Apache commons jexl 1.1 src

• Introduction
• Brief Example

Introduction

Java Expression Language (JEXL) is an expression language engine which can be embedded in applications and frameworks. JEXL is inspired by Jakarta Velocity and the Expression Language defined in the JavaServer Pages Standard Tag Library version 1.1 (JSTL) and JavaServer Pages version 2.0 (JSP).

JEXL attempts to bring some of the lessons learned by the Velocity community about expression languages in templating to a wider audience. Commons Jelly needed Velocity-ish method access, it just had to have it.

It must be noted that JEXL is not a compatibile implementation of EL as defined in JSTL 1.1 (JSR-052) or JSP 2.0 (JSR-152). For a compatible implementation of these specifications, see the Commons EL project.

A Brief Example

When evaluating expressions, JEXL merges an Expression with a JexlContext. An Expression is created using ExpressionFactory.createExpression(), passing a String containing valid JEXL syntax. A JexlContext is created using JexlHelper.createContext(), and variables are put into a map exposed through the getVars() method on JexlContext. The following example, takes a variable named foo, and invokes the bar() method on the property innerFoo:

    // Create an expression object
    String jexlExp = "foo.innerFoo.bar()";
    Expression e = ExpressionFactory.createExpression( jexlExp );

    // Create a context and add data
    JexlContext jc = JexlHelper.createContext();
    jc.getVars().put("foo", new Foo() );

    // Now evaluate the expression, getting the result
    Object o = e.evaluate(jc);

• Introduction

Introduction

This package only contains one JexlContext implementation, the HashMapContext. A HashMapContext is simply an extension of HashMap which implements the JexlContext interface.

• Introduction

Introduction

This package only contains one class, Asserter, which allows you to use a JEXL expression in a JUnit assertion. The following example demonstrates the use of the Asserter class. An instance is created, and the internal JexlContext is populated via calls to setVariable(). Calls to assertExpression() succeed if the expression evaluates to the value of the second parameter, otherwise an AssertionFailedException is thrown.

   Asserter asserter = new Asserter();
   asserter.setVariable("foo", new Foo());
   asserter.setVariable("person", "James");

   asserter.assertExpression("person", "James");
   asserter.assertExpression("size(person)", new Integer(5));
        
   asserter.assertExpression("foo.getCount()", new Integer(5));
   asserter.assertExpression("foo.count", new Integer(5));
  

• Introduction

Introduction

This package contains the Parser for JEXL script.