java - HttpURLConnection 不读取整个响应

Question

我使用 HttpURLConnection 执行 HTTP POST，但我并不总能得到完整的响应。我想调试这个问题，但是当我逐行检查它时，它就起作用了。我认为这一定是一个时间问题，所以我添加了 Thread.sleep，它确实使我的代码工作，但这只是一个临时的解决方法。我想知道为什么会发生这种情况以及如何解决。这是我的代码:

public static InputStream doPOST(String input, String inputMimeType, String url, Map<String, String> httpHeaders, String expectedMimeType) throws MalformedURLException, IOException {

    URL u = new URL(url);
    URLConnection c = u.openConnection();
    InputStream in = null;
    String mediaType = null;
    if (c instanceof HttpURLConnection) {

        //c.setConnectTimeout(1000000);
        //c.setReadTimeout(1000000);

        HttpURLConnection h = (HttpURLConnection)c;
        h.setRequestMethod("POST");
        //h.setChunkedStreamingMode(-1);
        setAccept(h, expectedMimeType);
        h.setRequestProperty("Content-Type", inputMimeType);

        for(String key: httpHeaders.keySet()) {
            h.setRequestProperty(key, httpHeaders.get(key));

            if (logger.isDebugEnabled()) {
                logger.debug("Request property key : " + key + " / value : " + httpHeaders.get(key));
            }

        }

        h.setDoOutput(true);
        h.connect();

        OutputStream out = h.getOutputStream();

        out.write(input.getBytes());

        out.close();

        mediaType = h.getContentType();

        logger.debug(" ------------------ sleep ------------------ START");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        logger.debug(" ------------------ sleep ------------------ END");

        if (h.getResponseCode() < 400) {
            in = h.getInputStream();
        } else {
            in = h.getErrorStream();
        }
    }
    return in;

}

稍后我执行以下操作来读取输入流

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        while (is.available() > 0) {
            bos.write(is.read());
        }
        is.close();

        //is.read(bytes);
        if (logger.isDebugEnabled()) {
            logger.debug(" Response lenght is : " + is.available());
            //logger.debug("RAW response is " + new String(bytes));
            logger.debug("RAW response is " + new String(bos.toByteArray()));
        }

它生成以下 HTTP header

POST /emailauthentication/ HTTP/1.1
Accept: application/xml
Content-Type: application/xml
Authorization: OAuth oauth_consumer_key="b465472b-d872-42b9-030e-4e74b9b60e39",oauth_nonce="YnDb5eepuLm%2Fbs",oauth_signature="dbN%2FWeWs2G00mk%2BX6uIi3thJxlM%3D", oauth_signature_method="HMAC-SHA1", oauth_timestamp="1276524919", oauth_token="", oauth_version="1.0"
User-Agent: Java/1.6.0_20
Host: test:6580
Connection: keep-alive
Content-Length: 1107

在其他帖子中，建议使用

关闭 keep-alive

http.keepAlive=false

系统属性，我试过了，标题变成了

POST /emailauthentication/ HTTP/1.1
Accept: application/xml
Content-Type: application/xml
Authorization: OAuth oauth_consumer_key="b465472b-d872-42b9-030e-4e74b9b60e39", oauth_nonce="Eaiezrj6X4Ttt0", oauth_signature="ND9fAdZMqbYPR2j%2FXUCZmI90rSI%3D", oauth_signature_method="HMAC-SHA1", oauth_timestamp="1276526608", oauth_token="", oauth_version="1.0"
User-Agent: Java/1.6.0_20
Host: test:6580
Connection: close
Content-Length: 1107

连接 header 是“关闭”，但我仍然无法阅读整个响应。知道我做错了什么吗？

Answer 1

我认为你的问题出在这一行:

while (is.available() > 0) {

根据 javadoc，available 不会阻塞并等待所有数据可用，因此您可能会收到第一个数据包，然后它会返回 false。从 InputStream 读取的正确方法是这样的:

int len;
byte[] buffer = new byte[4096];
while (-1 != (len = in.read(buffer))) {
  bos.write(buffer, 0, len);
}

当输入流中没有任何内容或连接关闭时，Read 将返回 -1，同时它会阻塞并等待网络。读取数组的性能也比使用单个字节高得多。