package org.apache.velocity.util.introspection;
/*
* 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.
*/
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import org.apache.velocity.util.MapFactory;
/**
*
* @author <a href="mailto:[email protected]">Jason van Zyl</a>
* @author <a href="mailto:[email protected]">Bob McWhirter</a>
* @author <a href="mailto:[email protected]">Christoph Reck</a>
* @author <a href="mailto:[email protected]">Geir Magnusson Jr.</a>
* @author <a href="mailto:[email protected]">Attila Szegedi</a>
* @version $Id: MethodMap.java 891385 2009-12-16 19:06:18Z nbubna $
*/
public class MethodMap
{
private static final int MORE_SPECIFIC = 0;
private static final int LESS_SPECIFIC = 1;
private static final int INCOMPARABLE = 2;
/**
* Keep track of all methods with the same name.
*/
Map methodByNameMap = MapFactory.create(false);
/**
* 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
*/
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);
}
/**
* <p>
* 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.
* </p>
*
* <p>
* This turns out to be a relatively rare case
* where this is needed - however, functionality
* like this is needed.
* </p>
*
* @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 getBestMatch(methodList, classes);
}
private static Method getBestMatch(List methods, Class[] args)
{
List equivalentMatches = null;
Method bestMatch = null;
Class[] bestMatchTypes = null;
for (Iterator i = methods.iterator(); i.hasNext(); )
{
Method method = (Method)i.next();
if (isApplicable(method, args))
{
if (bestMatch == null)
{
bestMatch = method;
bestMatchTypes = method.getParameterTypes();
}
else
{
Class[] methodTypes = method.getParameterTypes();
switch (compare(methodTypes, bestMatchTypes))
{
case MORE_SPECIFIC:
if (equivalentMatches == null)
{
bestMatch = method;
bestMatchTypes = methodTypes;
}
else
{
// have to beat all other ambiguous ones...
int ambiguities = equivalentMatches.size();
for (int a=0; a < ambiguities; a++)
{
Method other = (Method)equivalentMatches.get(a);
switch (compare(methodTypes, other.getParameterTypes()))
{
case MORE_SPECIFIC:
// ...and thus replace them all...
bestMatch = method;
bestMatchTypes = methodTypes;
equivalentMatches = null;
ambiguities = 0;
break;
case INCOMPARABLE:
// ...join them...
equivalentMatches.add(method);
break;
case LESS_SPECIFIC:
// ...or just go away.
break;
}
}
}
break;
case INCOMPARABLE:
if (equivalentMatches == null)
{
equivalentMatches = new ArrayList(bestMatchTypes.length);
}
equivalentMatches.add(method);
break;
case LESS_SPECIFIC:
// do nothing
break;
}
}
}
}
if (equivalentMatches != null)
{
throw new AmbiguousException();
}
return bestMatch;
}
/**
* 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;
}
/**
* 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 compare(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)
{
/*
* If one method accepts varargs and the other does not,
* call the non-vararg one more specific.
*/
boolean last1Array = c1[c1.length - 1].isArray();
boolean last2Array = c2[c2.length - 1].isArray();
if (last1Array && !last2Array)
{
return LESS_SPECIFIC;
}
if (!last1Array && last2Array)
{
return MORE_SPECIFIC;
}
/*
* 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 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
if (methodArgs.length == classes.length + 1 &&
methodArgs[methodArgs.length - 1].isArray())
{
// all the args preceding the vararg must match
for (int i = 0; i < classes.length; i++)
{
if (!isConvertible(methodArgs[i], classes[i], false))
{
return false;
}
}
return true;
}
else
{
return false;
}
}
else 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;
}
}
}
else 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;
}
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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