how to change Java code to access database using JDBC after creating JDBC connection pool in GlassFish? - oracle

Question

I'm new to JDBC. I've installed GlassFish 3.1.1 on Centos 6.2 and need to use it with an application that connects to an Oracle 11G database on another server. I've read through the documentation for GlassFish and think I understand how to create a JDBC connection pool as well as a JDBC resource. My question is, how do I use this information when coding the java middle-tier to connect to the database?
Currently (with just GlassFish install and no JDBC configuration), I am relying on the CentOS enviroment variables for java (such as CLASSPATH) to allow the web application to use the JDBC drivers. However, I'm getting the following error:
java.lang.NoClassDefFoundError: oracle/jdbc/pool/OracleDataSource
Thus, my attempt to create a JDBC connection pool and resource in GlassFish (so the app can use the JDBC driver). My java file starts out:
import java.sql.*;
import oracle.jdbc.*;
import oracle.jdbc.pool.OracleDataSource;
class JDBCexample {
public static void main(String args[]) throws SQLException {
Connection conn;
Statement stmt;
ResultSet rset;
String query;
String sqlString;
String person_firstName;
String person_lastName;
String person_email;
int person_salary;
// connect to database
OracleDataSource ds = new OracleDataSource();
ds.setURL("jdbc:oracle:thin:myID/myPWD#192.168.0.1:1521:mySID");
conn = ds.getConnection();
// read something in database
stmt = conn.createStatement();
query = "SELECT first_name, last_name, email, salary FROM HR.Employees where rownum < 6";
rset = stmt.executeQuery(query);
while (rset.next()) {
person_firstName = rset.getString("first_name");
person_lastName = rset.getString("last_name");
person_email = rset.getString("email");
person_salary = rset.getInt("salary");
System.out.format(person_firstName + " " + person_lastName + " " + person_email + " %d%n", person_salary)
}
and so on...
QUESTION: How would I change the above code after I create a JDBC Connection Pool (named: myPool) and a JDBC Resource (named: myDBPool)? If it matters, I'm using Oracle 11.2, CentOS 6.2, GlassFish 3.1.1 with mod_jk and fronted by Apache 2.2 webserver, JDK 1.6. I don't have any clustering or load-balancing.
UPDATE 1: I thought this link was a good reference (see section titled: "Creating a Data Source Instance, Registering with JNDI, and Connecting"). But when I modify the above Java file as follows (just preparing the java file; haven't touched GlassFish yet),
// Add These:
import javax.naming.Context;
import javax.naming.InitialContext;
// Change from this:
// connect to database
OracleDataSource ds = new OracleDataSource();
ds.setURL("jdbc:oracle:thin:myID/myPWD#192.168.0.1:1521:mySID");
conn = ds.getConnection();
// To this:
// connect to database
Context ctext = new InitialContext();
OracleDataSource ds = (OracleDataSource)ctext.lookup("jdbc/myDBPool");
conn = ds.getConnection();
I get the errors:
JitterClass.java:67: unreported exception javax.naming.NamingException; must be caught or declared to be thrown
Context ctext = new InitialContext();
^
JitterClass.java:68: unreported exception javax.naming.NamingException; must be caught or declared to be thrown
OracleDataSource ds = (OracleDataSource)ctext.lookup("jdbc/myDBPool");
^
UPDATE 2: I cleared those compile errors using cyril's comments below (to throw all exceptions). Then I created JDBC Connection Pool and JDBC Resource, and the Ping was successful. So then I run the application from the client and observe the following error:
java.lang.ClassCastException : com.sun.gjc.spi.jdbc40.DataSource40 cannot be cast to oracle.jdbc.pool.OracleDataSource
At this point, if I add an include javax.sql.DataSource to the program, and change this line:
OracleDataSource ds = (OracleDataSource)ctext.lookup("jdbc/myDBPool");
to become this line:
DataSource ds = (DataSource)ctext.lookup("jdbc/myDBPool");
it compiles without errors. But now I'm confused... aren't we supposed to be using OracleDataSource here? Or, does GlassFish somehow implement OracleDataSource since I do see a setting for this connection pool for Datasource Classname set to oracle.jdbc.pool.OracleDataSource (?). Hoping someone can explain this.

Answer 1

Do pings on your connection pool work?
If not, check your pool configuration w/ http://docs.oracle.com/cd/E18930_01/html/821-2416/beamw.html#beanh
Once pings work and the JDBC Resource is configured, you should be able to access it in your app code through JNDI:
InitialContext context = new InitialContext();
DataSource ds = (DataSource) context.lookup("jdbc/myDBPool"); // or whatever name you used when creating the resource
conn = ds.getConnection();
Hope it helps,
RESPONSE TO UPDATE 1:
That's just the compiler telling you to formally catch or declare a checked exception which may be thrown by JNDI.
For testing purposes, the easiest way out of this (and future errors like this) is to just widen your method signature to throw all exceptions, i.e.:
public static void main(String args[]) throws /*SQL*/Exception {
RESPONSE TO UPDATE 2:
There's no reason to cast JDBC interfaces down to Oracle implementations unless you need to access any custom feature not specified in the JDBC spec. The purpose of a DataSource is to be a factory for Connections, whose API is defined in the JDBC interface, so that should be all you need. When you define a connection pool and resource in GlassFish, the app server is adding value by wrapping the JDBC driver classes and proxying them seamlessly for you as long as you stick to import java.sql.*. No need for oracle imports :) The main advantage being that if you ever decide to switch to MySQL or some other data store later on, your code is then portable and doesn't need any change.

Answer 2

To add to cyril's good answer:
Instead of the JNDI lookup, you can also use Resource Injection to set up your DataSource:
#Resource(name = "jdbc/Your_DB_Res")
private DataSource ds;
On startup, the application server will then inject the JDBC ressource. This section of Java EE Tutorial has more on that matter.
By using resource injection, you can reduce the amount of boilerplate code. This article introduces the concepts.

Answer 3

Besides adding the driver to your classpath, you should try adding the appserv-rt.jar file to your project's build path (the jar is located in Glassfish's lib directory). If you don't want to include all the other jars you should first create a library containing the appserv-rt jar and then add it to your project's build path.