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。
