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Java example source code file (ProtobufDecoder.java)

This example Java source code file (ProtobufDecoder.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

bytebuf, exception, extensionregistrylite, has_parser, list, messagelite, messagetomessagedecoder, nullpointerexception, override, protobufdecoder, sharable, throwable, util

The ProtobufDecoder.java Java example source code

/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project 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 io.netty.handler.codec.protobuf;

import com.google.protobuf.ExtensionRegistry;
import com.google.protobuf.ExtensionRegistryLite;
import com.google.protobuf.Message;
import com.google.protobuf.MessageLite;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.MessageToMessageDecoder;

import java.util.List;

/**
 * Decodes a received {@link ByteBuf} into a
 * <a href="http://code.google.com/p/protobuf/">Google Protocol Buffers
 * {@link Message} and {@link MessageLite}. Please note that this decoder must
 * be used with a proper {@link ByteToMessageDecoder} such as {@link ProtobufVarint32FrameDecoder}
 * or {@link LengthFieldBasedFrameDecoder} if you are using a stream-based
 * transport such as TCP/IP. A typical setup for TCP/IP would be:
 * <pre>
 * {@link ChannelPipeline} pipeline = ...;
 *
 * // Decoders
 * pipeline.addLast("frameDecoder",
 *                  new {@link LengthFieldBasedFrameDecoder}(1048576, 0, 4, 0, 4));
 * pipeline.addLast("protobufDecoder",
 *                  new {@link ProtobufDecoder}(MyMessage.getDefaultInstance()));
 *
 * // Encoder
 * pipeline.addLast("frameEncoder", new {@link LengthFieldPrepender}(4));
 * pipeline.addLast("protobufEncoder", new {@link ProtobufEncoder}());
 * </pre>
 * and then you can use a {@code MyMessage} instead of a {@link ByteBuf}
 * as a message:
 * <pre>
 * void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
 *     MyMessage req = (MyMessage) msg;
 *     MyMessage res = MyMessage.newBuilder().setText(
 *                               "Did you say '" + req.getText() + "'?").build();
 *     ch.write(res);
 * }
 * </pre>
 */
@Sharable
public class ProtobufDecoder extends MessageToMessageDecoder<ByteBuf> {

    private static final boolean HAS_PARSER;

    static {
        boolean hasParser = false;
        try {
            // MessageLite.getParsetForType() is not available until protobuf 2.5.0.
            MessageLite.class.getDeclaredMethod("getParserForType");
            hasParser = true;
        } catch (Throwable t) {
            // Ignore
        }

        HAS_PARSER = hasParser;
    }

    private final MessageLite prototype;
    private final ExtensionRegistryLite extensionRegistry;

    /**
     * Creates a new instance.
     */
    public ProtobufDecoder(MessageLite prototype) {
        this(prototype, null);
    }

    public ProtobufDecoder(MessageLite prototype, ExtensionRegistry extensionRegistry) {
        this(prototype, (ExtensionRegistryLite) extensionRegistry);
    }

    public ProtobufDecoder(MessageLite prototype, ExtensionRegistryLite extensionRegistry) {
        if (prototype == null) {
            throw new NullPointerException("prototype");
        }
        this.prototype = prototype.getDefaultInstanceForType();
        this.extensionRegistry = extensionRegistry;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf msg, List<Object> out)
            throws Exception {
        final byte[] array;
        final int offset;
        final int length = msg.readableBytes();
        if (msg.hasArray()) {
            array = msg.array();
            offset = msg.arrayOffset() + msg.readerIndex();
        } else {
            array = new byte[length];
            msg.getBytes(msg.readerIndex(), array, 0, length);
            offset = 0;
        }

        if (extensionRegistry == null) {
            if (HAS_PARSER) {
                out.add(prototype.getParserForType().parseFrom(array, offset, length));
            } else {
                out.add(prototype.newBuilderForType().mergeFrom(array, offset, length).build());
            }
        } else {
            if (HAS_PARSER) {
                out.add(prototype.getParserForType().parseFrom(
                        array, offset, length, extensionRegistry));
            } else {
                out.add(prototype.newBuilderForType().mergeFrom(
                        array, offset, length, extensionRegistry).build());
            }
        }
    }
}

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