9.4. Collecting Items in Containers

If a bean ID resolver is set using setBeanIdResolver() or setBeanIdProperty(), the methods addBean(), addBeanAfter(), addBeanAt() and addAll() can be used to add items to the container. If one of these methods is called, the resolver is used to generate an identifier for the item (must not return null).

Note that explicit item identifiers can also be used when a resolver has been set by calling the addItem*() methods - the resolver is only used when adding beans using the addBean*() or addAll(Collection) methods.

Filters can be classified as atomic and composite. Atomic filters, such as SimpleStringFilter, define a single condition, usually for a specific container property. Composite filters make filtering decisions based on the result of one or more other filters. The built-in composite filters implement the logical operators AND, OR, or NOT.

For example, the following composite filter would filter out items where the name property contains the name "Douglas" somewhere and where the age property has value less than 42. The properties must have String and Integer types, respectively.

filter = new Or(new SimpleStringFilter("name",
        "Douglas", true, false),
        new Compare.Less("age", 42));

The built-in filter types are the following:

A custom filter needs to implement the Container.Filter interface.

A filter can use a single or multiple properties for the filtering logic. The properties used by the filter must be returned with the appliesToProperty() method. If the filter applies to a user-defined property or properties, it is customary to give the properties as the first argument for the constructor of the filter.

class MyCustomFilter implements Container.Filter {
    protected String propertyId;
    protected String regex;
    
    public MyCustomFilter(String propertyId, String regex) {
        this.propertyId = propertyId;
        this.regex      = regex;
    }

    /** Tells if this filter works on the given property. */
    @Override
    public boolean appliesToProperty(Object propertyId) {
        return propertyId != null &&
               propertyId.equals(this.propertyId);
    }

The actual filtering logic is done in the passesFilter() method, which simply returns true if the item should pass the filter and false if it should be filtered out.

    /** Apply the filter on an item to check if it passes. */
    @Override
    public boolean passesFilter(Object itemId, Item item)
            throws UnsupportedOperationException {
        // Acquire the relevant property from the item object
        Property p = item.getItemProperty(propertyId);
        
        // Should always check validity
        if (p == null || !p.getType().equals(String.class))
            return false;
        String value = (String) p.getValue();
        
        // The actual filter logic
        return value.matches(regex);
    }
}

You can use such a custom filter just like any other:

c.addContainerFilter(
    new MyCustomFilter("Name", (String) tf.getValue()));