No suitable driver found for Oracle Database connection

I have small Java Application, which execute every day and checks for data in database using Cronj Schedular and everything works fine, but recently I have observed that, it is failing due to

java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:@160.110.xx.xxx:1521/test

At the same time, when I run my test code to check Database connectivity that works fine without above exception. I’m unable to figure it out. Although, there was just slight code change, but that was nowhere related to Database or Database connection. Anyone, help me on this ?

dbconf.java

public class dbconf {

    private Connection connect;
    private String connstr;

    public Connection getConnection() throws SQLException {
        connstr = "jdbc:oracle:thin:@160.110.xx.xxx:1521/test";

        try {
                String uname = "scott";
                String pass = "tiger";
                Class.forName("oracle.jdbc.OracleDriver").newInstance();
                connect = DriverManager.getConnection(connstr, uname, pass);

        } catch (Exception e) {
            System.out.println(e.toString());
        }

            return connect;
    }
}

I’m using ojdbc6.jar and Oracle11g

Edited – Application Log file

Wed Jul 01 09:25:17 IST 2015:------- Initializing -------------------
Wed Jul 01 09:25:17 IST 2015:------- Scheduling Jobs ----------------
Wed Jul 01 09:25:17 IST 2015:------- Job Started Running ----------------
Thu Jul 02 06:00:00 IST 2015 : Job Executed..!! Bschedularv2.2
java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:@160.xxx.67.xxx:1521/test
Sat Jul 04 06:00:00 IST 2015 : Job Executed..!! Bschedularv2.2
Sun Jul 05 06:00:00 IST 2015 : Job Executed..!! Bschedularv2.2
java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:@160.xxx.67.xxx:1521/test

So, you can see, It failed on 3rd and 6th July. But, in between it ran fine.

==Update 1==

It seems, nobody is reading my question properly, I have clearly mentioned that, It is running fine for someday, but someday it is failing. If it was classpath issue, then It shouldn’t have ran any day.

===Update 2===

Many of below answers were pointless, but few were having some logical view. I have used printStracktrace and tried to debug each point and finally I got some clue. 3 Days back, I deployed new version of application on the same server (included printStackTrace and SysOut), First 2 days It ran fine, today it Failed with following error.

INFO: Illegal access: this web application instance has been stopped already.  Could not load com.schedular.job.BirthdayJob.  The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
java.lang.IllegalStateException
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1600)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
    at org.quartz.simpl.LoadingLoaderClassLoadHelper.loadClass(LoadingLoaderClassLoadHelper.java:59)
    at org.quartz.simpl.CascadingClassLoadHelper.loadClass(CascadingClassLoadHelper.java:99)
    at org.quartz.simpl.CascadingClassLoadHelper.loadClass(CascadingClassLoadHelper.java:138)
    at org.quartz.impl.jdbcjobstore.StdJDBCDelegate.selectJobDetail(StdJDBCDelegate.java:852)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.acquireNextTrigger(JobStoreSupport.java:2816)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport$40.execute(JobStoreSupport.java:2759)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport$40.execute(JobStoreSupport.java:2757)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.executeInNonManagedTXLock(JobStoreSupport.java:3787)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.acquireNextTriggers(JobStoreSupport.java:2756)
    at org.quartz.core.QuartzSchedulerThread.run(QuartzSchedulerThread.java:272)

Jul 13, 2015 6:00:00 AM org.apache.catalina.loader.WebappClassLoader loadClass
INFO: Illegal access: this web application instance has been stopped already.  Could not load com.schedular.job.BirthdayJob.  The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
java.lang.IllegalStateException
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1600)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
    at org.quartz.simpl.LoadingLoaderClassLoadHelper.loadClass(LoadingLoaderClassLoadHelper.java:59)
    at org.quartz.simpl.CascadingClassLoadHelper.loadClass(CascadingClassLoadHelper.java:99)
    at org.quartz.simpl.CascadingClassLoadHelper.loadClass(CascadingClassLoadHelper.java:138)
    at org.quartz.impl.jdbcjobstore.StdJDBCDelegate.selectJobDetail(StdJDBCDelegate.java:852)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.retrieveJob(JobStoreSupport.java:1385)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.triggerFired(JobStoreSupport.java:2964)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport$43.execute(JobStoreSupport.java:2908)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport$43.execute(JobStoreSupport.java:2901)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.executeInNonManagedTXLock(JobStoreSupport.java:3787)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.triggersFired(JobStoreSupport.java:2900)
    at org.quartz.core.QuartzSchedulerThread.run(QuartzSchedulerThread.java:336)

Answer

As someone approached me for the solution of this issue. I’m posting it now.

1. I undeployed the application, which was having this issue and cleaned up all related files from the server.
2. Then, I restarted the tomcat server. So that, it will flush up all temporary files and cache.
3. Then, I deployed the same application and it started working without any issue.