/*
* Copyright 2013 Stormpath, 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.stormpath.sdk.lang;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.InputStream;
import java.lang.reflect.Constructor;
/**
* @since 0.1
*/
public class Classes {
/**
* Private internal log instance.
*/
private static final Logger log = LoggerFactory.getLogger(Classes.class);
/**
* @since 0.1
*/
private static final ClassLoaderAccessor THREAD_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
@Override
protected ClassLoader doGetClassLoader() throws Throwable {
return Thread.currentThread().getContextClassLoader();
}
};
/**
* @since 0.1
*/
private static final ClassLoaderAccessor CLASS_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
@Override
protected ClassLoader doGetClassLoader() throws Throwable {
return Classes.class.getClassLoader();
}
};
/**
* @since 0.1
*/
private static final ClassLoaderAccessor SYSTEM_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
@Override
protected ClassLoader doGetClassLoader() throws Throwable {
return ClassLoader.getSystemClassLoader();
}
};
/**
* Attempts to load the specified class name from the current thread's
* {@link Thread#getContextClassLoader() context class loader}, then the
* current ClassLoader (<code>Classes.class.getClassLoader()</code>), then the system/application
* ClassLoader (<code>ClassLoader.getSystemClassLoader()</code>, in that order. If any of them cannot locate
* the specified class, an <code>UnknownClassException</code> is thrown (our RuntimeException equivalent of
* the JRE's <code>ClassNotFoundException</code>.
*
* @param fqcn the fully qualified class name to load
* @return the located class
* @throws UnknownClassException if the class cannot be found.
*/
public static <T> Class<T> forName(String fqcn) throws UnknownClassException {
Class<T> clazz = THREAD_CL_ACCESSOR.loadClass(fqcn);
if (clazz == null) {
if (log.isTraceEnabled()) {
log.trace("Unable to load class named [" + fqcn +
"] from the thread context ClassLoader. Trying the current ClassLoader...");
}
clazz = CLASS_CL_ACCESSOR.loadClass(fqcn);
}
if (clazz == null) {
if (log.isTraceEnabled()) {
log.trace("Unable to load class named [" + fqcn + "] from the current ClassLoader. " +
"Trying the system/application ClassLoader...");
}
clazz = SYSTEM_CL_ACCESSOR.loadClass(fqcn);
}
if (clazz == null) {
String msg = "Unable to load class named [" + fqcn + "] from the thread context, current, or " +
"system/application ClassLoaders. All heuristics have been exhausted. Class could not be found.";
if (fqcn != null && fqcn.startsWith("com.stormpath.sdk.impl")) {
msg += " Have you remembered to include the stormpath-sdk-impl .jar in your runtime classpath?";
}
throw new UnknownClassException(msg);
}
return clazz;
}
/**
* Returns the specified resource by checking the current thread's
* {@link Thread#getContextClassLoader() context class loader}, then the
* current ClassLoader (<code>Classes.class.getClassLoader()</code>), then the system/application
* ClassLoader (<code>ClassLoader.getSystemClassLoader()</code>, in that order, using
* {@link ClassLoader#getResourceAsStream(String) getResourceAsStream(name)}.
*
* @param name the name of the resource to acquire from the classloader(s).
* @return the InputStream of the resource found, or <code>null</code> if the resource cannot be found from any
* of the three mentioned ClassLoaders.
* @since 0.8
*/
public static InputStream getResourceAsStream(String name) {
InputStream is = THREAD_CL_ACCESSOR.getResourceStream(name);
if (is == null) {
is = CLASS_CL_ACCESSOR.getResourceStream(name);
}
if (is == null) {
is = SYSTEM_CL_ACCESSOR.getResourceStream(name);
}
return is;
}
public static boolean isAvailable(String fullyQualifiedClassName) {
try {
forName(fullyQualifiedClassName);
return true;
} catch (UnknownClassException e) {
return false;
}
}
public static <T> T newInstance(String fqcn) {
Class<T> clazz = forName(fqcn);
return newInstance(clazz);
}
public static <T> T newInstance(String fqcn, Object... args) {
Class<T> clazz = forName(fqcn);
return newInstance(clazz, args);
}
public static <T> T newInstance(Class<T> clazz) {
if (clazz == null) {
String msg = "Class method parameter cannot be null.";
throw new IllegalArgumentException(msg);
}
try {
return clazz.newInstance();
} catch (Exception e) {
throw new InstantiationException("Unable to instantiate class [" + clazz.getName() + "]", e);
}
}
public static <T> T newInstance(Class<T> clazz, Object... args) {
Class[] argTypes = new Class[args.length];
for (int i = 0; i < args.length; i++) {
argTypes[i] = args[i].getClass();
}
Constructor<T> ctor = getConstructor(clazz, argTypes);
return instantiate(ctor, args);
}
public static <T> Constructor<T> getConstructor(Class<T> clazz, Class... argTypes) {
try {
return clazz.getConstructor(argTypes);
} catch (NoSuchMethodException e) {
throw new IllegalStateException(e);
}
}
public static <T> T instantiate(Constructor<T> ctor, Object... args) {
try {
return ctor.newInstance(args);
} catch (Exception e) {
String msg = "Unable to instantiate instance with constructor [" + ctor + "]";
throw new InstantiationException(msg, e);
}
}
/**
* @since 1.0
*/
private static interface ClassLoaderAccessor {
<T> Class<T> loadClass(String fqcn);
InputStream getResourceStream(String name);
}
/**
* @since 1.0
*/
private static abstract class ExceptionIgnoringAccessor implements ClassLoaderAccessor {
@SuppressWarnings("unchecked")
public <T> Class<T> loadClass(String fqcn) {
Class<T> clazz = null;
ClassLoader cl = getClassLoader();
if (cl != null) {
try {
clazz = (Class<T>)cl.loadClass(fqcn);
} catch (ClassNotFoundException e) {
if (log.isTraceEnabled()) {
log.trace("Unable to load clazz named [" + fqcn + "] from class loader [" + cl + "]");
}
}
}
return clazz;
}
public InputStream getResourceStream(String name) {
InputStream is = null;
ClassLoader cl = getClassLoader();
if (cl != null) {
is = cl.getResourceAsStream(name);
}
return is;
}
protected final ClassLoader getClassLoader() {
try {
return doGetClassLoader();
} catch (Throwable t) {
if (log.isDebugEnabled()) {
log.debug("Unable to acquire ClassLoader.", t);
}
}
return null;
}
protected abstract ClassLoader doGetClassLoader() throws Throwable;
}
}