HttpClient中 RetryHandler的理解与使用

Posted 2022-11-28 OkidoGreen

使用httpClient的过程中，如果没有设置自定义的 retryHandler，系统会使用默认的 

DefaultHttpRequestRetryHandler.INSTANCE;

    public DefaultHttpRequestRetryHandler() 
        this(3, false);
    

    public DefaultHttpRequestRetryHandler(final int retryCount, final boolean requestSentRetryEnabled) 
        this(retryCount, requestSentRetryEnabled, Arrays.asList(
                InterruptedIOException.class,
                UnknownHostException.class,
                ConnectException.class,
                SSLException.class));
    

    protected DefaultHttpRequestRetryHandler(
            final int retryCount,
            final boolean requestSentRetryEnabled,
            final Collection<Class<? extends IOException>> clazzes) 
        super();
        this.retryCount = retryCount;
        this.requestSentRetryEnabled = requestSentRetryEnabled;
        this.nonRetriableClasses = new HashSet<Class<? extends IOException>>();
        for (final Class<? extends IOException> clazz: clazzes) 
            this.nonRetriableClasses.add(clazz);
        
    

可以看到，默认是超时3次，而且有一个属性 nonRetriableClasses ，标记了 遇到这种class类型，不会去重走 retry 逻辑，源码如下：

@Override
    public boolean retryRequest(
            final IOException exception,
            final int executionCount,
            final HttpContext context) 
        Args.notNull(exception, "Exception parameter");
        Args.notNull(context, "HTTP context");
        if (executionCount > this.retryCount) 
            // Do not retry if over max retry count
            return false;
        
        if (this.nonRetriableClasses.contains(exception.getClass())) 
            return false;
         else 
            for (final Class<? extends IOException> rejectException : this.nonRetriableClasses) 
                if (rejectException.isInstance(exception)) 
                    return false;
                
            
        

可以看到，直接return false，不尝试触发重试逻辑；

这时候我们去看 3个超时配置 对应的异常，

connectTimeout
socketTimeout
connectionRequestTimeout

对应到是异常：

SocketTimeoutException

public class SocketTimeoutException extends java.io.InterruptedIOException 

很明显，这个异常是 InterruptedIOException 的子类，也就是默认的 retryHandler中忽略重试的 类型，所以默认情况下，超时类的异常不会触发重试逻辑，大家可以通过重写retryHandler来使其生效

CloseableHttpClient httpClient=HttpClients.custom().setDefaultRequestConfig(requestConfig).setRetryHandler(new HttpRequestRetryHandler() 
            @Override
            public boolean retryRequest(IOException exception, int executionCount, HttpContext context) 
                if(executionCount >= 5) 
                    logger.info("executionCount = " + executionCount);
                    return false;
                
                return true;
            
        ).build()