How can I invoke static methods in JSP/EL?

Calling Static Methods in JSP/EL

In JSP, you often need to perform calculations or access static methods from Java classes. However, invoking static methods directly in Expression Language (EL) is not supported.

Scenario:

You have a table with a "balance" attribute and want to calculate a new value called "amount" using a static method in the "Calculate" class. Scriptlets embedded within JSTL tags, as you have tried, are not recommended.

EL Restriction:

EL can only invoke instance methods on classes that you have created as JavaBeans. Static methods, which are not part of an instance, cannot be directly accessed through EL.

Solutions:

1. Create an Instance Method:

   • Create a method within the bean that wraps the static method, passing in the necessary parameters.
   • Use the instance method in EL instead of the static method.

2. Register a Custom EL Function:

   • Create a tag library descriptor (TLD) file that declares a custom EL function.
   • Configure the TLD file in your JSP page using the <%@taglib...%> directive.
   • Use the custom EL function, which internally invokes the static method, within your EL expression.

Example with Instance Method:

public class Bean {

    private double balance;

    public double getAmount() {
        return Calculate.getAmount(balance);
    }

    // ...other methods
}

<c:forEach var="row" items="${rs.rows}">
    Amount: ${row.amount}  <!-- Invoke instance method -->
</c:forEach>

Example with Custom EL Function:

<!-- functions.tld -->
<taglib>
    ...
    <function>
        <name>calculateAmount</name>
        <function-class>com.example.Calculate</function-class>
        <function-signature>double getAmount(double)</function-signature>
    </function>
    ...
</taglib>

<%@taglib uri="http://example.com/functions" prefix="f"%>
...
Amount: ${f:calculateAmount(row.balance)}  <!-- Invoke custom EL function -->

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