来自URL的InputStream

Question

如何从URL获取InputStream？

例如,我想将文件放在url上,wwww.somewebsite.com/a.txt并通过servlet将其作为Java中的InputStream读取.

我试过了

InputStream is = new FileInputStream("wwww.somewebsite.com/a.txt");

但我得到的是一个错误:

java.io.FileNotFoundException

Answer 1

使用java.net.URL#openStream()正确的URL(包括协议!).例如

InputStream input = new URL("http://www.somewebsite.com/a.txt").openStream();
// ...

也可以看看:

• 使用java.net.URLConnection来触发和处理HTTP请求

Answer 2

尝试:

final InputStream is = new URL("http://wwww.somewebsite.com/a.txt").openStream();

Answer 3

(a)wwww.somewebsite.com/a.txt不是'文件网址'.它根本不是URL.如果你把http://它放在它的前面它将是一个HTTP URL,这显然是你想要的.

(b)FileInputStream用于文件,而不是URL.

(c)从任何 URL 获取输入流的方式是通过URL.openStream(),或URL.getConnection().getInputStream(),相当于你,但你可能有其他理由先得到URLConnection并使用它.

Answer 4

纯Java：

 urlToInputStream(url,httpHeaders);

我使用这种方法取得了一些成功。它处理重定向，并且可以将可变数量的HTTP 标头作为Map<String,String>. 它还允许从 HTTP 重定向到 HTTPS。

private InputStream urlToInputStream(URL url, Map<String, String> args) {
    HttpURLConnection con = null;
    InputStream inputStream = null;
    try {
        con = (HttpURLConnection) url.openConnection();
        con.setConnectTimeout(15000);
        con.setReadTimeout(15000);
        if (args != null) {
            for (Entry<String, String> e : args.entrySet()) {
                con.setRequestProperty(e.getKey(), e.getValue());
            }
        }
        con.connect();
        int responseCode = con.getResponseCode();
        /* By default the connection will follow redirects. The following
         * block is only entered if the implementation of HttpURLConnection
         * does not perform the redirect. The exact behavior depends to 
         * the actual implementation (e.g. sun.net).
         * !!! Attention: This block allows the connection to 
         * switch protocols (e.g. HTTP to HTTPS), which is <b>not</b> 
         * default behavior. See: /sf/ask/131896131/ 
         * for more info!!!
         */
        if (responseCode < 400 && responseCode > 299) {
            String redirectUrl = con.getHeaderField("Location");
            try {
                URL newUrl = new URL(redirectUrl);
                return urlToInputStream(newUrl, args);
            } catch (MalformedURLException e) {
                URL newUrl = new URL(url.getProtocol() + "://" + url.getHost() + redirectUrl);
                return urlToInputStream(newUrl, args);
            }
        }
        /*!!!!!*/

        inputStream = con.getInputStream();
        return inputStream;
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

完整的调用示例

private InputStream getInputStreamFromUrl(URL url, String user, String passwd) throws IOException {
        String encoded = Base64.getEncoder().encodeToString((user + ":" + passwd).getBytes(StandardCharsets.UTF_8));
        Map<String,String> httpHeaders=new Map<>();
        httpHeaders.put("Accept", "application/json");
        httpHeaders.put("User-Agent", "myApplication");
        httpHeaders.put("Authorization", "Basic " + encoded);
        return urlToInputStream(url,httpHeaders);
    }