PackageFunctions.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.jxpath;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Objects;
import java.util.Set;
import org.apache.commons.jxpath.functions.ConstructorFunction;
import org.apache.commons.jxpath.functions.MethodFunction;
import org.apache.commons.jxpath.util.ClassLoaderUtil;
import org.apache.commons.jxpath.util.MethodLookupUtils;
import org.apache.commons.jxpath.util.TypeUtils;
/**
* Extension functions provided by Java classes. The class prefix specified
* in the constructor is used when a constructor or a static method is called.
* Usually, a class prefix is a package name (hence the name of this class).
*
* Let's say, we declared a PackageFunction like this:
* <blockquote><pre>
* new PackageFunctions("java.util.", "util")
* </pre></blockquote>
*
* We can now use XPaths like:
* <dl>
* <dt><code>"util:Date.new()"</code></dt>
* <dd>Equivalent to <code>new java.util.Date()</code></dd>
* <dt><code>"util:Collections.singleton('foo')"</code></dt>
* <dd>Equivalent to <code>java.util.Collections.singleton("foo")</code></dd>
* <dt><code>"util:substring('foo', 1, 2)"</code></dt>
* <dd>Equivalent to <code>"foo".substring(1, 2)</code>. Note that in
* this case, the class prefix is not used. JXPath does not check that
* the first parameter of the function (the method target) is in fact
* a member of the package described by this PackageFunctions object.</dd>
* </dl>
*
* <p>
* If the first argument of a method or constructor is {@link ExpressionContext},
* the expression context in which the function is evaluated is passed to
* the method.
* </p>
* <p>
* There is one PackageFunctions object registered by default with each
* JXPathContext. It does not have a namespace and uses no class prefix.
* The existence of this object allows us to use XPaths like:
* <code>"java.util.Date.new()"</code> and <code>"length('foo')"</code>
* without the explicit registration of any extension functions.
* </p>
*/
public class PackageFunctions implements Functions {
private final String classPrefix;
private final String namespace;
private static final Object[] EMPTY_ARRAY = {};
/**
* Create a new PackageFunctions.
* @param classPrefix class prefix
* @param namespace namespace String
*/
public PackageFunctions(final String classPrefix, final String namespace) {
this.classPrefix = classPrefix;
this.namespace = namespace;
}
/**
* Returns the namespace specified in the constructor
* @return (singleton) namespace Set
*/
@Override
public Set getUsedNamespaces() {
return Collections.singleton(namespace);
}
/**
* Returns a {@link Function}, if found, for the specified namespace,
* name and parameter types.
* <p>
* @param namespace - if it is not the same as specified in the
* construction, this method returns null
* @param name - name of the method, which can one these forms:
* <ul>
* <li><b>methodname</b>, if invoking a method on an object passed as the
* first parameter</li>
* <li><b>Classname.new</b>, if looking for a constructor</li>
* <li><b>subpackage.subpackage.Classname.new</b>, if looking for a
* constructor in a subpackage</li>
* <li><b>Classname.methodname</b>, if looking for a static method</li>
* <li><b>subpackage.subpackage.Classname.methodname</b>, if looking for a
* static method of a class in a subpackage</li>
* </ul>
* @param parameters Object[] of parameters
* @return a MethodFunction, a ConstructorFunction or null if no function
* is found
*/
@Override
public Function getFunction(
final String namespace,
final String name,
Object[] parameters) {
if (!Objects.equals(this.namespace, namespace)) {
return null;
}
if (parameters == null) {
parameters = EMPTY_ARRAY;
}
if (parameters.length >= 1) {
Object target = TypeUtils.convert(parameters[0], Object.class);
if (target != null) {
Method method =
MethodLookupUtils.lookupMethod(
target.getClass(),
name,
parameters);
if (method != null) {
return new MethodFunction(method);
}
if (target instanceof NodeSet) {
target = ((NodeSet) target).getPointers();
}
method =
MethodLookupUtils.lookupMethod(
target.getClass(),
name,
parameters);
if (method != null) {
return new MethodFunction(method);
}
if (target instanceof Collection) {
final Iterator iter = ((Collection) target).iterator();
if (iter.hasNext()) {
target = iter.next();
if (target instanceof Pointer) {
target = ((Pointer) target).getValue();
}
}
else {
target = null;
}
}
}
if (target != null) {
final Method method =
MethodLookupUtils.lookupMethod(
target.getClass(),
name,
parameters);
if (method != null) {
return new MethodFunction(method);
}
}
}
final String fullName = classPrefix + name;
final int inx = fullName.lastIndexOf('.');
if (inx == -1) {
return null;
}
final String className = fullName.substring(0, inx);
final String methodName = fullName.substring(inx + 1);
Class functionClass;
try {
functionClass = ClassLoaderUtil.getClass(className, true);
}
catch (final ClassNotFoundException ex) {
throw new JXPathException(
"Cannot invoke extension function "
+ (namespace != null ? namespace + ":" + name : name),
ex);
}
if (methodName.equals("new")) {
final Constructor constructor =
MethodLookupUtils.lookupConstructor(functionClass, parameters);
if (constructor != null) {
return new ConstructorFunction(constructor);
}
}
else {
final Method method =
MethodLookupUtils.lookupStaticMethod(
functionClass,
methodName,
parameters);
if (method != null) {
return new MethodFunction(method);
}
}
return null;
}
}