How to compile with a bash script a multipackaged java project that uses jar file

I am developing a project for my Computer Network course. Actually I ended it, now I need to write a script to compile it, so the teacher will be able to run it

I developed with Netbeans and now I am struggling to compile it by command line.

I have 3 folders (packages)

client: classes of the client process
server: classes of the server process
sharedClasses: classes usefull to both client and server (like User.java)

Also I am using the Gson as a jar file which is needed in the sharedClasses package

for example in sharedClasses there is a class called Message that uses Gson to be transformed in a json string

I tried a lot to create a script that compile it all but every time I get "ClassNotFoundException" or stuff like that: the online guides to understand classpath and so on are pretty bad.

Can someone tell me how to do my script and explain why things are done the way they are? Thanks

Solution

Path variables are a concept in all Unix and Windows operating systems. They are not a Java invention, but Java bases its own classpath and module path concepts on them.

A path variable’s value is simply a string which contains a list of file locations, separated by a colon (:) in Unix or a semicolon (;) in Windows.

The most common path variable is simply PATH. (I believe that in Windows, the variable’s canonical name is Path, but environment variables are case-insensitive in Windows, so it can be referred to as PATH in most cases.)

When you try to execute a program on the command line, by specifying a command name with no directory components, the operating system checks each file location in PATH, in order, and for each location which is a directory, the system will look for a match there. The first match is the one the operating system uses.

Java borrows this concept for the classpath. In the very early days of Java, it was exactly the same: If your classpath were /home/giulio:/opt/libraries, and you were looking for a class named com.example.ConnectionFactory, Java would look for a compiled file named com/example/ConnectionFactory.class in /home/giulio and then in /opt/libraries.

It wasn’t long before the classpath was allowed to contain files which are compressed archives of classes, in addition to directories. Your classpath might contain /home/giulio:/opt/libraries/foolib.jar, in which case Java would first check for a requested class in /home/giulio, since that is a directory, and if that failed, it would look for a matching entry in the /opt/libraries/foolib.jar archive file. (Zip files are also acceptable, and in fact a .jar file is really just a zip file with a few special Java-specific entries.)

So, when you want to tell Java to look in certain places for libraries, specify them in the classpath.

For instance, when compiling your client code:

projectroot=`dirname "$0"`
javac -classpath "$projectroot"/sharedClasses/classes \
    -d "$projectroot"/client/classes \
    "$projectroot"/client/src/*.java

When you run your code:

java -classpath "$projectroot"/sharedClasses/classes:"$projectroot"/client/classes \
    edu.acme.giulio.client.Main