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本文主要研究一下httpclient的staleConnectionCheckEnabled

staleConnectionCheckEnabled

org/apache/http/client/config/RequestConfig.java

public class RequestConfig implements Cloneable {public static final RequestConfig DEFAULT = new Builder().build();private final boolean expectContinueEnabled;private final HttpHost proxy;private final InetAddress localAddress;private final boolean staleConnectionCheckEnabled;//....../*** Determines whether stale connection check is to be used. The stale* connection check can cause up to 30 millisecond overhead per request and* should be used only when appropriate. For performance critical* operations this check should be disabled.* <p>* Default: {@code false} since 4.4* </p>** @deprecated (4.4) Use {@link*   org.apache.http.impl.conn.PoolingHttpClientConnectionManager#getValidateAfterInactivity()}*/@Deprecatedpublic boolean isStaleConnectionCheckEnabled() {return staleConnectionCheckEnabled;}   public static class Builder {private boolean expectContinueEnabled;private HttpHost proxy;private InetAddress localAddress;private boolean staleConnectionCheckEnabled;//......Builder() {super();this.staleConnectionCheckEnabled = false;this.redirectsEnabled = true;this.maxRedirects = 50;this.relativeRedirectsAllowed = true;this.authenticationEnabled = true;this.connectionRequestTimeout = -1;this.connectTimeout = -1;this.socketTimeout = -1;this.contentCompressionEnabled = true;this.normalizeUri = true;}        /*** @deprecated (4.4) Use {@link*   org.apache.http.impl.conn.PoolingHttpClientConnectionManager#setValidateAfterInactivity(int)}*/@Deprecatedpublic Builder setStaleConnectionCheckEnabled(final boolean staleConnectionCheckEnabled) {this.staleConnectionCheckEnabled = staleConnectionCheckEnabled;return this;}  //......}       
}    

RequestConfig定義了staleConnectionCheckEnabled屬性，在4.4版本廢棄了，默認為false，替換設置是org.apache.http.impl.conn.PoolingHttpClientConnectionManager.setValidateAfterInactivity(int)；Builder方法也提供了setStaleConnectionCheckEnabled方法

MainClientExec

org/apache/http/impl/execchain/MainClientExec.java

    public CloseableHttpResponse execute(final HttpRoute route,final HttpRequestWrapper request,final HttpClientContext context,final HttpExecutionAware execAware) throws IOException, HttpException {Args.notNull(route, "HTTP route");Args.notNull(request, "HTTP request");Args.notNull(context, "HTTP context");AuthState targetAuthState = context.getTargetAuthState();if (targetAuthState == null) {targetAuthState = new AuthState();context.setAttribute(HttpClientContext.TARGET_AUTH_STATE, targetAuthState);}AuthState proxyAuthState = context.getProxyAuthState();if (proxyAuthState == null) {proxyAuthState = new AuthState();context.setAttribute(HttpClientContext.PROXY_AUTH_STATE, proxyAuthState);}if (request instanceof HttpEntityEnclosingRequest) {RequestEntityProxy.enhance((HttpEntityEnclosingRequest) request);}Object userToken = context.getUserToken();final ConnectionRequest connRequest = connManager.requestConnection(route, userToken);if (execAware != null) {if (execAware.isAborted()) {connRequest.cancel();throw new RequestAbortedException("Request aborted");}execAware.setCancellable(connRequest);}final RequestConfig config = context.getRequestConfig();final HttpClientConnection managedConn;try {final int timeout = config.getConnectionRequestTimeout();managedConn = connRequest.get(timeout > 0 ? timeout : 0, TimeUnit.MILLISECONDS);} catch(final InterruptedException interrupted) {Thread.currentThread().interrupt();throw new RequestAbortedException("Request aborted", interrupted);} catch(final ExecutionException ex) {Throwable cause = ex.getCause();if (cause == null) {cause = ex;}throw new RequestAbortedException("Request execution failed", cause);}context.setAttribute(HttpCoreContext.HTTP_CONNECTION, managedConn);if (config.isStaleConnectionCheckEnabled()) {// validate connectionif (managedConn.isOpen()) {this.log.debug("Stale connection check");if (managedConn.isStale()) {this.log.debug("Stale connection detected");managedConn.close();}}}final ConnectionHolder connHolder = new ConnectionHolder(this.log, this.connManager, managedConn);try {if (execAware != null) {execAware.setCancellable(connHolder);}HttpResponse response;for (int execCount = 1;; execCount++) {if (execCount > 1 && !RequestEntityProxy.isRepeatable(request)) {throw new NonRepeatableRequestException("Cannot retry request " +"with a non-repeatable request entity.");}if (execAware != null && execAware.isAborted()) {throw new RequestAbortedException("Request aborted");}if (!managedConn.isOpen()) {this.log.debug("Opening connection " + route);try {establishRoute(proxyAuthState, managedConn, route, request, context);} catch (final TunnelRefusedException ex) {if (this.log.isDebugEnabled()) {this.log.debug(ex.getMessage());}response = ex.getResponse();break;}}context.setAttribute(HttpCoreContext.HTTP_REQUEST, request);response = requestExecutor.execute(request, managedConn, context);//......}}        //......//......}    

MainClientExec的execute先通過connManager.requestConnection獲取ConnectionRequest，然后通過connRequest.get(timeout > 0 ? timeout : 0, TimeUnit.MILLISECONDS)獲取managedConn，之后判斷requestConfig的isStaleConnectionCheckEnabled，為true的話，會執行連接的校驗，先判斷是否open，再判斷是否stale，為stale的話則執行close；在managedConn關閉的時候，會通過establishRoute再進行連接

establishRoute

org/apache/http/impl/execchain/MainClientExec.java

    /*** Establishes the target route.*/void establishRoute(final AuthState proxyAuthState,final HttpClientConnection managedConn,final HttpRoute route,final HttpRequest request,final HttpClientContext context) throws HttpException, IOException {final RequestConfig config = context.getRequestConfig();final int timeout = config.getConnectTimeout();final RouteTracker tracker = new RouteTracker(route);int step;do {final HttpRoute fact = tracker.toRoute();step = this.routeDirector.nextStep(route, fact);switch (step) {case HttpRouteDirector.CONNECT_TARGET:this.connManager.connect(managedConn,route,timeout > 0 ? timeout : 0,context);tracker.connectTarget(route.isSecure());break;case HttpRouteDirector.CONNECT_PROXY:this.connManager.connect(managedConn,route,timeout > 0 ? timeout : 0,context);final HttpHost proxy  = route.getProxyHost();tracker.connectProxy(proxy, route.isSecure() && !route.isTunnelled());break;case HttpRouteDirector.TUNNEL_TARGET: {final boolean secure = createTunnelToTarget(proxyAuthState, managedConn, route, request, context);this.log.debug("Tunnel to target created.");tracker.tunnelTarget(secure);}   break;case HttpRouteDirector.TUNNEL_PROXY: {// The most simple example for this case is a proxy chain// of two proxies, where P1 must be tunnelled to P2.// route: Source -> P1 -> P2 -> Target (3 hops)// fact:  Source -> P1 -> Target       (2 hops)final int hop = fact.getHopCount()-1; // the hop to establishfinal boolean secure = createTunnelToProxy(route, hop, context);this.log.debug("Tunnel to proxy created.");tracker.tunnelProxy(route.getHopTarget(hop), secure);}   break;case HttpRouteDirector.LAYER_PROTOCOL:this.connManager.upgrade(managedConn, route, context);tracker.layerProtocol(route.isSecure());break;case HttpRouteDirector.UNREACHABLE:throw new HttpException("Unable to establish route: " +"planned = " + route + "; current = " + fact);case HttpRouteDirector.COMPLETE:this.connManager.routeComplete(managedConn, route, context);break;default:throw new IllegalStateException("Unknown step indicator "+ step + " from RouteDirector.");}} while (step > HttpRouteDirector.COMPLETE);}

establishRoute方法在循環里頭通過connManager.connect建立連接

requestConnection

org/apache/http/impl/conn/PoolingHttpClientConnectionManager.java

    public ConnectionRequest requestConnection(final HttpRoute route,final Object state) {Args.notNull(route, "HTTP route");if (this.log.isDebugEnabled()) {this.log.debug("Connection request: " + format(route, state) + formatStats(route));}final Future<CPoolEntry> future = this.pool.lease(route, state, null);return new ConnectionRequest() {@Overridepublic boolean cancel() {return future.cancel(true);}@Overridepublic HttpClientConnection get(final long timeout,final TimeUnit timeUnit) throws InterruptedException, ExecutionException, ConnectionPoolTimeoutException {final HttpClientConnection conn = leaseConnection(future, timeout, timeUnit);if (conn.isOpen()) {final HttpHost host;if (route.getProxyHost() != null) {host = route.getProxyHost();} else {host = route.getTargetHost();}final SocketConfig socketConfig = resolveSocketConfig(host);conn.setSocketTimeout(socketConfig.getSoTimeout());}return conn;}};}

PoolingHttpClientConnectionManager的requestConnection返回的ConnectionRequest的get方法是通過leaseConnection(future, timeout, timeUnit)來獲取連接的，而leaseConnection依賴的是pool.lease(route, state, null)返回的future

lease

org/apache/http/pool/AbstractConnPool.java

    /*** {@inheritDoc}* <p>* Please note that this class does not maintain its own pool of execution* {@link Thread}s. Therefore, one <b>must</b> call {@link Future#get()}* or {@link Future#get(long, TimeUnit)} method on the {@link Future}* returned by this method in order for the lease operation to complete.*/@Overridepublic Future<E> lease(final T route, final Object state, final FutureCallback<E> callback) {Args.notNull(route, "Route");Asserts.check(!this.isShutDown, "Connection pool shut down");return new Future<E>() {private final AtomicBoolean cancelled = new AtomicBoolean(false);private final AtomicBoolean done = new AtomicBoolean(false);private final AtomicReference<E> entryRef = new AtomicReference<E>(null);@Overridepublic boolean cancel(final boolean mayInterruptIfRunning) {if (done.compareAndSet(false, true)) {cancelled.set(true);lock.lock();try {condition.signalAll();} finally {lock.unlock();}if (callback != null) {callback.cancelled();}return true;}return false;}@Overridepublic boolean isCancelled() {return cancelled.get();}@Overridepublic boolean isDone() {return done.get();}@Overridepublic E get() throws InterruptedException, ExecutionException {try {return get(0L, TimeUnit.MILLISECONDS);} catch (final TimeoutException ex) {throw new ExecutionException(ex);}}@Overridepublic E get(final long timeout, final TimeUnit timeUnit) throws InterruptedException, ExecutionException, TimeoutException {for (;;) {synchronized (this) {try {final E entry = entryRef.get();if (entry != null) {return entry;}if (done.get()) {throw new ExecutionException(operationAborted());}final E leasedEntry = getPoolEntryBlocking(route, state, timeout, timeUnit, this);if (validateAfterInactivity > 0)  {if (leasedEntry.getUpdated() + validateAfterInactivity <= System.currentTimeMillis()) {if (!validate(leasedEntry)) {leasedEntry.close();release(leasedEntry, false);continue;}}}if (done.compareAndSet(false, true)) {entryRef.set(leasedEntry);done.set(true);onLease(leasedEntry);if (callback != null) {callback.completed(leasedEntry);}return leasedEntry;} else {release(leasedEntry, true);throw new ExecutionException(operationAborted());}} catch (final IOException ex) {if (done.compareAndSet(false, true)) {if (callback != null) {callback.failed(ex);}}throw new ExecutionException(ex);}}}}};}

lease返回的future的get(final long timeout, final TimeUnit timeUnit)方法在一個循環里頭去獲取連接，內部是通過getPoolEntryBlocking獲取到leasedEntry，然后在validateAfterInactivity大于0的時候進行連接校驗，在leasedEntry.getUpdated() + validateAfterInactivity <= System.currentTimeMillis()的時候進行validate，校驗不成功的話進行關閉掉leasedEntry，然后release掉leasedEntry，然后繼續循環獲取下一個連接

小結

httpclient的RequestConfig提供了staleConnectionCheckEnabled屬性用于在請求獲取到連接的時候進行連接檢測，不過這個屬性在4.4版本被廢棄了，并默認設置為false，替換設置是org.apache.http.impl.conn.PoolingHttpClientConnectionManager.setValidateAfterInactivity(int)，它是在ConnectionRequest的lease方法里頭根據leasedEntry.getUpdated() + validateAfterInactivity判斷是否需要校驗連接，若需要且校驗不通過則循環繼續獲取；而staleConnectionCheckEnabled則是在requestConnection之后根據RequestConfig的isStaleConnectionCheckEnabled來判斷，然后進行連接校驗，校驗不通過則關閉managedConn，最后會在判斷如果managedConn.isOpen()為false，則執行establishRoute，在循環里頭通過connManager.connect來建立新連接。