How do you query object collections in Java (Criteria/SQL-like)?

Question

Suppose you have a collection of a few hundred in-memory objects and you need to query this List to return objects matching some SQL or Criteria like query. For example, you

Answer 1

yes, I know it's an old post, but technologies appear everyday and the answer will change in the time.

I think this is a good problem to solve it with LambdaJ. You can find it here: http://code.google.com/p/lambdaj/

Here you have an example:

LOOK FOR ACTIVE CUSTOMERS // (Iterable version)

List activeCustomers = new ArrayList();  
for (Customer customer : customers) {  
  if (customer.isActive()) {  
    activeCusomers.add(customer);  
  }  
}  

LambdaJ version

List activeCustomers = select(customers, 
                                        having(on(Customer.class).isActive()));  

Of course, having this kind of beauty impacts in the performance (a little... an average of 2 times), but can you find a more readable code?

It has many many features, another example could be sorting:

Sort Iterative

List sortedByAgePersons = new ArrayList(persons);
Collections.sort(sortedByAgePersons, new Comparator() {
        public int compare(Person p1, Person p2) {
           return Integer.valueOf(p1.getAge()).compareTo(p2.getAge());
        }
}); 

Sort with lambda

List sortedByAgePersons = sort(persons, on(Person.class).getAge()); 

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Update: after java 8 you can use out of the box lambda expressions, like:

List activeCustomers = customers.stream()
                                          .filter(Customer::isActive)
                                          .collect(Collectors.toList());