Hi,
I'm new to the collections mailing list and I have a class I think would
be appropriate to be donated to the collections API.
This is an extension of the MultiHashMap and filters a given Collection
by a given field. It will put the objects into the map using the field
value as the key.
For example, lets say I have a class X which has an integer i. I have
four instances of X each with the following names and values of i.
x1 i=1
x2 i=2
x3 i=2
x4 i=5
The resulting MultiHashMap will contain the following after a call to
sortCollection(X.class, "i"); has been made.
key | Objects
1 | x1
2 | x2, x3
5 | x4
I can then get a Collection of sorted objects by asking the map for the
key value. I find this very useful in many situations I have come
across. I will of course make the required doc, package and src
formatting changes to the class before submitting it.
Please can you take a look and tell me if it is worth committing this to
the Collections repository. What is the process I need to go through
before committing? I'm a bit pressed for time at the mo' so I can't
really spend too much time working on the Collections API as a regular
developer. I am a big fan of the commons Collections API and commons
project in general, just wish I had more time to get involved.
Kind regards,
John Hunsley.
Technical Supervisor, Cy-nap Ltd.
package util;
import org.apache.commons.collections.MultiHashMap;
import org.apache.log4j.Logger;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
/**
* A given <class>Collection</class> contains objects with a know <class>Field</class>.
* The value of the <class>Field</class> is unknowm and the collection must be filtered
* by that unknown value. The given Collection is filtered and the objects within that Collection
* sorted into collections of matching Field value. These collections are put into a table, where
* the Field value becomes the key to that Collection. There is no gaurentee to the order in which
* the collections are put into the Hashtable.
*
* @author John Hunsley
* Date: 18-May-2006
* Time: 19:53:13
*/
public class CollectionFilter extends MultiHashMap {
private Collection sortable;
private Logger logger = Logger.getLogger(CollectionFilter.class);
/**
* Sort the sortable <interface>Collection</interface> by the given declared <class>Field</class>
* as a <class>String</class>. First find if the field exists in the given class, if not a
* IllegalAccessException is thrown.
* @param clazz
* @param field
* @throws IllegalAccessException
*/
public void sortCollection(Class clazz, String field) throws IllegalAccessException, NoSuchFieldException {
Field declaredField = clazz.getDeclaredField(field);
sortCollection(clazz, declaredField);
}
/**
* Sort the sortable <interface>Collection</interface> by the given declared <class>Field</class>
* @param clazz
* @param field
* @throws IllegalAccessException
*/
public void sortCollection(Class clazz, Field field) throws IllegalAccessException {
if(sortable != null) {
synchronized(sortable) {
Iterator itr = sortable.iterator();
while(itr.hasNext()) {
Object obj = itr.next();
//if the object doesnt have the field skip it
if(!clazz.isInstance(obj)) continue;
try {
if(obj.getClass().getDeclaredField(field.getName()) != null) {
if(!field.isAccessible()) field.setAccessible(true);
super.put(field.get(obj), obj);
}
} catch (NoSuchFieldException e) {
if(logger.isDebugEnabled())
logger.debug("Collection contains an object which doesn't have the given Field");
}
}
}
} else throw new IllegalAccessException("Collection to sort must not be null");
}
/**
*
* @param sortable
*/
public CollectionFilter(final Collection sortable) {
this.sortable = Collections.synchronizedList(new ArrayList());
this.sortable.addAll(sortable);
}
/**
*
* @return collection
*/
public Collection getSortable() {
return sortable;
}
/**
*
* @param sortable
*/
public void setSortable(Collection sortable) {
this.sortable = sortable;
}
/**
*
* @param object
* @return super.getCollection();
*/
public Collection getCollection(Object object) {
return super.getCollection(object);
}
}
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