001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.context.expression;
018
019import java.lang.reflect.Method;
020import java.util.Arrays;
021
022import org.springframework.core.ParameterNameDiscoverer;
023import org.springframework.expression.spel.support.StandardEvaluationContext;
024import org.springframework.lang.Nullable;
025import org.springframework.util.ObjectUtils;
026
027/**
028 * A method-based {@link org.springframework.expression.EvaluationContext} that
029 * provides explicit support for method-based invocations.
030 *
031 * <p>Expose the actual method arguments using the following aliases:
032 * <ol>
033 * <li>pX where X is the index of the argument (p0 for the first argument)</li>
034 * <li>aX where X is the index of the argument (a1 for the second argument)</li>
035 * <li>the name of the parameter as discovered by a configurable {@link ParameterNameDiscoverer}</li>
036 * </ol>
037 *
038 * @author Stephane Nicoll
039 * @author Juergen Hoeller
040 * @since 4.2
041 */
042public class MethodBasedEvaluationContext extends StandardEvaluationContext {
043
044        private final Method method;
045
046        private final Object[] arguments;
047
048        private final ParameterNameDiscoverer parameterNameDiscoverer;
049
050        private boolean argumentsLoaded = false;
051
052
053        public MethodBasedEvaluationContext(Object rootObject, Method method, Object[] arguments,
054                        ParameterNameDiscoverer parameterNameDiscoverer) {
055
056                super(rootObject);
057                this.method = method;
058                this.arguments = arguments;
059                this.parameterNameDiscoverer = parameterNameDiscoverer;
060        }
061
062
063        @Override
064        @Nullable
065        public Object lookupVariable(String name) {
066                Object variable = super.lookupVariable(name);
067                if (variable != null) {
068                        return variable;
069                }
070                if (!this.argumentsLoaded) {
071                        lazyLoadArguments();
072                        this.argumentsLoaded = true;
073                        variable = super.lookupVariable(name);
074                }
075                return variable;
076        }
077
078        /**
079         * Load the param information only when needed.
080         */
081        protected void lazyLoadArguments() {
082                // Shortcut if no args need to be loaded
083                if (ObjectUtils.isEmpty(this.arguments)) {
084                        return;
085                }
086
087                // Expose indexed variables as well as parameter names (if discoverable)
088                String[] paramNames = this.parameterNameDiscoverer.getParameterNames(this.method);
089                int paramCount = (paramNames != null ? paramNames.length : this.method.getParameterCount());
090                int argsCount = this.arguments.length;
091
092                for (int i = 0; i < paramCount; i++) {
093                        Object value = null;
094                        if (argsCount > paramCount && i == paramCount - 1) {
095                                // Expose remaining arguments as vararg array for last parameter
096                                value = Arrays.copyOfRange(this.arguments, i, argsCount);
097                        }
098                        else if (argsCount > i) {
099                                // Actual argument found - otherwise left as null
100                                value = this.arguments[i];
101                        }
102                        setVariable("a" + i, value);
103                        setVariable("p" + i, value);
104                        if (paramNames != null && paramNames[i] != null) {
105                                setVariable(paramNames[i], value);
106                        }
107                }
108        }
109
110}