Exception caused while querying Hive Derby database via JDBC - jdbc

Question

I am a new user to Hive and have just started using it for a project. I am having problem connecting to the database using java. It is explained as follows:
I ran Hive database on my machine that created a derby metastore_db using the Embedded Derby Driver. Now, I wish to query this metastore_db via a separate Java program for issuing queries.
I followed multiple tricks that I could find online but still am not able to get that working.
Snapshot of my Java file:
String url = "jdbc:derby:metastore_db;create=true";
String username = "APP";
String password = "mine";
String drivername = "org.apache.derby.jdbc.EmbeddedDriver";
Connection con = DriverManager.getConnection(url,username, password);
Statement stmt = con.createStatement();
res = stmt.executeQuery("describe " + tableName);
Running the java file:
I have placed it in the same folder as the metastore_db and then running it using the following command:
java -cp "derby-10.4.2.jar:." ConnectTesting
I get the following syntax exception:
java.sql.SQLException: Syntax error: Encountered "describe" at line 1, column 1.
Some of the things I have already tried:
url = "jdbc:derby:metastore_db;create=false";
url = "jdbc:derby://localhost:10000/metastore_db";
url = "jdbc:derby://localhost:1527/metastore_dbDB"; // By default port at which hive listens
The above two give error as:
No suitable driver found for jdbc:derby://localhost:10000/metastore_db
url = "jdbc:derby:<full_path_to_db>/metastore_db";
If I have my HIVE server already running, and then from another terminal I execute the java file, it says:
"Another instance of Derby may have already booted the database "
Can anyone kindly point out as to what am I doing wrong and how can I connect to the already existing database to issue queries.

Answer 1

That's a lot of different questions. Which one do you really need answered?
"describe" is a command implemented by the "ij" tool; it is not a SQL statement. So to run "describe", you have to run it from "ij" (or by using the RunScript utility to run "ij" within your application; you cannot run it directly from Statement.executeQuery().
In order to use the client-server driver, with the hostname:port syntax, you have to (a) use the derbyclient.jar rather than the derby.jar in your classpath, and (b) have the Network Server running.
And, you cannot have the same Derby (embedded) database open in multiple applications simultaneously, so while your application is running, you cannot run a second application against the same (embedded) database. If you need this functionality, you need to switch all your applications to using the client driver, and run the Network Server to provide multi-application access to your database.
Have you run the Derby tutorial yet? It covers most of these topics in more detail: http://db.apache.org/derby/docs/10.10/getstart/