Details
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Type:
New Feature
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Status:
Open
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Priority:
Major
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Resolution: Unresolved
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Affects Version/s: 1.1
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Fix Version/s: None
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Component/s: None
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Labels:None
Description
In order to keep the XML small, it would be nice to ignore fields for which the default values are not changed, similar to the way it is done in the XMLEncoder:
Eg:
public class MyClass {
private int m_value = 2;
public int getValue()
{ return m_value; }public void setValue(int value)
{ m_value = value; } public MyClass() {
}
}
Serializing a new instance of this class, without changing the value gives following output:
//XStream
<com.alcatel.ni.commands.core.MyClass>
<m_value>2</m_value>
</com.alcatel.ni.commands.core.MyClass>
//XMLEncoder:
<?xml version="1.0" encoding="UTF-8"?>
<java version="1.4.2" class="java.beans.XMLDecoder">
<object class="com.alcatel.ni.commands.core.MyClass"/>
</java>
Issue Links
Activity
a third simple option is to not save fields of which value are the same as the language default, i.e. don't save the field if it is an integer 0, boolean false, float 0.0 etc.
Hontvári József
added a comment - a third simple option is to not save fields of which value are the same as the language default, i.e. don't save the field if it is an integer 0, boolean false, float 0.0 etc. I looked at adding the following code after value = field.get(object) in com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider
if( value instanceof Number && field.getType().isPrimitive() && ((Number)value).doubleValue() == 0d)
{ value = null; }else if( value instanceof Boolean && field.getType().isPrimitive()&& ((Boolean)value).booleanValue() == false)
{ value = null; }I've only looked at the source for about an hour this morning so couldn't tell you if it has any knock on effects or is just gibberish, but it appears to work for the simple object heirarchy I it tested with.
Justin Birch
added a comment - I looked at adding the following code after value = field.get(object) in com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider
if( value instanceof Number && field.getType().isPrimitive() && ((Number)value).doubleValue() == 0d)
{
value = null;
}
else if( value instanceof Boolean && field.getType().isPrimitive()&& ((Boolean)value).booleanValue() == false)
{
value = null;
}
I've only looked at the source for about an hour this morning so couldn't tell you if it has any knock on effects or is just gibberish, but it appears to work for the simple object heirarchy I it tested with.
Problem is, that it is not easy to get a default value. XMLEncoder does it by requiring object to have a parameterless constructor, constructing another instance and retrieving value. I don't think it is acceptable for XStream.
Not writing zeros/nulls probably does make sense - and it seems to be done currently.
Artur Biesiadowski
added a comment - Problem is, that it is not easy to get a default value. XMLEncoder does it by requiring object to have a parameterless constructor, constructing another instance and retrieving value. I don't think it is acceptable for XStream.
Not writing zeros/nulls probably does make sense - and it seems to be done currently. It seems like annotations could provide a solution, at least for primitives, Strings, and collections. Something like this, perhaps?
class Person {
@XStreamDefaultValue("5")
private int age;
@XStreamDefaultValue("Fred")
private String name;
@XStreamDefaultValue("false")
private boolean likesBunnies;
@XStreamDefaultCollection(XStreamDefaultCollectionType.EMPTY_LIST)
private List<Person> friends;
}
The use case I'm thinking of is more applicable to dealing with hand-written XML, or XML that wasn't written by XStream.
Steven Swor
added a comment - - edited It seems like annotations could provide a solution, at least for primitives, Strings, and collections. Something like this, perhaps?
class Person {
@XStreamDefaultValue( "5" )
private int age;
@XStreamDefaultValue( "Fred" )
private String name;
@XStreamDefaultValue( " false " )
private boolean likesBunnies;
@XStreamDefaultCollection(XStreamDefaultCollectionType.EMPTY_LIST)
private List<Person> friends;
}
The use case I'm thinking of is more applicable to dealing with hand-written XML, or XML that wasn't written by XStream. 
I'd like this to be configurable, with the default being all properties serialized. I can see situations where both options would be desirable.
Also, if you serialize an object, change the object code (and default values), then de-serialize, you'll possibly have different behavior. Just something to be aware of. Again, I could see uses for this...