classutils.java

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/*
 * Copyright 2002-2007 the original author or authors.
 *
 * 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 org.springframework.util;

import java.beans.Introspector;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Miscellaneous class utility methods. Mainly for internal use within the
 * framework; consider Jakarta's Commons Lang for a more comprehensive suite
 * of class utilities.
 *
 * @author Keith Donald
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 1.1
 * @see TypeUtils
 * @see ReflectionUtils
 */
public abstract class ClassUtils {

	/** Suffix for array class names: "[]" */
	public static final String ARRAY_SUFFIX = "[]";

	/** Prefix for internal array class names: "[L" */
	private static final String INTERNAL_ARRAY_PREFIX = "[L";

	/** The package separator character '.' */
	private static final char PACKAGE_SEPARATOR = '.';

	/** The inner class separator character '$' */
	private static final char INNER_CLASS_SEPARATOR = '$';

	/** The CGLIB class separator character "$$" */
	public static final String CGLIB_CLASS_SEPARATOR = "$$";

	/** The ".class" file suffix */
	public static final String CLASS_FILE_SUFFIX = ".class";


	private static final Log logger = LogFactory.getLog(ClassUtils.class);

	/**
	 * Map with primitive wrapper type as key and corresponding primitive
	 * type as value, for example: Integer.class -> int.class.
	 */
	private static final Map primitiveWrapperTypeMap = new HashMap(8);

	/**
	 * Map with primitive type name as key and corresponding primitive
	 * type as value, for example: "int" -> "int.class".
	 */
	private static final Map primitiveTypeNameMap = new HashMap(16);


	static {
		primitiveWrapperTypeMap.put(Boolean.class, boolean.class);
		primitiveWrapperTypeMap.put(Byte.class, byte.class);
		primitiveWrapperTypeMap.put(Character.class, char.class);
		primitiveWrapperTypeMap.put(Double.class, double.class);
		primitiveWrapperTypeMap.put(Float.class, float.class);
		primitiveWrapperTypeMap.put(Integer.class, int.class);
		primitiveWrapperTypeMap.put(Long.class, long.class);
		primitiveWrapperTypeMap.put(Short.class, short.class);

		Set primitiveTypeNames = new HashSet(16);
		primitiveTypeNames.addAll(primitiveWrapperTypeMap.values());
		primitiveTypeNames.addAll(Arrays.asList(new Class[] {
				boolean[].class, byte[].class, char[].class, double[].class,
				float[].class, int[].class, long[].class, short[].class}));
		for (Iterator it = primitiveTypeNames.iterator(); it.hasNext();) {
			Class primitiveClass = (Class) it.next();
			primitiveTypeNameMap.put(primitiveClass.getName(), primitiveClass);
		}
	}


	/**
	 * Return the default ClassLoader to use: typically the thread context
	 * ClassLoader, if available; the ClassLoader that loaded the ClassUtils
	 * class will be used as fallback.
	 * <p>Call this method if you intend to use the thread context ClassLoader
	 * in a scenario where you absolutely need a non-null ClassLoader reference:
	 * for example, for class path resource loading (but not necessarily for
	 * <code>Class.forName</code>, which accepts a <code>null</code> ClassLoader
	 * reference as well).
	 * @return the default ClassLoader (never <code>null</code>)
	 * @see java.lang.Thread#getContextClassLoader()
	 */
	public static ClassLoader getDefaultClassLoader() {
		ClassLoader cl = null;
		try {
			cl = Thread.currentThread().getContextClassLoader();
		}
		catch (Throwable ex) {
			logger.debug("Cannot access thread context ClassLoader - falling back to system class loader", ex);
		}
		if (cl == null) {
			// No thread context class loader -> use class loader of this class.
			cl = ClassUtils.class.getClassLoader();
		}
		return cl;
	}

	/**
	 * Determine whether the {@link Class} identified by the supplied name is present
	 * and can be loaded. Will return <code>false</code> if either the class or
	 * one of its dependencies is not present or cannot be loaded.
	 * @param className the name of the class to check
	 * @return whether the specified class is present
	 */
	public static boolean isPresent(String className) {
		return isPresent(className, getDefaultClassLoader());
	}

	/**
	 * Determine whether the {@link Class} identified by the supplied name is present
	 * and can be loaded. Will return <code>false</code> if either the class or
	 * one of its dependencies is not present or cannot be loaded.
	 * @param className the name of the class to check
	 * @param classLoader the class loader to use
	 * (may be <code>null</code>, which indicates the default class loader)
	 * @return whether the specified class is present
	 */
	public static boolean isPresent(String className, ClassLoader classLoader) {
		try {
			forName(className, classLoader);
			return true;
		}
		catch (Throwable ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("Class [" + className + "] or one of its dependencies is not present: " + ex);
			}
			return false;
		}
	}

	/**
	 * Replacement for <code>Class.forName()</code> that also returns Class instances
	 * for primitives (like "int") and array class names (like "String[]").
	 * <p>Always uses the default class loader: that is, preferably the thread context
	 * class loader, or the ClassLoader that loaded the ClassUtils class as fallback.
	 * @param name the name of the Class
	 * @return Class instance for the supplied name
	 * @throws ClassNotFoundException if the class was not found
	 * @throws LinkageError if the class file could not be loaded
	 * @see Class#forName(String, boolean, ClassLoader)
	 * @see #getDefaultClassLoader()
	 */
	public static Class forName(String name) throws ClassNotFoundException, LinkageError {
		return forName(name, getDefaultClassLoader());
	}

	/**
	 * Replacement for <code>Class.forName()</code> that also returns Class instances
	 * for primitives (like "int") and array class names (like "String[]").
	 * @param name the name of the Class
	 * @param classLoader the class loader to use
	 * (may be <code>null</code>, which indicates the default class loader)
	 * @return Class instance for the supplied name
	 * @throws ClassNotFoundException if the class was not found
	 * @throws LinkageError if the class file could not be loaded
	 * @see Class#forName(String, boolean, ClassLoader)
	 */
	public static Class forName(String name, ClassLoader classLoader) throws ClassNotFoundException, LinkageError {
		Assert.notNull(name, "Name must not be null");

		Class clazz = resolvePrimitiveClassName(name);
		if (clazz != null) {
			return clazz;
		}

		// "java.lang.String[]" style arrays
		if (name.endsWith(ARRAY_SUFFIX)) {
			String elementClassName = name.substring(0, name.length() - ARRAY_SUFFIX.length());
			Class elementClass = forName(elementClassName, classLoader);
			return Array.newInstance(elementClass, 0).getClass();
		}

		// "[Ljava.lang.String;" style arrays
		int internalArrayMarker = name.indexOf(INTERNAL_ARRAY_PREFIX);
		if (internalArrayMarker != -1 && name.endsWith(";")) {
			String elementClassName = null;
			if (internalArrayMarker == 0) {
				elementClassName = name.substring(INTERNAL_ARRAY_PREFIX.length(), name.length() - 1);
			}
			else if (name.startsWith("[")) {
				elementClassName = name.substring(1);
			}
			Class elementClass = forName(elementClassName, classLoader);
			return Array.newInstance(elementClass, 0).getClass();
		}

		ClassLoader classLoaderToUse = classLoader;
		if (classLoaderToUse == null) {
			classLoaderToUse = getDefaultClassLoader();
		}
		return classLoaderToUse.loadClass(name);
	}

	/**
	 * Resolve the given class name into a Class instance. Supports
	 * primitives (like "int") and array class names (like "String[]").
	 * <p>This is effectively equivalent to the <code>forName</code>
	 * method with the same arguments, with the only difference being
	 * the exceptions thrown in case of class loading failure.
	 * @param className the name of the Class
	 * @param classLoader the class loader to use
	 * (may be <code>null</code>, which indicates the default class loader)
	 * @return Class instance for the supplied name
	 * @throws IllegalArgumentException if the class name was not resolvable
	 * (that is, the class could not be found or the class file could not be loaded)
	 * @see #forName(String, ClassLoader)
	 */
	public static Class resolveClassName(String className, ClassLoader classLoader) throws IllegalArgumentException {
		try {
			return forName(className, classLoader);
		}
		catch (ClassNotFoundException ex) {
			throw new IllegalArgumentException("Cannot find class [" + className + "]. Root cause: " + ex);
		}
		catch (LinkageError ex) {
			throw new IllegalArgumentException("Error loading class [" + className +
					"]: problem with class file or dependent class. Root cause: " + ex);
		}
	}

	/**
	 * Resolve the given class name as primitive class, if appropriate,
	 * according to the JVM's naming rules for primitive classes.
	 * <p>Also supports the JVM's internal class names for primitive arrays.
	 * Does <i>not</i> support the "[]" suffix notation for primitive arrays;
	 * this is only supported by {@link #forName}.
	 * @param name the name of the potentially primitive class
	 * @return the primitive class, or <code>null</code> if the name does not denote
	 * a primitive class or primitive array class
	 */
	public static Class resolvePrimitiveClassName(String name) {
		Class result = null;
		// Most class names will be quite long, considering that they
		// SHOULD sit in a package, so a length check is worthwhile.
		if (name != null && name.length() <= 8) {
			// Could be a primitive - likely.
			result = (Class) primitiveTypeNameMap.get(name);
		}
		return result;
	}