apache mina 学习（七）-----IoFilter

IoFilter是mina中一个非常重要的设计，它可以过滤IoService和IoHandler之间的所有的io流，经常会用到的过滤器：

1、日志过滤器LoggingFilter

2、协议编码过滤器ProtocolCodecFilter（可以把输入的bytebuffer转换为pojo）

3、压缩过滤器CompressionFilter用于压缩数据

4、sslFilter用于支持ssl

已经存在的过滤器及实现类：

Filter class Description

Blacklist	BlacklistFilter	Blocks connections from blacklisted remote addresses
Buffered Write	BufferedWriteFilter	Buffers outgoing requests like the BufferedOutputStream does
Compression	CompressionFilter
ConnectionThrottle	ConnectionThrottleFilter
ErrorGenerating	ErrorGeneratingFilter
Executor	ExecutorFilter
FileRegionWrite	FileRegionWriteFilter
KeepAlive	KeepAliveFilter
Logging	LoggingFilter	Logs event messages, like MessageReceived, MessageSent, SessionOpened, ...
MDC Injection	MdcInjectionFilter	Inject key IoSession properties into the MDC
Noop	NoopFilter	A filter that does nothing. Useful for tests.
Profiler	ProfilerTimerFilter	Profile event messages, like MessageReceived, MessageSent, SessionOpened, ...
ProtocolCodec	ProtocolCodecFilter	A filter in charge of encoding and decoding messages
Proxy	ProxyFilter
Reference counting	ReferenceCountingFilter	Keeps track of the number of usages of this filter
RequestResponse	RequestResponseFilter
SessionAttributeInitializing	SessionAttributeInitializingFilter
StreamWrite	StreamWriteFilter
SslFilter	SslFilter
WriteRequest	WriteRequestFilter

如果想实现自己的Filter只需集成

IoFilterAdapter抽象类即可。

下面是一个字节数组过滤成字符的Filter例子：

public void filterWrite(NextFilter nextFilter, IoSession session, WriteRequest request) {
    String m = (String) request.getMessage();
    ByteBuffer newBuffer = new MyByteBuffer(m, ByteBuffer.wrap(m.getBytes());

    nextFilter.filterWrite(
            session, new WriteRequest(newBuffer, request.getFuture(), request.getDestination()));
}

public void messageSent(NextFilter nextFilter, IoSession session, Object message) {
    if (message instanceof MyByteBuffer) {
        nextFilter.messageSent(session, ((MyByteBuffer) message).originalValue);
    } else {
        nextFilter.messageSent(session, message);
    }
}

private static class MyByteBuffer extends ByteBufferProxy {
    private final Object originalValue;
    private MyByteBuffer(Object originalValue, ByteBuffer encodedValue) {
        super(encodedValue);
        this.originalValue = originalValue;
    }
}