Writing method with dynamic return type without type casting

I have often come across this requirement across multiple projects, where we need to write a method, which can potentially return object of any class, and still you would not like to do a typecasting. Something like this:

MyClass myClass = getDynamicClass(MyClass.class);

Instead of :

MyClass myClass = (MyClass) getDynamicClass(MyClass.class);

Common example of such use case is where you would do some lookup of a dynamic service (as in OSGi) and return the object found. However, with Java 5 and above this is easy. So, if your earlier code was:

protected Object getDynamicClass(Class interfaceClass) {
    Object obj = null;
    // code to create / lookup the dynamic object
    return obj;
}

This code can be converted as follows:

protected <ReturnType> ReturnType getDynamicClass(Class<ReturnType> interfaceClass) {
    Object obj = null;
    // code to create / lookup the dynamic object
    if (interfaceClass.isInstance(obj)) {
        return interfaceClass.cast(obj);
    }
    return null;
}

This is very obvious code, but thought that sharing this would be useful. Enjoy!

Installing Java Plugin for Ubuntu / Linux for multiple users

If you are a Linux user like me and have encountered websites that require applet, you may be ok installing the default Java that comes with your distro, and most of the time you may be good to go with it.

But at times you may specifically want to install Sun Java on your system. Since Oracle has licensing restrictions, distros like Ubuntu do not have Sun Java in their repositories, and you will have to resort to some "longer" ways of installing Java as explained in here for Ubuntu.

But even by following the "longer" ways, you may be still annoyed when your browser says that Java plugin is missing (it happened for me for my Ubuntu 12.04). Or else, even when it may be working for you, it may not be working for other users on your computer, and you may have to create soft links to Java plugin executable in .mozilla/plugins directory of every user's home.

Assuming that you have already installed Java flavor of your choice, and want to enable Java plugin for your browser for every user of your computer, just create a soft link to the Java plugin executable under /usr/lib/mozilla/plugins/ directory.

cd /usr/lib/mozilla/plugins

ln -s /usr/lib/jvm/jdk1.7.0_17/jre/lib/amd64/libnpjp2.so

...and you are good to go. Now you can refresh your browser containing the applet to see that it is working, or you can test it at the Java's official test page here. For me here is how my browser looked after I configured Java as above:

Know your Geolocation right away with HTML5

Wondered how Google Maps tracks you current location? HTML5! Thats what enables most of the modern-day applications to track down your current location.

You can do it too right away!

Open up your JavaScript/Firebug console. You can hit F12 to work on most of the browsers. And paste the following JavaScript code snippet.

navigator.geolocation.getCurrentPosition(function(position){console.log(position);});

or

navigator.geolocation.getCurrentPosition(function(position){alert(position.coords.longitude + " / " + position.coords.latitude);});

Did you see a confirmation asked on your browser? Allow it! Thats it! It was so simple. You can now see your location in terms of longitude and latitude on the console. You can use this data along with Google Maps API to spot your location on a map.

Developing Java / OSGi applications on Day CQ

Day CQ is a very popular enterprise CMS (Content Management System) suite from Adobe. Although most of the time the development on Day CQ is related to CMS and most of the development can be mapped to a proper CMS system, there are times when you would need to develop some logic in your application, or need to develop some feature that may not be available readily within Day CQ. In these cases, you may need to write some application code.

Day CQ is a Java based software, and Java is the most popular way to develop custom features and application logic. To be specific, Day CQ is largely built using OSGi - a technology that enables you to develop truly modular applications. Developing any custom Java application modules also needs to be built on OSGi.

I have noticed that developing OSGi modules is often a pain for a CMS developer, largely because of the lack of full development support  (or call it a buggy development support) from the CRXDE (The bundled Eclipse based IDE), which makes OSGi module development to take long time and painful. This post intends to give more insights to a CQ developer on OSGi, and also to do faster development of OSGi modules with OSGi.

Solving eclipse error with SVN 1.6 (loading JavaHL library)

If you are using Eclipse and SVN (Subversion), there are high chances that you are using the Eclipse plugin - Subclipse. And if you recently upgraded to subclipse 1.6, there is a good chance that you have encountered the error or loading JavaHL Library, that says something like this:

Problem:

Failed to load JavaHL Library.
These are the errors that were encountered:
no libsvnjavahl-1 in java.library.path
no svnjavahl-1 in java.library.path
no svnjavahl in java.library.path
java.library.path = /opt/jdk/64/jdk1.6.0_20/jre/lib/amd64/server:/opt/jdk/64/jdk1.6.0_20/jre/lib/amd64:/opt/jdk/64/jdk1.6.0_20/jre/../lib/amd64:/usr/lib64/xulrunner-addons:/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib

If this is the case, then few tips to get this working. As always, I will suggest solutions with the least number of steps, and all simple.

1. When installing/updating subclipse 1.6, use the update site - http://subclipse.tigris.org/update_1.6.x/ from within Eclipse.
2. The installation screen shows the features. Make sure that all features marked "required" are selected for installation. (You will anyway be not allowed to proceed otherwise).

If it still does not work, it is highly possible that the Java native libraries required for the SVN to work together with Java (thats Java HL) is not available to the Java. Either not installed or just that Java is not able to find it.

1. Install Java HL

You can refer to here for a generic discussion on this topic, especially for Windows and Mac OS. For Linux, I have simpler solutions :).
Install through your package manager, a package named libsvn-java, that contains the JavaHL. You must make sure that it is for SVN 1.6.
For Ubuntu or other Debian based Linux, the command should be handy:

sudo  apt-get install libsvn-java

However, it is possible that the installation is requiring you to install the whole Java binaries itself, although you already have one (an old version, or a manually configured Java for example), and you are not willing to install the Java packages. In that case, just go to your package maintainer's site, and manually download the package, and unzip it to your system (yes, you will need root permissions), so that the dependencies are not installed.

If you had installations fine, without any hacks, restarting Eclipse should get your Subclipse working. If not, follow what is below.

2. Make Eclipse runtime aware of the new JavaHL binaries.

. There are two options for doing this:

1. Tell JVM/Eclipse about the JavaHL libraries when starting JVM with the system property, that points to the java library path where the JavaHL binaries are installed. eg:

      -Djava.library.path=/usr/lib/jni
   

   This option can be specified in config.ini as well.
2. Put the JavaHL binaries in paths that JVM normally searches for native libraries. Normally these paths are listed, in the error above. Above the paths are listed as:

   java.library.path = /opt/jdk/64/jdk1.6.0_20/jre/lib/amd64/server:/opt/jdk/64/jdk1.6.0_20/jre/lib/amd64:/opt/jdk/64/jdk1.6.0_20/jre/../lib/amd64:/usr/lib64/xulrunner-addons:/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib
   

I went for the second option, since that one seemed most non-intrusive and easy to me. Let me show it how I did that:

1. Choose any of the listed Java library paths. In a terminal, move into that directory:

cd /usr/lib/jvm/java-6-sun/jre/lib/i386

2. Make softlinks to the JavaHL libraries.

   sudo ln -s /usr/lib/jni/libsvnjavahl-1.so libsvnjavahl-1.so
   sudo ln -s /usr/lib/jni/libsvnjavahl-1.so.0 libsvnjavahl-1.so.0
   sudo ln -s /usr/lib/jni/libsvnjavahl-1.so.0.0.0 libsvnjavahl-1.so.0.0.0
   

Now restarting Eclipse should get everything working fine. If it does not, review your steps, and also read in full length about JavaHL from http://subclipse.tigris.org/wiki/JavaHL, and try the steps again.