the XMLEncoder (java.beans)

[Mihai Radulescu]

I try to serilaize an Object with the XMLEncoder but all that I got is an
Exception because I don't have a default constuctor
:java.lang.InstantiationException
and if I create one I get :
<?xml version="1.0" encoding="UTF-8"?>
<java version="1.4.2_05" class="java.beans.XMLDecoder">
<object class="MyClass"/>
</java>

No others properties!
What I do wrong.

[Lasse Koskela]

It would help if you would post your Java class for us to see as well.

[Mihai Radulescu]

and here comes the class :

..................

import java.util.*;
 
 
public class Node extends Leaf {
 
    private final List children = new ArrayList();
 
    public Node (String name) {
        setProperty(NAME, name);
    }
 
    public boolean add(Component component) {
        if(component.getProperty(NAME) == null) {
            return false;
        }
        children.add(component);
        return true;
    }
 
    public List getChilderen() {
        return Collections.unmodifiableList(children);
    }
 
    public Component getComponent(String path) {
        checkPath(path);
        return  getChildFromPath(path);
    }
 
    public boolean removeComponent(Component component) {
        return children.remove(component);
    }
 
    public boolean removeComponent(String path) {
        checkPath(path);
        return removeChild(path);
    }
 
    public boolean moveUpComponent(String path) {
        return false;
    }
 
    public boolean moveDownComponent(String path) {
        return false;
    }
 
    private Component getChildFromPath(String path) {
 
        Component component = this;
        for(StringTokenizer stk = new StringTokenizer(path, "."); stk.hasMoreTokens()  :wink:   {
 
            String name = stk.nextToken();
            component = getChild(name, component.getChilderen());
 
            if(component == null && stk.hasMoreTokens()) {
                final String msg =
                        "The node : " + name
                        + " is wrong, the (node)path must be continuous.Your node : "
                        + name + " has no childern and its path : " + path
                        +" expect some.";
                throw new IllegalPathException(msg);
            }
        }
 
        return component;
    }
 
    private Component getChild(String name, List childrenList) {
        for(ListIterator li = childrenList.listIterator(); li.hasNext()  :wink:   {
            Component tmpComp = (Component) li.next();
            if(tmpComp.getProperty(NAME).equals(name)) {
                return tmpComp;
            }
        }
        return null;
    }
 
    private void checkPath(String path) throws IllegalPathException {
        if(path.indexOf(".") == -1) {
            final String msg =
                    "The path : " + path
                    + "is wrong, the path must be at least rwo level deep(by ex : aa.bb).Use insetad the one level operation!";
            throw new IllegalPathException(msg);
        }
    }
 
    //TODO : throws an exception if the path is wrong!
    private boolean removeChild(String path) {
        Component parent = this;
 
        for(StringTokenizer stk = new StringTokenizer(path, "."); stk.hasMoreTokens()  :wink:   {
 
            String name = stk.nextToken();
            Component component = getChild(name, parent.getChilderen());
 
            if(!stk.hasMoreTokens()) {
                return parent.removeComponent(component);
            }
 
            parent = component;
        }
 
        return false;
    }
 
    public String toString() {
        return "Composite propeties : " + propertiesToString()
                + " ,composite chlidern : " + children;
    }
 
    public boolean equals(Object anObject){
        if(!(anObject instanceof Node)) {
            return false;
        }
 
        final Node inNode = (Node) anObject;
        if(getProperty(NAME) == null) {
            return false;
        }
 
        String realString1 = getProperty(NAME).intern();
        String realString2 = inNode.getProperty(NAME).intern();
        return realString1.equals(realString2);
    }
 
    public int hashCode() {
        return getProperty(NAME) == null
                ? 123456789
                : getProperty(NAME).intern().hashCode();
    }
    
}

Edit Comment: Added [ code ] [ / code ] tags.
[ November 04, 2004: Message edited by: Madhav Lakkapragada ]

[Axel Janssen]

Though I don't know no much about XMLEncoder, I got the impression that you need a constructor without any parameters.
As we all know Java creates automatically default constructor, if there is no constructor in class.
But your class has:

public Node (String name) {
setProperty(NAME, name);
}

there is no without-parameters constructor.

Often things that work with introspection impose the restriction that the class has a constructor without parameters.

So you might put in a

public Node() {}

and set property name other way.

Axel
[ November 04, 2004: Message edited by: Axel Janssen ]

[Mihai Radulescu]

I tried with an default constructor but then my xml file was :
<?xml version="1.0" encoding="UTF-8"?>
<java version="1.4.2_05" class="java.beans.XMLDecoder">
<object class="com.oce.prismapro.xpdc.util.presistentcomposite.Node"/>
</java>