Java NIO框架Netty教程(九)
阿新 • • 發佈:2018-12-23
看到題目,有的同學可能會想,上回不是說過物件傳遞了嗎?是的,只是在《Java NIO框架Netty教程(八)-Object物件傳遞》中,我們只是介紹如何使用Netty提供的編/解碼工具,完成物件的序列化。這節是想告訴你Netty具體是怎麼做的,也許有的同學想自己完成序列化呢?況且,物件的序列化,隨處可用:) 先看怎麼編碼。
@Override
protected Object encode(ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
ChannelBufferOutputStream bout =
new ChannelBufferOutputStream(dynamicBuffer(
estimatedLength, ctx.getChannel().getConfig().getBufferFactory()));
bout.write(LENGTH_PLACEHOLDER);
ObjectOutputStream oout = new CompactObjectOutputStream(bout);
oout.writeObject(msg);
oout .flush();
oout.close();
ChannelBuffer encoded = bout.buffer();
encoded.setInt(0, encoded.writerIndex() - 4);
return encoded;
}
其實你早已經應該想到了,在Java中對物件的序列化自然跑不出ObjectOutputStream了。Netty這裡只是又做了一層包裝,在流的開頭增加了一個4位元組的標誌位。所以,Netty宣告,該編碼和解碼的類必須配套使用,與單純的ObjectIntputStream不相容。
* An encoder which serializes a Java object into a {@link ChannelBuffer}.<br />
* <p><br />
* Please note that the serialized form this encoder produces is not<br />
* compatible with the standard {@link ObjectInputStream}. Please use<br />
* {@link ObjectDecoder} or {@link ObjectDecoderInputStream} to ensure the<br />
* interoperability with this encoder.</p>
那麼解碼,自然是先解析出多餘的4位,然後再通過ObjectInputStream解析。
關於Java物件序列化的細節問題,不在文字討論的範圍內,不過不知您是否感興趣試試自己寫一個呢?所謂,多動手嘛。
/**
* Object編碼類
*
* @author lihzh
* @alia OneCoder
* @blog http://www.coderli.com
*/
public class MyObjEncoder implements ChannelDownstreamHandler {
@Override
public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)
throws Exception {
// 處理收發資訊的情形
if (e instanceof MessageEvent) {
MessageEvent mEvent = (MessageEvent) e;
Object obj = mEvent.getMessage();
if (!(obj instanceof Command)) {
ctx.sendDownstream(e);
return;
}
ByteArrayOutputStream out = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(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,自動流轉。比如,bind,connected
ctx.sendDownstream(e);
}
}
}
/**
* Object解碼類
*
* @author lihzh
* @alia OneCoder
* @blog http://www.coderli.com
*/
public class MyObjDecoder implements ChannelUpstreamHandler {
@Override
public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e)
throws Exception {
if (e instanceof MessageEvent) {
MessageEvent mEvent = (MessageEvent) e;
if (!(mEvent.getMessage() instanceof ChannelBuffer)) {
ctx.sendUpstream(mEvent);
return;
}
ChannelBuffer buffer = (ChannelBuffer) mEvent.getMessage();
ByteArrayInputStream input = new ByteArrayInputStream(buffer.array());
ObjectInputStream ois = new ObjectInputStream(input);
Object obj = ois.readObject();
Channels.fireMessageReceived(e.getChannel(), obj);
}
}
}
怎麼樣,是不是也好用?所謂,模仿,學以致用。
不過,提醒一下大家,這個實現裡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。