httpclient connect连接请求方法源码解读

public interface HttpClientConnectionOperator {

    void connect(
            ManagedHttpClientConnection conn,
            HttpHost host,
            InetSocketAddress localAddress,
            int connectTimeout,
            SocketConfig socketConfig,
            HttpContext context) throws IOException;

    void upgrade(
            ManagedHttpClientConnection conn,
            HttpHost host,
            HttpContext context) throws IOException;

}

public class DefaultHttpClientConnectionOperator implements HttpClientConnectionOperator {
    static final String SOCKET_FACTORY_REGISTRY = "http.socket-factory-registry";
    private final Log log = LogFactory.getLog(getClass());
    private final Lookup<ConnectionSocketFactory> socketFactoryRegistry;
    private final SchemePortResolver schemePortResolver;
    private final DnsResolver dnsResolver;
    public DefaultHttpClientConnectionOperator(
            final Lookup<ConnectionSocketFactory> socketFactoryRegistry,
            final SchemePortResolver schemePortResolver,
            final DnsResolver dnsResolver) {
        super();
        Args.notNull(socketFactoryRegistry, "Socket factory registry");
        this.socketFactoryRegistry = socketFactoryRegistry;
        this.schemePortResolver = schemePortResolver != null ? schemePortResolver :
            DefaultSchemePortResolver.INSTANCE;
        this.dnsResolver = dnsResolver != null ? dnsResolver :
            SystemDefaultDnsResolver.INSTANCE;
    }
    //......
    public void connect(
            final ManagedHttpClientConnection conn,
            final HttpHost host,
            final InetSocketAddress localAddress,
            final int connectTimeout,
            final SocketConfig socketConfig,
            final HttpContext context) throws IOException {
        final Lookup<ConnectionSocketFactory> registry = getSocketFactoryRegistry(context);
        final ConnectionSocketFactory sf = registry.lookup(host.getSchemeName());
        if (sf == null) {
            throw new UnsupportedSchemeException(host.getSchemeName() +
                    " protocol is not supported");
        }
        final InetAddress[] addresses = host.getAddress() != null ?
                new InetAddress[] { host.getAddress() } : this.dnsResolver.resolve(host.getHostName());
        final int port = this.schemePortResolver.resolve(host);
        for (int i = 0; i < addresses.length; i++) {
            final InetAddress address = addresses[i];
            final boolean last = i == addresses.length - 1;
            Socket sock = sf.createSocket(context);
            sock.setSoTimeout(socketConfig.getSoTimeout());
            sock.setReuseAddress(socketConfig.isSoReuseAddress());
            sock.setTcpNoDelay(socketConfig.isTcpNoDelay());
            sock.setKeepAlive(socketConfig.isSoKeepAlive());
            if (socketConfig.getRcvBufSize() > 0) {
                sock.setReceiveBufferSize(socketConfig.getRcvBufSize());
            }
            if (socketConfig.getSndBufSize() > 0) {
                sock.setSendBufferSize(socketConfig.getSndBufSize());
            }
            final int linger = socketConfig.getSoLinger();
            if (linger >= 0) {
                sock.setSoLinger(true, linger);
            }
            conn.bind(sock);
            final InetSocketAddress remoteAddress = new InetSocketAddress(address, port);
            if (this.log.isDebugEnabled()) {
                this.log.debug("Connecting to " + remoteAddress);
            }
            try {
                sock = sf.connectSocket(
                        connectTimeout, sock, host, remoteAddress, localAddress, context);
                conn.bind(sock);
                if (this.log.isDebugEnabled()) {
                    this.log.debug("Connection established " + conn);
                }
                return;
            } catch (final SocketTimeoutException ex) {
                if (last) {
                    throw new ConnectTimeoutException(ex, host, addresses);
                }
            } catch (final ConnectException ex) {
                if (last) {
                    final String msg = ex.getMessage();
                    throw "Connection timed out".equals(msg)
                                    ? new ConnectTimeoutException(ex, host, addresses)
                                    : new HttpHostConnectException(ex, host, addresses);
                }
            } catch (final NoRouteToHostException ex) {
                if (last) {
                    throw ex;
                }
            }
            if (this.log.isDebugEnabled()) {
                this.log.debug("Connect to " + remoteAddress + " timed out. " +
                        "Connection will be retried using another IP address");
            }
        }
    }
}

public class PlainConnectionSocketFactory implements ConnectionSocketFactory {

    public static final PlainConnectionSocketFactory INSTANCE = new PlainConnectionSocketFactory();

    public static PlainConnectionSocketFactory getSocketFactory() {
        return INSTANCE;
    }

    public PlainConnectionSocketFactory() {
        super();
    }

    @Override
    public Socket createSocket(final HttpContext context) throws IOException {
        return new Socket();
    }

    @Override
    public Socket connectSocket(
            final int connectTimeout,
            final Socket socket,
            final HttpHost host,
            final InetSocketAddress remoteAddress,
            final InetSocketAddress localAddress,
            final HttpContext context) throws IOException {
        final Socket sock = socket != null ? socket : createSocket(context);
        if (localAddress != null) {
            sock.bind(localAddress);
        }
        try {
            sock.connect(remoteAddress, connectTimeout);
        } catch (final IOException ex) {
            try {
                sock.close();
            } catch (final IOException ignore) {
            }
            throw ex;
        }
        return sock;
    }

}

private SocketConfig resolveSocketConfig(final HttpHost host) {
        SocketConfig socketConfig = this.configData.getSocketConfig(host);
        if (socketConfig == null) {
            socketConfig = this.configData.getDefaultSocketConfig();
        }
        if (socketConfig == null) {
            socketConfig = SocketConfig.DEFAULT;
        }
        return socketConfig;
    }

public void setDefaultSocketConfig(final SocketConfig defaultSocketConfig) {
        this.configData.setDefaultSocketConfig(defaultSocketConfig);
    }

    public void setSocketConfig(final HttpHost host, final SocketConfig socketConfig) {
        this.configData.setSocketConfig(host, socketConfig);
    }

public class SocketConfig implements Cloneable {

    public static final SocketConfig DEFAULT = new Builder().build();

    //......

    public static class Builder {

        private int soTimeout;
        private boolean soReuseAddress;
        private int soLinger;
        private boolean soKeepAlive;
        private boolean tcpNoDelay;
        private int sndBufSize;
        private int rcvBufSize;
        private int backlogSize;

        Builder() {
            this.soLinger = -1;
            this.tcpNoDelay = true;
        }

        //......
    }
}