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7.2. Callbacks

The descriptor shown in Example 7.3, “Callbacks to Collect and Filter Beans” allows you to collect all beans of a certain type, and even limit the number of matching beans.
In conjunction with the descriptor in Example 7.3, “Callbacks to Collect and Filter Beans”, the Java code shown in Example 7.4, “A Parser to Collect all Editors” shows a Parser which collects all Editors.

Example 7.3. Callbacks to Collect and Filter Beans

<bean name="checker" class="org.jboss.demos.ioc.callback.Checker">
  <constructor>
    <parameter>
      <value-factory bean="parser" method="parse">
	<parameter>
	  <array elementClass="java.lang.Object">
	    <value>http://www.jboss.org</value>
	    <value>SI</value>
	    <value>3.14</value>
	    <value>42</value>
	  </array>
	</parameter>
      </value-factory>
    </parameter>
  </constructor>
</bean>
<bean name="editorA" class="org.jboss.demos.ioc.callback.DoubleEditor"/>
<bean name="editorB" class="org.jboss.demos.ioc.callback.LocaleEditor"/>
<bean name="parser" class="org.jboss.demos.ioc.callback.Parser">
  <incallback method="addEditor" cardinality="4..n"/>
  <uncallback method="removeEditor"/>
</bean>
<bean name="editorC" class="org.jboss.demos.ioc.callback.LongEditor"/>
<bean name="editorD" class="org.jboss.demos.ioc.callback.URLEditor"/>
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Example 7.4. A Parser to Collect all Editors

public class Parser {
    private Set<Editor> editors = new HashSet<Editor>();
    ...
	public void addEditor(Editor editor)
    {
	editors.add(editor);
    }
    public void removeEditor(Editor editor)
    {
	editors.remove(editor);
    }
}
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Notice that incallback and uncallback use the method name for matching. 
<incallback method="addEditor" cardinality="4..n"/>
<uncallback method="removeEditor"/>
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A bottom limit controls how many editors actually cause the bean to progress from a Configured state: cardinality=4..n/>
Eventually, Checker gets created and checks the parser. This is illustrated in Example 7.5, “The Checker for the Parser”.

Example 7.5. The Checker for the Parser

public void create() throws Throwable {
    Set<String> strings = new TreeSet<String>(String.CASE_INSENSITIVE_ORDER);
    for (Object element : elements)
	strings.add(element.toString());
    if (expected.equals(strings) == false)
	throw new IllegalArgumentException("Illegal expected set: " + expected + "!=" + strings);
}
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