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From alexis <alz...@gmail.com>
Subject Re: recovering connections on jdbc connection pool
Date Sun, 08 May 2011 17:04:26 GMT

On May 8, 2011, at 1:22 PM, Felix Schumacher wrote:

> Am Sonntag, den 08.05.2011, 12:29 -0300 schrieb alexis:
>> Here's a snippet of my code, this method was with the described problem
>> 
>> 
>> public void insertVDNInfo(VDNInfo vdns) throws SQLException {
> Why do you want to throw a SQLException?
> 

Because all methods regarding database access are called from the same class, im throwing
the sqlexception and then catch that exception on the class that call all those methods. 


>> 
>>        Calendar c = Calendar.getInstance();
>> 
>>        Iterator<VDNInfo.VDN> it = vdns.getVdns().iterator();
> Seems like you can use
> for (VDNInfo.VND v: vdns.getVdns()) {
> ...
> }
> instead of x=y.iterator() combined with while(x.hasNext())
> { v=x.next(); }
> 

yes, you're right

>>        Connection c1 = null;
>>        Statement s1 = null;
>> 
>>        try {
>>            while (it.hasNext()) {
>>                c1 = getConnection();
> Your getConnection method can return null, so you should guard against
> it.
> 



>>                s1 = c1.createStatement();
>>                VDNInfo.VDN v = it.next();
>> 
>>                String query = "INSERT INTO list.vdn VALUES ("
>>                        + "'" + v.getName() + "'," + v.getExt() + "," + v.isVdnovr()
+ "," + v.getCor() + "," + v.getTn() + "," + v.getVecNum() + ",'" + v.getMeas() + "',"
>>                        + v.isOrigAnnc() + "," + v.isEvntNotiAdj() + ",'" + sdfTimestamp.format(c.getTime())
+ "')";
> You should read about SQL-injections and Prepared Statements. You can
> declare the prepared statement outside of your loop and set the values
> inside the loop.

Yes, im aware about injection, but there's no chance in the way this app works that injection
can be done, all public access has no way to reach database or methods that uses the database
at all. But, im aware that using preparedstatements is more effective and easy to code.


>> 
>>                s1.execute(query);
>>            }
>>        } finally {
>>            if (s1 != null) {
>>                s1.close();
>>            }
> if s1.close() throws an error you will not close c1, so you have to
> catch that exception:
>    if (s1!=null) { try { s1.close } catch (SQLException e) { // Ignore
> or event better log
>    };
>>            s1 = null;
>>            if (c1 != null) {
>>                c1.close();
> catch the possible Exception
>  if (c1!=null) { try {c1.close();} catch (SQLException e) { // Ignore
> or log
> };
> 

yes, you're right. i will

>>            }
>>            c1 = null;
>>        }
>>    }
>> 
>> 
>> 
>> Objects are created like
>> 
>> private Connection getConnection() {
>>        DataSource ds = null;
>>        Connection c1 = null;
>>        try {
>>            ds = (DataSource) new InitialContext().lookup("java:/comp/env/jdbc/pgsql");
>>            c1 = ds.getConnection();
>>        } catch (NamingException ex) {
>>            log.error("", ex);
> Error messages should be a bit more meaningful than "".
>>        } catch (SQLException ex) {
>>            log.error("", ex);
>>        }
>>        return c1;
> You will return null, if you have catched an Exception. Is that what you
> want?


no problem with that only if i handle the null after that (ill correct the call to handle
the null)

>>    }
>> 
>> 
>> 
>> what i can see different from the example on http://tomcat.apache.org/tomcat-7.0-doc/jndi-datasource-examples-howto.html
is that the SQLException is now thrown but catched locally in the method.
> That difference can be essential, as explained above.
> 

good to know, thanks again. changing now

>> 
>> 
>> and here's my resource pool config
>> 
>> 
>> <Context antiJARLocking="true" path="/xcall3">
>>    <Resource 
>>    auth="Container" 
>>    driverClassName="org.postgresql.Driver" 
>>    maxActive="10" 
>>    maxIdle="3" 
>>    name="jdbc/pgsql" 
>>    password="xcall3" 
>>    type="javax.sql.DataSource" 
>>    url="jdbc:postgresql://localhost/xcall3" 
>>    username="xcall3"
>>    validationQuery="select version();" 
> I think you should not place the ";" at the end of the statement.
> 
>>    maxWait = "5000"
>>    />
>> 
>> 
>> here's what logs the database 
>> 
>> 2011-05-07 23:02:25 ARTLOG:  execute <unnamed>: INSERT INTO list.vdn VALUES
('Atencion a Clientes',7022,false,1,1,33,'int',false,false,'2011-05-07 23:02:25')
>> 2011-05-07 23:02:25 ARTLOG:  unexpected EOF on client connection
>> 
>> until i lose all my connections.
>> 
>> here's what i got from the webapp log after that
>> 
>> 2011-05-06 13:34:38,430 ERROR DAO:47 -
>> org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot get a connection, general
error
>>        at org.apache.tomcat.dbcp.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:118)
>>        at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
>>        at com.lesi.xcall3.core.DAO.getConnection(DAO.java:43)
>>        at com.lesi.xcall3.core.DAO.getSchedulerTasks(DAO.java:317)
>>        at com.lesi.xcall3.core.Scheduler.run(Scheduler.java:35)
>>        at java.lang.Thread.run(Thread.java:662)
>> Caused by: java.lang.InterruptedException
>>        at java.lang.Object.wait(Native Method)
>>        at java.lang.Object.wait(Object.java:485)
>>        at org.apache.tomcat.dbcp.pool.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:1104)
>>        at org.apache.tomcat.dbcp.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:106)
>>        ... 5 more
>> Exception in thread "XCALL3-Scheduler" java.lang.NullPointerException
>>        at java.util.ArrayList.toArray(ArrayList.java:303)
>>        at com.lesi.xcall3.core.DAO.getSchedulerTasks(DAO.java:384)
>>        at com.lesi.xcall3.core.Scheduler.run(Scheduler.java:35)
>>        at java.lang.Thread.run(Thread.java:662)
>> 
> Do you get any abandoned log entries, if you add the configuration
>  ...
>  removeAbandoned="true"
>  removeAbandonedTimeout="60"
> 
>  logAbandoned="true"
>  ...
> to your resource?
> 

adding now.

> Bye
> Felix
>> 
>> 
>> 
>> On May 8, 2011, at 12:19 PM, Felix Schumacher wrote:
>> 
>>> Am Sonntag, den 08.05.2011, 11:42 -0300 schrieb alexis:
>>>> Hello all, is there any way to recover lost connectios on a pool?
>>>> 
>>>> Here's the issue, for an application, using postgresql jdbc (same happens
with mysql as i tried), having query errors syntax or duplicated keys, actually no big deal,
it throws an sqlexception upon que sql error, as this call executes ~150 queries to insert,
on each query i lost the connection, so suddenly i have all my connections lost and my app
useless.
>>>> 
>>>> How can i do from the catch clause of the SQLException to ask the pool to
reconnect? Because today we are in debug stage but soon to be production and when this happens
(we've corrected a lot of queries and situations but for sure some new one will arise) we
need to restart the webapp.
>>> SQL Connections should not get lost when used properly. You have to
>>> close the connections and every resources you got out of that connection
>>> in case of a program error. Look for "jdbc try finally".
>>> 
>>> As a helper to find connections, you did not close properly you can
>>> configure your jdbc pool to show your abandoned connections. Another
>>> safety net are the validation queries. For further information look at
>>> http://tomcat.apache.org/tomcat-7.0-doc/jndi-datasource-examples-howto.html
>>> 
>>> Regards
>>> Felix
>>>> 
>>>> thanks in advance. 
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>>> 
>>> 
>>> 
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>> 
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> 
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