Question

In my application I need to cache data in HashMap or TreeMap it saves a lot of time because it is very time consuming task to fetch the records every time from DB server and process it.
I am also doing profiling of this application using JProfiler and I feel that when I am getting records from DataBase to put in the Map connection to the ResultSet and Statement are not closed because it is showing me these classes taking so much memory.
Is this something that I am overreacting over this or it is really a problem?

By the way I am closing the connection in finally block. I am posting the code of it.

public Map someFunction() throws SomeException{
Connection con=null;
    Statement stmt=null;
    ResultSet rs=null;
    String sql=null;
    Map <String,String> testMap=new TreeMap<String, String>();

    try {
        con=HMDBUtil.getConnection();
        if(cacheSize==0) {
            sql = "SELECT SOMETHING FROM SOMEWHERE";
        }else {
            sql = "SELECT SOMETHING FROM SOMEWHERE_ELSE where rownum<"+cacheSize;
        }
        stmt=con.createStatement();
        stmt.setFetchSize(100000);
        rs=stmt.executeQuery(sql);
        long count=0;
        while(rs.next()) {
            testMap.put(rs.getString(1).trim(), rs.getString(2));
            count++;
        }
    } catch (SQLException e) {

        log.fatal("SQLException while fetching Data",e);
        throw new SomeException("SQLException while fetching Data",e);          
    }finally {
        HMDBUtil.close(con, stmt, rs);
    }

    return testMap;
}

HMDBUtil.close() method—

public static void close(Connection con, Statement stmt, ResultSet rs)
        throws SomeException {
    if (log.isDebugEnabled())
        log.debug("Invoked");
    close(rs);
    close(stmt);
    close(con);

    if (log.isDebugEnabled())
        log.debug("Leaving");
}

All close methods that are used to close all the connections —

    public static void close(Connection con) throws SomeException {
    try {

        if (log.isDebugEnabled())
            log.debug("Invoked");
        if (con != null) {
            con.close();
            con = null;
        }

        if (log.isDebugEnabled())
            log.debug("Leaving");

    } catch (SQLException e) {
        log.fatal("SQLException while Closing connection ", e);
        throw new SomeException("SQLException while Closing connection ",
                e, false, true);
    }
}


public static void close(Statement stmt) throws SomeException {
    try {
        if (log.isDebugEnabled())
            log.debug("Invoked");

        if (stmt != null) {
            stmt.close();
            stmt = null;
        }
        if (log.isDebugEnabled())
            log.debug("Leaving");

    } catch (SQLException e) {
        // log.error("Exception while Closing statement ", e);
        log.fatal("SQLException while Closing statement ", e);
        throw new SomeException("SQLException while Closing statement ", e, false, true);

    }
}


public static void close(ResultSet rs) throws SomeException {

    try {
        if (log.isDebugEnabled())
            log.debug("Invoked");
        if (rs != null) {
            rs.close();
            rs = null;
        }
        if (log.isDebugEnabled())
            log.debug("Leaving");

    } catch (SQLException e) {
        log.fatal("SQLException while Closing rs", e);
        throw new SomeException("SQLException while Closing rs", e, false, true);
    }
}

Answer 1

Result Set and statement won’t be removed from heap straightway after you closed connection. You need to have at least one run of garbage collector for this to happen.

Also, are you sure that HMDBUtil.close() method works as expected. It could leak connection as well.

+1 for using 3rd party caching provider.

EDIT: Just to avoid confusion. Classes will be present in heap till you process ends and will reside in Permanent Generation.

Instances of classes (objects) should be garbage collected. If they not that mean that your process holds references to them somehow somewhere, or garbage collector hasn’t been run.

I’m not sure about JProfiler but with YourKit you could easy navigate object graph and find which object holds references to uncollected objects. It helped me a lot with finding memory leaks in the past.