Apache HttpClient throws java.net.SocketException: Connection reset if I use it as singletone

Question

I created an Apache HTTP client

             CloseableHttpClient client = HttpClients.custom()
                .setMaxConnPerRoute(25)
                .setMaxConnTotal(50)
                .setDefaultRequestConfig(RequestConfig.custom()
                        .setConnectionRequestTimeout(20_000)
                        .build())
                .build();

I am using it as a singleton. I have this method for sending requests:

public RestResponse sendPost(String serverUrl, String body) throws RestException {
        try {
            HttpPost httpPost = new HttpPost(serverUrl);
            httpPost.setEntity(new StringEntity(body));

            try (CloseableHttpResponse response = client.execute(httpPost)) {
                RestResponse restResponse = new RestResponse();
                restResponse.setCode(response.getStatusLine().getStatusCode());
                restResponse.setBody(EntityUtils.toString(response.getEntity()));
                return restResponse;
            }
        } catch (Exception e) {
            throw new RestException(e);
        }
    }

It works fine. But after some time (5-6 min) of idle, if I send a request I get "java.net.SocketException: Connection reset"

I have 2 questions

How can I find a place where this time is outset? those parameters don't work for me

             .setSocketTimeout(25_000)
             .setConnectTimeout(26_000)

What is the best way to fix this problem? (I mean retry request or change timeout or reconnect after or before each request)

You probably need to configure your connection pool to test connections — Boris the Spider
– Boris the Spider, Commented Nov 30, 2021 at 20:51

ok2c · Accepted Answer · 2021-12-01 10:45:35Z

7

This is a general limitation of the classic (blocking) i/o: blocking connections cannot react to any i/o events when idle (not engaged in an i/o operations). Likewise, timeout settings have no effect on idle connections.

There are several defensive measures one can employ to minimize the chances of a persistent connection reset:

Validate persistent connections upon lease from the connection pool after a certain period of inactivity (for example, after 1s)

    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setValidateAfterInactivity(1000);
    CloseableHttpClient httpclient = HttpClients.custom()
            .setConnectionManager(cm)
            .build();

Proactively evict expired connections and those that have been idle over a certain period of time (for example, 5s) from the connection pool

    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setValidateAfterInactivity(1000);
    CloseableHttpClient httpclient = HttpClients.custom()
            .setConnectionManager(cm)
            .evictExpiredConnections()
            .evictIdleConnections(5L, TimeUnit.SECONDS)
            .build();

If everything else fails, retry requests that are safe to retry. One might want to use a custom HttpRequestRetryHandler implementation instead of the default one when more control is necessary.

    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setValidateAfterInactivity(1000);
    CloseableHttpClient httpclient = HttpClients.custom()
            .setConnectionManager(cm)
            .setRetryHandler(DefaultHttpRequestRetryHandler.INSTANCE)
            .build();

Evict connections from the pool manually when expecting a long period inactivity. This is what HttpClient does for you automatically when configured with evictIdleConnections method at the cost of an extra monitor thread.

    cm.closeIdleConnections(0, TimeUnit.MICROSECONDS);

answered Dec 1, 2021 at 10:45

ok2c

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3 Comments

Pavel Petrashov Over a year ago

can you describe, how does it work? I mean, I use a connection pool/ I close response after each request. Why httpClient holds a connection after closing?

ok2c Over a year ago

It is called connection persistence. Please see datatracker.ietf.org/doc/html/rfc7230#section-6.3

Pavel Petrashov Over a year ago

Thank you! but I still do not understand what is the meaning of closing response.close()

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