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From Jason Lea <ja...@kumachan.net.nz>
Subject Re: [DBCP] using dbcp in struts throws sometimes a NoSuchElementException / SQLNestedException
Date Thu, 26 Aug 2004 09:38:10 GMT
First don't use removeAbandoned.  It could cause random errors by 
removing connections which are still in use.  Better to test the system 
to find leaks than have them cleaned up by removeAbandoned in a 
production system.  TestOnBorrow should be enough for the system to hand 
out working connections to your application.

So do this

      <set-property property="removeAbandoned" value="false" />


Next, for testing use maxActive of 1, so only 1 connection can be given 
out.  This should cause the system to fail quickly if you have forgotten 
to close a connection somewhere.  This should mean your system will 
always fail at the same point, if there is a problem, instead of randomly.

Then rewrite your method as follows:

public ArrayList getResult( ... ) {
    ArrayList data = new ArrayList();
    int counter = 0;

    Connection connection = null;
    CallableStatement cstmt = null;
    ResultSet rset = null;
    
    try  {
      connection = dataSource.getConnection();
      cstmt=conn.prepareCall( "my sql statement" );
      rset = cstmt.executeQuery()

      while( rset.next() ) {
          .. do something with the result
      }
    } catch (SQLException e)  {
      e.printStackTrace();
    } finally {
	close(conn,rset,ctmt);
    }
    return data;
  }

//you could put this code somewhere handy where it can be called where you need it
//eg make it a static method somewhere so can use DbUtils.close(conn,rs,stmt) from anywhere
private void close(Connection conn, ResultSet rs, Statement stmt) {
    try {
        if (null != stmt)
            stmt.close();
    } catch (SQLException s) {
        //ignore
    }

    try {
        if (null != rs)
            rs.close();
    } catch (SQLException s) {
        //ignore
    }


    try {
        if (null != conn)
            conn.close();
    } catch (SQLException s) {
        //ignore
    }
}


The conn.close() does not close the connection, instead it passes it 
back to the pool so it can be reused.  I normally use call a method to 
open my connection, and in that method put debugging information such as 
when the conneciton is opened and what the current number of connections 
in the pool is.

Once you have it working with maxActive set to 1, test it with maxActive 
40 then deploy to the production system.



PANTA-RHEI WOLF wrote:

>Hi there, i have a very strange behaviour using DBCP. I have a small set of JSPs talking
to an oracledatabase. after a while
>it looks if my application hang. 2 till 3 minutes later it seems to work fine again. When
i have a look in my logfile, i can see
>the following exception. I do not know what happen exactly, can anyone help me please?
>
>Another question, i check always if the resultset/statement and connection is available
and then i close the connection.
>Is it correct closing it after use?
>
>Below is the Exception, the datasource-config and a snippet from my application.
>
>Thank you in advance
>
>Mirko
>
>The Exception is the following:
>
>04/08/24 15:51:59 org.apache.commons.dbcp.SQLNestedException: Cannot get a connection,
pool exhausted 04/08/24 15:51:59
> 	at org.apache.commons.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:103)
04/08/24 15:51:59 
>	at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:540) 04/08/24
15:51:59
> 	at de.orb.quick.model.CommunicationLayer.executeStatement(CommunicationLayer.java:86)
04/08/24 15:51:59
> 	at de.orb.quick.model.TreeDataBean.getResult(TreeDataBean.java:57) 04/08/24 15:51:59

>               ....
> 	at org.apache.commons.dbcp.AbandonedObjectPool.borrowObject(AbandonedObjectPool.java:74)
04/08/24 15:51:59 
>	at org.apache.commons.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:95)
04/08/24 15:51:59 	... 62 more 
>
>The datasource Configuration in struts-config.xml:
>
>    <data-source type="org.apache.commons.dbcp.BasicDataSource">
>      <set-property property="driverClassName" value="oracle.jdbc.driver.OracleDriver"
/>
>      <set-property property="url" value="jdbc:oracle:thin:@host:1521:SID" />
>      <set-property property="username" value="user" />
>      <set-property property="password" value="pass" />
>      <set-property property="initialSize" value="5" />
>      <set-property property="maxActive" value="40" />
>      <set-property property="maxIdle" value="5" />
>      <set-property property="testOnBorrow" value="true" />
>      <set-property property="maxWait" value="120000" />
>      <set-property property="defaultAutoCommit" value="false" />
>      <set-property property="validationQuery" value="select sysdate from dual" />
>      <set-property property="removeAbandoned" value="true" />
>    </data-source>
>
>
>the application snippet: 
>// -----------------------------------------------------------------
> public ArrayList getResult( ... ) {
>    ArrayList data = new ArrayList();
>    ResultSet rset = null;
>    int counter = 0;
>    
>    try  {
>      rset = executeStatement( "my sql statement" );
>      if(rset != null){
>        while( rset.next() ) {
>         
>          .. do something with the result
>
>        }
>      }
>    } catch (Exception ex)  {
>      ex.printStackTrace();
>    } finally {
>      try {
>        if (rset!= null && rset.getStatement() != null && rset.getStatement().getConnection()
!= null) { // Close resultset & statements
>           rset.getStatement().getConnection().close();
>        }
>       } catch (Exception ignored) {       }
>    }
>    return data;
>  }
>
>// -----------------------------------------------------------------
>    public ResultSet executeStatement( List parameter ) {
>      ResultSet rset = null;
>      CallableStatement cstmt = null;
>      try {
>       
>        Connection connection = dataSource.getConnection();
>        String dbBuffer = new StringBuffer( parameter.get(0).toString() );
>
>        if (connection != null) {
>          cstmt = connection.prepareCall( dbBuffer );
>          rset = cstmt.executeQuery();
>        }
>      } catch (SQLException ex) {
>        ex.printStackTrace();
>      } 
>      return rset;
>    }
>
>
>
>Mit freundlichen Grüßen
>
>Mirko Wolf
>
>-----------------------------------------------------------------------------------------------------------------------------------------
>panta rhei systems gmbh
>budapester straße 31
>10787 berlin
>tel +49.30.26 01-14 17
>fax +49.30.26 01-414 13
>wolf@panta-rhei.de 
>www.panta-rhei.de 
>
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-- 
Jason Lea



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