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 */
017package org.apache.commons.jxpath;
018
019import java.lang.reflect.Constructor;
020import java.lang.reflect.Method;
021import java.util.Collections;
022import java.util.Set;
023
024import org.apache.commons.jxpath.functions.ConstructorFunction;
025import org.apache.commons.jxpath.functions.MethodFunction;
026import 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 19:46:46 +0200 (Fr, 02 Mai 2008) $
053 */
054public 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}