com.google.gwt.user.client.rpc.impl.ReflectionHelper Maven / Gradle / Ivy
/*
* Copyright 2010 Google Inc.
*
* 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.google.gwt.user.client.rpc.impl;
import com.google.gwt.dev.util.Pair;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.LinkedHashMap;
/**
* Provides access to reflection capability, but only when running from
* bytecode.
*/
public class ReflectionHelper {
// Only used from single-threaded JS. Doesn't need to be thread-safe.
private static class Cache
extends LinkedHashMap {
private static final int MAX_SIZE = 1024;
// These values lifted from defaults.
private static final int INITIAL_CAPACITY = 16;
private static final float LOAD_FACTOR = 0.75f;
public Cache() {
super(INITIAL_CAPACITY, LOAD_FACTOR, true);
}
@Override
protected boolean removeEldestEntry(
java.util.Map.Entry eldest) {
return size() > MAX_SIZE;
}
}
private static final Cache, Constructor> constructorCache
= new Cache, Constructor>();
private static final Cache,String>, Field> fieldCache
= new Cache,String>, Field>();
private static Field findField(Class klass, String name) {
Pair, String> key = Pair.,String>create(klass, name);
Field f = fieldCache.get(key);
if (f == null) {
try {
f = klass.getDeclaredField(name);
} catch (NoSuchFieldException ex) {
throw new RuntimeException(
"Unable to find field " + klass.getName() + "." + name, ex);
}
f.setAccessible(true);
fieldCache.put(key, f);
}
return f;
}
/**
* Gets the value of a field.
*/
public static Object getField(Class klass, Object obj, String name) {
Field f = findField(klass, name);
try {
return f.get(obj);
} catch (IllegalAccessException ex) {
throw new RuntimeException("Unexpected failure", ex);
}
}
/**
* Loads {@code klass} using Class.forName.
*/
public static Class loadClass(String klass) {
try {
return Class.forName(klass);
} catch (ClassNotFoundException ex) {
throw new RuntimeException("Unable to find class " + klass, ex);
}
}
/**
* Creates a new instance of {@code klass}. The class must have a no-arg
* constructor. The constructor may have any access modifier (for example,
* private).
*/
@SuppressWarnings("unchecked")
public static T newInstance(Class klass) {
Constructor c = (Constructor) constructorCache.get(klass);
try {
if (c == null) {
c = klass.getDeclaredConstructor();
c.setAccessible(true);
constructorCache.put(klass, c);
}
return c.newInstance();
} catch (Exception ex) {
throw new RuntimeException("Unexpected failure", ex);
}
}
/**
* Sets the value of a field.
*/
public static void setField(Class klass, Object obj, String name,
Object value) throws Exception {
Field f = findField(klass, name);
try {
f.set(obj, value);
} catch (IllegalAccessException ex) {
throw new RuntimeException("Unexpected failure", ex);
}
}
}