Collection/Array contains method

Question

i was wondering if there's contains method for collections/array in EL 2.2 or i will have to make a custom one ?

REQUIREMENT: i have a string array, and i want to find if it contains a specific string.

CASE: i am looping on list of input checkboxes to render them, and i want to check the current checkbox, if it's value exists in the array of checkboxes.

UPDATE:

• is such method is available in EL?

• If such method is not available, then please provide your suggestion for best performance method for a string array contains an element.

Mitchellmitchem

Answer 1

For a Collection it's easy, just use the Colleciton#contains() method in EL.

<h:panelGroup id="p1" rendered="#{bean.panels.contains('p1')}">...</h:panelGroup>
<h:panelGroup id="p2" rendered="#{bean.panels.contains('p2')}">...</h:panelGroup>
<h:panelGroup id="p3" rendered="#{bean.panels.contains('p3')}">...</h:panelGroup>

For an Object[] (array), you'd need a minimum of EL 3.0 and utilize its new Lambda support.

<h:panelGroup id="p1" rendered="#{bean.panels.stream().anyMatch(v -> v == 'p1').get()}">...</h:panelGroup>
<h:panelGroup id="p2" rendered="#{bean.panels.stream().anyMatch(v -> v == 'p2').get()}">...</h:panelGroup>
<h:panelGroup id="p3" rendered="#{bean.panels.stream().anyMatch(v -> v == 'p3').get()}">...</h:panelGroup>

If you're not on EL 3.0 yet, you'd need to create a custom EL function. For a concrete example, see How to create a custom EL function to invoke a static method? E.g.

public static boolean contains(Object[] array, Object item) {
    return Arrays.asList(array).contains(item);
}

which is registered as

<function>
    <function-name>contains</function-name>
    <function-class>com.example.Functions</function-class>
    <function-signature>boolean contains(java.lang.Object[], java.lang.Object)</function-signature>
</function>

and to be used as

<h:panelGroup ... rendered="#{func:contains(bean.panels, 'u1')}">

This is not available in JSTL. There's a fn:contains(), but that works on String values only.

Ferdinand

Just don't use arrays if you want to do a bit more than just holding the data. Use collections then. – Ferdinand

well, i am using it on an input attribute, but the method is not getting called: checked="#{utils.contains(myBean.array,'myBean.someIndicator') ? 'checked' : ''}" – Mitchellmitchem

Are there any EL errors? By the way, the way how you use checked is not entirely right. A checkbox/radiobutton is checked when the whole attribute is present, regardless of its value. You basically want to print the attribute name instead of the attribute value conditionally. – Ferdinand

aha, got you, and no i can't see EL errors, shouldn't an exception thrown if there's an EL error ? – Mitchellmitchem

Oh, I see, you're using . instead of :. Since #{utils} doesn't exist as managed bean, nothing will happen. To call functions, you need #{prefix:functionName()} with : instead. – Ferdinand

the above method doesn't work so fine, when the value of the input is an int. – Mitchellmitchem

meaning if the value is 1 instead of u1 in this case equality will fail. – Mitchellmitchem

i have to convert item to string before comparing to work fine, but i am afraid that this may cause a problem with large numbers. – Mitchellmitchem

Just use Integer instead or modify the method to loop over the array instead of converting int[] to List<int> (which is invalid). – Ferdinand

Answer 2

If you are using a String[], you can first concatenate all the elements of an array into a string using fn:join():

<c:set var="concat" value="${fn:join(myArray, '-')}"/>

And then use the fn:contains()` function in order to check if a value exists in that string:

<c:if test="${fn:contains(concat, 'myString')}">Found!</c:if>

Mcginty

This simple solution helped me as I wanted to check a ${ param.stringArray } of checkbox values. – Reductive