Making a database connection inside a thread

[Kim Kantola]

I have a thread in my application that instantiates a class called DBConnect which has a getConnection method :

public Connection getConnection(){
    
    java.sql.Connection conn = null;   
    try {
       conn = DriverManager.getConnection (_databaseURL+"/"+_database+"?user="+_dbUser+"&password="+_dbPass+"&autoReconnect=true"); 
    } catch (Exception e) {
        logger.severe("Database.constructor: Error connecting or reading table:"+e.getMessage());
        System.exit (0);
    }
    return conn;
}    

This thread uses the DBConnect object to get a database connection. This thread then has to spawn other threads which all also need to make database connections. Right now, to spawn the other threads, I am extending the class java.util.TimerTask. In the run method of the TimerTask, I create a new object of DBConnect. I think that using this class is probably wrong, that I should just start a new java Thread, because I am getting the following error inside my TimerTask code :

SEVERE: Database.constructor: Error connecting or reading table:Server connection failure during transaction. Due to underlying exception: 'java.net.BindException: Address already in use: connect'.



** BEGIN NESTED EXCEPTION **



java.net.BindException

MESSAGE: Address already in use: connect



STACKTRACE:



java.net.BindException: Address already in use: connect

at java.net.PlainSocketImpl.socketConnect(Native Method)

at java.net.PlainSocketImpl.doConnect(Unknown Source)

at java.net.PlainSocketImpl.connectToAddress(Unknown Source)

at java.net.PlainSocketImpl.connect(Unknown Source)

at java.net.Socket.connect(Unknown Source)

at java.net.Socket.connect(Unknown Source)

at java.net.Socket.<init>(Unknown Source)

at java.net.Socket.<init>(Unknown Source)

at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:124)

at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:225)

at com.mysql.jdbc.Connection.createNewIO(Connection.java:1899)

at com.mysql.jdbc.Connection.<init>(Connection.java:450)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:411)

at java.sql.DriverManager.getConnection(Unknown Source)

at java.sql.DriverManager.getConnection(Unknown Source)

at com.radianse.alerts.utility.DBConnect.getConnection(Unknown Source)

at com.radianse.alerts.repository.AlertBucketDAO.getAlertBucketItems(Unknown Source)

at com.radianse.alerts.businessobjects.AlertBucketImpl.getBucketItems(Unknown Source)

at com.radianse.alerts.jms.AlertEvaluator.run(Unknown Source)

** END NESTED EXCEPTION **

Attempted reconnect 3 times. Giving up.

My question is,

should I stop using the TimerTask

should I use the DBConnect object I already have in the thread that spawns the TimerTask in the TimerTask run method instead of making a new object of it

should I use some other method to achieve what I am trying to do ?

Thank you for any input,
Kim

[Henry Wong]

My question is,

should I stop using the TimerTask

should I use the DBConnect object I already have in the thread that spawns the TimerTask in the TimerTask run method instead of making a new object of it

should I use some other method to achieve what I am trying to do ?

Thank you for any input,

This is not really a threads issue. It looks like a networking issue. You are trying to open a connection to a port that is already in use, probably by another DBconnect object.

So... given the three choices in this multiple choice question, I guess I would go with the second one.

Henry

[Kim Kantola]

Wow, thanks Henry for replying. This is too funny because I was thinking I need to understand this better so I went out on my lunch break and bought your book "Java Threads"!

It has already helped me on one thing and I was wondering if I could confirm this with you ? I was reading more about the Timer class and realized that I had misunderstood it. My one thread that has a constant while(true) loop will periodically need to start the new TimerTasks. I thought I needed to create a new Timer() object for each task, but if I am understanding correctly I can just make one Timer class, and then add the tasks to it as needed, thus cutting down on the number of threads greatly. Is that correct? The Timer object itself starts a thread, and then all the tasks will get handled by that one thread?

Thanks again very much for your reply.
Kim

[Henry Wong]

It has already helped me on one thing and I was wondering if I could confirm this with you ? I was reading more about the Timer class and realized that I had misunderstood it. My one thread that has a constant while(true) loop will periodically need to start the new TimerTasks. I thought I needed to create a new Timer() object for each task, but if I am understanding correctly I can just make one Timer class, and then add the tasks to it as needed, thus cutting down on the number of threads greatly. Is that correct? The Timer object itself starts a thread, and then all the tasks will get handled by that one thread?

Glad to hear that it helped ...

Yes. You can "just make one Timer class, and then add the tasks to it as needed, thus cutting down on the number of threads greatly". And yes, "all the tasks will get handled by that one thread" of the java.util.Timer class.

Keep in mind that the tasks must be short lived, since there is only one thread, if your tasks take too long to run, you can starve out the other tasks.

Also, there may not be a need for your "thread that has a constant while(true) loop [which] will periodically need to start [or add] the new TimerTasks". If you are running the same timer task, at regular intervals, there is an overload schedule() method that lets you do this.

Henry