I need some help concerning using 2 jar files in Java

Question

Well I have 2 .jar files. The main jar file is the jar file for my whole project and the other .jar file being the MySql JDBC Connector.

Well basically whats happening right now is that when I build the project I have the one main .jar file with everything but the MySql JDBC Connector .jar file is inside the main jar file when it builds in NetBeans.

Now when I am just running the project from within NetBeans the MySql JDBC driver can be found inside the src/com/game/mysql folder that I have it in. But when I build the project the Java application cannot locate the JDBC driver from within the main jar file.

When I open the main jar file with WinRar I can see that the JDBC jar file is still in its /com/game/mysql/ folder. But why cant the Java application access it?

I have heard that nested .jar files are not supported in Java so Im thinking this might be the reason although Im not sure if thats true. Is there a way that I can make it so that the application can find the JDBC .jar file within the main jar file?

Also I have done the thing in NetBeans where you add the .jar file through right clicking project -> properties -> Library -> Add Folder/Jar. Thats what makes it work in the NetBeans run but still not the App build.

Answer 1

I have heard that nested .jar files are not supported in Java

More precise, classes in a JAR file which is packaged as a child JAR inside a main JAR are indeed by default invisible to classes in the main JAR.

You have basically 2 options:

1. Ship your application with 2 loose JARs: your.jar and mysql.jar and define the relative path to the mysql.jar in the Class-Path entry of the MANIFEST.MF file of your.jar.

   Class-Path: mysql.jar
   

   When you put both JARs in the same folder and execute your.jar by java -jar your.jar, then it will work.

2. Let your IDE repackage all loose classes of mysql.jar inside your.jar or add a special classloader which preloads the classes of any embedded JARs. Since I don't do Netbeans, I can't tell whether it supports it and if so, how to do it. In Eclipse, however, this is definitely possible. See also this answer.