You are trying to print out a message that contains data returned by a method.

Commons JEXL can evaluate any method that is made available to the interpreter. The following expression invokes the language() method on an Opera bean. The acts property of Opera is a List, and this expression invokes the size( ) method on this List to obtain the number of acts in the Opera:

${opera.name} was composed by ${opera.composer} in ${opera.year}.
This opera has ${opera.acts.size( )}, and it is performed in ${opera.
language( )}

The following code creates and populates an expression and a context, merging the two to create a message:

import org.apache.commons.jexl.Expression;
import org.apache.commons.jexl.ExpressionFactory;
import org.apache.commons.jexl.JexlContext;
import org.apache.commons.jexl.JexlHelper;

Opera opera = new Opera( );
opera.setName("The Magic Flute");
opera.setComposer("Mozart");
opera.setYear(1791);
opera.acts( new ArrayList(2) );

String expr = 
    "${opera.name} was composed by ${opera.composer} in ${opera.year}.";
    "This opera has ${opera.acts.size( )} acts, and it is performed in " +
    "${opera.language( )}";

Expression e = ExpressionFactory.createExpression( expr );
               JexlContext jc = JexlHelper.createContext( );
               jc.getVars( ).put("opera", opera);
               String message = (String) e.evaluate(jc);

System.out.println( message );

The following message is printed to the console:

The Magic Flute was composed by Mozart in 1791.  This opera has
2 acts, and it is performed in German.

This code is almost the same as the previous recipe, but you will notice that the expression contains a direct call to the opera.language( ) method and a call to the size( ) method on the acts property of opera.

Because JEXL is not governed by the Java Community Process (JCP), JEXL is free to extend the feature set of EL. Table 9-2 presents valid JEXL expressions that are actually invalid JSP 2.0 EL expressions.

For more information about Commons JEXL’s improvements on JSP 2.0 EL, see the Commons JEXL page (http://jakarta.apache.org/commons/jexl/).