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LambdaExpression.java
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/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright (c) 2012 Oracle and/or its affiliates. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common Development
* and Distribution License("CDDL") (collectively, the "License"). You
* may not use this file except in compliance with the License. You can
* obtain a copy of the License at
* https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
* or packager/legal/LICENSE.txt. See the License for the specific
* language governing permissions and limitations under the License.
*
* When distributing the software, include this License Header Notice in each
* file and include the License file at packager/legal/LICENSE.txt.
*
* GPL Classpath Exception:
* Oracle designates this particular file as subject to the "Classpath"
* exception as provided by Oracle in the GPL Version 2 section of the License
* file that accompanied this code.
*
* Modifications:
* If applicable, add the following below the License Header, with the fields
* enclosed by brackets [] replaced by your own identifying information:
* "Portions Copyright [year] [name of copyright owner]"
*
* Contributor(s):
* If you wish your version of this file to be governed by only the CDDL or
* only the GPL Version 2, indicate your decision by adding "[Contributor]
* elects to include this software in this distribution under the [CDDL or GPL
* Version 2] license." If you don't indicate a single choice of license, a
* recipient has the option to distribute your version of this file under
* either the CDDL, the GPL Version 2 or to extend the choice of license to
* its licensees as provided above. However, if you add GPL Version 2 code
* and therefore, elected the GPL Version 2 license, then the option applies
* only if the new code is made subject to such option by the copyright
* holder.
*/
package javax.el;
import java.util.List;
import java.util.Map;
import java.util.HashMap;
import java.util.ArrayList;
/**
* <p>Encapsulates a parameterized {@link ValueExpression}.</p>
*
* <p>A <code>LambdaExpression</code> is a representation of the EL Lambda
* expression syntax. It consists of a list of the formal parameters and a
* body, represented by a {@link ValueExpression}.
* The body can be any valid <code>Expression</code>, including another
* <code>LambdaExpression</code>.</p>
* A <code>LambdaExpression</code> is created when an EL expression containing
* a Lambda expression is evaluated.</p>
* <p>A <code>LambdaExpression</code> can be invoked by calling
* {@link LambdaExpression#invoke}, with
* an {@link javax.el.ELContext} and a list of the actual arguments.
* Alternately, a <code>LambdaExpression</code> can be invoked without passing
* a <code>ELContext</code>, in which case the <code>ELContext</code> previously
* set by calling {@link LambdaExpression#setELContext} will be used.
* The evaluation of the <code>ValueExpression</code> in the body uses the
* {@link ELContext} to resolve references to the parameters, and to evaluate
* the lambda expression.
* The result of the evaluation is returned.</p>
* @see ELContext#getLambdaArgument
* @see ELContext#enterLambdaScope
* @see ELContext#exitLambdaScope
*/
public class LambdaExpression {
private List<String> formalParameters = new ArrayList<String>();
private ValueExpression expression;
private ELContext context;
// Arguments from nesting lambdas, when the body is another lambda
private Map<String, Object> envirArgs = null;
/**
* Creates a new LambdaExpression.
* @param formalParameters The list of String representing the formal
* parameters.
* @param expression The <code>ValueExpression</code> representing the
* body.
*/
public LambdaExpression (List<String> formalParameters,
ValueExpression expression) {
this.formalParameters = formalParameters;
this.expression = expression;
this.envirArgs = new HashMap<String, Object>();
}
/**
* Set the ELContext to use in evaluating the LambdaExpression.
* The ELContext must to be set prior to the invocation of the LambdaExpression,
* unless it is supplied with {@link LambdaExpression#invoke}.
* @param context The ELContext to use in evaluating the LambdaExpression.
*/
public void setELContext(ELContext context) {
this.context = context;
}
/**
* Invoke the encapsulated Lambda expression.
* <p> The supplied arguments are matched, in
* the same order, to the formal parameters. If there are more arguments
* than the formal parameters, the extra arguments are ignored. If there
* are less arguments than the formal parameters, an
* <code>ELException</code> is thrown.</p>
*
* <p>The actual Lambda arguments are added to the ELContext and are
* available during the evaluation of the Lambda expression. They are
* removed after the evaluation.</p>
*
* @param elContext The ELContext used for the evaluation of the expression
* The ELContext set by {@link #setELContext} is ignored.
* @param args The arguments to invoke the Lambda expression. For calls with
* no arguments, an empty array must be provided. A Lambda argument
* can be <code>null</code>.
* @return The result of invoking the Lambda expression
* @throws ELException if not enough arguments are provided
* @throws NullPointerException is elContext is null
*/
public Object invoke(ELContext elContext, Object... args)
throws ELException {
int i = 0;
Map<String, Object> lambdaArgs = new HashMap<String, Object>();
// First get arguments injected from the outter lambda, if any
lambdaArgs.putAll(envirArgs);
for (String fParam: formalParameters) {
if (i >= args.length) {
throw new ELException("Expected Argument " + fParam +
" missing in Lambda Expression");
}
lambdaArgs.put(fParam, args[i++]);
}
elContext.enterLambdaScope(lambdaArgs);
Object ret = expression.getValue(elContext);
// If the result of evaluating the body is another LambdaExpression,
// whose body has not been evaluated yet. (A LambdaExpression is
// evaluated iff when its invoke method is called.) The current lambda
// arguments may be needed in that body when it is evaluated later,
// after the current lambda exits. To make these arguments available
// then, they are injected into it.
if (ret instanceof LambdaExpression) {
((LambdaExpression) ret).envirArgs.putAll(lambdaArgs);
}
elContext.exitLambdaScope();
return ret;
}
/**
* Invoke the encapsulated Lambda expression.
* <p> The supplied arguments are matched, in
* the same order, to the formal parameters. If there are more arguments
* than the formal parameters, the extra arguments are ignored. If there
* are less arguments than the formal parameters, an
* <code>ELException</code> is thrown.</p>
*
* <p>The actual Lambda arguments are added to the ELContext and are
* available during the evaluation of the Lambda expression. They are
* removed after the evaluation.</p>
*
* The ELContext set by {@link LambdaExpression#setELContext} is used in
* the evaluation of the lambda Expression.
*
* @param args The arguments to invoke the Lambda expression. For calls with
* no arguments, an empty array must be provided. A Lambda argument
* can be <code>null</code>.
* @return The result of invoking the Lambda expression
* @throws ELException if not enough arguments are provided
*/
public Object invoke(Object... args) {
return invoke(this.context, args);
}
}