DDevelopment & Design

Modular Web Application using Eclipse Snaps

Few days ago, new milestone 3.0.0.M03 of Eclipse Virgo was released. Final release of this well prepared OSGi-based application Server getting closer so I decided to take a look at how to use it to write simple modular web application.

What does it mean a modular web application in OSGi environment? I imagine that this application should:

1) Change their look after installation of some extensions.

2) Also we should be able to write new request handlers for our application or modify flow control of existed.

First idea which occurred to me how to resolve first mentioned problem is to use fragment bundles mechanism. Fragment bundles give opportunity to create bundles with resources and classes which will be accessible from host bundle classloader. A key use case of its was “providing translation files for different locales“. So we can do few fragments with jsp files which should be able to include in index servlet page. Also we can provide some configuration files with class names of new request handlers which could be created using java reflection.

But fragment bundles have some disadvantages. How we can read in specification: “The new content of the updated fragment must not be allowed to attach to the host bundles until the Framework is restarted or the host bundle is refreshed“. This mean that we cannot do installation of extention without refreshing host bundle. Also new jsps must be compiled as a part of host application’s jsps so it is second reason why host bundle should be restarted. The last thing is that fragment bundles can’t have Bundle Activator which is also useful in many cases.

Eclipse Virgo gives component which resolves this problems – Virgo Snaps. It is easy in use extension which helps create modular web application framework. Sources are available here

After build of project and copy artifacts to virgo:

cd build-snaps

ant jar

cd ..

cp org.eclipse.virgo.snaps.api/target/artifacts/org.eclipse.virgo.snaps.api.jar ${virgo.home}/repository/usr/

cp org.eclipse.virgo.snaps.core/target/artifacts/org.eclipse.virgo.snaps.core.jar ${virgo.home}/repository/usr/

… and restart of server, we are ready to use snaps.

In samples dir there is example menu-bar showing idea of Snaps. In host bundle – animal.menu.bar we can see in top.jsp usage of taglib snaps:

  • “> ${snap.properties[‘link.text’]}

 

 

It is simple way to iterate through snaps associated with this host. Only thing which we must to do is to add this snippet to MANIFEST.MF:

Snap-Host: animal.menu.bar;version="[1.0, 2.0)"

Snap-ContextPath: /cat

In first line we are manifesting that this snap will be used as a part of host animal.menu.bar. In the second that all servlets will be deployed in this subcontext of context of host.

In this example also were used properties from file snap.properties which are available in session as attribute properties of snap.

After install host bundle at url: http://localhost:8080/animal-menu-bar we can see page without menu items. After installation of new items are become available.

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DDevelopment & Design

Phonegap / Cordova and cross domain ssl request problem on android.

In one app I have participated, there was a use case:
  • User fill up a form.
  • User submit the form.
  • System send data via https to server and show a response.
During development there wasn’t any problem, but when we were going to release production version then some unsuspected situation occurred. I prepare the production version accordingly with standard flow for Android environment:
  • ant release
  • align
  • signing
During conduct tests on that version, every time I try to submit the form, a connection error appear. In that situation, at the first you should check whitelist in cordova settings. Every URL you want to connect to, must be explicit type in: 
res/xml/cordova.xml
If whitelist looks fine, the error is most likely caused by inner implementation of Android System. The Android WebView does not allow by default self-signed SSL certs. When app is debug-signed the SSL error is ignored, but if app is release-signed connection to untrusted services is blocked.



Workaround


You have to remember that secure connection to service with self-signed certificate is risky and unrecommended. But if you know what you are doing there is some workaround of the security problem. Behavior of method 
CordovaWebViewClient.onReceivedSslError
must be changed.


Thus add new class extended CordovaWebViewClient and override ‘onReceivedSslError’. I strongly suggest to implement custom onReceiveSslError as secure as possible. I know that the problem occours when app try connect to example.domain.com and in spite of self signed certificate the domain is trusted, so only for that case the SslError is ignored. 

public class MyWebViewClient extends CordovaWebViewClient {

   private static final String TAG = MyWebViewClient.class.getName();
   private static final String AVAILABLE_SLL_CN 
                               = "example.domain.com";

   public MyWebViewClient(DroidGap ctx) {
       super(ctx);
   }

   @Override
   public void onReceivedSslError(WebView view, 
                                  SslErrorHandler handler, 
                                  android.net.http.SslError error) {

       String errorSourceCName = error.getCertificate().
                                  getIssuedTo().getCName();

       if( AVAILABLE_SLL_CN.equals(errorSourceCName) ) {
           Log.i(TAG, "Detect ssl connection error: " + 
                       error.toString() + 
                       „ so the error is ignored”);

           handler.proceed();
           return;
       }

       super.onReceivedSslError(view, handler, error);
   }
}
Next step is forcing yours app to  use custom implementation of WebViewClient. 

public class Start extends DroidGap
{
   private static final String TAG = Start.class.getName();

   @Override
   public void onCreate(Bundle savedInstanceState)
   {
       super.onCreate(savedInstanceState);
       super.setIntegerProperty("splashscreen", R.drawable.splash);
       super.init();

       MyWebViewClient myWebViewClient = new MyWebViewClient(this);
       myWebViewClient.setWebView(this.appView);

       this.appView.setWebViewClient(myWebViewClient);
       
       // yours code

   }
}
That is all ypu have to do if minSdk of yours app is greater or equals 8. In older version of Android there is no class 
android.net.http.SslError
So in class MyCordovaWebViewClient class there are errors because compliator doesn’t see SslError class. Fortunately Android is(was) open source, so it is easy to find source of the class. There is no inpediments to ‘upgrade’ app and just add the file to project. I suggest to keep original packages. Thus after all operations the source tree looks like:

Class SslError placed in source tree. 
 Now the app created in release mode can connect via https to services with self-signed SSl certificates.