unable to release db file after close connection

[ke wang]

I have a program running some db modification stuff. I have multiple threads, each one connect to a different db. In each of these threads, when there is exception happened, I want to delete the db file the thread is modifying. I try to add these code in the catch clause. But even I call conn.close() and set singleconnection = true. The file still can't be release at once, after about 2 minutes, it can be released.

My code is like this:
public class WorkerThread implements Runnable{
...

public void run() {
            ...

    try {
        for(File file : files){
                                    ...
                handler = (FormHandler) constructor.newInstance(env);

                handler.init(file);
                handler.handle();
                handler.cleanUp();// call conn.close()
            }
        }

                    ...

    } catch(RuntimeException | SAXException | IOException | MessagingException | ClassNotFoundException | NoSuchMethodException | InstantiationException | IllegalAccessException | InvocationTargetException e)
    {
        try {
            handler.cleanUp();
        } catch (IOException e2) {
            // TODO Auto-generated catch block
            e2.printStackTrace();
        }
                    //delete db file.

    }
}

In the constructor of (FormHandler)handler, a connection to a db is create(each thread connect to different db):

class Form4Handler{
public Form4Handler(HHREnvironment env) {

    gmDao = new GestMeaningDAO();
    File db = new File(parent + language + "_godanddeaf.mdb");
    gmDao.useDB(db.getAbsolutePath());
}

}

class GestMeaningDao{
public void useDB(String name){
try {
conn = new UCanAcessDBManager(name).getConnection();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

public class UCanAcessDBManager {

   public UCanAcessDBManager(String name){
    this.dbUrl = DB_URL_ROOT + name;
    Properties p = new Properties();
    p.put("user", USER);
    p.put("password", PASS);
    p.put("ingleconnection", true);
    // System.out.println(dbUrl);
    try {
        Class.forName(JDBC_DRIVER);
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        // e.printStackTrace();
    }
    try {
        connection = DriverManager.getConnection(this.dbUrl, p);
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

   public Connection getConnection() throws SQLException{
       return connection; 
   }

}

Some one can give me some help on this problem? The same problem won't happen if there is no exception in the program. Thanks.

[Marco Amadei]

Hi Ke Wang, you're welcome,
and thank you for the accurate problem description. You aren't using a connection pool.
Firstly, may you re-try with the correct singleconnection parameter setting?

p.put("singleconnection", "true");
and not
p.put("ingleconnection", true);

And please, let me know your findings.

[ke wang]

Hi Amadei,
Oh, no I didn't use thread pool. What I really use is a thread pool. The typo is a big mistake. I can't believe myself! Hope That's the cause of all these mysteries. I will try it again and let you know what happened. Thank you very much.

[ke wang]

Hi Amadei,
I try to fix the typo, but the same problem still happened. The program has to wait for about 2 minutes after called conn.close to delete the db file.

[Marco Amadei]

So sorry, I didn't see another mistake or misunderstanding in your code.
If you pass a Properties to the DriverManager, you should use it as a Properties, not as an Hashtable. So both key and value in each entry should be a string even if the compiler allows the use of the put method from the base class Hashtable.
In this case
p.put("singleconnection", true); you put a Boolean instead and the driver can't understand, because a string is expected.
This solves your issue:
p.put("singleconnection", "true");
or (better)
p.setProperty("singleconnection", "true");

[ke wang]

Oh, I didn't notice the difference because I am a java noob. I will try to change that to see if things getting better. Thanks.

[ke wang]

Hi Amadei,
I change the true to string type. Then it works fine! This is truly great. Thanks for you help.