Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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.apache.commons.lang3; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.ObjectStreamClass; import java.io.OutputStream; import java.io.Serializable; import java.util.HashMap; import java.util.Map; /** * <p>Assists with the serialization process and performs additional functionality based * on serialization.</p> * * <ul> * <li>Deep clone using serialization * <li>Serialize managing finally and IOException * <li>Deserialize managing finally and IOException * </ul> * * <p>This class throws exceptions for invalid {@code null} inputs. * Each method documents its behaviour in more detail.</p> * * <p>#ThreadSafe#</p> * @since 1.0 * @version $Id$ */ public class SerializationUtils { /** * <p>SerializationUtils instances should NOT be constructed in standard programming. * Instead, the class should be used as {@code SerializationUtils.clone(object)}.</p> * * <p>This constructor is public to permit tools that require a JavaBean instance * to operate.</p> * @since 2.0 */ public SerializationUtils() { super(); } // Clone //----------------------------------------------------------------------- /** * <p>Deep clone an {@code Object} using serialization.</p> * * <p>This is many times slower than writing clone methods by hand * on all objects in your object graph. However, for complex object * graphs, or for those that don't support deep cloning this can * be a simple alternative implementation. Of course all the objects * must be {@code Serializable}.</p> * * @param <T> the type of the object involved * @param object the {@code Serializable} object to clone * @return the cloned object * @throws SerializationException (runtime) if the serialization fails */ public static <T extends Serializable> T clone(final T object) { if (object == null) { return null; } final byte[] objectData = serialize(object); final ByteArrayInputStream bais = new ByteArrayInputStream(objectData); ClassLoaderAwareObjectInputStream in = null; try { // stream closed in the finally in = new ClassLoaderAwareObjectInputStream(bais, object.getClass().getClassLoader()); /* * when we serialize and deserialize an object, * it is reasonable to assume the deserialized object * is of the same type as the original serialized object */ @SuppressWarnings("unchecked") // see above final T readObject = (T) in.readObject(); return readObject; } catch (final ClassNotFoundException ex) { throw new SerializationException("ClassNotFoundException while reading cloned object data", ex); } catch (final IOException ex) { throw new SerializationException("IOException while reading cloned object data", ex); } finally { try { if (in != null) { in.close(); } } catch (final IOException ex) { throw new SerializationException("IOException on closing cloned object data InputStream.", ex); } } } /** * Performs a serialization roundtrip. Serializes and deserializes the given object, great for testing objects that * implement {@link Serializable}. * * @param <T> * the type of the object involved * @param msg * the object to roundtrip * @return the serialized and deseralized object * @since 3.3 */ @SuppressWarnings("unchecked") // OK, because we serialized a type `T` public static <T extends Serializable> T roundtrip(final T msg) { return (T) SerializationUtils.deserialize(SerializationUtils.serialize(msg)); } // Serialize //----------------------------------------------------------------------- /** * <p>Serializes an {@code Object} to the specified stream.</p> * * <p>The stream will be closed once the object is written. * This avoids the need for a finally clause, and maybe also exception * handling, in the application code.</p> * * <p>The stream passed in is not buffered internally within this method. * This is the responsibility of your application if desired.</p> * * @param obj the object to serialize to bytes, may be null * @param outputStream the stream to write to, must not be null * @throws IllegalArgumentException if {@code outputStream} is {@code null} * @throws SerializationException (runtime) if the serialization fails */ public static void serialize(final Serializable obj, final OutputStream outputStream) { if (outputStream == null) { throw new IllegalArgumentException("The OutputStream must not be null"); } ObjectOutputStream out = null; try { // stream closed in the finally out = new ObjectOutputStream(outputStream); out.writeObject(obj); } catch (final IOException ex) { throw new SerializationException(ex); } finally { try { if (out != null) { out.close(); } } catch (final IOException ex) { // NOPMD // ignore close exception } } } /** * <p>Serializes an {@code Object} to a byte array for * storage/serialization.</p> * * @param obj the object to serialize to bytes * @return a byte[] with the converted Serializable * @throws SerializationException (runtime) if the serialization fails */ public static byte[] serialize(final Serializable obj) { final ByteArrayOutputStream baos = new ByteArrayOutputStream(512); serialize(obj, baos); return baos.toByteArray(); } // Deserialize //----------------------------------------------------------------------- /** * <p> * Deserializes an {@code Object} from the specified stream. * </p> * * <p> * The stream will be closed once the object is written. This avoids the need for a finally clause, and maybe also * exception handling, in the application code. * </p> * * <p> * The stream passed in is not buffered internally within this method. This is the responsibility of your * application if desired. * </p> * * <p> * If the call site incorrectly types the return value, a {@link ClassCastException} is thrown from the call site. * Without Generics in this declaration, the call site must type cast and can cause the same ClassCastException. * Note that in both cases, the ClassCastException is in the call site, not in this method. * </p> * * @param <T> the object type to be deserialized * @param inputStream * the serialized object input stream, must not be null * @return the deserialized object * @throws IllegalArgumentException * if {@code inputStream} is {@code null} * @throws SerializationException * (runtime) if the serialization fails */ public static <T> T deserialize(final InputStream inputStream) { if (inputStream == null) { throw new IllegalArgumentException("The InputStream must not be null"); } ObjectInputStream in = null; try { // stream closed in the finally in = new ObjectInputStream(inputStream); @SuppressWarnings("unchecked") // may fail with CCE if serialised form is incorrect final T obj = (T) in.readObject(); return obj; } catch (final ClassCastException ex) { throw new SerializationException(ex); } catch (final ClassNotFoundException ex) { throw new SerializationException(ex); } catch (final IOException ex) { throw new SerializationException(ex); } finally { try { if (in != null) { in.close(); } } catch (final IOException ex) { // NOPMD // ignore close exception } } } /** * <p> * Deserializes a single {@code Object} from an array of bytes. * </p> * * <p> * If the call site incorrectly types the return value, a {@link ClassCastException} is thrown from the call site. * Without Generics in this declaration, the call site must type cast and can cause the same ClassCastException. * Note that in both cases, the ClassCastException is in the call site, not in this method. * </p> * * @param <T> the object type to be deserialized * @param objectData * the serialized object, must not be null * @return the deserialized object * @throws IllegalArgumentException * if {@code objectData} is {@code null} * @throws SerializationException * (runtime) if the serialization fails */ public static <T> T deserialize(final byte[] objectData) { if (objectData == null) { throw new IllegalArgumentException("The byte[] must not be null"); } return SerializationUtils.<T>deserialize(new ByteArrayInputStream(objectData)); } /** * <p>Custom specialization of the standard JDK {@link java.io.ObjectInputStream} * that uses a custom <code>ClassLoader</code> to resolve a class. * If the specified <code>ClassLoader</code> is not able to resolve the class, * the context classloader of the current thread will be used. * This way, the standard deserialization work also in web-application * containers and application servers, no matter in which of the * <code>ClassLoader</code> the particular class that encapsulates * serialization/deserialization lives. </p> * * <p>For more in-depth information about the problem for which this * class here is a workaround, see the JIRA issue LANG-626. </p> */ static class ClassLoaderAwareObjectInputStream extends ObjectInputStream { private static final Map<String, Class<?>> primitiveTypes = new HashMap<String, Class<?>>(); private final ClassLoader classLoader; /** * Constructor. * @param in The <code>InputStream</code>. * @param classLoader classloader to use * @throws IOException if an I/O error occurs while reading stream header. * @see java.io.ObjectInputStream */ public ClassLoaderAwareObjectInputStream(final InputStream in, final ClassLoader classLoader) throws IOException { super(in); this.classLoader = classLoader; primitiveTypes.put("byte", byte.class); primitiveTypes.put("short", short.class); primitiveTypes.put("int", int.class); primitiveTypes.put("long", long.class); primitiveTypes.put("float", float.class); primitiveTypes.put("double", double.class); primitiveTypes.put("boolean", boolean.class); primitiveTypes.put("char", char.class); primitiveTypes.put("void", void.class); } /** * Overriden version that uses the parametrized <code>ClassLoader</code> or the <code>ClassLoader</code> * of the current <code>Thread</code> to resolve the class. * @param desc An instance of class <code>ObjectStreamClass</code>. * @return A <code>Class</code> object corresponding to <code>desc</code>. * @throws IOException Any of the usual Input/Output exceptions. * @throws ClassNotFoundException If class of a serialized object cannot be found. */ @Override protected Class<?> resolveClass(final ObjectStreamClass desc) throws IOException, ClassNotFoundException { final String name = desc.getName(); try { return Class.forName(name, false, classLoader); } catch (final ClassNotFoundException ex) { try { return Class.forName(name, false, Thread.currentThread().getContextClassLoader()); } catch (final ClassNotFoundException cnfe) { final Class<?> cls = primitiveTypes.get(name); if (cls != null) { return cls; } throw cnfe; } } } } }