Hi,
Who told you that the JDBC connection should not be done at init() method? If you do
it anywhere else, it is not possible to get a persistent connection.
If you are going to use conection pooling also, the object of the class that is going
to make a db connection should be created inside the init() method.
Note: In connection pooling , instead of having a single connection being shared
between the multiple threads, a pool say around 5 connections are created and given to
the threads on demand. The connections are maintained in a hash. When a request arises
when all the connections are used up, a new connection will be generated and added to
the hash. Once a thread finishes its job, it will return the connection to the hash by
setting it to be in free state.
bye
---
Veena T
Assistant Profesor,
Manipal Center for Information Science,
Manipal.
576 119
Email: [EMAIL PROTECTED]
Telephone: 91+08252-71915/71914
On Mon, 22 May 2000 07:23:49 Aniket Manohar Shende wrote:
>may i know why connections shouldn't be built in the init method . how do
>you manage connection pooling otherwise ??
>
>> ----------
>> From: Varalakshmi Allamaraju[SMTP:[EMAIL PROTECTED]]
>> Reply To: A mailing list for discussion about Sun Microsystem's Java
>> Servlet API Technology.
>> Sent: Monday, May 22, 2000 4:51 PM
>> To: [EMAIL PROTECTED]
>> Subject: Re: JDBC connection problem
>>
>> - 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.
>>
>>
>> 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?
>> > f"Ye -d8-e>=d::gs"g"5e- g"Yf4;
>> > http://www.chinaren.com
>> >
>> >
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>
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