com.aspectran.core.util.ClassUtils Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2022 The Aspectran Project
*
* 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.aspectran.core.util;
import com.aspectran.core.lang.Nullable;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
/**
* Miscellaneous class utility methods.
*/
public abstract class ClassUtils {
/** The package separator character '.' */
public static final char PACKAGE_SEPARATOR_CHAR = '.';
/** The ".class" file suffix */
public static final String CLASS_FILE_SUFFIX = ".class";
/**
* Method that can be called to try to create an instance of
* specified type. Instantiation is done using default no-argument
* constructor.
* @param the generic type
* @param cls the class to check
* @return an instantiated object
* @throws IllegalArgumentException if instantiation fails for any reason;
* except for cases where constructor throws an unchecked exception
* (which will be passed as is)
*/
public static T createInstance(Class cls) {
Constructor ctor;
try {
ctor = findConstructor(cls);
} catch (NoSuchMethodException e) {
throw new IllegalArgumentException("Class " + cls.getName() +
" has no default (no arg) constructor");
}
try {
return ctor.newInstance();
} catch (Exception e) {
throw ExceptionUtils.unwrapAndThrowAsIAE(e, "Unable to instantiate class " +
cls.getName() + ": " + e.getMessage());
}
}
/**
* Method that can be called to try to create an instantiate of
* specified type.
* @param the generic type
* @param cls the class to check
* @param args the arguments
* @return an instantiated object
* @throws IllegalArgumentException if instantiation fails for any reason;
* except for cases where constructor throws an unchecked exception
* (which will be passed as is)
*/
public static T createInstance(Class cls, Object... args) {
Class[] argTypes = new Class[args.length];
for (int i = 0; i < args.length; i++) {
argTypes[i] = args[i].getClass();
}
return createInstance(cls, args, argTypes);
}
/**
* Method that can be called to try to create an instance of
* specified type.
* @param the generic type
* @param cls the class to check
* @param args the arguments
* @param argTypes the argument types of the desired constructor
* @return an instantiated object
* @throws IllegalArgumentException if instantiation fails for any reason;
* except for cases where constructor throws an unchecked exception
* (which will be passed as is)
*/
public static T createInstance(Class cls, Object[] args, Class[] argTypes) {
Constructor ctor;
try {
ctor = findConstructor(cls, argTypes);
} catch (NoSuchMethodException e) {
throw new IllegalArgumentException("Class " + cls.getName() +
" has no constructor which can accept the given arguments");
}
try {
return ctor.newInstance(args);
} catch (Exception e) {
throw ExceptionUtils.unwrapAndThrowAsIAE(e, "Unable to instantiate class " + cls.getName()
+ ", problem: " + e.getMessage());
}
}
/**
* Obtain an accessible constructor for the given class and parameters.
* @param cls the class to check
* @param argTypes the argument types of the desired constructor
* @param the generic type
* @return the constructor reference
* @throws NoSuchMethodException if no such constructor exists
*/
public static Constructor findConstructor(Class cls, Class... argTypes)
throws NoSuchMethodException {
Constructor ctor;
try {
ctor = cls.getDeclaredConstructor(argTypes);
} catch (NoSuchMethodException e) {
throw e;
} catch (Exception e) {
throw new IllegalArgumentException("Unable to find constructor of class " + cls.getName() +
", problem: " + e.getMessage(), ExceptionUtils.getRootCause(e));
}
// must be public
if (!Modifier.isPublic(ctor.getModifiers())) {
throw new IllegalArgumentException("Constructor for " + cls.getName() +
" is not accessible (non-public?): not allowed to try modify access via Reflection: can not instantiate type");
}
return ctor;
}
/**
* Check whether the given class is visible in the given ClassLoader.
* @param clazz the class to check (typically an interface)
* @param classLoader the ClassLoader to check against
* (may be {@code null} in which case this method will always return {@code true})
* @return true if the given class is visible; otherwise false
* @since 6.0.0
*/
public static boolean isVisible(Class clazz, ClassLoader classLoader) {
if (classLoader == null) {
return true;
}
try {
if (clazz.getClassLoader() == classLoader) {
return true;
}
} catch (SecurityException ex) {
// Fall through to loadable check below
}
// Visible if same Class can be loaded from given ClassLoader
return isLoadable(clazz, classLoader);
}
/**
* Check whether the given class is loadable in the given ClassLoader.
* @param clazz the class to check (typically an interface)
* @param classLoader the ClassLoader to check against
* @return true if the given class is loadable; otherwise false
* @since 6.0.0
*/
private static boolean isLoadable(Class clazz, ClassLoader classLoader) {
try {
return (clazz == classLoader.loadClass(clazz.getName()));
// Else: different class with same name found
} catch (ClassNotFoundException ex) {
// No corresponding class found at all
return false;
}
}
/**
* Returns the default class loader within the current context.
* If there is a context classloader it is returned, otherwise the classloader
* which loaded the ClassUtils Class is returned.
* @return the appropriate default classloader which is guaranteed to be non-null
*/
public static ClassLoader getDefaultClassLoader() {
ClassLoader cl = null;
try {
cl = Thread.currentThread().getContextClassLoader();
} catch (Throwable ex) {
// ignore
}
if (cl == null) {
cl = ClassUtils.class.getClassLoader();
}
if (cl == null) {
cl = ClassLoader.getSystemClassLoader();
}
return cl;
}
/**
* Override the thread context ClassLoader with the environment's bean ClassLoader
* if necessary, i.e. if the bean ClassLoader is not equivalent to the thread
* context ClassLoader already.
* @param classLoaderToUse the actual ClassLoader to use for the thread context
* @return the original thread context ClassLoader, or {@code null} if not overridden
*/
@Nullable
public static ClassLoader overrideThreadContextClassLoader(@Nullable ClassLoader classLoaderToUse) {
Thread currentThread = Thread.currentThread();
ClassLoader threadContextClassLoader = currentThread.getContextClassLoader();
if (classLoaderToUse != null && !classLoaderToUse.equals(threadContextClassLoader)) {
currentThread.setContextClassLoader(classLoaderToUse);
return threadContextClassLoader;
} else {
return null;
}
}
public static void restoreThreadContextClassLoader(@Nullable ClassLoader classLoader) {
if (classLoader != null) {
Thread.currentThread().setContextClassLoader(classLoader);
}
}
}