MethodMap.java
package org.codehaus.plexus.util.introspection;
/*
* Copyright The Codehaus Foundation.
*
* Licensed 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.Hashtable;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
/**
* @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
* @author <a href="mailto:bob@werken.com">Bob McWhirter</a>
* @author <a href="mailto:Christoph.Reck@dlr.de">Christoph Reck</a>
* @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
* @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
*
*/
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<String, List<Method>> methodByNameMap = new Hashtable<String, List<Method>>();
/**
* 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<Method> l = get(methodName);
if (l == null) {
l = new ArrayList<Method>();
methodByNameMap.put(methodName, l);
}
l.add(method);
}
/**
* Return a list of methods with the same name.
*
* @param key The name of the method.
* @return List list of methods
*/
public List<Method> get(String key) {
return 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<Method> 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
*/
public static class AmbiguousException extends Exception {}
private static Method getMostSpecific(List<Method> methods, Class[] classes) throws AmbiguousException {
LinkedList<Method> applicables = getApplicables(methods, classes);
if (applicables.isEmpty()) {
return null;
}
if (applicables.size() == 1) {
return 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<Method> maximals = new LinkedList<Method>();
for (Method app : applicables) {
Class[] appArgs = app.getParameterTypes();
boolean lessSpecific = false;
for (Iterator<Method> maximal = maximals.iterator(); !lessSpecific && maximal.hasNext(); ) {
Method max = 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 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;
for (int i = 0; i < c1.length; ++i) {
if (c1[i] != c2[i]) {
c1MoreSpecific = c1MoreSpecific || isStrictMethodInvocationConvertible(c2[i], c1[i]);
c2MoreSpecific = c2MoreSpecific || isStrictMethodInvocationConvertible(c1[i], c2[i]);
}
}
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<Method> getApplicables(List<Method> methods, Class[] classes) {
LinkedList<Method> list = new LinkedList<Method>();
for (Object method1 : methods) {
Method method = (Method) method1;
if (isApplicable(method, classes)) {
list.add(method);
}
}
return list;
}
/**
* Returns true if the supplied method is applicable to actual argument types.
*
* @param method The method to check for applicability
* @param classes The arguments
* @return true if the method applies to the parameter types
*/
private static boolean isApplicable(Method method, Class[] classes) {
Class[] methodArgs = method.getParameterTypes();
if (methodArgs.length != classes.length) {
return false;
}
for (int i = 0; i < classes.length; ++i) {
if (!isMethodInvocationConvertible(methodArgs[i], classes[i])) {
return false;
}
}
return true;
}
/**
* Determines whether a type represented by a class object is convertible to another type represented by a class
* object using a method invocation conversion, treating object types of primitive types as if they were primitive
* types (that is, a Boolean actual parameter type matches boolean primitive formal type). This behavior is because
* this method is used to determine applicable methods for an actual parameter list, and primitive types are
* represented by their object duals in reflective method calls.
*
* @param formal the formal parameter type to which the actual parameter type should be convertible
* @param actual the actual parameter type.
* @return true if either formal type is assignable from actual type, or formal is a primitive type and actual is
* its corresponding object type or an object type of a primitive type that can be converted to the formal
* type.
*/
private static boolean isMethodInvocationConvertible(Class formal, Class actual) {
/*
* if it's a null, it means the arg was null
*/
if (actual == null && !formal.isPrimitive()) {
return true;
}
/*
* Check for identity or widening reference conversion
*/
if (actual != null && formal.isAssignableFrom(actual)) {
return true;
}
/*
* Check for boxing with widening primitive conversion. Note that actual parameters are never primitives.
*/
if (formal.isPrimitive()) {
if (formal == Boolean.TYPE && actual == Boolean.class) return true;
if (formal == Character.TYPE && actual == Character.class) return true;
if (formal == Byte.TYPE && actual == Byte.class) return true;
if (formal == Short.TYPE && (actual == Short.class || actual == Byte.class)) return true;
if (formal == Integer.TYPE && (actual == Integer.class || actual == Short.class || actual == Byte.class))
return true;
if (formal == Long.TYPE
&& (actual == Long.class
|| actual == Integer.class
|| actual == Short.class
|| actual == Byte.class)) return true;
if (formal == Float.TYPE
&& (actual == Float.class
|| actual == Long.class
|| actual == Integer.class
|| actual == Short.class
|| actual == Byte.class)) return true;
if (formal == Double.TYPE
&& (actual == Double.class
|| actual == Float.class
|| actual == Long.class
|| actual == Integer.class
|| actual == Short.class
|| actual == Byte.class)) return true;
}
return false;
}
/**
* Determines whether a type represented by a class object is convertible to another type represented by a class
* object using a method invocation conversion, without matching object and primitive types. This method is used to
* determine the more specific type when comparing signatures of methods.
*
* @param formal the formal parameter type to which the actual parameter type should be convertible
* @param actual the actual parameter type.
* @return true if either formal type is assignable from actual type, or formal and actual are both primitive types
* and actual can be subject to widening conversion to formal.
*/
private static boolean isStrictMethodInvocationConvertible(Class formal, Class actual) {
/*
* we shouldn't get a null into, but if so
*/
if (actual == null && !formal.isPrimitive()) {
return true;
}
/*
* Check for identity or widening reference conversion
*/
if (formal.isAssignableFrom(actual)) {
return true;
}
/*
* Check for widening primitive conversion.
*/
if (formal.isPrimitive()) {
if (formal == Short.TYPE && (actual == Byte.TYPE)) return true;
if (formal == Integer.TYPE && (actual == Short.TYPE || actual == Byte.TYPE)) return true;
if (formal == Long.TYPE && (actual == Integer.TYPE || actual == Short.TYPE || actual == Byte.TYPE))
return true;
if (formal == Float.TYPE
&& (actual == Long.TYPE || actual == Integer.TYPE || actual == Short.TYPE || actual == Byte.TYPE))
return true;
if (formal == Double.TYPE
&& (actual == Float.TYPE
|| actual == Long.TYPE
|| actual == Integer.TYPE
|| actual == Short.TYPE
|| actual == Byte.TYPE)) return true;
}
return false;
}
}