解决httpclient的NoHttpResponseExcep

在项目实际运行中，偶发异常：org.apache.http.NoHttpResponseException。

官网解释是：

In some circumstances, usually when under heavy load, the web server may be able to receive requests but unable to process them. A lack of sufficient resources like worker threads is a good example. This may cause the server to drop the connection to the client without giving any response. HttpClient throws NoHttpResponseException when it encounters such a condition. In most cases it is safe to retry a method that failed with NoHttpResponseException.

重试方案

CloseableHttpClient httpClient = HttpClients.custom()
    .setDefaultRequestConfig(config)
    .setConnectionManager(getPoolManager())

    //不使用这种方式，不方便看日志，使用下面自定义的retry
//  .setRetryHandler(new DefaultHttpRequestRetryHandler(3,true))

    .setRetryHandler((exception, executionCount, context) -> {
        if (executionCount > 3) {
            log.warn("Maximum tries reached for client http pool ");
            return false;
        }

        if (exception instanceof NoHttpResponseException     //NoHttpResponseException 重试
                || exception instanceof ConnectTimeoutException //连接超时重试
//              || exception instanceof SocketTimeoutException    //响应超时不重试，避免造成业务数据不一致
                ) {
            log.warn("NoHttpResponseException on " + executionCount + " call");
            return true;
        }
        return false;
    })
    .build();

参考资料

参考资料：

官方文档
http://hc.apache.org/httpclient-3.x/exception-handling.html

https://stackoverflow.com/questions/10570672/get-nohttpresponseexception-for-load-testing/10680629#10680629