setExpectContinueEnabled是什么意思？

Question

I am using Apache HttpClient in our project by using PoolingHttpClientConnectionManager . I understood most of the property but I was confuse what does setExpectContinueEnabled mean? Does this be kept always true or false ? Can anyone provide some explanation what does it mean in general?

    private ClientHttpRequestFactory clientHttpRequestFactory() {
        HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory();
        RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(1000).setConnectTimeout(1000)
                .setSocketTimeout(1000).setStaleConnectionCheckEnabled(false).build();

        SocketConfig socketConfig = SocketConfig.custom().setSoKeepAlive(true).setTcpNoDelay(true).build();

        PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager();
        poolingHttpClientConnectionManager.setMaxTotal(800);
        poolingHttpClientConnectionManager.setDefaultMaxPerRoute(700);

        CloseableHttpClient httpClientBuilder = HttpClientBuilder.create()
                .setConnectionManager(poolingHttpClientConnectionManager).setDefaultRequestConfig(requestConfig)
                .setDefaultSocketConfig(socketConfig).build();

        requestFactory.setHttpClient(httpClientBuilder);
        return requestFactory;
    }

Answer 1

Methods of the form setXyzEnabled set a flag that controls whether an optional feature is used/allowed or not, in this case for request(s) using the RequestConfig. "Expect Continue" is an option in the HTTP/1.1 protocol where the client sends only the header of a request and waits for a response, normally "100 Continue", before sending the body. This allows it to skip sending the body if the server determines an error based (only) on the header.

See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.20 (request) and http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.2.3 (response) or more picturesquely http://httpstatusdogs.com/100-continue .

This is a bad idea if your server doesn't, or doesn't always, or isn't definitely known to, support Continue. It may be a good idea if your server(s) definitely does support Continue and you have requests with large or huge bodies that the server is significantly likely to reject.