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.cassandra.serializers; import java.nio.BufferUnderflowException; import java.nio.ByteBuffer; import java.util.*; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; import org.apache.cassandra.db.marshal.AbstractType; import org.apache.cassandra.transport.ProtocolVersion; import org.apache.cassandra.utils.ByteBufferUtil; import org.apache.cassandra.utils.Pair; public class MapSerializer<K, V> extends CollectionSerializer<Map<K, V>> { // interning instances private static final ConcurrentMap<Pair<TypeSerializer<?>, TypeSerializer<?>>, MapSerializer> instances = new ConcurrentHashMap<Pair<TypeSerializer<?>, TypeSerializer<?>>, MapSerializer>(); public final TypeSerializer<K> keys; public final TypeSerializer<V> values; private final Comparator<Pair<ByteBuffer, ByteBuffer>> comparator; public static <K, V> MapSerializer<K, V> getInstance(TypeSerializer<K> keys, TypeSerializer<V> values, Comparator<ByteBuffer> comparator) { Pair<TypeSerializer<?>, TypeSerializer<?>> p = Pair.<TypeSerializer<?>, TypeSerializer<?>>create(keys, values); MapSerializer<K, V> t = instances.get(p); if (t == null) t = instances.computeIfAbsent(p, k -> new MapSerializer<>(k.left, k.right, comparator)); return t; } private MapSerializer(TypeSerializer<K> keys, TypeSerializer<V> values, Comparator<ByteBuffer> comparator) { this.keys = keys; this.values = values; this.comparator = (p1, p2) -> comparator.compare(p1.left, p2.left); } public List<ByteBuffer> serializeValues(Map<K, V> map) { List<Pair<ByteBuffer, ByteBuffer>> pairs = new ArrayList<>(map.size()); for (Map.Entry<K, V> entry : map.entrySet()) pairs.add(Pair.create(keys.serialize(entry.getKey()), values.serialize(entry.getValue()))); Collections.sort(pairs, comparator); List<ByteBuffer> buffers = new ArrayList<>(pairs.size() * 2); for (Pair<ByteBuffer, ByteBuffer> p : pairs) { buffers.add(p.left); buffers.add(p.right); } return buffers; } public int getElementCount(Map<K, V> value) { return value.size(); } public void validateForNativeProtocol(ByteBuffer bytes, ProtocolVersion version) { try { ByteBuffer input = bytes.duplicate(); int n = readCollectionSize(input, version); for (int i = 0; i < n; i++) { keys.validate(readValue(input, version)); values.validate(readValue(input, version)); } if (input.hasRemaining()) throw new MarshalException("Unexpected extraneous bytes after map value"); } catch (BufferUnderflowException e) { throw new MarshalException("Not enough bytes to read a map"); } } public Map<K, V> deserializeForNativeProtocol(ByteBuffer bytes, ProtocolVersion version) { try { ByteBuffer input = bytes.duplicate(); int n = readCollectionSize(input, version); if (n < 0) throw new MarshalException("The data cannot be deserialized as a map"); // If the received bytes are not corresponding to a map, n might be a huge number. // In such a case we do not want to initialize the map with that initialCapacity as it can result // in an OOM when put is called (see CASSANDRA-12618). On the other hand we do not want to have to resize // the map if we can avoid it, so we put a reasonable limit on the initialCapacity. Map<K, V> m = new LinkedHashMap<K, V>(Math.min(n, 256)); for (int i = 0; i < n; i++) { ByteBuffer kbb = readValue(input, version); keys.validate(kbb); ByteBuffer vbb = readValue(input, version); values.validate(vbb); m.put(keys.deserialize(kbb), values.deserialize(vbb)); } if (input.hasRemaining()) throw new MarshalException("Unexpected extraneous bytes after map value"); return m; } catch (BufferUnderflowException e) { throw new MarshalException("Not enough bytes to read a map"); } } @Override public ByteBuffer getSerializedValue(ByteBuffer collection, ByteBuffer key, AbstractType<?> comparator) { try { ByteBuffer input = collection.duplicate(); int n = readCollectionSize(input, ProtocolVersion.V3); for (int i = 0; i < n; i++) { ByteBuffer kbb = readValue(input, ProtocolVersion.V3); int comparison = comparator.compareForCQL(kbb, key); if (comparison == 0) return readValue(input, ProtocolVersion.V3); else if (comparison > 0) // since the map is in sorted order, we know we've gone too far and the element doesn't exist return null; else // comparison < 0 skipValue(input, ProtocolVersion.V3); } return null; } catch (BufferUnderflowException e) { throw new MarshalException("Not enough bytes to read a map"); } } @Override public ByteBuffer getSliceFromSerialized(ByteBuffer collection, ByteBuffer from, ByteBuffer to, AbstractType<?> comparator, boolean frozen) { if (from == ByteBufferUtil.UNSET_BYTE_BUFFER && to == ByteBufferUtil.UNSET_BYTE_BUFFER) return collection; try { ByteBuffer input = collection.duplicate(); int n = readCollectionSize(input, ProtocolVersion.V3); int startPos = input.position(); int count = 0; boolean inSlice = from == ByteBufferUtil.UNSET_BYTE_BUFFER; for (int i = 0; i < n; i++) { int pos = input.position(); ByteBuffer kbb = readValue(input, ProtocolVersion.V3); // key // If we haven't passed the start already, check if we have now if (!inSlice) { int comparison = comparator.compareForCQL(from, kbb); if (comparison <= 0) { // We're now within the slice inSlice = true; startPos = pos; } else { // We're before the slice so we know we don't care about this element skipValue(input, ProtocolVersion.V3); // value continue; } } // Now check if we're done int comparison = to == ByteBufferUtil.UNSET_BYTE_BUFFER ? -1 : comparator.compareForCQL(kbb, to); if (comparison > 0) { // We're done and shouldn't include the key we just read input.position(pos); break; } // Otherwise, we'll include that element skipValue(input, ProtocolVersion.V3); // value ++count; // But if we know if was the last of the slice, we break early if (comparison == 0) break; } if (count == 0 && !frozen) return null; return copyAsNewCollection(collection, count, startPos, input.position(), ProtocolVersion.V3); } catch (BufferUnderflowException e) { throw new MarshalException("Not enough bytes to read a map"); } } public String toString(Map<K, V> value) { StringBuilder sb = new StringBuilder(); sb.append('{'); boolean isFirst = true; for (Map.Entry<K, V> element : value.entrySet()) { if (isFirst) isFirst = false; else sb.append(", "); sb.append(keys.toString(element.getKey())); sb.append(": "); sb.append(values.toString(element.getValue())); } sb.append('}'); return sb.toString(); } public Class<Map<K, V>> getType() { return (Class) Map.class; } }