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");     
      .. 
}