这一层主要是用于实现网络通信，现在都是基于Tcp/Ip，而Tcp/Ip协议栈由socket来实现，换句话说就是现在网络通信服务底层大都是通过socket实现的，在thrift源码中，就是将socket包装成各种transport来使用。
TTransport:这是一个基类，并且是一个抽象类。
TIOStreamTransport继承TTransport类，是最常用的base transport, It takes an InputStream and an OutputStream and uses those to perform all transport operations.主要是由inputStream和OutputStream进行读写操作，主要有open,close,read,write,flush等方法。代码如下：
1 public class TIOStreamTransport extends TTransport { 2 3 private static final Logger LOGGER = LoggerFactory.getLogger(TIOStreamTransport.class.getName()); 4 5 /** Underlying inputStream */ 6 protected InputStream inputStream_ = null; 7 8 /** Underlying outputStream */ 9 protected OutputStream outputStream_ = null; 10 11 /** 12 * Subclasses can invoke the default constructor and then assign the input 13 * streams in the open method. 14 */ 15 protected TIOStreamTransport() {} 16 17 /** 18 * Input stream constructor. 19 * 20 * @param is Input stream to read from 21 */ 22 public TIOStreamTransport(InputStream is) { 23 inputStream_ = is; 24 } 25 26 /** 27 * Output stream constructor. 28 * 29 * @param os Output stream to read from 30 */ 31 public TIOStreamTransport(OutputStream os) { 32 outputStream_ = os; 33 } 34 35 /** 36 * Two-way stream constructor. 37 * 38 * @param is Input stream to read from 39 * @param os Output stream to read from 40 */ 41 public TIOStreamTransport(InputStream is, OutputStream os) { 42 inputStream_ = is; 43 outputStream_ = os; 44 } 45 46 /** 47 * The streams must already be open at construction time, so this should 48 * always return true. 49 * 50 * @return true 51 */ 52 public boolean isOpen() { 53 return true; 54 } 55 56 /** 57 * The streams must already be open. This method does nothing. 58 */ 59 public void open() throws TTransportException {} 60 61 /** 62 * Closes both the input and output streams. 63 */ 64 public void close() { 65 if (inputStream_ != null) { 66 try { 67 inputStream_.close(); 68 } catch (IOException iox) { 69 LOGGER.warn("Error closing input stream.", iox); 70 } 71 inputStream_ = null; 72 } 73 if (outputStream_ != null) { 74 try { 75 outputStream_.close(); 76 } catch (IOException iox) { 77 LOGGER.warn("Error closing output stream.", iox); 78 } 79 outputStream_ = null; 80 } 81 } 82 83 /** 84 * Reads from the underlying input stream if not null. 85 */ 86 public int read(byte[] buf, int off, int len) throws TTransportException { 87 if (inputStream_ == null) { 88 throw new TTransportException(TTransportException.NOT_OPEN, "Cannot read from null inputStream"); 89 } 90 int bytesRead; 91 try { 92 bytesRead = inputStream_.read(buf, off, len); 93 } catch (IOException iox) { 94 throw new TTransportException(TTransportException.UNKNOWN, iox); 95 } 96 if (bytesRead < 0) { 97 throw new TTransportException(TTransportException.END_OF_FILE); 98 } 99 return bytesRead;100 }101 102 /**103 * Writes to the underlying output stream if not null.104 */105 public void write(byte[] buf, int off, int len) throws TTransportException {106 if (outputStream_ == null) {107 throw new TTransportException(TTransportException.NOT_OPEN, "Cannot write to null outputStream");108 }109 try {110 outputStream_.write(buf, off, len);111 } catch (IOException iox) {112 throw new TTransportException(TTransportException.UNKNOWN, iox);113 }114 }115 116 /**117 * Flushes the underlying output stream if not null.118 */119 public void flush() throws TTransportException {120 if (outputStream_ == null) {121 throw new TTransportException(TTransportException.NOT_OPEN, "Cannot flush null outputStream");122 }123 try {124 outputStream_.flush();125 } catch (IOException iox) {126 throw new TTransportException(TTransportException.UNKNOWN, iox);127 }128 }129 } TSocket继承了TIOStreamTransport类，封装了Socket接口，含有host,port,socket,timeout几个私有变量，并且有open,isOpen,initSocket,getSocket,setTimeout方法，由于继承自TIOStreamTransport,因此父类的读写方法都可以使用，也就是说TSocket的通信根本还是使用的输入输出流。
TserverSocket继承自TserverTransport,
TNoblockingServerTransport继承自TserverTransport,
TNoblockingServerSocket继承自TNoblockingServerTransport
图中的XoaServerTransport暂时忽略（公司内部xoa框架使用)
以上是用于服务端，而客户端则如右下图所示，不再赘述。
