How to catch exception when have max connection pool

Question

hi,
i have define in oracle user that i could have max 10 sessions at the same time.
I have jdbc datasource & connection pool defined at glassfish server(JSF application).
now, if in application is too many queries to the database then i have error: nullpointer exception - becouse when i try to do:
con = Database.createConnection(); - it generates nullpointer exception becouse there isn't free connection pool
i try to catch exception like this:
public List getrep_dws_wnioski_wstrzymane_graph() {     int i = 0;     try {     con = Database.createConnection();     ps =    (Statement) con.createStatement();     rs = ps.executeQuery("select data, klasa, ile_dni_wstrzymana, ile_wnioskow from stg1230.dwsww_wstrzymane_dws8 order by data, klasa, ile_dni_wstrzymana, ile_wnioskow");     while(rs.next()){       rep_dws_wnioski_wstrzymane_graph.add(i,new get_rep_dws_wnioski_wstrzymane_graph(rs.getString(1),rs.getString(2),rs.getString(3),rs.getString(4)));       i++;     }     } catch (NamingException e) {         e.printStackTrace();     } catch (SQLException e) {         e.printStackTrace();     } catch (NullPointerException e) {         e.printStackTrace();         throw new NoConnectionException();  // catch null 1     } finally {     try {         con.close();     } catch (SQLException e) {         e.printStackTrace();     } catch (NullPointerException e) {         e.printStackTrace();         throw new NoConnectionException();  // catch null 2     }     } return rep_dws_wnioski_wstrzymane_graph; }
but at line:
con.close();
i have nullpointerexception
and
at line
throw new NoConnectionException(); // catch null 2
i have: caused by exception.NoConnectionException
what's wrong with my exception class? how to resolve it?
public class NoConnectionException extends RuntimeException{     public NoConnectionException(String msg, Throwable cause){       super(msg, cause);     }     public NoConnectionException(){       super();     } }
at web.xml i have defined:
<error-page>         <exception-type>exception.NoConnectionException</exception-type>         <location>/NoConnectionExceptionPage.jsp</location>     </error-page>

Answer 1

thanks,
i did it and i have error:
java.sql.SQLException: Error in allocating a connection. Cause: Connection could not be allocated because: ORA-02391: exceeded simultaneous SESSIONS_PER_USER limit
at com.sun.gjc.spi.base.DataSource.getConnection(DataSource.java:115)
at logic.Database.createConnection(Database.java:37): conn = ds.getConnection();
public class Database {
     public static Connection createConnection() throws NamingException,
                SQLException {
            Connection conn = null;
            try{
                Context ctx = new InitialContext();
          if (ctx == null) {
               throw new NamingException("No initial context");
          DataSource ds = (DataSource) ctx.lookup("jdbc/OracleReports");
          if (ds == null) {
               throw new NamingException("No data source");
          conn = ds.getConnection();  // here's exception when max connections to database
          if (conn == null) {
               throw new SQLException("No database connection");
            } catch (NamingException e) {
                e.printStackTrace();
                throw new NoConnectionException(); 
         } catch (SQLException e) {
             e.printStackTrace();
                throw new NoConnectionException(); 
            catch (NullPointerException e) {
             e.printStackTrace();
                throw new NoConnectionException();  // obsluga bledy na wypadek jesli braknie wolnych polaczen do bazy
        return conn;
}and at my ealier code i have error:
at logic.GetDataOracle.getrep_dws_wnioski_wstrzymane_graph(GetDataOracle.java:192)
at line: con = Database.createConnection();
in code:
public List getrep_dws_wnioski_wstrzymane_graph() {
    int i = 0;
    try {
    con = Database.createConnection();
    ps =    (Statement) con.createStatement();
    rs = ps.executeQuery("select data, klasa, ile_dni_wstrzymana, ile_wnioskow from stg1230.dwsww_wstrzymane_dws8 order by data, klasa, ile_dni_wstrzymana, ile_wnioskow");
    while(rs.next()){
      rep_dws_wnioski_wstrzymane_graph.add(i,new get_rep_dws_wnioski_wstrzymane_graph(rs.getString(1),rs.getString(2),rs.getString(3),rs.getString(4)));
      i++;
    } catch (NamingException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    } catch (NullPointerException e) {
        e.printStackTrace();
        throw new NoConnectionException();
    } finally {
    try {
        if(con != null)
        con.close();
    } catch (SQLException e) {
        e.printStackTrace();
    } catch (NullPointerException e) {
        e.printStackTrace();
        throw new NoConnectionException(); 
return rep_dws_wnioski_wstrzymane_graph;
}so what's wrong?
i have limit max sessions 10 at oracle so i set at my connection pool 5 connections as max. But when i get max 5 sesssins and try to execute next query then i can't catch exception..