Java NIO框架Netty教程(九) Object對象編/解碼
看到題目，有的同學可能會想，上回不是說過對象傳遞了嗎？是的，只是在Java NIO框架Netty教程(八) Object對象傳遞中，我們只是介紹如何使用Netty提供的編/解碼工具，完成對象的序列化。這節是想告訴你Netty具體是怎麽做的，也許有的同學想自己完成序列化呢？況且，對象的序列化，隨處可用：）
先看怎麽編碼。
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01.@Override
02.protected Object encode(ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
03.ChannelBufferOutputStream bout =
04.new ChannelBufferOutputStream(dynamicBuffer(
05.estimatedLength, ctx.getChannel().getConfig().getBufferFactory()));
06.bout.write(LENGTH_PLACEHOLDER);
07.ObjectOutputStream oout = new CompactObjectOutputStream(bout);
08.oout.writeObject(msg);
09.oout.flush();
10.oout.close();11.
12.ChannelBuffer encoded = bout.buffer();
13.encoded.setInt(0, encoded.writerIndex() - 4);
14.return encoded;
15.}
其實你早已經應該想到了，在Java中對對象的序列化自然跑不出ObjectOutputStream了。Netty這裏只是又做了一層包裝，在流的開頭增加了一個4字節的標誌位。所以，Netty聲明，該編碼和解碼的類必須配套使用，與單純的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.
解碼自然是先解析出多余的4位，然後再通過ObjectInputStream解析。
關於Java對象序列化的細節問題，不在文本討論的範圍內，不過不知您是否感興趣試試自己寫一個呢？所謂，多動手嘛。
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01./**
02.* Object編碼類
03.*
04.* @author lihzh
05.* @alia OneCoder
06.* @blog http://www.it165.net
07.*/
08.public class MyObjEncoder implements ChannelDownstreamHandler {
09.
10.@Override
11.public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)
12.throws Exception {
13.// 處理收發信息的情形
14.if (e instanceof MessageEvent) {
15.MessageEvent mEvent = (MessageEvent) e;
16.Object obj = mEvent.getMessage();
17.if (!(obj instanceof Command)) {
18.ctx.sendDownstream(e);
19.return;
20.}
21.ByteArrayOutputStream out = new ByteArrayOutputStream();
22.ObjectOutputStream oos = new ObjectOutputStream(out);
23.oos.writeObject(obj);
24.oos.flush();
25.oos.close();
26.ChannelBuffer buffer = ChannelBuffers.dynamicBuffer();
27.buffer.writeBytes(out.toByteArray());
28.e.getChannel().write(buffer);
29.} else {
30.// 其他事件，自動流轉。比如，bind，connected
31.ctx.sendDownstream(e);
32.}
33.}
34.}
35./**
36.* Object解碼類
37.*
38.* @author lihzh
39.* @alia OneCoder
40.* @blog http://www.it165.net
41.*/
42.public class MyObjDecoder implements ChannelUpstreamHandler {
43.
44.@Override
45.public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e)
46.throws Exception {
47.if (e instanceof MessageEvent) {
48.MessageEvent mEvent = (MessageEvent) e;
49.if (!(mEvent.getMessage() instanceof ChannelBuffer)) {
50.ctx.sendUpstream(mEvent);
51.return;
52.}
53.ChannelBuffer buffer = (ChannelBuffer) mEvent.getMessage();
54.ByteArrayInputStream input = new ByteArrayInputStream(buffer.array());
55.ObjectInputStream ois = new ObjectInputStream(input);
56.Object obj = ois.readObject();
57.Channels.fireMessageReceived(e.getChannel(), obj);
58.}
59.}
60.}
怎麽樣，是不是也好用？所謂，模仿，學以致用。
不過，提醒一下大家，這個實現裏有很多硬編碼的東西，切勿模仿，只是為了展示Object，編解碼的處理方式和在Netty中的應用而已。
Java NIO框架Netty教程(九) Object對象編/解碼