org.apache.commons.jexl.util.introspection.MethodMap Maven / Gradle / Ivy
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* 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.jexl.util.introspection;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
/**
* @author Jason van Zyl
* @author Bob McWhirter
* @author Christoph Reck
* @author Geir Magnusson Jr.
* @author Attila Szegedi
* @version $Id: MethodMap.java 584046 2007-10-12 05:14:37Z proyal $
* @since 1.0
*/
public class MethodMap {
/**
* whether a method is more specific than a previously compared one.
*/
private static final int MORE_SPECIFIC = 0;
/**
* whether a method is less specific than a previously compared one.
*/
private static final int LESS_SPECIFIC = 1;
/**
* A method doesn't match a previously compared one.
*/
private static final int INCOMPARABLE = 2;
/**
* Keep track of all methods with the same name.
*/
Map methodByNameMap = new Hashtable();
/**
* Add a method to a list of methods by name. For a particular class we are
* keeping track of all the methods with the same name.
*
* @param method the method.
*/
public void add(Method method) {
String methodName = method.getName();
List l = get(methodName);
if (l == null) {
l = new ArrayList();
methodByNameMap.put(methodName, l);
}
l.add(method);
}
/**
* Return a list of methods with the same name.
*
* @param key
* @return List list of methods
*/
public List get(String key) {
return (List) methodByNameMap.get(key);
}
/**
*
* Find a method. Attempts to find the
* most specific applicable method using the
* algorithm described in the JLS section
* 15.12.2 (with the exception that it can't
* distinguish a primitive type argument from
* an object type argument, since in reflection
* primitive type arguments are represented by
* their object counterparts, so for an argument of
* type (say) java.lang.Integer, it will not be able
* to decide between a method that takes int and a
* method that takes java.lang.Integer as a parameter.
*
*
*
* This turns out to be a relatively rare case
* where this is needed - however, functionality
* like this is needed.
*
*
* @param methodName name of method
* @param args the actual arguments with which the method is called
* @return the most specific applicable method, or null if no
* method is applicable.
* @throws AmbiguousException if there is more than one maximally
* specific applicable method
*/
public Method find(String methodName, Object[] args)
throws AmbiguousException {
List methodList = get(methodName);
if (methodList == null) {
return null;
}
int l = args.length;
Class[] classes = new Class[l];
for (int i = 0; i < l; ++i) {
Object arg = args[i];
/*
* if we are careful down below, a null argument goes in there
* so we can know that the null was passed to the method
*/
classes[i] =
arg == null ? null : arg.getClass();
}
return getMostSpecific(methodList, classes);
}
/**
* Simple distinguishable exception, used when
* we run across ambiguous overloading. Caught
* by the introspector.
*/
public static class AmbiguousException extends RuntimeException {
/**
* Version Id for serializable
*/
private static final long serialVersionUID = -2314636505414551663L;
}
private static Method getMostSpecific(List methods, Class[] classes)
throws AmbiguousException {
LinkedList applicables = getApplicables(methods, classes);
if (applicables.isEmpty()) {
return null;
}
if (applicables.size() == 1) {
return (Method) applicables.getFirst();
}
/*
* This list will contain the maximally specific methods. Hopefully at
* the end of the below loop, the list will contain exactly one method,
* (the most specific method) otherwise we have ambiguity.
*/
LinkedList maximals = new LinkedList();
for (Iterator applicable = applicables.iterator();
applicable.hasNext();) {
Method app = (Method) applicable.next();
Class[] appArgs = app.getParameterTypes();
boolean lessSpecific = false;
for (Iterator maximal = maximals.iterator();
!lessSpecific && maximal.hasNext();) {
Method max = (Method) maximal.next();
switch (moreSpecific(appArgs, max.getParameterTypes())) {
case MORE_SPECIFIC: {
/*
* This method is more specific than the previously
* known maximally specific, so remove the old maximum.
*/
maximal.remove();
break;
}
case LESS_SPECIFIC: {
/*
* This method is less specific than some of the
* currently known maximally specific methods, so we
* won't add it into the set of maximally specific
* methods
*/
lessSpecific = true;
break;
}
}
}
if (!lessSpecific) {
maximals.addLast(app);
}
}
if (maximals.size() > 1) {
// We have more than one maximally specific method
throw new AmbiguousException();
}
return (Method) maximals.getFirst();
}
/**
* Determines which method signature (represented by a class array) is more
* specific. This defines a partial ordering on the method signatures.
*
* @param c1 first signature to compare
* @param c2 second signature to compare
* @return MORE_SPECIFIC if c1 is more specific than c2, LESS_SPECIFIC if
* c1 is less specific than c2, INCOMPARABLE if they are incomparable.
*/
private static int moreSpecific(Class[] c1, Class[] c2) {
boolean c1MoreSpecific = false;
boolean c2MoreSpecific = false;
// compare lengths to handle comparisons where the size of the arrays
// doesn't match, but the methods are both applicable due to the fact
// that one is a varargs method
if (c1.length > c2.length) {
return MORE_SPECIFIC;
}
if (c2.length > c1.length) {
return LESS_SPECIFIC;
}
// ok, move on and compare those of equal lengths
for (int i = 0; i < c1.length; ++i) {
if (c1[i] != c2[i]) {
boolean last = (i == c1.length - 1);
c1MoreSpecific =
c1MoreSpecific ||
isStrictConvertible(c2[i], c1[i], last);
c2MoreSpecific =
c2MoreSpecific ||
isStrictConvertible(c1[i], c2[i], last);
}
}
if (c1MoreSpecific) {
if (c2MoreSpecific) {
/*
* Incomparable due to cross-assignable arguments (i.e.
* foo(String, Object) vs. foo(Object, String))
*/
return INCOMPARABLE;
}
return MORE_SPECIFIC;
}
if (c2MoreSpecific) {
return LESS_SPECIFIC;
}
/*
* Incomparable due to non-related arguments (i.e.
* foo(Runnable) vs. foo(Serializable))
*/
return INCOMPARABLE;
}
/**
* Returns all methods that are applicable to actual argument types.
*
* @param methods list of all candidate methods
* @param classes the actual types of the arguments
* @return a list that contains only applicable methods (number of
* formal and actual arguments matches, and argument types are assignable
* to formal types through a method invocation conversion).
*/
private static LinkedList getApplicables(List methods, Class[] classes) {
LinkedList list = new LinkedList();
for (Iterator imethod = methods.iterator(); imethod.hasNext();) {
Method method = (Method) imethod.next();
if (isApplicable(method, classes)) {
list.add(method);
}
}
return list;
}
/**
* Returns true if the supplied method is applicable to actual
* argument types.
*
* @param method method that will be called
* @param classes arguments to method
* @return true if method is applicable to arguments
*/
private static boolean isApplicable(Method method, Class[] classes) {
Class[] methodArgs = method.getParameterTypes();
if (methodArgs.length > classes.length) {
// if there's just one more methodArg than class arg
// and the last methodArg is an array, then treat it as a vararg
return methodArgs.length == classes.length + 1 &&
methodArgs[methodArgs.length - 1].isArray();
}
if (methodArgs.length == classes.length) {
// this will properly match when the last methodArg
// is an array/varargs and the last class is the type of array
// (e.g. String when the method is expecting String...)
for (int i = 0; i < classes.length; ++i) {
if (!isConvertible(methodArgs[i], classes[i], false)) {
// if we're on the last arg and the method expects an array
if (i == classes.length - 1 && methodArgs[i].isArray()) {
// check to see if the last arg is convertible
// to the array's component type
return isConvertible(methodArgs[i], classes[i], true);
}
return false;
}
}
return true;
}
if (methodArgs.length > 0) {// more arguments given than the method accepts; check for varargs
// check that the last methodArg is an array
Class lastarg = methodArgs[methodArgs.length - 1];
if (!lastarg.isArray()) {
return false;
}
// check that they all match up to the last method arg
for (int i = 0; i < methodArgs.length - 1; ++i) {
if (!isConvertible(methodArgs[i], classes[i], false)) {
return false;
}
}
// check that all remaining arguments are convertible to the vararg type
Class vararg = lastarg.getComponentType();
for (int i = methodArgs.length - 1; i < classes.length; ++i) {
if (!isConvertible(vararg, classes[i], false)) {
return false;
}
}
return true;
}
return false;
}
private static boolean isConvertible(Class formal, Class actual,
boolean possibleVarArg) {
return IntrospectionUtils.
isMethodInvocationConvertible(formal, actual, possibleVarArg);
}
private static boolean isStrictConvertible(Class formal, Class actual,
boolean possibleVarArg) {
return IntrospectionUtils.
isStrictMethodInvocationConvertible(formal, actual, possibleVarArg);
}
}
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