- Never ever try to create connections objects in the constructor/init
methods of a servlet. Please refer to any good material on how
connections are created, and their relation to transactions!
- You mention that you make sure that only one request can access the
connectoon variable at a time. I don't see any such magic code in your
code.
- There have been several discussions on how and where to create
connections. Look into the archives. There is also an article in the JDJ
March issue.
cheers.
zengjj wrote:
>
> Hi there,
> Now I use the javawebserver2.0 to develope a three-tier Database Applications.
> The client want to query the database in the applet through our servlet.
> Because it usually take serveral minuters to build a connection, so I use a global
>Connection variable,
> this connection will be built in the init function.
> And all request will use this global Connection
> variable to query the database. Certainly I ensure the only a request can
> aceess the variable at the same time.
> I test the servlet using the servletrunner. There are no
> problem in all cases.
> But when I use the servlet in the javawebserver2.0(trial version) and connect the
>oracle
> database, I found a problem:
> first query has no problem, but later query will hang forever (do not
> return).
>
> The problem do not happen when connecting other database. If using the
> servletrunner to test this servlet, it can connect to all database including the
>oracle database too.
>
> My oracle version is 7.3.3 in the WindowsNT.
>
> Following is my code segment:
>
> public class MapdPHServlet extends HttpServlet
> {
> Connection connection ;
>
> public MapdPHServlet()
> {
> super () ;
> try
> {
> String URL=new String("jdbc:odbc:testdb");
> Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
> connection = DriverManager.getConnection(URL);
> }
> catch (Exception e) {System.out.println ("# Initialize Error : " +
> e.toString()) ;} ;
> }
>
> public void init (ServletConfig config) throws ServletException
> {
> super.init (config) ;
> System.out.println (" # Initalize MapdPH Servlet...") ;
> }
>
> public void destroy()
> {
> super.destroy();
> try
> {
> connection.close();
> }
> catch (Exception e) {System.out.println ("# Destroy MapdPH Servlet
> Eorror") ;} ;
> System.out.println (" # Destory...") ;
> }
>
> /************* doPost() ***********************/
>
> protected void doPost (HttpServletRequest req,
> HttpServletResponse res)
> throws ServletException,IOException
> {
> // do a simple query and return the result to the client
> // I ensure there are only a request at the same time
> try {
>
> Statement statement=connection.createStatement();
> String SQLStatement = "Select * from person";
> if( statement.execute(SQLStatement) )
> { //send the result to the client
> .....
> }
> else // with Result Set
> {
> }
>
> statement.close();
> }
> catch (Exception e)
> {
> System.out.println (e) ;
> }
>
> } // end of doPost()
>
> Do you think it is my problem or the javawebserver's problem? Can you give
> me some
> suggestion to deal with the problem? At present, I build the connection in
> the doPost and
> close the connection before exit the doPost in order to solve this problem.
>
> By the way, there are some parameters in the javawebserver:
> Service Tuning ----- General ------------ Capacity
> --- Handler Threads
> --- Connection Persistence
> I found the javawebserver often hang when there are two many users(about 50)
> accessing the server simultaneously if I use the default value of these parameters.
> Even if I maximize all parameters, the javawebserver still hang occasionally.
> Do you think it is my problem or the javawebserver's problem?
>
> thanks in advance,
>
> jianjiang zeng
>
> ________________________
> Are you ChinaRen?
> 感受中国人的电子生活
> http://www.chinaren.com
>
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