How to handle Collections

Question

Hi all. I am exporting some methods as Web Services and find out that jax-rpc does not have collections serializers yet. So, because I don't want to write my owns, I thought that I should be able to change "on the fly" (on demand), lets say, an ArrayList to an Array (that is supported in jax-rpc) in the following way:
private ArrayList allCriteria = new ArrayList(); // the collection I manage
private Criteria[] criteria; // the auxiliar structure I need to use jax-rpc
public void setCriteria(Criteria[] criteria) {
allCriteria = new ArrayList(Arrays.asList(criteria)); // copy the Array to the ArratList
this.criteria = criteria; // sets the Array
public Criteria[] getCriteria() {
criteria = new Criteria[allCriteria.size()]; // create an Array the same size the ArrayList
Iterator iterator = allCriteria.iterator();
for(int i = 0; iterator.hasNext(); i++) { // iterate over the ArrayList
criteria[i] = (Criteria) iterator.next(); // fill the Array
return criteria; // return the Array filled like the ArrayList
I suposed that this strategy leads me to a solution: criteria is a valid bean, and I do some special process inside the get/set methods to exchange info with the ArrayList. But the fact is that the Arrays are created with the right size, but empty elements at all !!!
I don't know what going wrong. If you have the answer, or any ideas on how to solve the problem around web services and collections please let me know.
Thanks in advance,
Leonardo

Answer 1

This is just a thought but the problem lies with using Arrays.asList(Object []). The list returned by this method actually references the inputted array i.e. the list does not get a copy of the values in the input array but references them. This feature was designed in order that if the underlying array is changed then these changes will be reflected in the list representation.
The problem is in your setCriteria in the first line. You are using asList with a local instance i.e. the parameter passed in to setCriteria. The value of the local instance or the parameter is the reference to the array not the actual array itself. As you are maintaining a reference, it is possible that the array it points to may be removed somewhere else in the program or changed and as a result you will not get the same values of the array when you use it in getCriteria as when setCriteria was called. .So you have a number of options:
1 You use System.arraycopy() to create a copy of criteria and you keep a reference in the class which has setCriteria. You will then use the copy array to convert it into an array list.
private Criteria [] criteria;
private ArrayList allCriteria = new ArrayList();
e.g. public void setCriteria(Criteria [] inputcriteria){
this.criteria = new Criteria[inputcriteria.length];
System.arraycopy(inputcriteria, 0, criteria, 0, inputCriteria.length);
//At this point critiera has all the values of inputcriteria
allCriteria = new ArrayList(criteria);
NB: I HAVE NOT complied this code but the general idea should work.
OR 2. In your getCriteria you are iterating through the values in allCriteria and returning the Criteria Array could you not do this in your setCriteria and then you will not have to do a System.arraycopy() but use the input Criteria array?
HTH.