e1042. getting the requesting url in a servlet.txt

这里面包含了一百多个JAVA源文件

A servlet container breaks up the requesting URL into convenient components for the servlet. The standard API does not require the original requesting URL to be saved and therefore it is not possible to get the requesting URL exactly as the client sent it. However, a functional equivalent of the original URL can be constructed. The following example assumes the original requesting URL is: 
    http://hostname.com/mywebapp/servlet/MyServlet/a/b;c=123?d=789

The most convenient method for reconstructing the original URL is to use ServletRequest.getRequestURL(), which returns all but the query string. Adding the query string reconstructs an equivalent of the original requesting URL: 
    // http://hostname.com/mywebapp/servlet/MyServlet/a/b;c=123?d=789
    public static String getUrl(HttpServletRequest req) {
        String reqUrl = req.getRequestURL().toString();
        String queryString = req.getQueryString();   // d=789
        if (queryString != null) {
            reqUrl += "?"+queryString;
        }
        return reqUrl;
    }

If the hostname is not needed, ServletRequest.getRequestURI() should be used: 
    // /mywebapp/servlet/MyServlet/a/b;c=123?d=789
    public static String getUrl2(HttpServletRequest req) {
        String reqUri = req.getRequestURI().toString();
        String queryString = req.getQueryString();   // d=789
        if (queryString != null) {
            reqUri += "?"+queryString;
        }
        return reqUri;
    }

The original URL can also be reconstructed from more basic components available to the servlet: 
    // http://hostname.com:80/mywebapp/servlet/MyServlet/a/b;c=123?d=789
    public static String getUrl3(HttpServletRequest req) {
        String scheme = req.getScheme();             // http
        String serverName = req.getServerName();     // hostname.com
        int serverPort = req.getServerPort();        // 80
        String contextPath = req.getContextPath();   // /mywebapp
        String servletPath = req.getServletPath();   // /servlet/MyServlet
        String pathInfo = req.getPathInfo();         // /a/b;c=123
        String queryString = req.getQueryString();          // d=789
    
        // Reconstruct original requesting URL
        String url = scheme+"://"+serverName+":"+serverPort+contextPath+servletPath;
        if (pathInfo != null) {
            url += pathInfo;
        }
        if (queryString != null) {
            url += "?"+queryString;
        }
        return url;
    }

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