CODEWITHSUNDEEP
javamysqlservlets
user8565055
user8565055

Reputation:

Querying and updating 2 separate tables in my sql one servlet

Currently I'm making an application that is a car rental application. The application can rent out a car, return a car ect. For returning a car I'm pulling in the user name of the person returning the car, attempting to query the db and pull out which car they are renting, then updating the user to no longer have a car rented out and updating the car details to become available. However I notice when I am querying the DB I'm getting a null return. I see my table has this user, so maybe I'm wrong in my syntax please help.

protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
    String carid = "";
    String uname = req.getParameter("User_Name");
    String defaulted = "User has no car";

    int rs;
    Connection conn = null;
    java.sql.PreparedStatement st = null;
    String nativeSQL = "";
    ResultSet result  =null;

    try {
        Context ctx = new InitialContext();
        Context env = (Context) ctx.lookup("java:comp/env");
        DataSource ds = (DataSource) env.lookup("jdbc/carRentalSystem");
        conn = ds.getConnection();

        conn.setAutoCommit(false);
        result = st.executeQuery("SELECT * FROM userdetails where User_Name='"+ uname+"'");
        if(result.next()) {
            carid= result.getString("Car_Rental");
        }

        st = conn.prepareStatement("update userdetails SET Car_Rental ='" + defaulted+ "' where User_Name='" + uname+ "' ");
        st.clearParameters();
        rs = st.executeUpdate();

        st = conn.prepareStatement("update cardetails SET Availability = 'Available' where id='" + carid+ "'");
        st.clearParameters();
        rs = st.executeUpdate();
        if (rs != 0) {
            res.sendRedirect("carRental.jsp");
            return;
        } else {

        } 
        conn.commit();


    } catch (Exception e) {
        try{conn.rollback();}catch(Exception e1){}
        e.printStackTrace();
    } finally {
        try {
            if (st != null)
                st.close();
        } catch (java.sql.SQLException e) {
        }
        try {
            if (conn != null)
                conn.close();
        } catch (java.sql.SQLException e) {
        }

    }
}

}

My error reads as follows

INFO: Server startup in 7620 ms

java.lang.NullPointerException at com.rental.servlet.AdminReturnCarServlet.doPost(AdminReturnCarServlet.java:63) at javax.servlet.http.HttpServlet.service(HttpServlet.java:648) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1539) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1495) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748)

Upvotes: 1

Views: 265

Answers (1)

P3trur0
P3trur0

Reputation: 3225

Your error is because the java.sql.PreparedStatement st = null; is not initialized before its execution at line:

st.executeQuery("SELECT * FROM userdetails where User_Name='"+ uname+"'");

Hope it helps.

Upvotes: 1

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