HttpClient的“Going to buffer response body of large or unknown size. Using getRes

使用HttpClient，总是报出“Going to buffer response body of large or unknown size. Using getResponseBodyAsStream instead is recommended.”的WARN日志，定位到HttpClient的源码如下：

 public byte[] getResponseBody() throws IOException {
        if (this.responseBody == null) {
            InputStream instream = getResponseBodyAsStream();
            if (instream != null) {
                long contentLength = getResponseContentLength();
                if (contentLength > Integer.MAX_VALUE) { //guard below cast from overflow
                    throw new IOException("Content too large to be buffered: "+ contentLength +" bytes");
                }
                int limit = getParams().getIntParameter(HttpMethodParams.BUFFER_WARN_TRIGGER_LIMIT, 1024*1024);
                if ((contentLength == -1) || (contentLength > limit)) {
                    LOG.warn("Going to buffer response body of large or unknown size. "
                            +"Using getResponseBodyAsStream instead is recommended.");
                }
                LOG.debug("Buffering response body");
                ByteArrayOutputStream outstream = new ByteArrayOutputStream(
                        contentLength > 0 ? (int) contentLength : DEFAULT_INITIAL_BUFFER_SIZE);
                byte[] buffer = new byte[4096];
                int len;
                while ((len = instream.read(buffer)) > 0) {
                    outstream.write(buffer, 0, len);
                }
                outstream.close();
                setResponseStream(null);
                this.responseBody = outstream.toByteArray();
            }
        }
        return this.responseBody;
    }

  报WARN的条件是 ((contentLength == -1) || (contentLength > limit))，也就是说，或者是返回的HTTP头没有指定contentLength，或者是contentLength大于上限（默认是1M）。如果能确定返回结果的大小对程序没有显著影响，这个WARN就可以忽略，可以在日志的配置中把HttpClient的日志级别调到ERROR，不让它报出来。

当然，这个警告也是有意义的，HttpClient建议使用InputStream getResponseBodyAsStream()代替byte[] getResponseBody()。对于返回结果很大或无法预知的情况，就需要使用InputStream getResponseBodyAsStream()，避免byte[] getResponseBody()可能带来的内存的耗尽问题。