typeHandler.getResult(rs, column);
  }
}

// ExampleTypeHandler.java
@MappedJdbcTypes(JdbcType.VARCHAR)
public class ExampleTypeHandler extends BaseTypeHandler<String> {
  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {
    ps.setString(i, parameter);
  }
  @Override
  public String getNullableResult(ResultSet rs, String columnName) throws SQLException {
    return rs.getString(columnName);
  }
  @Override
  public String getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    return rs.getString(columnIndex);
  }
  @Override
  public String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    return cs.getString(columnIndex);
  }
}
<!-- mybatis-config.xml -->
<typeHandlers>
  <typeHandler handler="org.mybatis.example.ExampleTypeHandler" />
</typeHandlers>
<!-- typeHandler指定JavaType jdbcType -->
<typeHandler handler="org.mybatis.example.ExampleTypeHandler" 
javaType="java.lang.String" jdbcType="VARCHAR" />

<!-- mybatis-config.xml -->
<typeHandlers>
  <package name="org.mybatis.example"/>
</typeHandlers>

//GenericTypeHandler.java
public class GenericTypeHandler<E extends MyObject> extends BaseTypeHandler<E> {
  private Class<E> type;
  public GenericTypeHandler(Class<E> type) {
    if (type == null) throw new IllegalArgumentException("Type argument cannot be null");
    this.type = type;
  }
  //...

public class BigIntegerTypeHandler extends BaseTypeHandler<BigInteger> {
  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, BigInteger parameter, JdbcType jdbcType) throws SQLException {
    ps.setBigDecimal(i, new BigDecimal(parameter));
  }
  @Override
  public BigInteger getNullableResult(ResultSet rs, String columnName) throws SQLException {
    BigDecimal bigDecimal = rs.getBigDecimal(columnName);
    return bigDecimal == null ? null : bigDecimal.toBigInteger();
  }
  @Override
  public BigInteger getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    BigDecimal bigDecimal = rs.getBigDecimal(columnIndex);
    return bigDecimal == null ? null : bigDecimal.toBigInteger();
  }
  @Override
  public BigInteger getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    BigDecimal bigDecimal = cs.getBigDecimal(columnIndex);
    return bigDecimal == null ? null : bigDecimal.toBigInteger();
  }
}

public interface TypeHandler<T> {
  void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;
  T getResult(ResultSet rs, String columnName) throws SQLException;
  T getResult(ResultSet rs, int columnIndex) throws SQLException;
  T getResult(CallableStatement cs, int columnIndex) throws SQLException;
}

public class MyEnumEmpStatusTypeHandler implements TypeHandler<EmpStatus> {
   //定义当前数据如何保存到数据库中
  @Override
  public void setParameter(PreparedStatement ps, int i, EmpStatus parameter,
      JdbcType jdbcType) throws SQLException {
    System.out.println("要保存的状态码："+parameter.getCode());
    ps.setString(i, parameter.getCode().toString());
  }
  @Override
  public EmpStatus getResult(ResultSet rs, String columnName)
      throws SQLException {
    //需要根据从数据库中拿到的枚举的状态码返回一个枚举对象
    int code = rs.getInt(columnName);
    System.out.println("从数据库中获取的状态码："+code);
    EmpStatus status = EmpStatus.getEmpStatusByCode(code);
    return status;
  }
  @Override
  public EmpStatus getResult(ResultSet rs, int columnIndex)
      throws SQLException {
    int code = rs.getInt(columnIndex);
    System.out.println("从数据库中获取的状态码："+code);
    EmpStatus status = EmpStatus.getEmpStatusByCode(code);
    return status;
  }
  @Override
  public EmpStatus getResult(CallableStatement cs, int columnIndex)
      throws SQLException {
    int code = cs.getInt(columnIndex);
    System.out.println("从数据库中获取的状态码："+code);
    EmpStatus status = EmpStatus.getEmpStatusByCode(code);
    return status;
  }
}

<typeHandlers>
  <typeHandler handler="com.mybatis.typehandler.MyEnumEmpStatusTypeHandler"  
  javaType="com.mybatis.bean.EmpStatus"/>
</typeHandlers>

<resultMap type="com.mybatis.bean.Employee" id="MyEmp">
  <id column="id" property="id"/>
  <result column="empStatus" property="empStatus" typeHandler="XXXXX"/>
</resultMap>

<insert id="addEmp" useGeneratedKeys="true" keyProperty="id">
  insert into tbl_employee(last_name,email,gender,empStatus) 
  values
  (#{lastName},#{email},#{gender},#{empStatus,typeHandler=xxxx})
</insert>