001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *     http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.jxpath;
018    
019    import java.lang.reflect.Constructor;
020    import java.lang.reflect.Method;
021    import java.util.Collections;
022    import java.util.Set;
023    
024    import org.apache.commons.jxpath.functions.ConstructorFunction;
025    import org.apache.commons.jxpath.functions.MethodFunction;
026    import org.apache.commons.jxpath.util.MethodLookupUtils;
027    
028    /**
029     * Extension functions provided by a Java class.
030     *
031     * Let's say we declared a ClassFunction like this:
032     * <blockquote><pre>
033     *     new ClassFunctions(Integer.class, "int")
034     * </pre></blockquote>
035     *
036     * We can now use XPaths like:
037     * <dl>
038     *  <dt><code>"int:new(3)"</code></dt>
039     *  <dd>Equivalent to <code>new Integer(3)</code></dd>
040     *  <dt><code>"int:getInteger('foo')"</code></dt>
041     *  <dd>Equivalent to <code>Integer.getInteger("foo")</code></dd>
042     *  <dt><code>"int:floatValue(int:new(4))"</code></dt>
043     *  <dd>Equivalent to <code>new Integer(4).floatValue()</code></dd>
044     * </dl>
045     *
046     * <p>
047     * If the first argument of a method is {@link ExpressionContext}, the
048     * expression context in which the function is evaluated is passed to
049     * the method.
050     *
051     * @author Dmitri Plotnikov
052     * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
053     */
054    public class ClassFunctions implements Functions {
055        private static final Object[] EMPTY_ARRAY = new Object[0];
056    
057        private Class functionClass;
058        private String namespace;
059    
060        /**
061         * Create a new ClassFunctions.
062         * @param functionClass Class providing the functions
063         * @param namespace assigned ns
064         */
065        public ClassFunctions(Class functionClass, String namespace) {
066            this.functionClass = functionClass;
067            this.namespace = namespace;
068        }
069    
070        /**
071         * Returns a set of one namespace - the one specified in the constructor.
072         *
073         * @return a singleton
074         */
075        public Set getUsedNamespaces() {
076            return Collections.singleton(namespace);
077        }
078    
079        /**
080         * Returns a {@link Function}, if any, for the specified namespace,
081         * name and parameter types.
082         *
083         * @param namespace if it is not the namespace specified in the constructor,
084         *     the method returns null
085         * @param name is a function name or "new" for a constructor.
086         * @param parameters Object[] of parameters
087         *
088         * @return a MethodFunction, a ConstructorFunction or null if there is no
089         *      such function.
090         */
091        public Function getFunction(
092            String namespace,
093            String name,
094            Object[] parameters) {
095            if (namespace == null) {
096                if (this.namespace != null) {
097                    return null;
098                }
099            }
100            else if (!namespace.equals(this.namespace)) {
101                return null;
102            }
103    
104            if (parameters == null) {
105                parameters = EMPTY_ARRAY;
106            }
107    
108            if (name.equals("new")) {
109                Constructor constructor =
110                    MethodLookupUtils.lookupConstructor(functionClass, parameters);
111                if (constructor != null) {
112                    return new ConstructorFunction(constructor);
113                }
114            }
115            else {
116                Method method = MethodLookupUtils.
117                    lookupStaticMethod(functionClass, name, parameters);
118                if (method != null) {
119                    return new MethodFunction(method);
120                }
121    
122                method = MethodLookupUtils.
123                    lookupMethod(functionClass, name, parameters);
124                if (method != null) {
125                    return new MethodFunction(method);
126                }
127            }
128    
129            return null;
130        }
131    }