JDBC connection object returns null in Servlet/Web application

Question

I am trying to connect my Java Web application to a mysql server. I am deploying on tomcat. I have a JDBC class which a I have created which returns the connection object in a normal java main program. However when I use the JDBC class on a deployed tomcat application, it returns null. I do not understand this. It will return connection in main but not in servlet/Web app. Thanks. Code:

Registration.Servlet:

    Jdbc dbConn = new Jdbc();
    Connection con = dbConn.connect();
    String insert_member = "INSERT INTO Members (id, name, address, dob, "
            + "dor, status, balance)"  + " VALUES (?, ?, ?, ?, ?, ?, ?)";
    //String c = con.toString();
    //con = null for some reason
    pstmt = con.prepareStatement(insert_member);
    pstmt.setString(1, "coo");
    pstmt.setString(2, "aa");
    pstmt.setString(3, "26 road");
    pstmt.setDate(4, new java.sql.Date(new Date().getTime()));
    pstmt.setDate(5, new java.sql.Date(new Date().getTime()));
    pstmt.setString(6, "APPLIED");
    pstmt.setFloat(7, 10);
    pstmt.execute();

JDBC class:

public class Jdbc {
Connection connection;
Statement statement;
ResultSet rs;

    public Jdbc() {
        String db = "xyz_assoc";
                try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection
                ("jdbc:mysql://localhost:3306/"+db.trim(), "root", "");
        }
        catch(ClassNotFoundException cfe){    

        }
        //SQL exception
        catch (SQLException ex) {
            Logger.getLogger(Jdbc.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    //open connection to database
    public Connection connect(){
        return connection;
    }

    //execute mysql queryS
    public ResultSet executeQuery(String sql_query) throws SQLException {
        statement = null;
        statement = connection.createStatement();
        rs = statement.executeQuery(sql_query);
        return rs;
    }

    //close connection to database
    //destroy any remaining objects
    public void close() throws SQLException{
        statement.close();
        rs.close();
        connection.close();
    }

 }
}

StackTrace:

Nov 30, 2016 11:12:18 AM org.apache.catalina.core.ApplicationContext log INFO: SessionListener: contextDestroyed() Nov 30, 2016 11:12:18 AM org.apache.catalina.core.ApplicationContext log INFO: ContextListener: contextDestroyed() Nov 30, 2016 11:12:23 AM org.apache.catalina.core.ApplicationContext log INFO: ContextListener: contextInitialized() Nov 30, 2016 11:12:23 AM org.apache.catalina.core.ApplicationContext log INFO: SessionListener: contextInitialized() Nov 30, 2016 11:12:23 AM org.apache.catalina.core.ApplicationContext log INFO: ContextListener: attributeAdded('org.apache.jasper.compiler.TldLocationsCache', 'org.apache.jasper.compiler.TldLocationsCache@7f4e2bf7') Nov 30, 2016 11:12:59 AM org.apache.catalina.core.StandardWrapperValve invoke SEVERE: Servlet.service() for servlet [Registration] in context with path [/XYZGroup] threw exception [Servlet execution threw an exception] with root cause java.lang.ClassNotFoundException: model.Jdbc at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571) at model.MemberManager.addMember(MemberManager.java:46) at web.Registration.processRequest(Registration.java:52) at web.Registration.doPost(Registration.java:101) at javax.servlet.http.HttpServlet.service(HttpServlet.java:646) at javax.servlet.http.HttpServlet.service(HttpServlet.java:727) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745)

Jeremy Gurr Jeremy Gurr · Accepted Answer · 2016-11-30T18:17:40

The most likely cause is that this line of code:

connection = DriverManager.getConnection
            ("jdbc:mysql://localhost:3306/"+db.trim(), "root", "");

is throwing an exception and not setting the connection. You swallow up one of the exceptions, the case where the driver class can't be found. You should log that. Then run this again and you should see in the logs the exception that is causing your problem.

If you are able to attach a debugger to this, you could set a breakpoint after that line and check the logs right after it is executed, making it a little easier to see where the exception is.

JDBC connection object returns null in Servlet/Web application

1 Answers