How do I use a Custom Type Handler with complex property or Type Safe Enumeration

Here is an example of how to set up a custom type handler with a complex property. This example uses the enum features of Java 1.5 but could be used with a Type Safe Enumeration in anything below 1.5.

Lets start by defining the database table

SHAPE {
      name    varchar2(25),
       color   number(100)
}

As you see the color is stored as a number, but in the class Shape is is a Color object. There are two question that I ran into. First, how do you cleanly map the number stored in the database with the instance of a Color? Second, how can iBatis and custom type handlers help?

To answer the first let me show you the code for the Shape class.

/*
 * Shape.java
 *
 * Created on September 23, 2005
 */
package domain;
/**
 *
 * @author nmaves
 */
public class Shape {
    public enum Color {
        BLUE(1, "0000FF"), RED(2, "FF0000"), GREEN(3, "00FF00");

        private int id;
        private String rgb;

        private Type(int id, String name) {
            this(id, name, "no mime type");

        }

        private Type(int id, String rgb) {
            this.id = id;
            this. rgb = rgb;
        }

        public int getId() {
            return this.id;
        }

        public String getRGB() {
            return this.name;
        }

        public static Type getInstance(int i) {
            for(Color color : Color.values()) {
                if(color.id == i) {
                    return type;
                }
            }

            throw new IllegalArgumentException("No such Color");
        }
    }

    private String name;
    private Color color;

    /** Creates a new instance of Frequency */
    private Shape(String name, Color color) {
        this.color = color;
        this.name = name;
    }


    public String toString() {
        return this.name;
    }


    public void setName(String name) {
       this.name = name;
    }
    public void setColor(Color color) {
       this.color = color;
    }

    public String getName() {
       return this.name;
    }
    public Color getColor() {
       return this.color;
    }

}

As you see the getInstance(int i) method allows for the mapping of the number stored in the database to an instance of this class. I am sure there is a better way of pulling these initial value from a properties file but this is only an example.

For the second part you will need a way to allow iBatis to make the conversion. This is where the custom type handler comes into play.

Below is my ColorTypeHandler.java

package dao.ibatis;

import com.ibatis.sqlmap.client.extensions.ParameterSetter;
import com.ibatis.sqlmap.client.extensions.ResultGetter;
import com.ibatis.sqlmap.client.extensions.TypeHandlerCallback;
import java.sql.SQLException;
import java.sql.Types;
import Shape.Color;


public class ColorTypeHandler implements TypeHandlerCallback {
    public Object getResult(ResultGetter getter) throws SQLException {
        int value = getter.getInt();
        if (getter.wasNull()) {
            return null;
        }
        Color color = Color.getInstance(value);

        return color;
    }

    public void setParameter(ParameterSetter setter, Object parameter)
                      throws SQLException {
        if (parameter == null) {
            setter.setNull(Types.INTEGER);
        } else {
            Color color = (Color) parameter;
            setter.setInt(color.getId());
        }
    }

    public Object valueOf(String s) {
        return s;
    }
}

You are almost there! All you need left to do is tell iBatis to map instances of Frequency object to this handler.

I added the following line into my SqlMapConfig file.

<typeHandler javaType="domain.Shape$Color" callback="dao.ibatis.ColorTypeHandler"/>

Useful Information

Notice the $ in the class name. This is how Java 1.5 denotes enums. If this were a type safe enum you would just use standard notation.

That is it. No need to change any of your other sqlmap entries. Here is an example of a select and insert that use this handler.

<resultMap class="Shape" id="ShapeResult">
        <result column="name" property="name" />
        <result column="color" property="color" />
</resultMap>

<select id="getShapeByName" parameterClass="string" resultMap="ShapeResult">
        SELECT
            *
        FROM
            SHAPE
        WHERE
            name = #value#
</select>

<insert id="insertReport" parameterClass="Report">
        INSERT INTO
            SHAPE (
                name,
                color
                )
            values (
                #name#,
                #color#,
            )
</insert>

Notice that there is nothing special that need to be done for the color columns.

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