Hibernate Memory Management

Question

I have an application using sleep mode. On the one hand, I'm trying to get documents. Each document has an account number. The model looks something like this:

    private Long _id;
private String _acct;  
private String _message;  
private String _document;    
private String _doctype;  
private Date _review_date;  

Then I get the documents using the document service. Part of the code is here:

public List<Doc_table> getDocuments(int hours_, int dummyFlag_,List<String> accts) {
        List<Doc_table> documents = new ArrayList<Doc_table>();
    Session session = null;
    Criteria criteria = null;
    try {
        // Lets create a previous Date by subtracting the number of
        // subtractHours_ passed.
        session = HibernateUtil.getSession();
        session.beginTransaction();
        if (accts == null) {
            Calendar cutoffTime = Calendar.getInstance();
            cutoffTime.add(Calendar.HOUR_OF_DAY, hours_);
            criteria = session.createCriteria(Doc_table.class).add(
                    Restrictions.gt("dbcreate_date",  cutoffTime.getTime()))
                    .add(Restrictions.eq("dummyflag", dummyFlag_));
        } else 
        {   criteria = session.createCriteria(Doc_table.class).add(Restrictions.in("acct", accts));
        }
        documents = criteria.list();
        for (int x = 0; x < documents.size(); x++) {
            Doc_table document = documents.get(x);
               ......... more stuff here
                    }

This works great if I get a small amount of documents. But when the size of the document is large, I get an error in the heap area, probably because the documents take up a lot of space, and when you extract a few thousand from them, bad things happen.

All I really want to do is get every document that matches my criteria, grab the account number and return a list of account numbers (a much smaller object than a list of objects). If it were jdbc, I would know exactly what to do.

. , , Doc_table.

, , - , , ( , , ).

Answer 1

:

• ( ) , :

  accts = session.createQuery( "SELECT d._acct FROM Doc d WHERE..." );

 List<String> accts = session.createCriteria(Doc.class).
             setProjection(Projections.property("_acct")).
             list();

• , , .
• ( ), , ,

Answer 2

, , .. , . , , . , .