Connection to a URL from within an applet using Ap

问题:

In the following code, I have verified that connecting to a URL from within an applet preserves the browser's session if JDK's URLConnection class is used. However, this is not the case if Apache's HttpClient library is used. Does anyone know why? Alternatively, is there a way for me to set the connection instance to be used by an HttpClient instance?

import java.applet.Applet;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URISyntaxException;
import java.net.URL;

import javax.net.ssl.SSLException;

import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;

public class HttpClientTesterApplet extends Applet {
    private static final long serialVersionUID = -1599714556710568947L;

    public void testHttpClient() throws ClientProtocolException, IOException,
            URISyntaxException {
        URL url = new URL(String.format("%s://localhost:%s/%s/testHttpClient",
                getParameter("protocol"), getParameter("port"),
                getParameter("context")));

        HttpClient client = new DefaultHttpClient();

        HttpPost post = new HttpPost(url.toURI());

        System.out.println("Executing request " + post.getURI());

        try {
            System.out
                    .println(client.execute(post, new BasicResponseHandler()));
        } catch (SSLException e) {
            System.out.println(e.getMessage());
        }

        System.out.println("Executed request " + post.getURI());

        System.out.println("Opening connection " + url);

        HttpURLConnection urlConnection = (HttpURLConnection) url
                .openConnection();

        System.out.println("Opened connection " + url);

        urlConnection.setRequestMethod("POST");

        System.out.println("Connecting");

        urlConnection.connect();

        System.out.println("Connected");

        InputStream inputStream = urlConnection.getInputStream();

        try {
            while (inputStream.read() != -1) {
                System.out.println("Reading");
            }
        } finally {
            inputStream.close();
        }
    }
}

回答1:

This is a common problem with libraries implementing their own URL connection via Socket. Apparently, the JRE implementation of the URLConnection class can get to the browser information directly. We had to employ the technique as mentioned by oscargm above, i.e. on the appserver writing the request cookies to be the parameters to the applet AND getting to the browser's document cookies using JavaScript (this is for the case of SSO where the set of cookies may not be the same because of the intermediate agent -- proxy servers). Note that if the cookies are HttpOnly -- the javascript code will fail.

回答2:

You must send the jsessionid cookie or rewrite your URL to use the jsessionid.

That's the way the server knows your session.

If you generate the applet tag in a JSP page dynamically you can pass the jsessionidvalue to the applet as a parameter and then use it.

post.setHeader("Cookie", "jsessionid=" + jsessionidValue );

回答3:

I think that you're using an older version of HttpClient. Check out HttpClient's website.

In the current API, you can use HttpState in the execute method, so that your code could look like this:

HttpClient client = new HttpClient();
HttpMethod method = new PostMethod(url.toURI());
HttpState state = new HttpState();

client.executeMethod(HttpConfiguration.ANY_HOST_CONFIGURATION, method, state);

In the next execution, pass the same "state" object, and you'll get the credentials and cookies preserved.

回答4:

Possible causes, is that you have not done a disconnect() when using URLConnection, however, the apache library will close the connection when you are done with it.

回答5:

Thi is an important issue.

The standard java.net.URLConnection class integrates seamlessly with the java plugin and the web browser, can inherit session, HTTP authentication tokens, proxy connectors, etc.

The guys at Apache Commons made a gross mistake when they decided to implement HttpClient from Socket (ie, from scratch) instead of just developing on top of the standard java.net.URL* classes. HttpClient does not inherit from java.net.URLConnection so it cannot inherit its advanced enterprise features.

Maybe OpenSource projects are not so smart as they think.

回答6:

I could make it work without passing cookies as arguments from the Web Page with this code:

private String retrieveCookies(URL url) throws IOException, URISyntaxException 
{ 
     String cookieValue = null;

     CookieHandler handler = CookieHandler.getDefault();
     if (handler != null)    {
          Map<String, List<String>> headers = handler.get(url.toURI(), new HashMap<String, List<String>>());

          List<String> cookiesList = headers.get("Cookie");
          if (cookiesList != null)
          {
              for (String v : cookiesList) {
                  if (cookieValue == null) 
                      cookieValue = v; 
                  else
                      cookieValue = cookieValue + ";" + v; 
              }
          }
     } 
     return cookieValue; 
}

...

httppost.addHeader("Cookie", retrieveCookies(new URL(uploadUrl)));

JDK's class CookieHandler can fortunately get the cookies from the "system" store. In this case it's the browser store, accesed via the Java Plugin.

Sort of "manual work", but it works.

NOTE: I found the code here