Tomcat连接池被放弃的问题

Question

I'm struggling with a Tomcat connection pool error.The below error is thrown at runtime after running a simple stored procedure that generates a String value.

WARNING: Connection has been abandoned PooledConnection[ConnectionID:45 ClientConnectionId: 7817280c-3f7e-4239-a009-3aedd0a855e8]:java.lang.Exception
    at org.apache.tomcat.jdbc.pool.ConnectionPool.getThreadDump(ConnectionPool.java:1096)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:799)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:648)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.getConnection(ConnectionPool.java:200)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.getConnection(DataSourceProxy.java:128)
    at util.ThreadLocalUtil.getConnection(ThreadLocalUtil.java:55)
    at webapp.dao.WebApplicationDAO.getConnection(WebApplicationDAO.java:30)
    at webapp.dao.AccountDAO.generateAccountId(AccountDAO.java:827)
    at webapp.bo.Account.generateUserAccountId(Account.java:285)
    at webapp.actions.AddUserAccountUNZAction.execute(AddUserAccountUNZAction.java:79)
    at org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58)
    at org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67)
    at org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)

My knowledge of that error is that a connection was opened and not closed. The connection is opened when running the stored proc in the account dao. Below is the block of code which calls the stored procedure.

Connection conn = null;
    CallableStatement stmt = null;
    ResultSet rs = null;
    try {

        conn = getConnection();
        stmt = conn.prepareCall(sqlWebAppGenerateUserId);
        stmt.setString(1, base);
        rs = stmt.executeQuery();
        String res = null;
        if (rs.next()) {
            res = rs.getString(1);
        }

        if (res == null) {
            throw new RuntimeException("Failed to generate user id.");
        }

        return res;
    } catch (SQLException e) {
        LOG.error("{}", e);
        throw new RuntimeException(e);
    }finally {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                LOG.error(e.getMessage(), e);
            }
        }
        if (rs != null) {
            try {
                rs.close();
                conn.close();
            } catch (SQLException e) {
                LOG.error(e.getMessage(), e);
            }
        }

    }

As you can see, I'm using a finally block to close the connection etc.

I'm at a loss to explain the reason why the error is being thrown still and as to how I can debug and solve this issue. Any help would be greatly appreciated

Answer 1

You close conn only if rs != null , meaning that every time a query fails the connection won't be closed.

I also recommend switching to try-with-resources instead of writing clumsy finally blocks which may cause bugs.

Answer 2

What @Kayaman said. Also if the statement execution takes longer than removeAbandonedTimeout this can happen.

Answer 3

@Kayaman and @Gorazd thank you for the advice. The issue with down to missing jar files in the tomcat lib folder. More specifically mail-1.4.jar.

As this jar file was missing, a function that sends emails failed. Previous to the call to send the mail, connection.autocommit is set to true. After the mail sends it will set autocommit back to false. This to me looks like where the abandoned error was occurring from.

When looking through logs file I found the mail sending error. This was in actual fact the true error whereas the abandoned error can be looked at as a red herring.