Java 7/J2SE 1.7 API 文档（英文版，CHM 格式）

Redirection between HTTP URL and HTTPS URL is not followed. Symptoms When running applet in browser using Sun JVM, if the applet makes HTTP requests to a server which redirects to a HTTPS URL, the redirection would fail. It fails also in the case of making HTTPS requested to a server which redirects to a HTTP URL. The same applet runs properly in Microsoft VM. Cause The issue is caused by the HTTP/HTTPS redirection policy implemented in Sun JVM; because of serious security consequences, redirection between HTTP and HTTPS is not automatically followed. HTTP/HTTPS redirection is followed in MSVM, given a security warning dialog prompts the users everytime before the redirection is followed. Resolution To workaround the problem, it is the application responsibility to check the response code and recognize it as a redirect. The Location header field value can be checked for the redirect information, and then the application must decide whether or not to follow the redirect using the new protocol. For example, public void makeConnection(URL url) { URLConnection conn = url.openConnection(); InputStream is = conn.getInputStream(); .... is.close(); } The code should be changed to private InputStream openConnectionCheckRedirects(URLConnection c) throws IOException { boolean redir; int redirects = 0; InputStream in = null; do { if (c instanceof HttpURLConnection) { ((HttpURLConnection) c).setInstanceFollowRedirects(false); } // We want to open the input stream before // getting headers, because getHeaderField() // et al swallow IOExceptions. in = c.getInputStream(); redir = false; if (c instanceof HttpURLConnection) { HttpURLConnection http = (HttpURLConnection) c; int stat = http.getResponseCode(); if (stat >= 300 && stat <= 307 && stat != 306 && stat != HttpURLConnection.HTTP_NOT_MODIFIED) { URL base = http.getURL(); String loc = http.getHeaderField("Location"); URL target = null; if (loc != null) { target = new URL(base, loc); } http.disconnect(); // Redirection should be allowed only for HTTP // and HTTPS, and should be limited to 5 // redirections at most. // if (target == null || !(target.getProtocol().equals("http") || target.getProtocol().equals("https")) || redirects >= 5) { { throw new SecurityException("illegal URL redirect"); } redir = true; c = target.openConnection(); redirects++; } } } while (redir); return in; } public void makeConnection(URL url) { URLConnection conn = url.openConnection(); InputStream is = openConnectionCheckRedirects(conn); .... is.close(); } Related Information