Java NIO框架Netty教程(九)-Object对象编/解码

看到题目，有的同学可能会想，上回不是说过对象传递了吗？是的，只是在《Java NIO框架Netty教程(八)-Object对象传递》中，我们只是介绍如何使用Netty提供的编/解码工具，完成对象的序列化。这节是想告诉你Netty具体是怎么做的，也许有的同学想自己完成序列化呢？况且，对象的序列化，随处可用：）

先看怎么编码。

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ObjectEncoder.java

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@Override

    protectedObject encode(ChannelHandlerContext ctx, Channel channel, Object msg) throwsException {

        ChannelBufferOutputStream bout =

            newChannelBufferOutputStream(dynamicBuffer(

                    estimatedLength, ctx.getChannel().getConfig().getBufferFactory()));

        bout.write(LENGTH_PLACEHOLDER);

        ObjectOutputStream oout = newCompactObjectOutputStream(bout);

        oout.writeObject(msg);

        oout.flush();

        oout.close();

 

        ChannelBuffer encoded = bout.buffer();

        encoded.setInt(0, encoded.writerIndex() - 4);

        returnencoded;

    }

其实你早已经应该想到了，在Java中对对象的序列化自然跑不出ObjectOutputStream了。Netty这里只是又做了一层包装，在流的开头增加了一个4字节的标志位。所以，Netty声明，该编码和解码的类必须配套使用，与单纯的ObjectIntputStream不兼容。

* An encoder which serializes a Java object into a {@link ChannelBuffer}.
* <p>
* Please note that the serialized form this encoder produces is not
* compatible with the standard {@link ObjectInputStream}.  Please use
* {@link ObjectDecoder} or {@link ObjectDecoderInputStream} to ensure the
* interoperability with this encoder.

解码自然是先解析出多余的4位，然后再通过ObjectInputStream解析。

关于Java对象序列化的细节问题，不在文本讨论的范围内，不过不知您是否感兴趣试试自己写一个呢？所谓，多动手嘛。

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/**

 * Object编码类

 *

 * @author lihzh

 * @alia OneCoder

 * @blog http://www.coderli.com

 */

publicclass MyObjEncoder implementsChannelDownstreamHandler {

 

    @Override

    publicvoid handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)

            throwsException {

        // 处理收发信息的情形

        if(e instanceofMessageEvent) {

            MessageEvent mEvent = (MessageEvent) e;

            Object obj = mEvent.getMessage();

            if(!(obj instanceofCommand)) {

                ctx.sendDownstream(e);

                return;

            }

            ByteArrayOutputStream out = newByteArrayOutputStream();

            ObjectOutputStream oos = newObjectOutputStream(out);

            oos.writeObject(obj);

            oos.flush();

            oos.close();

            ChannelBuffer buffer = ChannelBuffers.dynamicBuffer();

            buffer.writeBytes(out.toByteArray());

            e.getChannel().write(buffer);

        }else{

            // 其他事件，自动流转。比如，bind，connected

            ctx.sendDownstream(e);

        }

    }

}

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/**

 * Object解码类

 *

 * @author lihzh

 * @alia OneCoder

 * @blog http://www.coderli.com

 */

publicclass MyObjDecoder implementsChannelUpstreamHandler {

 

    @Override

    publicvoid handleUpstream(ChannelHandlerContext ctx, ChannelEvent e)

            throwsException {

        if(e instanceofMessageEvent) {

            MessageEvent mEvent = (MessageEvent) e;

            if(!(mEvent.getMessage() instanceofChannelBuffer)) {

                ctx.sendUpstream(mEvent);

                return;

            }

            ChannelBuffer buffer = (ChannelBuffer) mEvent.getMessage();

            ByteArrayInputStream input = newByteArrayInputStream(buffer.array());

            ObjectInputStream ois = newObjectInputStream(input);

            Object obj = ois.readObject();

            Channels.fireMessageReceived(e.getChannel(), obj);

        }

    }

}

怎么样，是不是也好用？所谓，模仿，学以致用。

不过，提醒一下大家，这个实现里有很多硬编码的东西，切勿模仿，只是为了展示Object，编解码的处理方式和在Netty中的应用而已。

如非特别注明，本站内容均为OneCoder原创，转载请务必注明作者和原始出处。
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