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Parallel programming on the go
/*
* 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.
*/
package com.gh.bmd.jrt.common;
import java.lang.reflect.Constructor;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Arrays;
import java.util.HashMap;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
/**
* Reflection utility class.
*
* Created by davide on 9/9/14.
*/
public class Reflection {
/**
* Constant defining an empty argument array for methods or constructors.
*/
public static final Object[] NO_ARGS = new Object[0];
private static final HashMap, Class> sBoxMap = new HashMap, Class>(9);
/**
* Avoid direct instantiation.
*/
private Reflection() {
}
/**
* Returns the class boxing the specified primitive type.
*
* If the passed class does not represent a primitive type the same class is returned.
*
* @param type the primitive type.
* @return the boxing class.
*/
@Nonnull
public static Class boxingClass(@Nonnull final Class type) {
if (!type.isPrimitive()) {
return type;
}
return sBoxMap.get(type);
}
/**
* Finds the constructor of the specified class best matching the passed arguments.
*
* Note that clashing of signature is automatically avoided, since constructors are not
* identified by their name. Hence the best match will be always unique in the class.
*
* @param type the target class.
* @param args the constructor arguments.
* @param the target type.
* @return the best matching constructor.
* @throws java.lang.IllegalArgumentException if no constructor taking the specified objects as
* parameters was found.
*/
@Nonnull
@SuppressWarnings("unchecked")
public static Constructor findConstructor(@Nonnull final Class type,
@Nonnull final Object... args) {
Constructor constructor = findBestMatchingConstructor(type.getConstructors(), args);
if (constructor == null) {
constructor = findBestMatchingConstructor(type.getDeclaredConstructors(), args);
if (constructor == null) {
throw new IllegalArgumentException(
"no suitable constructor found for type: " + type.getName());
}
}
if (!constructor.isAccessible()) {
AccessController.doPrivileged(new SetAccessibleAction(constructor));
}
return (Constructor) constructor;
}
@Nullable
private static Constructor findBestMatchingConstructor(
@Nonnull final Constructor[] constructors, @Nonnull final Object[] args) {
final int argsLength = args.length;
Constructor bestMatch = null;
int maxConfidence = 0;
for (final Constructor constructor : constructors) {
final Class[] params = constructor.getParameterTypes();
final int length = params.length;
if (length != argsLength) {
continue;
}
boolean isValid = true;
int confidence = 0;
for (int i = 0; i < argsLength; ++i) {
final Object contextArg = args[i];
final Class param = params[i];
if (contextArg != null) {
final Class boxingClass = boxingClass(param);
if (!boxingClass.isInstance(contextArg)) {
isValid = false;
break;
}
if (contextArg.getClass().equals(boxingClass)) {
++confidence;
}
} else if (param.isPrimitive()) {
isValid = false;
break;
}
}
if (!isValid) {
continue;
}
if ((bestMatch == null) || (confidence > maxConfidence)) {
bestMatch = constructor;
maxConfidence = confidence;
} else if (confidence == maxConfidence) {
throw new IllegalArgumentException(
"more than one constructor found for arguments: " + Arrays.toString(args));
}
}
return bestMatch;
}
/**
* Privileged action used to grant accessibility to a constructor.
*/
private static class SetAccessibleAction implements PrivilegedAction {
private final Constructor mmConstructor;
/**
* Constructor.
*
* @param constructor the constructor instance.
*/
private SetAccessibleAction(@Nonnull final Constructor constructor) {
mmConstructor = constructor;
}
public Void run() {
mmConstructor.setAccessible(true);
return null;
}
}
static {
final HashMap, Class> boxMap = sBoxMap;
boxMap.put(boolean.class, Boolean.class);
boxMap.put(byte.class, Byte.class);
boxMap.put(char.class, Character.class);
boxMap.put(double.class, Double.class);
boxMap.put(float.class, Float.class);
boxMap.put(int.class, Integer.class);
boxMap.put(long.class, Long.class);
boxMap.put(short.class, Short.class);
boxMap.put(void.class, Void.class);
}
}