How to retrieve new incoming data by polling and feed it back

Question

Here the method reads the database which has an unique ID with the sequence number which keeps on increasing, since am a beginner in java,can I know how to implement this repetitive polling and check for new incoming message each time.

public void run() {
int seqId = 0;
    while(true) {
        List<KpiMessage> list = null;
        try {
            list = fullPoll(seqId);
            if (!list.isEmpty()) {
                seqId = list.get(0).getSequence();
                incomingMessages.addAll(list);
                System.out.println("waiting 3 seconds");
                System.out.println("new incoming message");
                Thread.sleep(3000);

            }
        } catch (Exception e1) {
            e1.printStackTrace();
        }


    }
}

//Method which defines polling of the database and also count the number of Queries
public List<KpiMessage> fullPoll(int lastSeq) throws Exception {
    Statement st = dbConnection.createStatement();
    ResultSet rs = st.executeQuery("select * from msg_new_to_bde where ACTION =  804 and SEQ >" + lastSeq + "order by SEQ DESC");     
    List<KpiMessage> pojoCol = new ArrayList<KpiMessage>();
    while (rs.next()) {
        KpiMessage filedClass = convertRecordsetToPojo(rs);
        pojoCol.add(filedClass);
    }
    for (KpiMessage pojoClass : pojoCol) {
        System.out.print(" " + pojoClass.getSequence());
        System.out.print(" " + pojoClass.getTableName());
        System.out.print(" " + pojoClass.getAction());
        System.out.print(" " + pojoClass.getKeyInfo1());
        System.out.print(" " + pojoClass.getKeyInfo2());
        System.out.println(" " + pojoClass.getEntryTime());
    }
    //          return seqId;           
    return pojoCol;
}  

My goal is to Poll the table from the database and also check for new incoming message, which I can find from the Header field SequenceID in table which is unique and keeps on increasing for new entries. Now my problem is

1.Lets say after I poll the first time, it reads all the entries and makes the thread to sleep for 6 seconds, by the mean time how can I get the new incoming data and Poll it again ?

2.Also how to add the new data ,when it does Polling for the second time and pass the new data to another class.

Answer 1

Poller calls fullPoll every 6 secs and passes lastSeq param to it. Initially lastSeq = 0. When Poller gets result list it replaces the lastSeq with max SEQ value. fullPoll retrieves only records with SEQ > lastSeq.

void run() throws Exception {
    int seqId = 0;
    while(true) {
          List<KpiMessage> list = fullPoll(seqId);
          if (!list.isEmpty()) {
            seqId = list.get(0).getSequene();
          }
          Thread.sleep(6000); 
    }
}

public List<KAMessage> fullPoll(int lastSeq) throws Exception {
       ...
       ResultSet rs = st.executeQuery("select * from msg_new_to_bde where ACTION =  804 and SEQ > " + lastSeq + " order by SEQ 
      DESC");     
      .. 
}