javax.el

Class ELProcessor

java.lang.Object

javax.el.ELProcessor

public class ELProcessor
extends Object

Provides an API for using EL in a stand-alone environment.

This class provides a direct and simple interface for

• Evaluating EL expressions.
• Assigning values to beans or setting a bean property.
• Setting a ValueExpression to a EL variable.
• Defining a static method as an EL function.
• Defining an object instance as an EL name.

This API is not a replacement for the APIs in EL 2.2. Containers that maintains EL environments can continue to do so, without using this API.

For EL users who want to manipulate EL environments, like adding custom ELResolvers, ELManager can be used.

Scope and Life Cycle

Since it maintains the state of the EL environments, ELProcessor is not thread safe. In the simplest case, an instance can be created and destroyed before and after evaluating EL expressions. A more general usage is to use an instance of ELProcessor for a session, so that the user can configure the EL evaluation environment for that session.

Automatic Bracketing of Expressions

A note about the EL expressions strings used in the class. The strings allowed in the methods getValue(java.lang.String, java.lang.Class<?>), setValue(java.lang.String, java.lang.Object), and setVariable(java.lang.String, java.lang.String) are limited to non-composite expressions, i.e. expressions of the form ${...} or #{...} only. Also, it is not necessary (in fact not allowed) to bracket the expression strings with ${ or #{ and } in these methods: they will be automatically bracketed. This reduces the visual cluster, without any lost of functionalities (thanks to the addition of the concatenation operator).

Example

The following code snippet illustrates the use of ELProcessor to define a bean and evaluate its property.

   ELProcessor elp = new ELProcessor();
   elp.defineBean("employee", new Employee("Charlie Brown"));
   String name = elp.eval("employee.name");
 

Since:

EL 3.0

Constructor Summary

Constructors

Constructor and Description
ELProcessor()

Method Summary

Methods

Modifier and Type	Method and Description
void	defineBean(String name, Object bean) Define a bean in a local bean repository, hiding other beans of the same name.
void	defineFunction(String prefix, String function, Method method) Define an EL function in the local function mapper.
void	defineFunction(String prefix, String function, String className, String method) Define an EL function in the local function mapper.
Object	eval(String expression) Evaluates an EL expression.
ELManager	getELManager() Return the ELManager used for EL porcessing.
Object	getValue(String expression, Class<?> expectedType) Evaluates an EL expression, and coerces the result to the specified type.
void	setValue(String expression, Object value) Sets an expression with a new value.
void	setVariable(String var, String expression) Assign an EL expression to an EL variable.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ELProcessor

public ELProcessor()

Method Detail

getELManager

public ELManager getELManager()

Return the ELManager used for EL porcessing.

Returns:

The ELManager used for EL porcessing.

eval

public Object eval(String expression)

Evaluates an EL expression.

Parameters:

expression - The EL expression to be evaluated.

Returns:

The result of the expression evaluation.

getValue

public Object getValue(String expression,
              Class<?> expectedType)

Evaluates an EL expression, and coerces the result to the specified type.

Parameters:

expression - The EL expression to be evaluated.

expectedType - Specifies the type that the resultant evaluation will be coerced to.

Returns:

The result of the expression evaluation.

setValue

public void setValue(String expression,
            Object value)

Sets an expression with a new value. The target expression is evaluated, up to the last property resolution, and the resultant (base, property) pair is set to the provided value.

Parameters:

expression - The target expression

value - The new value to set.

Throws:

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

PropertyNotWritableException - if the final variable or property resolution failed because the specified variable or property is not writable.

ELException - if an exception was thrown while attempting to set the property or variable. The thrown exception must be included as the cause property of this exception, if available.

setVariable

public void setVariable(String var,
               String expression)

Assign an EL expression to an EL variable. The expression is parsed, but not evaluated, and the parsed expression is mapped to the EL variable in the local variable map. Any previously assigned expression to the same variable will be replaced. If the expression is null, the variable will be removed.

Parameters:

var - The name of the variable.

expression - The EL expression to be assigned to the variable.

defineFunction

public void defineFunction(String prefix,
                  String function,
                  String className,
                  String method)
                    throws ClassNotFoundException,
                           NoSuchMethodException

Define an EL function in the local function mapper.

Parameters:

prefix - The namespace for the function or "" for no namesapce.

function - The name of the function. If empty (""), the method name is used as the function name.

className - The full Java class name that implements the function.

method - The name (specified without parenthesis) or the signature (as in the Java Language Spec) of the static method that implements the function. If the name (e.g. "sum") is given, the first declared method in class that matches the name is selected. If the signature (e.g. "int sum(int, int)" ) is given, then the declared method with the signature is selected.

Throws:

NullPointerException - if any of the arguments is null.

ClassNotFoundException - if the specified class does not exists.

NoSuchMethodException - if the method (with or without the signature) is not a declared method of the class, or if the method signature is not valid.

defineFunction

public void defineFunction(String prefix,
                  String function,
                  Method method)

Define an EL function in the local function mapper.

Parameters:

prefix - The namespace for the function or "" for no namesapce.

function - The name of the function. If empty (""), the method name is used as the function name.

method - The java.lang.reflect.Method instance of the method that implements the function.

Throws:

NullPointerException - if any of the arguements is null.

defineBean

public void defineBean(String name,
              Object bean)

Define a bean in a local bean repository, hiding other beans of the same name.

Parameters:

name - The name of the bean

bean - The bean instance to be defined. If null, the name will be removed from the local bean repository.