HTTP客戶端警告：Going to buffer response body of large or unknown size

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原編碼問題

HttpClient發現拋出Going to buffer response body of large or unknown size. Using getResponseBodyAsStream instead is recommended，查看原有代碼中的邏輯如下：

HttpClient httpclient = new HttpClient();
GetMethod getMethod = new GetMethod(url);
int statusCode = httpclient.executeMethod(getMethod);
String respContent = getMethod.getResponseBodyAsString();

源碼分析 getResponseBodyAsString()源碼

	//getResponseBodyAsString()方法源碼public String getResponseBodyAsString() throws IOException {byte[] rawdata = null;if (this.responseAvailable()) {//調用了getResponseBody()，容易消耗內存rawdata = this.getResponseBody();}return rawdata != null ? EncodingUtil.getString(rawdata, this.getResponseCharSet()) : null;}//responseAvailable()方法源碼private boolean responseAvailable() {return this.responseBody != null || this.responseStream != null;}//getResponseBody()方法源碼public byte[] getResponseBody() throws IOException {if (this.responseBody == null) {InputStream instream = this.getResponseBodyAsStream();if (instream != null) {long contentLength = this.getResponseContentLength();if (contentLength > 2147483647L) {throw new IOException("Content too large to be buffered: " + contentLength + " bytes");}int limit = this.getParams().getIntParameter("http.method.response.buffer.warnlimit", 1048576);if (contentLength == -1L || contentLength > (long)limit) {//這里是warn的原文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 > 0L ? (int)contentLength : 4096);byte[] buffer = new byte[4096];int len;while((len = instream.read(buffer)) > 0) {outstream.write(buffer, 0, len);}outstream.close();this.setResponseStream((InputStream)null);this.responseBody = outstream.toByteArray();}}return this.responseBody;}

從源碼中可以看出，warn的條件是(contentLength == -1L || contentLength > (long)limit)，如果http頭沒有指定contentLength或大于上限值（默認1M），就會拋異常。其實，如果返回的結果比較確定，對程序沒有太大影響。而對于返回結果不確定時，源碼也建議我們使用下面的getResponseBodyAsStream()方法。

getResponseBodyAsStream()源碼

public InputStream getResponseBodyAsStream() throws IOException {if (this.responseStream != null) {return this.responseStream;} else if (this.responseBody != null) {InputStream byteResponseStream = new ByteArrayInputStream(this.responseBody);LOG.debug("re-creating response stream from byte array");return byteResponseStream;} else {return null;}}

從源碼中可以看出，getResponseBodyAsStream()內部沒有使用getResponseBody()方法，避免了內存耗盡問題，而是使用了InputStream流方式處理。

優化原編碼

HttpClient httpclient = new HttpClient();
GetMethod getMethod = new GetMethod(url);
int statusCode = httpclient.executeMethod(getMethod);
//String respContent = getMethod.getResponseBodyAsString();
//使用getResponseBodyAsStream()
InputStream inputStream = getMethod.getResponseBodyAsStream();
BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
StringBuffer stringBuffer = new StringBuffer();
String str = "";
while ((str = br.readLine()) != null) {stringBuffer.append(str);
}
LOGGER.info("respContent: {}", stringBuffer.toString());