Re: Page or component with dynamic attributes

David Solis wrote:

> Is it possible to have a page or component with dynamic properties?
>
> In our applications, almost 50% (maybe more) of code is in getters and 
> setters. I'm wondering about the possibility to integrate Jakarta 
> DynaBeans to Tapestry in order to eliminate these getters and setters.
>
> Does it make sense?
>
> I'm not sure about features overlap between ognl and dynabeans,
>
Using OGNL you can register a custom PropertyAccessor to make your 
object's dynamic properties appear as if they are true properties with 
getters and setters:

Foo.java:
-------------------------
public class Foo
{
    private Map        variables = new HashMap()
    private int        count = 0;
  
    public int getCount()
    {
        return count;
    }

    public void setCount(int value)
    {
        count = value;
    }

    public Object getVariableValue(String key)
    {
        return variables.get(key);
    }

    public void setVariableValue(String key, Object value)
    {
        variables.put(key, value);
    }
}

FooPropertyAccessor.java:
-------------------------
import java.util.*;
import ognl.ObjectPropertyAccessor;
import ognl.OgnlException;
import ognl.OgnlRuntime;
import ognl.PropertyAccessor;

public class FooPropertyAccessor
{
    private ObjectPropertyAccessor            defaultAccessor;

    /*===================================================================
        Private methods
      ===================================================================*/
    {
        try {
            defaultAccessor = 
(ObjectPropertyAccessor)OgnlRuntime.getPropertyAccessor(Object.class);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    /*===================================================================
        PropertyAccessor interface
      ===================================================================*/
    public Object getProperty(Map context, Object target, Object name) 
throws OgnlException
    {
        Object                    result = null;

        if ((result = defaultAccessor.getPossibleProperty(context, 
target, name.toString())) == OgnlRuntime.NotFound) {
            try {
                result = ((Foo)target).getVariableValue(name.toString());
            } catch (OgnlException ex) {
                throw ex;
            } catch (Exception ex) {
                throw new OgnlException("getting property '" + name + 
"'", ex);
            }
        }
        return result;
    }

    public void setProperty(Map context, Object target, Object name, 
Object value) throws OgnlException
    {
        if (defaultAccessor.setPossibleProperty(context, target, 
name.toString(), value) == OgnlRuntime.NotFound) {
            try {
                ((Foo)target).setVariableValue(name.toString(), value);
            } catch (OgnlException ex) {
                throw ex;
            } catch (Exception ex) {
                throw new OgnlException("setting property '" + name + 
"'", ex);
            }
        }
    }
}

Now foo.xxx will get the variable value from getVariableValue("xxx") and 
foo.count will call the getCount() method (that's the defaultAccessor). 
 You could potentially make a page or component abstract superclass with 
this pattern and subclass all of your components from that (or register 
as many property accessors as necessary).

Presto! Dynamic properties.

- Drew

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< Drew Davidson | OGNL Technology >
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