Question

I have been trying to create an XML using the simplexml library (v2.6.2)
http://simple.sourceforge.net/home.php

The XML I want to create has to hold an enum value, which should be case-sensitive. Following is the POJO :

 package pojos;

public enum MyEnum {

    NEW("new"),
    OLD("old");

     private final String value;

     MyEnum(String v)
     {
         value = v;
     }

     public String value() {
            return value;
        }

        public static MyEnum fromValue(String v) {
            for (MyEnum c: MyEnum.values()) {
                if (c.value.equals(v)) {
                    return c;
                }
            }
            throw new IllegalArgumentException(v);
        }

}

Following is the serializer code :

import java.io.File;

import org.simpleframework.xml.Serializer;
import org.simpleframework.xml.core.Persister;

import pojos.MyEnum;


public class TestEnum {

    /**
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub

        Serializer serializer = new Persister();
        MyEnum example = MyEnum.NEW;
        File result = new File("myenum.xml");

        serializer.write(example, result);

    }

}

The resultant output :

<myEnum>NEW</myEnum>

The desired output :

<myEnum>new</myEnum>

How should I proceed ? I cannot change the variable name in the enum as it happens to be the keyword “new” !

Thanks.

Answer 1

After some investigation of the source code, i have discovered that the library uses interface Transform to transform values to Strings. The default behavior of enum transformations is defined by class EnumTransform. In order to customize that, you can define you own Transform class. The following version of Transform implementation would call toString() instead of the default name() on the enum objects.

class MyEnumTransform implements Transform<Enum> {
    private final Class type;

    public MyEnumTransform(Class type) {
        this.type = type;
    }

    public Enum read(String value) throws Exception {
        for (Object o : type.getEnumConstants()) {
            if (o.toString().equals(value)) {
                return (Enum) o;
            }
        }
        return null;
    }

    public String write(Enum value) throws Exception {
        return value.toString();
    }
}

Transform objects are returned from match method by objects of Matcher interface. There could be several Matcher objects. The library tries them one by one until it finds one that returns a non-null Transformer object. You can define your own Matcher object and pass it as argument to the constructor of Persister class. This object will get the highest priority.

Persister serializer = new Persister(new Matcher() {
    public Transform match(Class type) throws Exception {
        if (type.isEnum()) {
            return new MyEnumTransform(type);
        }
        return null;
    }
 });

Finally, you wont forget to define a toString method on your enum classes. Then the combination of codes above will do you the work of encoding enum objects using their toString values.