聊聊HttpClient的HttpRoutePlanner

/**
 * Encapsulates logic to compute a {@link HttpRoute} to a target host.
 * Implementations may for example be based on parameters, or on the
 * standard Java system properties.
 * <p>
 * Implementations of this interface must be thread-safe. Access to shared
 * data must be synchronized as methods of this interface may be executed
 * from multiple threads.
 * </p>
 *
 * @since 4.0
 */
public interface HttpRoutePlanner {

    /**
     * Determines the route for a request.
     *
     * @param target    the target host for the request.
     *                  Implementations may accept {@code null}
     *                  if they can still determine a route, for example
     *                  to a default target or by inspecting the request.
     * @param request   the request to execute
     * @param context   the context to use for the subsequent execution.
     *                  Implementations may accept {@code null}.
     *
     * @return  the route that the request should take
     *
     * @throws HttpException    in case of a problem
     */
    HttpRoute determineRoute(HttpHost target,
                                    HttpRequest request,
                                    HttpContext context) throws HttpException;

}

/**
 * Default implementation of an {@link HttpRoutePlanner}. It will not make use of
 * any Java system properties, nor of system or browser proxy settings.
 *
 * @since 4.3
 */
@Contract(threading = ThreadingBehavior.IMMUTABLE_CONDITIONAL)
public class DefaultRoutePlanner implements HttpRoutePlanner {

    private final SchemePortResolver schemePortResolver;

    public DefaultRoutePlanner(final SchemePortResolver schemePortResolver) {
        super();
        this.schemePortResolver = schemePortResolver != null ? schemePortResolver :
            DefaultSchemePortResolver.INSTANCE;
    }

    @Override
    public HttpRoute determineRoute(
            final HttpHost host,
            final HttpRequest request,
            final HttpContext context) throws HttpException {
        Args.notNull(request, "Request");
        if (host == null) {
            throw new ProtocolException("Target host is not specified");
        }
        final HttpClientContext clientContext = HttpClientContext.adapt(context);
        final RequestConfig config = clientContext.getRequestConfig();
        final InetAddress local = config.getLocalAddress();
        HttpHost proxy = config.getProxy();
        if (proxy == null) {
            proxy = determineProxy(host, request, context);
        }

        final HttpHost target;
        if (host.getPort() <= 0) {
            try {
                target = new HttpHost(
                        host.getHostName(),
                        this.schemePortResolver.resolve(host),
                        host.getSchemeName());
            } catch (final UnsupportedSchemeException ex) {
                throw new HttpException(ex.getMessage());
            }
        } else {
            target = host;
        }
        final boolean secure = target.getSchemeName().equalsIgnoreCase("https");
        return proxy == null
                        ? new HttpRoute(target, local, secure)
                        : new HttpRoute(target, local, proxy, secure);
    }

    /**
     * This implementation returns null.
     *
     * @throws HttpException may be thrown if overridden
     */
    protected HttpHost determineProxy(
            final HttpHost target,
            final HttpRequest request,
            final HttpContext context) throws HttpException {
        return null;
    }

}

/**
 * Strategy for default port resolution for protocol schemes.
 *
 * @since 4.3
 */
public interface SchemePortResolver {

    /**
     * Returns the actual port for the host based on the protocol scheme.
     */
    int resolve(HttpHost host) throws UnsupportedSchemeException;

}

@Contract(threading = ThreadingBehavior.IMMUTABLE)
public class DefaultSchemePortResolver implements SchemePortResolver {

    public static final DefaultSchemePortResolver INSTANCE = new DefaultSchemePortResolver();

    @Override
    public int resolve(final HttpHost host) throws UnsupportedSchemeException {
        Args.notNull(host, "HTTP host");
        final int port = host.getPort();
        if (port > 0) {
            return port;
        }
        final String name = host.getSchemeName();
        if (name.equalsIgnoreCase("http")) {
            return 80;
        } else if (name.equalsIgnoreCase("https")) {
            return 443;
        } else {
            throw new UnsupportedSchemeException(name + " protocol is not supported");
        }
    }

}