How to Invoke Static Methods in JSP/EL?

Calling Static Methods in JSP/EL

In JSP, static methods cannot be invoked directly in EL expressions. EL is designed to invoke only instance methods.

Consider the following scenario: a JSP page retrieves a "balance" value from a database and needs to calculate an "amount" value based on it. Using scriptlets to insert Java code into JSTL tags is not recommended, as scriptlets should be avoided in favor of EL.

Solution Options

There are two main solutions to this issue:

1. Wrapping the Static Method in an Instance Method

Create a getter method in your Java bean that wraps the static method and returns the calculated value. For example:

public class MyBean {
    private double balance;
    
    public double getAmount() {
        return Calculate.getAmount(balance);
    }
    
    // Other getters and setters...
}

Then, in your JSP page, use the instance method:

<foreach var="row" items="${rs.rows}">
    Amount: ${row.amount}
</foreach>

2. Declaring the Static Method as an EL Function

Create a functions.tld file to define the static method as an EL function. For example:

<taglib>
  <uri>http://example.com/functions</uri>
  <function>
    <name>calculateAmount</name>
    <function-class>com.example.Calculate</function-class>
    <function-signature>double getAmount(double)</function-signature>
  </function>
</taglib>

In your JSP page, use the EL function:

...
Amount: ${f:calculateAmount(row.balance)}

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