ClassLoader util for loading classes and finding resources.
//Copyright 2007-2009 David Yu dyuproject@gmail.com
//------------------------------------------------------------------------
//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.dyuproject.util;
import java.net.URL;
/**
* ClassLoader util for loading classes and finding resources.
* No checked exceptions.
*
* @author David Yu
* @created Jan 20, 2009
*/
public final class ClassLoaderUtil
{
/**
* Loads a class from the classloader;
* If not found, the classloader of the {@code context} class specified will be used.
*/
public static Class<?> loadClass(String className, Class<?> context)
{
return loadClass(className, context, false);
}
/**
* Loads a class from the classloader;
* If not found, the classloader of the {@code context} class specified will be used.
* If the flag {@code checkParent} is true, the classloader's parent is included in
* the lookup.
*/
public static Class<?> loadClass(String className, Class<?> context, boolean checkParent)
{
Class<?> clazz = null;
try
{
clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
}
catch(ClassNotFoundException e)
{
if(context!=null)
{
ClassLoader loader = context.getClassLoader();
while(loader!=null)
{
try
{
clazz = loader.loadClass(className);
return clazz;
}
catch(ClassNotFoundException e1)
{
loader = checkParent ? loader.getParent() : null;
}
}
}
}
return clazz;
}
/**
* Instantiates an object using its default constructor if the {@code className} is
* found in the classpath and loaded.
*/
@SuppressWarnings("unchecked")
public static <T> T newInstance(String className, Class<?> context) throws Exception
{
Class<T> clazz = (Class<T>)loadClass(className, context, false);
if(clazz==null)
throw new Exception(className + " not found in the classpath.");
return clazz.newInstance();
}
/**
* Instantiates an object using its default constructor if the {@code className} is
* found in the classpath and loaded.
*/
@SuppressWarnings("unchecked")
public static <T> T newInstance(String className, Class<?> context, boolean checkParent)
throws Exception
{
Class<T> clazz = (Class<T>)loadClass(className, context, checkParent);
if(clazz==null)
throw new Exception(className + " not found in the classpath.");
return clazz.newInstance();
}
/**
* Loads a {@link URL} resource from the classloader;
* If not found, the classloader of the {@code context} class specified will be used.
*/
public static URL getResource(String resource, Class<?> context)
{
return getResource(resource, context, false);
}
/**
* Loads a {@link URL} resource from the classloader;
* If not found, the classloader of the {@code context} class specified will be used.
* If the flag {@code checkParent} is true, the classloader's parent is included in
* the lookup.
*/
public static URL getResource(String resource, Class<?> context, boolean checkParent)
{
URL url = Thread.currentThread().getContextClassLoader().getResource(resource);
if(url!=null)
return url;
if(context!=null)
{
ClassLoader loader = context.getClassLoader();
while(loader!=null)
{
url = loader.getResource(resource);
if(url!=null)
return url;
loader = checkParent ? loader.getParent() : null;
}
}
return ClassLoader.getSystemResource(resource);
}
}
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