(Quick Reference)

6 Custom TypeHandlers - Reference Documentation

Authors: Franjo Žilić

Version: 0.0.2

6 Custom TypeHandlers

Writing custom MyBatis TypeHandlers

What are TypeHandlers

Type handlers are used for data transformation. For example, you are connecting to a legacy database that stores list of data in a single VARCHAR field, and each item is enclosed with brackets. You have to extract that data, and you can do it with a custom type handler.

Writing a TypeHandler

TypeHandlers are artefact classes which should be placed in grails-app/typeHandlers and end with "TypeHandler"

package org.grails.mybatis.exampleimport 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 org.apache.ibatis.type.MappedJdbcTypes
import org.apache.ibatis.type.MappedTypes
@MappedJdbcTypes(JdbcType.VARCHAR)
@MappedTypes([List])
class ExampleTypeHandler extends BaseTypeHandler<List<String>>{
  def static dataSourceName = 'dataSource'
  @Override
  public void setNonNullParameter(PreparedStatement statement, int index, List<String> parameter, JdbcType jdbcType) throws SQLException {
    def builder = "" as StringBuilder
    parameter.each {
      builder += "[$it]"
    }
    statement.setString(index, builder.toString())
  }
  List<String> decodeValue(String value) {
    def matcher = value =~ /[(.*?)]/
    def results = []
    matcher.each {
      results << it[1]
    }
    return results
  }
  @Override
  public List<String> getNullableResult(ResultSet resultSet, String columnName) throws SQLException {
    def encoded = resultSet.getString(columnName)
    return decodeValue(encoded)
  }
  @Override
  public List<String> getNullableResult(ResultSet resultSet, int columnIndex) {
    def encoded = resultSet.getString(columnIndex)
    return decodeValue(encoded)
  }
  @Override
  public List<String> getNullableResult(CallableStatement statement, int columnIndex) throws SQLException {
    def encoded = statement.getString(columnIndex)
    return decodeValue(encoded)
  }
}

You have to register that type handler to a specific MyBatis result using typeHanlder attribute in mapper file.

Custom Enum type handlers

From time to time old databases store some enumerated information in a specific way (single character). If you need to map such values to your enums it can be done by extending AbstractEnumTypeHandler class provided in this plugin

package org.grails.plugins.mybatis.enumsenum SampleEnum {
  VALUE_ONE('O'), VALUE_TWO('T')
  String dbCode
  SampleEnum(dbCode){
    this.dbCode = dbCode
  }
}

package org.grails.plugins.mybatis.enumsclass SampleEnumTypeHandler extends AbstractEnumTypeHandler<SampleEnum> {
  SampleEnumTypeHandler() {
    super(SampleEnum, "dbCode")
  }
}