在HTTP GET请求上有效URL的404状态的FileNotFoundException

Question

我有以下代码在以下网址上执行GET请求：

http://rt.hnnnglmbrg.de/server.php/someReferenceNumber

但是，这是Logcat的输出：

java.io.FileNotFoundException: http://rt.hnnnglmbrg.de/server.php/6

为什么在网址明显有效时会返回404？

这是我的连接代码：

/**
 * Performs an HTTP GET request that returns base64 data from the server
 * 
 * @param ref
 *            The Accident's reference
 * @return The base64 data from the server.
 */
public static String performGet(String ref) {
    String returnRef = null;
    try {
        URL url = new URL(SERVER_URL + "/" + ref);
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
        con.setRequestMethod("GET");

        BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));

        StringBuilder builder = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            builder.append(line);
        }

        returnRef = builder.toString();

    } catch (IOException e) {
        e.printStackTrace();
    }
    return returnRef;
}

Answer 1

当您请求URL时，它实际上返回了代码未找到的HTTP代码404。如果您可以控制PHP脚本，请将标头设置为200以指示找到文件。

Answer 2

如上所述，您正在获得404。为避免异常，请尝试以下方法：

HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestMethod("GET");
con.connect () ; 
int code = con.getResponseCode() ;
if (code == HttpURLConnection.HTTP_NOT_FOUND)
{
    // Handle error
}
else
{
    BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));

    // etc...
}

Answer 3

永远不要相信您在浏览器中看到的内容。总是尝试使用像curl这样的东西模仿您的请求，并且您将清楚地看到您正在获取HTTP 404响应代码。

java.net会将HTTP 404代码转换为FileNotFoundException

curl -v  http://rt.hnnnglmbrg.de/server.php/4
* About to connect() to rt.hnnnglmbrg.de port 80 (#0)
*   Trying 217.160.115.112... connected
* Connected to rt.hnnnglmbrg.de (217.160.115.112) port 80 (#0)
> GET /server.php/4 HTTP/1.1
> User-Agent: curl/7.21.4 (universal-apple-darwin11.0) libcurl/7.21.4 OpenSSL/0.9.8r zlib/1.2.5
> Host: rt.hnnnglmbrg.de
> Accept: */*
> 
< HTTP/1.1 404 Not Found
< Date: Mon, 11 Jun 2012 07:34:55 GMT
< Server: Apache
< X-Powered-By: PHP/5.2.17
< Transfer-Encoding: chunked
< Content-Type: text/html
< 
* Connection #0 to host rt.hnnnglmbrg.de left intact
* Closing connection #0
0

来自http://docs.oracle.com/javase/6/docs/api/java/net/HttpURLConnection.html的javadoc

如果连接失败但服务器仍然发送了有用的数据，则返回错误流。典型示例是HTTP服务器以404响应，这将导致在连接中抛出FileNotFoundException，但服务器发送了一个HTML帮助页面，其中包含有关如何操作的建议。