DefaultIoFilterChainBuilder chain = acceptor.getFilterChain();

    MdcInjectionFilter mdcInjectionFilter = new MdcInjectionFilter();
    chain.addLast("mdc", mdcInjectionFilter);

3.源碼解讀_DefaultIoFilterChainBuilder

        1.DefaultIoFilterChainBuilder內部維護一個Entry的列表
                List<Entry> entries = new CopyOnWriteArrayList<Entry>();

        2.public synchronized void addLast(String name, IoFilter filter) 內部調用register方法:register(entries.size(), new EntryImpl(name, filter))
                其核心代碼為:entries.add(index, e);
          同理其內部addFirst/addBore/addAfter,均是將filter-pair(Entry)加入到list的不同位置.
       
        3.其實現IoFilterChainBuilder接口內的方法:buildFilterChain(IoFilterChain chain)
                for (Entry e : entries) {
                        chain.addLast(e.getName(), e.getFilter());
                 }
            即調用IoFilerChain的方法組裝filter
       
        ->所以IoFilterChainBuilder是IoFilerChain的構建接口.

4.源碼解讀_DefaultIoFilterChain

        1.其整體內部實現了一個雙向鏈表.
                這里從head,tail以及EntryImpl的定義prevEntry/nextEntry可見一斑.

        2.public synchronized void addLast(String name, IoFilter filter)->內部調用register方法:register(tail.prevEntry, name, filter)
                將尾部指針的前驅節點(tail.prevEntry)傳入作為新節點的前驅節點->
                ->將tail.prevEntry.nextEntry這里即tail作為新節點的后繼節點

        3.private void register(EntryImpl prevEntry, String name, IoFilter filter)
                1.新建節點newEntry
                2.調用filter.onPreAdd
                3.調整鏈表的前驅后繼關系并將newEntry加入Map<String, Entry> name2entry
                4.調用filter.onPostAdd

5.源碼解讀_NextFilter

        1.DefaultIoFilterChain中節點EntryImpl中有一個private final NextFilter nextFilter
                ->其表示當前節點filter的下一個IoFilter

        2.EntryImp初始化nextFiler是用一個匿名內部類初始化并覆寫接口方法
                1.messageReceived(IoSession session, Object message)
                        ->調用callNextMessageReceived(nextEntry,session,message),其中nextEntry為當前節點的后繼節點
                        ->后繼節點執行filter.messageReceived(nextFilter, session, message),其中nextFiler為后繼節點的NextFiler對象.

                也就是說每個Filter的實現類如果在messageReceived(NextFilter nextFilter, IoSession session, Object message)中調用了nextFiler.messageReceive方法，則表示沿著過濾鏈繼續forward>>>>>>.而IoFilterAdapter的默認實現則是這樣.

                2.filterWrite(IoSession session, WriteRequest writeRequest)
                        ->調用callPreviousFilterWrite(nextEntry, session, writeRequest),其中nextEntry為當前節點的前驅節點
                        ->前驅節點執行filter.filterWrite(nextFilter, session, writeRequest),其中nextFiler為前驅節點的NextFiler對象.

                同上,即每個Filer的實現類如果在filterWrite(NextFilter nextFilter, IoSession session, WriteRequest writeRequest)中調用了nextFilter.filterWrite方法，則表示沿著過濾鏈繼續forward<<<<<<<.

6.源碼解讀_HeadFilter

     1.此為DefaultIoFilterChain中頭結點的過濾器.

     2.此過濾器繼承了IoFilterAdapter,所以其messageReceived方法默認調用了nextFiler.messageReceived方法,即收到消息不處理，直接轉發后繼節點進行過濾處理.

     3.其主要覆寫了filterWrite(NextFilter nextFilter, IoSession session, WriteRequest writeRequest) 方法
      ->由processor處理write.

7.源碼解讀_TailFilter

     1.此為DefaultIoFilterChain中尾節點的過濾器.

     2.其繼承了IoFilterAdapter并覆寫了所有方法:
      其中sessionCreated/sessionOpened/sessionIdle/exceptionCaught/messageReceived/messageSent均調用了session.getHandler()的相關方法,即IoHandler,這個我們經常用到且經常寫的IoHandler.
     而filterWrite/filterClose則直接調用nextFilter.相關方法,即繼續沿著過濾鏈<<<<<forward.

8源碼解讀_ProtocolCodecFilter
     1.此為編解碼過濾器,用來編碼為二進制數據或者將特定協議的數據解碼成消息對象.

     2.其覆寫了messageReceived:
          1.一個while循環,直到buffer沒有數據.while(in.hasRemaining)
          2.循環內業務為調用decoder.decode方法進行解碼
          3.調用decoderOut.flush完成解碼->{@link ProtocolDecoderOutputImpl #flush}->調用nextFilter.messageReceived,即繼續在過濾鏈進行forward>>>>>>

     3.其覆寫了filterWrite
          1.調用encoder.encoder進行編碼
          2.調用nextFilter.filterWrite,即繼續沿著過濾鏈進行<<<<<<forward

8.總結
    mina的內部采用filer_chain模式進行消息的流轉(雙向)處理

    以讀寫消息來簡單的說明一下filter_chain過程:

       1.processor...binary_msg-->>HeadFilter#messageReceived-->>....-->>XXXFilter#messageReceived...-->>TailFilter#messageReceived-->>調用IoHandler#messageReceived
 在HeadFilter和TailFilter之間自定義過濾器,如firewall,log,decoder等

      2.procotol_msg-->>TailFilter#filterWrite-->>....-->>XXXFilter#FilterWrite....-->>HeaderFilter-->>由processor處理write
 在TailFilter和HeadFiler之間可自定義過濾器,如encoder等.