Re: [Tapestry-developer] Page or component with dynamic attributes

[Drew Davidson]

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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