从前面几小节的学习，我们可能知道在发送和接收消息重要的类ConnectionFactory， Connection，Channel和 QueueingConsumer。
ConntectionFactory类是方便创建与AMQP代理相关联的Connection；下面来看看ConntectionFactory是如何创建一个Contention.
首先通过new ConnectionFactory()创建一个ConnectionFactory；并设置此连接工厂的主机设置为localhost。通过ConnectionFactory的newConnection()方法 创建一个Connection; newConnection方法通过得到当前连接的地址及端口号来获得一个Address，通过createFrameHandler的方法 来得到FrameHandler;再通过new AMQConnection(this, frameHandler)来得到Connection并启动。如代码清单7-1所示。
代码清单7-1 创建Connection的源码（ConnectionFactory.java中）
1. protected FrameHandler createFrameHandler(Address addr)
2. throws IOException {
3.
4. String hostName = addr.getHost();
5. int portNumber = portOrDefault(addr.getPort());//得到端口号
6. Socket socket = factory.createSocket();
7. configureSocket(socket);//这里Socket通过TCP无迟延的协议
8. socket.connect(new InetSocketAddress(hostName, portNumber), connectionTimeout);
9. return createFrameHandler(socket);
10. }
11.
12. protected FrameHandler createFrameHandler(Socket sock)
13. throws IOException
14. {
15. return new SocketFrameHandler(sock);
16. }
17.
18. /**
19. * Provides a hook to insert custom configuration of the sockets
20. * used to connect to an AMQP server before they connect.
21. *
22. * The default behaviour of this method is to disable Nagle's
23. * algorithm to get more consistently low latency. However it
24. * may be overridden freely and there is no requirement to retain
25. * this behaviour.
26. *
27. * @param socket The socket that is to be used for the Connection
28. */
29. protected void configureSocket(Socket socket) throws IOException{
30. // disable Nagle's algorithm, for more consistently low latency
31. socket.setTcpNoDelay(true);
32. }
33.
34. /**
35. * Create a new broker connection
36. * @param addrs an array of known broker addresses (hostname/port pairs) to try in order
37. * @return an interface to the connection
38. * @throws IOException if it encounters a problem
39. */
40. public Connection newConnection(Address[] addrs)
41. throws IOException
42. {
43. IOException lastException = null;
44. for (Address addr : addrs) {
45. try {
46. FrameHandler frameHandler = createFrameHandler(addr);
47. AMQConnection conn = new AMQConnection(this,
48. frameHandler);
49. conn.start();
50. return conn;
51. } catch (IOException e) {
52. lastException = e;
53. }
54. }
55.
56. if (lastException == null) {
57. throw new IOException("failed to connect");
58. } else {
59. throw lastException;
60. }
61. }
62.
63. /**
64. * Create a new broker connection
65. * @return an interface to the connection
66. * @throws IOException if it encounters a problem
67. */
68. public Connection newConnection() throws IOException {
69. return newConnection(new Address[] {
70. new Address(getHost(), getPort())});
71. }
代码清单7-2 连接启动
/**
* Start up the connection, including the MainLoop thread.
* Sends the protocol
* version negotiation header, and runs through
* Connection.Start/.StartOk, Connection.Tune/.TuneOk, and then
* calls Connection.Open and waits for the OpenOk. Sets heartbeat
* and frame max values after tuning has taken place.
* @throws java.io.IOException if an error is encountered; IOException
* subtypes {@link ProtocolVersionMismatchException} and
* {@link PossibleAuthenticationFailureException} will be thrown in the
* corresponding circumstances.
*/
public void start()
throws IOException
{
// Make sure that the first thing we do is to send the header,
// which should cause any socket errors to show up for us, rather
// than risking them pop out in the MainLoop
AMQChannel.SimpleBlockingRpcContinuation connStartBlocker =
new AMQChannel.SimpleBlockingRpcContinuation();
// We enqueue an RPC continuation here without sending an RPC
// request, since the protocol specifies that after sending
// the version negotiation header, the client (connection
// initiator) is to wait for a connection.start method to
// arrive.
_channel0.enqueueRpc(connStartBlocker);
// The following two lines are akin to AMQChannel's
// transmit() method for this pseudo-RPC.
_frameHandler.setTimeout(HANDSHAKE_TIMEOUT);
_frameHandler.sendHeader();
// start the main loop going
Thread ml = new MainLoop();
ml.setName("AMQP Connection " + getHostAddress() + ":" + getPort());
ml.start();
AMQP.Connection.Start connStart = null;
try {
connStart =
(AMQP.Connection.Start) connStartBlocker.getReply().getMethod();
_serverProperties = connStart.getServerProperties();
Version serverVersion =
new Version(connStart.getVersionMajor(),
connStart.getVersionMinor());
if (!Version.checkVersion(clientVersion, serverVersion)) {
_frameHandler.close(); //this will cause mainLoop to terminate
throw new ProtocolVersionMismatchException(clientVersion,
serverVersion);
}
} catch (ShutdownSignalException sse) {
throw AMQChannel.wrap(sse);
}
String[] mechanisms = connStart.getMechanisms().toString().split(" ");
SaslMechanism sm = _factory.getSaslConfig().getSaslMechanism(mechanisms);
if (sm == null) {
throw new IOException("No compatible authentication mechanism found - " +
"server offered [" + connStart.getMechanisms() + "]");
}
LongString challenge = null;
LongString response = sm.handleChallenge(null, _factory);
AMQP.Connection.Tune connTune = null;
do {
Method method = (challenge == null)
? new AMQImpl.Connection.StartOk(_clientProperties,
sm.getName(),
response, "en_US")
: new AMQImpl.Connection.SecureOk(response);
try {
Method serverResponse = _channel0.rpc(method).getMethod();
if (serverResponse instanceof AMQP.Connection.Tune) {
connTune = (AMQP.Connection.Tune) serverResponse;
} else {
challenge = ((AMQP.Connection.Secure) serverResponse).getChallenge();
response = sm.handleChallenge(challenge, _factory);
}
} catch (ShutdownSignalException e) {
throw new PossibleAuthenticationFailureException(e);
}
} while (connTune == null);
int channelMax =
negotiatedMaxValue(_factory.getRequestedChannelMax(),
connTune.getChannelMax());
_channelManager = new ChannelManager(channelMax);
int frameMax =
negotiatedMaxValue(_factory.getRequestedFrameMax(),
connTune.getFrameMax());
setFrameMax(frameMax);
int heartbeat =
negotiatedMaxValue(_factory.getRequestedHeartbeat(),
connTune.getHeartbeat());
setHeartbeat(heartbeat);
_channel0.transmit(new AMQImpl.Connection.TuneOk(channelMax,
frameMax,
heartbeat));
// 0.9.1: insist [on not being redirected] is deprecated, but
// still in generated code; just pass a dummy value here
_channel0.exnWrappingRpc(new AMQImpl.Connection.Open(_virtualHost,
"",
false)).getMethod();
return;
}
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