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I am working on the frontend of a project that gives me Java Expression Language tags to work with. In one instance I need to see if it is returning an array or just one bit of data and I don't know how to work with it.

Example:

The page has

<p>${WebAppContext.buildings[0].location.name}</p>

which will output something like:

<p>Acme</p>

Problem is I need to output more if there is more in that buildings bit:

Something like (in pseudocode):

if isArray(${WebAppContext.buildings}){
 foreach(${WebAppContext.buildings} as foo){
    //iterate over whatever is in the array
}
}

so I can output something like:

<p>${WebAppContext.buildings[0].location.name}</p>
<p>${WebAppContext.buildings[1].location.name}</p>

I asked the Java people responsible for generating this code and they said "Dunnokindofbusyrightnowbuhbye." so I'm hoping you folks will have some insight.

Beyond sticking the code in the page I don't have a clue how to work with this Java Expression Language (I even had to look it up to see what the heck it is called). So any advice/resources would be helpful.

---

EDIT:

I've tried the following and am not getting any results:

<c:forEach var='building' items='${WebAppContext.buildings}'>
  <p>${building.location.name}</p>
</c:forEach>

In the source of the page it just shows:

<c:forEach var='meeting' items='[Lorg.foo.bar.baz.bat.serviceapi.webserviceobject.xsd.BuildingsWSO;@3823ff8'>
  <p></p>
</c:forEach>

I'll admit that, not knowing anything about Java Expression Language, I don't understand why the items='' gets translated like it does though I can see that it follows a path in the setup we use. Now when I use:

<p>${WebAppContext.buildings[0].location.name}</p>
<p>${WebAppContext.buildings[1].location.name}</p>

I get:

<p>Krustylu Studios</p>
<p>Springfield Nuclear Power Plant</p>

I am working on the frontend of a project that gives me Java Expression Language tags to work with. In one instance I need to see if it is returning an array or just one bit of data and I don't know how to work with it.

Example:

The page has

<p>${WebAppContext.buildings[0].location.name}</p>

which will output something like:

<p>Acme</p>

Problem is I need to output more if there is more in that buildings bit:

Something like (in pseudocode):

if isArray(${WebAppContext.buildings}){
 foreach(${WebAppContext.buildings} as foo){
    //iterate over whatever is in the array
}
}

so I can output something like:

<p>${WebAppContext.buildings[0].location.name}</p>
<p>${WebAppContext.buildings[1].location.name}</p>

I asked the Java people responsible for generating this code and they said "Dunnokindofbusyrightnowbuhbye." so I'm hoping you folks will have some insight.

Beyond sticking the code in the page I don't have a clue how to work with this Java Expression Language (I even had to look it up to see what the heck it is called). So any advice/resources would be helpful.

---

EDIT:

I've tried the following and am not getting any results:

<c:forEach var='building' items='${WebAppContext.buildings}'>
  <p>${building.location.name}</p>
</c:forEach>

In the source of the page it just shows:

<c:forEach var='meeting' items='[Lorg.foo.bar.baz.bat.serviceapi.webserviceobject.xsd.BuildingsWSO;@3823ff8'>
  <p></p>
</c:forEach>

I'll admit that, not knowing anything about Java Expression Language, I don't understand why the items='' gets translated like it does though I can see that it follows a path in the setup we use. Now when I use:

<p>${WebAppContext.buildings[0].location.name}</p>
<p>${WebAppContext.buildings[1].location.name}</p>

I get:

<p>Krustylu Studios</p>
<p>Springfield Nuclear Power Plant</p>

• java
• javascript
• jsp
• el

Share Improve this question Follow edited Dec 1, 2010 at 13:58 BalusC 1.1m376376 gold badges3.7k3.7k silver badges3.6k3.6k bronze badges asked Nov 23, 2010 at 22:04 rg88rg88 21k1818 gold badges7979 silver badges110110 bronze badges 6

• download.oracle./javaee/5/tutorial/doc/bnake.html – McDowell Commented Nov 23, 2010 at 22:08
• Can you really not use taglibs like JSTL? You're working with JSP, right? – BalusC Commented Nov 23, 2010 at 22:47
• @BalusC: I just updated my question to show what I am getting when I try the forEach suggestion offered below. – rg88 Commented Nov 24, 2010 at 0:17
• Did you install JSTL and declare the core taglib in top of JSP? – BalusC Commented Nov 24, 2010 at 1:44
• No I didn't... I will, though. Thanks for the replies. I never deal with Java in any way, shape or form so this is all uncharted territory for me (I had never even heard of something called JSTL before today). – rg88 Commented Nov 24, 2010 at 7:32

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4 Answers 4

Sorted by: Reset to default 4

I don't think that kind of advanced functionality is supported by EL; you can try using the JSTL c:forEach tag to iterate over your list.

If you're seeing <c:forEach var='meeting' items='[Lorg.foo.bar.baz.bat.serviceapi.webserviceobject.xsd.BuildingsWSO;@3823ff8'> when you view page source from your browser, that implies that the <c:forEach> tag isn't being processed.

Make sure you've declared the tag library in the JSP page:

<%@ taglib prefix="c" uri="http://java.sun./jsp/jstl/core" %>

The prefix="c" is where you get the c: part of <c:forEach> ... if you were to say prefix="foo" the tag would then be <foo:forEach>

This should be possible:

<c:forEach var='building' items='${WebAppContext.buildings}'>
  <p>${building.location.name}</p>
</c:forEach>

Now, how will you check to see whether WebAppContext.buildings is actually an array? There's no direct easy way to do that with JSTL unless you have the power and ability to extend a local custom suite of EL functions to use from JSTL.

If you really need to know if an object is an array, you could create a custom JSP function.

public static boolean isArray(final Object o) {
    return o instanceof Object[];
}

Then just map it in a TLD such as:

<function>
    <description>
        Checks if the supplied object is an array.
    </description>
    <name>isArray</name>
    <function-class>.example.JspFunctions</function-class>
    <function-signature>boolean isArray(java.lang.Object)</function-signature>
    <example>
        ${f:isArray(someVar)}
    </example>
</function>

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