摘要:序本文主要研究一下的参数这里有一个类型的变量,用来记录请求次数另外还有一个,读取的是值,读取不到默认取,为进入该方法的时候,调用,递增请求次数,然后判断有无超出限制,有则返回带有异常的,即通过返回如果没有超出限制,但是执行请求失败,则
序
本文主要研究一下jdk httpclient的retry参数
DEFAULT_MAX_ATTEMPTSjava.net.http/jdk/internal/net/http/MultiExchange.java
class MultiExchange{ static final Logger debug = Utils.getDebugLogger("MultiExchange"::toString, Utils.DEBUG); private final HttpRequest userRequest; // the user request private final HttpRequestImpl request; // a copy of the user request final AccessControlContext acc; final HttpClientImpl client; final HttpResponse.BodyHandler responseHandler; final HttpClientImpl.DelegatingExecutor executor; final AtomicInteger attempts = new AtomicInteger(); HttpRequestImpl currentreq; // used for retries & redirect HttpRequestImpl previousreq; // used for retries & redirect Exchange exchange; // the current exchange Exchange previous; volatile Throwable retryCause; volatile boolean expiredOnce; volatile HttpResponse response = null; // Maximum number of times a request will be retried/redirected // for any reason static final int DEFAULT_MAX_ATTEMPTS = 5; static final int max_attempts = Utils.getIntegerNetProperty( "jdk.httpclient.redirects.retrylimit", DEFAULT_MAX_ATTEMPTS ); //...... }
这里有一个AtomicInteger类型的attempts变量,用来记录请求次数
另外还有一个max_attempts,读取的是jdk.httpclient.redirects.retrylimit值,读取不到默认取DEFAULT_MAX_ATTEMPTS,为5
MultiExchange.responseAsyncImpljava.net.http/jdk/internal/net/http/MultiExchange.java
private CompletableFutureresponseAsyncImpl() { CompletableFuture cf; if (attempts.incrementAndGet() > max_attempts) { cf = failedFuture(new IOException("Too many retries", retryCause)); } else { if (currentreq.timeout().isPresent()) { responseTimerEvent = ResponseTimerEvent.of(this); client.registerTimer(responseTimerEvent); } try { // 1. apply request filters // if currentreq == previousreq the filters have already // been applied once. Applying them a second time might // cause some headers values to be added twice: for // instance, the same cookie might be added again. if (currentreq != previousreq) { requestFilters(currentreq); } } catch (IOException e) { return failedFuture(e); } Exchange exch = getExchange(); // 2. get response cf = exch.responseAsync() .thenCompose((Response response) -> { HttpRequestImpl newrequest; try { // 3. apply response filters newrequest = responseFilters(response); } catch (IOException e) { return failedFuture(e); } // 4. check filter result and repeat or continue if (newrequest == null) { if (attempts.get() > 1) { Log.logError("Succeeded on attempt: " + attempts); } return completedFuture(response); } else { this.response = new HttpResponseImpl<>(currentreq, response, this.response, null, exch); Exchange oldExch = exch; return exch.ignoreBody().handle((r,t) -> { previousreq = currentreq; currentreq = newrequest; expiredOnce = false; setExchange(new Exchange<>(currentreq, this, acc)); return responseAsyncImpl(); }).thenCompose(Function.identity()); } }) .handle((response, ex) -> { // 5. handle errors and cancel any timer set cancelTimer(); if (ex == null) { assert response != null; return completedFuture(response); } // all exceptions thrown are handled here CompletableFuture errorCF = getExceptionalCF(ex); if (errorCF == null) { return responseAsyncImpl(); } else { return errorCF; } }) .thenCompose(Function.identity()); } return cf; }
进入该方法的时候,调用attempts.incrementAndGet(),递增请求次数,然后判断有无超出限制,有则返回带有new IOException("Too many retries", retryCause)异常的failedFuture,即通过CompletableFuture.completeExceptionally返回
如果没有超出限制,但是执行请求失败,则调用getExceptionalCF来判断是否应该重试,如果返回null,则重试,通过再次调用responseAsyncImpl,通过这种递归调用完成重试逻辑
MultiExchange.getExceptionalCFjava.net.http/jdk/internal/net/http/MultiExchange.java
/** * Takes a Throwable and returns a suitable CompletableFuture that is * completed exceptionally, or null. */ private CompletableFuturegetExceptionalCF(Throwable t) { if ((t instanceof CompletionException) || (t instanceof ExecutionException)) { if (t.getCause() != null) { t = t.getCause(); } } if (cancelled && t instanceof IOException) { if (!(t instanceof HttpTimeoutException)) { t = toTimeoutException((IOException)t); } } else if (retryOnFailure(t)) { Throwable cause = retryCause(t); if (!(t instanceof ConnectException)) { if (!canRetryRequest(currentreq)) { return failedFuture(cause); // fails with original cause } } // allow the retry mechanism to do its work retryCause = cause; if (!expiredOnce) { if (debug.on()) debug.log(t.getClass().getSimpleName() + " (async): retrying...", t); expiredOnce = true; // The connection was abruptly closed. // We return null to retry the same request a second time. // The request filters have already been applied to the // currentreq, so we set previousreq = currentreq to // prevent them from being applied again. previousreq = currentreq; return null; } else { if (debug.on()) { debug.log(t.getClass().getSimpleName() + " (async): already retried once.", t); } t = cause; } } return failedFuture(t); } private boolean retryOnFailure(Throwable t) { return t instanceof ConnectionExpiredException || (RETRY_CONNECT && (t instanceof ConnectException)); } /** Returns true if the given request can be automatically retried. */ private static boolean canRetryRequest(HttpRequest request) { if (RETRY_ALWAYS) return true; if (isIdempotentRequest(request)) return true; return false; } /** Returns true is given request has an idempotent method. */ private static boolean isIdempotentRequest(HttpRequest request) { String method = request.method(); switch (method) { case "GET" : case "HEAD" : return true; default : return false; } } private Throwable retryCause(Throwable t) { Throwable cause = t instanceof ConnectionExpiredException ? t.getCause() : t; return cause == null ? t : cause; } /** True if ALL ( even non-idempotent ) requests can be automatic retried. */ private static final boolean RETRY_ALWAYS = retryPostValue(); /** True if ConnectException should cause a retry. Enabled by default */ private static final boolean RETRY_CONNECT = retryConnect(); private static boolean retryPostValue() { String s = Utils.getNetProperty("jdk.httpclient.enableAllMethodRetry"); if (s == null) return false; return s.isEmpty() ? true : Boolean.parseBoolean(s); } private static boolean retryConnect() { String s = Utils.getNetProperty("jdk.httpclient.disableRetryConnect"); if (s == null) return false; return s.isEmpty() ? true : Boolean.parseBoolean(s); }
如果cancelled为true且是IOException则直接返回,否则先判断retryOnFailure再判断canRetryRequest(如果不是ConnectException才走canRetryRequest这个判断)
retryOnFailure方法判断如果是ConnectionExpiredException或者是ConnectException且开启retryConnect,则返回true
RETRY_CONNECT读取的是jdk.httpclient.disableRetryConnect参数,如果值为null,则方法返回false,即不进行retryConnect
canRetryRequest首先判断RETRY_ALWAYS,在判断isIdempotentRequest(GET、HEAD方法才重试),都不是则返回false
RETRY_ALWAYS读取的是jdk.httpclient.enableAllMethodRetry,如果值为null,则方法返回false,即不进行retryPostValue
如果该重试的话,则返回null,responseAsyncImpl里头在getExceptionalCF返回null的时候,重新调用了一次responseAsyncImpl,通过递归调用来完成重试逻辑
NetPropertiesjava.base/sun/net/NetProperties.java
public class NetProperties { private static Properties props = new Properties(); static { AccessController.doPrivileged( new PrivilegedAction() { public Void run() { loadDefaultProperties(); return null; }}); } private NetProperties() { }; /* * Loads the default networking system properties * the file is in jre/lib/net.properties */ private static void loadDefaultProperties() { String fname = StaticProperty.javaHome(); if (fname == null) { throw new Error("Can"t find java.home ??"); } try { File f = new File(fname, "conf"); f = new File(f, "net.properties"); fname = f.getCanonicalPath(); InputStream in = new FileInputStream(fname); BufferedInputStream bin = new BufferedInputStream(in); props.load(bin); bin.close(); } catch (Exception e) { // Do nothing. We couldn"t find or access the file // so we won"t have default properties... } } /** * Get a networking system property. If no system property was defined * returns the default value, if it exists, otherwise returns * null
. * @param key the property name. * @throws SecurityException if a security manager exists and its *checkPropertiesAccess
method doesn"t allow access * to the system properties. * @return theString
value for the property, * ornull
*/ public static String get(String key) { String def = props.getProperty(key); try { return System.getProperty(key, def); } catch (IllegalArgumentException e) { } catch (NullPointerException e) { } return null; } /** * Get an Integer networking system property. If no system property was * defined returns the default value, if it exists, otherwise returns *null
. * @param key the property name. * @param defval the default value to use if the property is not found * @throws SecurityException if a security manager exists and its *checkPropertiesAccess
method doesn"t allow access * to the system properties. * @return theInteger
value for the property, * ornull
*/ public static Integer getInteger(String key, int defval) { String val = null; try { val = System.getProperty(key, props.getProperty(key)); } catch (IllegalArgumentException e) { } catch (NullPointerException e) { } if (val != null) { try { return Integer.decode(val); } catch (NumberFormatException ex) { } } return defval; } /** * Get a Boolean networking system property. If no system property was * defined returns the default value, if it exists, otherwise returns *null
. * @param key the property name. * @throws SecurityException if a security manager exists and its *checkPropertiesAccess
method doesn"t allow access * to the system properties. * @return theBoolean
value for the property, * ornull
*/ public static Boolean getBoolean(String key) { String val = null; try { val = System.getProperty(key, props.getProperty(key)); } catch (IllegalArgumentException e) { } catch (NullPointerException e) { } if (val != null) { try { return Boolean.valueOf(val); } catch (NumberFormatException ex) { } } return null; } }
这里通过loadDefaultProperties先加载默认配置,读取的是JAVA_HOME/conf/net.properties文件
然后getString、getInteger、getBoolean方法采用的是System.getProperty来读取,而net.properties值仅仅作为System.getProperty的defaultValue
因此要设置httpclient相关参数,只需要通过System.setProperty或者-D来设置即可
net.properties
/Library/java/JavaVirtualMachines/jdk-11.jdk/Contents/home/conf/net.properties
java.net.useSystemProxies=false http.nonProxyHosts=localhost|127.*|[::1] ftp.nonProxyHosts=localhost|127.*|[::1] jdk.http.auth.tunneling.disabledSchemes=Basic
net.properties文件默认设置了如上四个参数相关异常 HttpTimeoutException
java.net.http/java/net/http/HttpTimeoutException.java
/** * Thrown when a response is not received within a specified time period. * * @since 11 */ public class HttpTimeoutException extends IOException { private static final long serialVersionUID = 981344271622632951L; /** * Constructs an {@code HttpTimeoutException} with the given detail message. * * @param message * The detail message; can be {@code null} */ public HttpTimeoutException(String message) { super(message); } }
属于java.net.http包,继承至IOException
如果设置了request的timeout,则注册ResponseTimerEvent,在超时时抛出HttpTimeoutException: request timed out,同时设置MultiExchange的cancelled为true
这类由于客户端设置超时引起的HttpTimeoutException,不会进行重试,即使开启相关重试参数
如果这个时间设置得太短,则在connect的时候就超时了,这个时候会抛出HttpConnectTimeoutException,而非HttpTimeoutException: request timed out
HttpConnectTimeoutExceptionjava.net.http/java/net/http/HttpConnectTimeoutException.java
/** * Thrown when a connection, over which an {@code HttpRequest} is intended to be * sent, is not successfully established within a specified time period. * * @since 11 */ public class HttpConnectTimeoutException extends HttpTimeoutException { private static final long serialVersionUID = 321L + 11L; /** * Constructs an {@code HttpConnectTimeoutException} with the given detail * message. * * @param message * The detail message; can be {@code null} */ public HttpConnectTimeoutException(String message) { super(message); } }
属于java.net.http包,继承至HttpTimeoutException
如果设置了client的connectTimeout,则会注册ConnectTimerEvent,在超时时抛出ConnectException("HTTP connect timed out"),同时设置MultiExchange的cancelled为true,这个在MultiExchange.getExceptionalCF方法里头会被包装为HttpConnectTimeoutException
ConnectionExpiredExceptionjava.net.http/jdk/internal/net/http/common/ConnectionExpiredException.java
/** * Signals that an end of file or end of stream has been reached * unexpectedly before any protocol specific data has been received. */ public final class ConnectionExpiredException extends IOException { private static final long serialVersionUID = 0; /** * Constructs a {@code ConnectionExpiredException} with a detail message of * "subscription is finished" and the given cause. * * @param cause the throwable cause */ public ConnectionExpiredException(Throwable cause) { super("subscription is finished", cause); } }
一般是在read error的时候触发,比如EOFException,IOException("connection reset by peer),或者SSLHandshakeException
小结jdk httpclient的retry参数涉及到的参数如下:
jdk.httpclient.redirects.retrylimit(默认为5,用来控制重试次数,不过实际上还有expiredOnce参数,看代码貌似顶多重试一次)
jdk.httpclient.disableRetryConnect(默认为null,即RETRY_CONNECT为false,不在ConnectException的时候retry)
jdk.httpclient.enableAllMethodRetry(默认为null,即RETRY_ALWAYS为false,即需要判断请求方法是否幂等来决定是否重试)
是否重试的判断逻辑如下:
如果重试次数超过限制,则返回失败,否则往下
如果cancelled为true(这里如果request设置了timeout,触发时cancelled设置为true)且是IOException(例如设置了连接超时抛出的HttpConnectTimeoutException),则不走重试逻辑;否则往下
如果retryOnFailure(ConnectionExpiredException,或者ConnectException且开启retryConnect),则往下
如果是异常不是ConnectException,则还额外判断canRetryRequest(判断该请求类型是否允许重试),满足则往下
如果expiredOnce为false,则返回null,即满足重试条件,走递归重试
docHttpClient javadoc
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