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POWhat could be the possibilities of using a thread-unsafe java.sql.Connection object in java?
 

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  1. POWhat could be the possibilities of using a thread-unsafe java.sql.Connection object in java?
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    <p>I am dealing with a legacy code where there the connection object in the singleton dao class is a member variable and is prone to race-conditions.</p> <p>I know this is a potential design issue however I am interested in knowing about the different types of problems that could be thought of when dealing with the jdbc connection object in java.</p> <p>Following is the EventLoggerDAO class code:</p> <pre><code>package com.code.ref.dao; import java.sql.Connection; import java.sql.PreparedStatement; import com.code.ref.utils.common.DBUtil; import com.code.ref.utils.common.PCMLLogger; public class EventLoggerDAO { private static EventLoggerDAO staticobj_EventLoggerDAO; private Connection obj_ClsConnection; private PreparedStatement obj_ClsPreparedStmt; private EventLoggerDAO() { try { obj_ClsConnection = DBUtil.getConnection(); } catch (Exception e) { PCMLLogger.logMessage(EventLoggerDAO.class, "EventLoggerDAO()", "Some problem in creating db connection:" + e); } } public static synchronized EventLoggerDAO getInstance() { if (staticobj_EventLoggerDAO == null) { synchronized (EventLoggerDAO.class) { if (staticobj_EventLoggerDAO == null) staticobj_EventLoggerDAO = new EventLoggerDAO(); } } return staticobj_EventLoggerDAO; } public void addEvent(String sName, String sType, String sAction, String sModifiedBy) throws Exception { StringBuffer sbQuery = new StringBuffer(); sbQuery.append("INSERT INTO TM_EVENT_LOG (NAME, TYPE, ACTION, MODIFIED_BY) ").append("VALUES (?, ?, ?, ?) "); if(obj_ClsConnection == null) obj_ClsConnection = DBUtil.getConnection(); obj_ClsPreparedStmt = obj_ClsConnection.prepareStatement(sbQuery.toString()); obj_ClsPreparedStmt.setString(1, sName); obj_ClsPreparedStmt.setString(2, sType); obj_ClsPreparedStmt.setString(3, sAction); obj_ClsPreparedStmt.setString(4, sModifiedBy); obj_ClsPreparedStmt.executeUpdate(); if (obj_ClsPreparedStmt != null) { obj_ClsPreparedStmt.close(); obj_ClsPreparedStmt = null; } } } </code></pre> <p><strong>Problem observed</strong>:</p> <p>Sometimes it happens that the table <code>TM_EVENT_LOG</code> stops inserting and there is not even exception in the server logs.</p> <p>I suspect that during race conditions the connection objects held by different threads might be leading to inconsistent state and might also not be commiting the data. The connection is derived through a websphere datasource maintaining a connection pool.</p> <p>Any thoughts or ideas why this might be happening?</p>
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      1. POWhat could be the possibilities of using a thread-unsafe java.sql.Connection object in java?
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    1. COThanks Carl for formatting the code. I tried intially but in vain.
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    2. COYou've got obvious and very serious problems with race conditions here. I would recommend fixing the problems you know about rather than trying to figure out how/if they are causing the observed symptoms. (Occam's Razor and all that).
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      1. USDavid Gelhar
    3. COWhat I observed fron the application server logs is that there was "java.sql.SQLException: ORA-01000: maximum open cursors exceeded" for the above code. Is it mandatory to close the connection each time after running a sql statement even if in my wildest thoughts I want this object to keep hold of this connecion without returning it to the connection pool?
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