Java tutorial
/* * Copyright (C) 2008 The Guava 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 com.google.common.collect; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.lang.reflect.Field; import java.util.Collection; import java.util.Map; /** * Provides static methods for serializing collection classes. * * <p>This class assists the implementation of collection classes. Do not use * this class to serialize collections that are defined elsewhere. * * @author Jared Levy */ final class Serialization { private Serialization() { } /** * Reads a count corresponding to a serialized map, multiset, or multimap. It * returns the size of a map serialized by {@link * #writeMap(Map, ObjectOutputStream)}, the number of distinct elements in a * multiset serialized by {@link * #writeMultiset(Multiset, ObjectOutputStream)}, or the number of distinct * keys in a multimap serialized by {@link * #writeMultimap(Multimap, ObjectOutputStream)}. */ static int readCount(ObjectInputStream stream) throws IOException { return stream.readInt(); } /** * Stores the contents of a map in an output stream, as part of serialization. * It does not support concurrent maps whose content may change while the * method is running. * * <p>The serialized output consists of the number of entries, first key, * first value, second key, second value, and so on. */ static <K, V> void writeMap(Map<K, V> map, ObjectOutputStream stream) throws IOException { stream.writeInt(map.size()); for (Map.Entry<K, V> entry : map.entrySet()) { stream.writeObject(entry.getKey()); stream.writeObject(entry.getValue()); } } /** * Populates a map by reading an input stream, as part of deserialization. * See {@link #writeMap} for the data format. */ static <K, V> void populateMap(Map<K, V> map, ObjectInputStream stream) throws IOException, ClassNotFoundException { int size = stream.readInt(); populateMap(map, stream, size); } /** * Populates a map by reading an input stream, as part of deserialization. * See {@link #writeMap} for the data format. The size is determined by a * prior call to {@link #readCount}. */ static <K, V> void populateMap(Map<K, V> map, ObjectInputStream stream, int size) throws IOException, ClassNotFoundException { for (int i = 0; i < size; i++) { @SuppressWarnings("unchecked") // reading data stored by writeMap K key = (K) stream.readObject(); @SuppressWarnings("unchecked") // reading data stored by writeMap V value = (V) stream.readObject(); map.put(key, value); } } /** * Stores the contents of a multiset in an output stream, as part of * serialization. It does not support concurrent multisets whose content may * change while the method is running. * * <p>The serialized output consists of the number of distinct elements, the * first element, its count, the second element, its count, and so on. */ static <E> void writeMultiset(Multiset<E> multiset, ObjectOutputStream stream) throws IOException { int entryCount = multiset.entrySet().size(); stream.writeInt(entryCount); for (Multiset.Entry<E> entry : multiset.entrySet()) { stream.writeObject(entry.getElement()); stream.writeInt(entry.getCount()); } } /** * Populates a multiset by reading an input stream, as part of * deserialization. See {@link #writeMultiset} for the data format. */ static <E> void populateMultiset(Multiset<E> multiset, ObjectInputStream stream) throws IOException, ClassNotFoundException { int distinctElements = stream.readInt(); populateMultiset(multiset, stream, distinctElements); } /** * Populates a multiset by reading an input stream, as part of * deserialization. See {@link #writeMultiset} for the data format. The number * of distinct elements is determined by a prior call to {@link #readCount}. */ static <E> void populateMultiset(Multiset<E> multiset, ObjectInputStream stream, int distinctElements) throws IOException, ClassNotFoundException { for (int i = 0; i < distinctElements; i++) { @SuppressWarnings("unchecked") // reading data stored by writeMultiset E element = (E) stream.readObject(); int count = stream.readInt(); multiset.add(element, count); } } /** * Stores the contents of a multimap in an output stream, as part of * serialization. It does not support concurrent multimaps whose content may * change while the method is running. The {@link Multimap#asMap} view * determines the ordering in which data is written to the stream. * * <p>The serialized output consists of the number of distinct keys, and then * for each distinct key: the key, the number of values for that key, and the * key's values. */ static <K, V> void writeMultimap(Multimap<K, V> multimap, ObjectOutputStream stream) throws IOException { stream.writeInt(multimap.asMap().size()); for (Map.Entry<K, Collection<V>> entry : multimap.asMap().entrySet()) { stream.writeObject(entry.getKey()); stream.writeInt(entry.getValue().size()); for (V value : entry.getValue()) { stream.writeObject(value); } } } /** * Populates a multimap by reading an input stream, as part of * deserialization. See {@link #writeMultimap} for the data format. */ static <K, V> void populateMultimap(Multimap<K, V> multimap, ObjectInputStream stream) throws IOException, ClassNotFoundException { int distinctKeys = stream.readInt(); populateMultimap(multimap, stream, distinctKeys); } /** * Populates a multimap by reading an input stream, as part of * deserialization. See {@link #writeMultimap} for the data format. The number * of distinct keys is determined by a prior call to {@link #readCount}. */ static <K, V> void populateMultimap(Multimap<K, V> multimap, ObjectInputStream stream, int distinctKeys) throws IOException, ClassNotFoundException { for (int i = 0; i < distinctKeys; i++) { @SuppressWarnings("unchecked") // reading data stored by writeMultimap K key = (K) stream.readObject(); Collection<V> values = multimap.get(key); int valueCount = stream.readInt(); for (int j = 0; j < valueCount; j++) { @SuppressWarnings("unchecked") // reading data stored by writeMultimap V value = (V) stream.readObject(); values.add(value); } } } // Secret sauce for setting final fields; don't make it public. static <T> FieldSetter<T> getFieldSetter(final Class<T> clazz, String fieldName) { try { Field field = clazz.getDeclaredField(fieldName); return new FieldSetter<T>(field); } catch (NoSuchFieldException e) { throw new AssertionError(e); // programmer error } } // Secret sauce for setting final fields; don't make it public. static final class FieldSetter<T> { private final Field field; private FieldSetter(Field field) { this.field = field; field.setAccessible(true); } void set(T instance, Object value) { try { field.set(instance, value); } catch (IllegalAccessException impossible) { throw new AssertionError(impossible); } } void set(T instance, int value) { try { field.set(instance, value); } catch (IllegalAccessException impossible) { throw new AssertionError(impossible); } } } }