Call methods in Expression Language

问题:

How can I invoke a method in JSP using EL (Expression Language)?

For example:

<c:forEach var="item" items="${listStr}" begin="0" end="2" step="2">
    <p>${item.indexOf("h")}</p>
</c:forEach>

Here, the item is an object of type java.lang.String. This causes errors when run on Tomcat.

回答1:

This is only supported since EL 2.2. This goes in turn hand in hand with Servlet 3.0. So if you make sure that you target a Servlet 3.0 compatible container (Tomcat 7, Glassfish 3, etc) with a Servlet 3.0 compatible web.xml declaration, then it'll just work the way you intend. If you're however targeting an older versioned servlet container, or have an older versioned or even the wrong web.xml root declaration, then it won't work.

See also:

• Our EL wiki page

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Update: Your particular problem is likely caused by a bug in Tomcat 7. It doesn't find the right overloaded method based on the given argument. Your expression works fine in Glassfish 3. All non-overloaded methods should work just fine in Tomcat.

回答2:

I can't get it to work either(Apache Tomcat/7.0.27).

javax.el.ELException: Cannot convert h of type class java.lang.String to int

El refuses to see the method with the correct signature. Same thing happens with indexOf("h",0). I did have success with

${x.contains("h")}
${x.lastIndexOf("h")}
${x.indexOf(104)}  Ascii value of 'h' is 104