Apache Mina 学习笔记(4) - Filters

IoFilter是MINA的另外一个核心部分，他为IoService 和 IoHandler filters所有的I/O事件和请求，类似于web中的servlet filter.

在本教程中，我们会开发一个实际例子中的IoFilter，通常它很容易实现，但是你可能需要了解一些MINA内部的细节。

下面是一些已经存在着的Filter：

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

你可以继承IoAdapter代替直接实现的IoFilter，除非重写，否则任何接受到的事件都会被通过下面的filter：

public class MyFilter extends IoFilterAdapter {
    @Override
    public void sessionOpened(NextFilter nextFilter, IoSession session) throws Exception {
        // Some logic here...
        nextFilter.sessionOpened(session);
        // Some other logic here...
    }
}

Transforming a Write Request

Be Careful When Filtering sessionCreated Event

Watch out the Empty Buffers!