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How to implement multi threading for invoking REST URL with multiple data

I have below code base which is gonna hit REST URI and return a response back:
#ApiOperation(responseContainer = "request", response = ETLRequest.class, value = "testValidation")
#Produces(MediaType.APPLICATION_JSON)
#Consumes(MediaType.APPLICATION_JSON)
#RequestMapping(value = "/getValue", produces = MediaType.APPLICATION_JSON, method = RequestMethod.PUT)
#ResponseBody
public Response getETLResponse(#RequestParam("unID") String httpEntity,#RequestParam(value = "PId", defaultValue = "Optional") String pId)throws Exception
{
try {
if (httpEntity.contains(","))
{
if (resultSet.size() > 0)
{
resultSet.clear();
}
String[] strArray = httpEntity.split(",");
for (String str : strArray)
{
System.out.println(str + "FIRST....");
response = RESTInvoker.validateREST(JSONToPOJO
.buildURL(str));
System.out.println(response + "\t RESPONSE");
resultSet.add(response);
}
return Response.status(Response.Status.ACCEPTED)
.entity(resultSet).build();
}
} catch (Exception ex) {
ex.printStackTrace();
return Response.status(Response.Status.BAD_REQUEST).build();
}
}
Sample Request
{
"unID": "1946249809, 194602775536,194624982809, 19462475536,19462775536,194624002779,19002775536,12494002775536,19462495536,194940536,1949775536,19402775536,1946945536,194475536,194600536,194775536,1946275536,1946205536,1902775536,14002775536,775536",
"PId": "optional"
}
The above code works fine. It will get the UnID as query param, and separate the value by using (,) delimiter. And one record of UnID will append into request URI, and will return response as String response above code base.
I just want to achieve the above task in multi threading concept. Like I want to fetch 10 records (10 different threads) from UnID query parm (if it has comma separated values), and invoke the REST URI to speed up the process.
The above code will tak one second to invoke a response. If I have 10 input values in UnId will take 10 seconds to run all. The time will increase based upon test data, and sequence execution.I just want to pick 10 inputs in a second and invoke with REST URI by using different threads.
I'm using Java 7.
Any leads?

In Java 7, you could use use a "ThreadPoolExecutor", essential a pool of threads. Each thread in the pool runs "simultaneously". The following code example demonstrates how each thread is run (with a delay). The static class Task implements runnable, and is executed by the ThreadPoolExecutor:
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class BasicThreadPoolExecutorExample {
static class Task implements Runnable {
private String name;
Task(String name) {
this.name = name;
}
String getName() {
return name;
}
#Override
public void run() {
try {
Long duration = (long) (Math.random() * 10);
System.out.println("Doing a task during : " + name);
TimeUnit.SECONDS.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
for (int i = 0; i <= 5; i++) {
Task task = new Task("Task " + i);
System.out.println("A new task has been added : " + task.getName());
executor.execute(task);
}
executor.shutdown();
}
}
Running the code produces the following output:
A new task has been added : Task 0
A new task has been added : Task 1
A new task has been added : Task 2
A new task has been added : Task 3
A new task has been added : Task 4
A new task has been added : Task 5
Doing a task during : Task 0
Doing a task during : Task 1
Doing a task during : Task 2
Doing a task during : Task 3
Doing a task during : Task 5
Doing a task during : Task 4

In java 7 you can do
int numberOfTasks = strArray.length;
ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
try {
for (int i = 0; i < numberOfTasks; i++) {
executor.execute(new MyRunnable(strArray[i], resultSet));
}
} catch (Exception err) {
err.printStackTrace();
}
executor.shutdown();
And you have to create class:
class MyRunnable implements Runnable {
List<String> resultSet;
String str;
public MyRunnable(String str, List<String> resultSet) {
this.str = str;
this.resultSet = resultSet;
}
#Override
public void run() {
System.out.println(str + "FIRST....");
final String response = RESTInvoker.validateREST(JSONToPOJO .buildURL(str));
System.out.println(response + "\t RESPONSE");
resultSet.add(response);
}
}

I think you may change execution of loop for by a parallel stream:
Arrays.stream(strArray).parallel().forEach(str -> {
System.out.println(str + "FIRST....");
final String response = RESTInvoker.validateREST(JSONToPOJO
.buildURL(str));
System.out.println(response + "\t RESPONSE");
resultSet.add(response);
});

Check out
private ReadWriteLock iolock = new ReentrantReadWriteLock();
iolock.readLock().tryLock(); /** and */ iolock.readLock.unlock();
iolock.writeLock.tryLock(); /** and */ iolock.writeLock().unlock();

High latency on increasing thread count

In below code DataGather = endDataGather - beginDataGather takes 1.7ms
& time for service to respond = service_COMPLETED - service_REQUEST_SENT
which vary from 20us to 200 us(since they are mocked dummy on same lan hence so low)
now if i increase tomcat8 thread from 10 to 200,DataGather increase to 150ms + and even if I increase thread from 200 to 1000 then it even increase 250+.Machine specs 8 core Xenon,64gb ram. Time is measured when apache benchmark runs with -n 40000 -c 100 args , is this due to thread scheduling/context swtiching or something else? How do I get rid of this variation? Will it remain when real services will come into picture which have latency of 20-100ms.
public List<ServiceResponse> getData(final List<Service> services, final Data data) {
//beginDateGather;
final List<ServiceResponse> serviceResponses = Collections.synchronizedList(new ArrayList<>());
try {
final CountDownLatch latch = new CountDownLatch(services.size());
Map<Future<HttpResponse>, HttpRequestBase> responseRequestMap = new HashMap<Future<HttpResponse>, HttpRequestBase>();
for (final service service : services) {
//creating request for a service
try {
HttpRequestBase request = RequestCreator.getRequestBase(service, data);
//service_REQUEST_SENT
Future<HttpResponse> response = client.execute(request,
new MyFutureCallback(service, data, latch, serviceResponses));
responseRequestMap.put(response, request);
} catch (Exception e) {
latch.countDown();
}
}
try {
boolean isWaitIsOver = latch.await(timeout, TimeUnit.MILLISECONDS);
if (!isWaitIsOver) {
for (Future<HttpResponse> response : responseRequestMap.keySet()) {
if (!response.isDone()) {
response.cancel(true);
}
}
}
} catch (InterruptedException e) {
}
} catch (Exception e) {
}
//endDataGather
return serviceResponses;
}
public class MyFutureCallback implements FutureCallback<HttpResponse> {
private Service service;
private Data data;
private CountDownLatch latch;
private List<serviceResponse> serviceResponses;
public MyFutureCallback( Service service, Data data, CountDownLatch latch, List<ServiceResponse> serviceResponses) {
this.service = service;
this.data = data;
this.latch = latch;
this.serviceResponses = serviceResponses;
}
#Override
public void completed(HttpResponse result) {
try {
ServiceResponse serviceResponse = parseResponse(result, data, service);
serviceResponses.add(serviceResponse);
} catch (Exception e) {
} finally {
//service_COMPLETED
latch.countDown();
}
}
#Override
public void failed(Exception ex) {
latch.countDown();
}
#Override
public void cancelled() {
latch.countDown();
}
}

Yes it seems due to context switching of threads.
Increasing the number of threads won't help in this case.
You can use a thread pool for callbacks.
Check this link for your reference and try to use .PoolingClientAsyncConnectionManager
How to use HttpAsyncClient with multithreaded operation?

How can I terminate Tasks that have timed out in multithreading?

I need to make a library in which I will have synchronous and asynchronous methods in it.
executeSynchronous() - waits until I have a result, returns the result.
executeAsynchronous() - returns a Future immediately which can be processed after other things are done, if needed.
Core Logic of my Library
The customer will use our library and they will call it by passing DataKey builder object. We will then construct a URL by using that DataKey object and make a HTTP client call to that URL by executing it and after we get the response back as a JSON String, we will send that JSON String back to our customer as it is by creating DataResponse object. Some customer will call executeSynchronous() and some might call executeAsynchronous() so that's why I need to provide two method separately in my library.
Interface:
public interface Client {
// for synchronous
public DataResponse executeSynchronous(DataKey key);
// for asynchronous
public Future<DataResponse> executeAsynchronous(DataKey key);
}
And then I have my DataClient which implements the above Client interface:
public class DataClient implements Client {
private RestTemplate restTemplate = new RestTemplate();
private ExecutorService executor = Executors.newFixedThreadPool(10);
// for synchronous call
#Override
public DataResponse executeSynchronous(DataKey key) {
DataResponse dataResponse = null;
Future<DataResponse> future = null;
try {
future = executeAsynchronous(key);
dataResponse = future.get(key.getTimeout(), TimeUnit.MILLISECONDS);
} catch (TimeoutException ex) {
PotoLogging.logErrors(ex, DataErrorEnum.TIMEOUT_ON_CLIENT, key);
dataResponse = new DataResponse(null, DataErrorEnum.TIMEOUT_ON_CLIENT, DataStatusEnum.ERROR);
// does this look right the way I am doing it?
future.cancel(true); // terminating tasks that have timed out.
} catch (Exception ex) {
PotoLogging.logErrors(ex, DataErrorEnum.CLIENT_ERROR, key);
dataResponse = new DataResponse(null, DataErrorEnum.CLIENT_ERROR, DataStatusEnum.ERROR);
}
return dataResponse;
}
//for asynchronous call
#Override
public Future<DataResponse> executeAsynchronous(DataKey key) {
Future<DataResponse> future = null;
try {
Task task = new Task(key, restTemplate);
future = executor.submit(task);
} catch (Exception ex) {
PotoLogging.logErrors(ex, DataErrorEnum.CLIENT_ERROR, key);
}
return future;
}
}
Simple class which will perform the actual task:
public class Task implements Callable<DataResponse> {
private DataKey key;
private RestTemplate restTemplate;
public Task(DataKey key, RestTemplate restTemplate) {
this.key = key;
this.restTemplate = restTemplate;
}
#Override
public DataResponse call() {
DataResponse dataResponse = null;
String response = null;
try {
String url = createURL();
response = restTemplate.getForObject(url, String.class);
// it is a successful response
dataResponse = new DataResponse(response, DataErrorEnum.NONE, DataStatusEnum.SUCCESS);
} catch (RestClientException ex) {
PotoLogging.logErrors(ex, DataErrorEnum.SERVER_DOWN, key);
dataResponse = new DataResponse(null, DataErrorEnum.SERVER_DOWN, DataStatusEnum.ERROR);
} catch (Exception ex) {
PotoLogging.logErrors(ex, DataErrorEnum.CLIENT_ERROR, key);
dataResponse = new DataResponse(null, DataErrorEnum.CLIENT_ERROR, DataStatusEnum.ERROR);
}
return dataResponse;
}
// create a URL by using key object
private String createURL() {
String url = somecode;
return url;
}
}
Problem Statement:-
When I started working on this solution, I was not terminating the tasks that have timed out. I was reporting the timeout to the client, but the task continues to run in the thread pool (potentially occupying one of my limited 10 threads for a long time). So I did some research online and I found that I can cancel my tasks those have timed out by using cancel on future as shown below -
future.cancel(true);
But I wanted to make sure, does it look right the way I am doing in my executeSynchronous method to cancel the tasks that have got timedout?
Since I am calling cancel() on theFuture which will stop it from running if tasks is still in the queue so I am not sure what I am doing is right or not? What is the right approach to do this?
If there is any better way, then can anyone provide an example for that?

If task is still in the queue then cancelling it by simply calling future.cancel() is ok but obviously you don't know if that is in the queue. Also even if you ask future to interrupt the task it may not work as your task can still be doing something which is ignoring the thread interrupted status.
So you can use the future.cancel(true) but you need to make sure that your task (thread) does regard the thread interrupted status. For example as you mentioned you make http call, so you might need to close the http client resource as soon as thread is interrupted.
Please refer to the example below.
I have tried to implement the task cancellation scenario. Normally a thread can check isInterrupted() and try to terminate itself. But this becomes more complex when you are using thread pool executors, callable and if the task is not really like while(!Thread.isInterrupted()) {// execute task}.
In this example, a task is writing a file (I did not use http call to keep the it simple). A thread pool executor starts running the task but the caller wants to cancel it just after 100 milli seconds. Now future sends the interrupt signal to the thread but the callable task can not check it immediately while writing to file. So to make this happen callable maintains a list of IO resources it is going to use and as soon as future wants to cancel the task it just calls cancel() on all IO resources which terminates the task with IOException and then thread finishes.
public class CancellableTaskTest {
public static void main(String[] args) throws Exception {
CancellableThreadPoolExecutor threadPoolExecutor = new CancellableThreadPoolExecutor(0, 10, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
long startTime = System.currentTimeMillis();
Future<String> future = threadPoolExecutor.submit(new CancellableTask());
while (System.currentTimeMillis() - startTime < 100) {
Thread.sleep(10);
}
System.out.println("Trying to cancel task");
future.cancel(true);
}
}
class CancellableThreadPoolExecutor extends ThreadPoolExecutor {
public CancellableThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
#Override
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
return new CancellableFutureTask<T>(callable);
}
}
class CancellableFutureTask<V> extends FutureTask<V> {
private WeakReference<CancellableTask> weakReference;
public CancellableFutureTask(Callable<V> callable) {
super(callable);
if (callable instanceof CancellableTask) {
this.weakReference = new WeakReference<CancellableTask>((CancellableTask) callable);
}
}
public boolean cancel(boolean mayInterruptIfRunning) {
boolean result = super.cancel(mayInterruptIfRunning);
if (weakReference != null) {
CancellableTask task = weakReference.get();
if (task != null) {
try {
task.cancel();
} catch (Exception e) {
e.printStackTrace();
result = false;
}
}
}
return result;
}
}
class CancellableTask implements Callable<String> {
private volatile boolean cancelled;
private final Object lock = new Object();
private LinkedList<Object> cancellableResources = new LinkedList<Object>();
#Override
public String call() throws Exception {
if (!cancelled) {
System.out.println("Task started");
// write file
File file = File.createTempFile("testfile", ".txt");
BufferedWriter writer = new BufferedWriter(new FileWriter(file));
synchronized (lock) {
cancellableResources.add(writer);
}
try {
long lineCount = 0;
while (lineCount++ < 100000000) {
writer.write("This is a test text at line: " + lineCount);
writer.newLine();
}
System.out.println("Task completed");
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
file.delete();
synchronized (lock) {
cancellableResources.clear();
}
}
}
return "done";
}
public void cancel() throws Exception {
cancelled = true;
Thread.sleep(1000);
boolean success = false;
synchronized (lock) {
for (Object cancellableResource : cancellableResources) {
if (cancellableResource instanceof Closeable) {
((Closeable) cancellableResource).close();
success = true;
}
}
}
System.out.println("Task " + (success ? "cancelled" : "could not be cancelled. It might have completed or not started at all"));
}
}
For your REST Http client related requirement you can modify the factory class something like this -
public class CancellableSimpleClientHttpRequestFactory extends SimpleClientHttpRequestFactory {
private List<Object> cancellableResources;
public CancellableSimpleClientHttpRequestFactory() {
}
public CancellableSimpleClientHttpRequestFactory(List<Object> cancellableResources) {
this.cancellableResources = cancellableResources;
}
protected HttpURLConnection openConnection(URL url, Proxy proxy) throws IOException {
HttpURLConnection connection = super.openConnection(url, proxy);
if (cancellableResources != null) {
cancellableResources.add(connection);
}
return connection;
}
}
Here you need to use this factory while creating RestTemplate in your runnable task.
RestTemplate template = new RestTemplate(new CancellableSimpleClientHttpRequestFactory(this.cancellableResources));
Make sure that you pass the same list of cancellable resources that you have maintained in CancellableTask.
Now you need to modify the cancel() method in CancellableTask like this -
synchronized (lock) {
for (Object cancellableResource : cancellableResources) {
if (cancellableResource instanceof HttpURLConnection) {
((HttpURLConnection) cancellableResource).disconnect();
success = true;
}
}
}

How do we know threadPoolExecutor has finished execution

I have a parent thread that sends messages to MQ and it manages a ThreadPoolExecutor for worker threads which listen to MQ and writes message to output file. I manage a threadpool of size 5. So when I run my program, I have 5 files with messages. Everything works fine until here. I now need to merge these 5 files in my parent thread.
How do I know ThreadPoolExecutor finished processing so I can start merging files.
public class ParentThread {
private MessageSender messageSender;
private MessageReciever messageReciever;
private Queue jmsQueue;
private Queue jmsReplyQueue;
ExecutorService exec = Executors.newFixedThreadPool(5);
public void sendMessages() {
System.out.println("Sending");
File xmlFile = new File("c:/filename.txt");
List<String> lines = null;
try {
lines = FileUtils.readLines(xmlFile, null);
} catch (IOException e) {
e.printStackTrace();
}
for (String line : lines){
messageSender.sendMessage(line, this.jmsQueue, this.jmsReplyQueue);
}
int count = 0;
while (count < 5) {
messageSender.sendMessage("STOP", this.jmsQueue, this.jmsReplyQueue);
count++;
}
}
public void listenMessages() {
long finishDate = new Date().getTime();
for (int i = 0; i < 5; i++) {
Worker worker = new Worker(i, this.messageReciever, this.jmsReplyQueue);
exec.execute(worker);
}
exec.shutdown();
if(exec.isTerminated()){ //PROBLEM is HERE. Control Never gets here.
long currenttime = new Date().getTime() - finishDate;
System.out.println("time taken: "+currenttime);
mergeFiles();
}
}
}
This is my worker class
public class Worker implements Runnable {
private boolean stop = false;
private MessageReciever messageReciever;
private Queue jmsReplyQueue;
private int processId;
private int count = 0;
private String message;
private File outputFile;
private FileWriter outputFileWriter;
public Worker(int processId, MessageReciever messageReciever,
Queue jmsReplyQueue) {
this.processId = processId;
this.messageReciever = messageReciever;
this.jmsReplyQueue = jmsReplyQueue;
}
public void run() {
openOutputFile();
listenMessages();
}
private void listenMessages() {
while (!stop) {
String message = messageReciever.receiveMessage(null,this.jmsReplyQueue);
count++;
String s = "message: " + message + " Recieved by: "
+ processId + " Total recieved: " + count;
System.out.println(s);
writeOutputFile(s);
if (StringUtils.isNotEmpty(message) && message.equals("STOP")) {
stop = true;
}
}
}
private void openOutputFile() {
try {
outputFile = new File("C:/mahi/Test", "file." + processId);
outputFileWriter = new FileWriter(outputFile);
} catch (IOException e) {
System.out.println("Exception while opening file");
stop = true;
}
}
private void writeOutputFile(String message) {
try {
outputFileWriter.write(message);
outputFileWriter.flush();
} catch (IOException e) {
System.out.println("Exception while writing to file");
stop = true;
}
}
}
How will I know when the ThreadPool has finished processing so I can do my other clean up work?
Thanks

If you Worker class implements Callable instead of Runnable, then you'd be able to see when your threads complete by using a Future object to see if the Thread has returned some result (e.g. boolean which would tell you whether it has finished execution or not).
Take a look in section "8. Futures and Callables" # website below, it has exactly what you need imo:
http://www.vogella.com/articles/JavaConcurrency/article.html
Edit: So after all of the Futures indicate that their respective Callable's execution is complete, its safe to assume your executor has finished execution and can be shutdown/terminated manually.

Something like this:
exec.shutdown();
// waiting for executors to finish their jobs
while (!exec.awaitTermination(50, TimeUnit.MILLISECONDS));
// perform clean up work

You can use a thread for monitoring ThreadPoolExecutor like that
import java.util.concurrent.ThreadPoolExecutor;
public class MyMonitorThread implements Runnable {
private ThreadPoolExecutor executor;
private int seconds;
private boolean run=true;
public MyMonitorThread(ThreadPoolExecutor executor, int delay)
{
this.executor = executor;
this.seconds=delay;
}
public void shutdown(){
this.run=false;
}
#Override
public void run()
{
while(run){
System.out.println(
String.format("[monitor] [%d/%d] Active: %d, Completed: %d, Task: %d, isShutdown: %s, isTerminated: %s",
this.executor.getPoolSize(),
this.executor.getCorePoolSize(),
this.executor.getActiveCount(),
this.executor.getCompletedTaskCount(),
this.executor.getTaskCount(),
this.executor.isShutdown(),
this.executor.isTerminated()));
try {
Thread.sleep(seconds*1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
And add
MyMonitorThread monitor = new MyMonitorThread(executorPool, 3);
Thread monitorThread = new Thread(monitor);
monitorThread.start();
to your class where ThreadPoolExecutor is located.
It will show your threadpoolexecutors states in every 3 seconds.

How to achieve multi threading while one thread is at sleep mode

I have a problem where my class is performing the first run method after which it is not proceeding into a second, overidden run method.
The program execution beings in a controller class which has a main method and a thread pool:
public class RunnableController {
// Main method
public static void main(String[] args) throws InterruptedException {
try {
RunnableController controller = new RunnableController();
controller.initializeDb();
controller.initialiseThreads();
System.out.println("Polling");
} catch (Exception e) {
e.printStackTrace();
}
}
private void initialiseThreads() {
try {
threadExecutorRead = Executors.newFixedThreadPool(10);
PollingSynchronizer read = new PollingSynchronizer(incomingQueue, dbConncetion);
threadExecutorRead.submit(read);
} catch (Exception e){
e.printStackTrace();
}
}
}
My poller class which fetches new data and should do updating simulateously:
public class PollingSynchronizer implements Runnable {
public PollingSynchronizer(Collection<KamMessage> incomingQueue,
Connection dbConnection) {
super();
this.incomingQueue = incomingQueue;
this.dbConnection = dbConnection;
}
private int seqId;
public int getSeqId() {
return seqId;
}
public void setSeqId(int seqId) {
this.seqId = seqId;
}
// The method which runs Polling action and record the time at which it is done
public void run() {
int seqId = 0;
while (true) {
List<KamMessage> list = null;
try {
list = fullPoll(seqId);
if (!list.isEmpty()) {
seqId = list.get(0).getSequence();
incomingQueue.addAll(list);
this.outgoingQueue = incomingQueue;
System.out.println("waiting 3 seconds");
System.out.println("new incoming message");
Thread.sleep(3000);//at this wait I should execute run()
//when I debug my execution stops here and throws " Class not found Exception "
// its does not enters the message processor class
MessageProcessor processor = new MessageProcessor() {
//the run method which should fetch the message processor class.
final public void run() {
MessageProcessor(outgoingQueue).generate(outgoingQueue);
}
};
new Thread(processor).start();
}
} catch (Exception e1) {
e1.printStackTrace();
}
}
}
}
My message processor class:
public abstract class MessageProcessor implements Runnable {
private Connection dbConnection;
Statement st = null;
ResultSet rs = null;
PreparedStatement pstmt = null;
private Collection<KamMessage> outgoingQueue;
public KamMsg804 MessageProcessor(Collection<KamMessage> outgoingQueue,
Connection dbConnection) {
this.outgoingQueue = outgoingQueue;
this.dbConnection = dbConnection;
return (KpiMsg804) fetchedMessages;
}
public Collection<KamMessage> generate(Collection<KamMessage> outgoingQueue) {
while (true) {
try {
while (rs.next()) {
KamMessage filedClass = convertRecordsetToPojo(rs);
outgoingQueue.add(filedClass);
}
for (KamMessage pojoClass : outgoingQueue) {
KamMsg804 updatedValue = createKamMsg804(pojoClass);
System.out.print(" " + pojoClass.getSequence());
System.out.print(" " + pojoClass.getTableName());
System.out.print(" " + pojoClass.getAction());
System.out.print(" " + updatedValue.getKeyInfo1());
System.out.print(" " + updatedValue.getKeyInfo2());
System.out.println(" " + pojoClass.getEntryTime());
}
return outgoingQueue;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
My problem is exactly at the second run(9 method where I am getting exception in MessageProcessor class and it loops back to Polling.
How do I implement multithreading here, as when the thread sleeps for 3 seocnds in polling it should simultaneously update the database.
After which, how can the data be fed and updated back into the db.
My program flow - I have three classes:
1.Controller
2.PollerSynchro
3.Msgprocessor
I have database records, which are converted into POJO form and stored in a Collection. With these POJOs my classes try to do multiprocessing and updating in a single stretch.
Controller - has the thread pool, initiates poller class with poll method - done
Poller - should poll for new incoming messages and stores it in incoming queue - done
MsgProcessor - should look for new incoming messages and pass them from outgoing queue to incoming queue - also done
Problem:
Now my problem is
I have to implement this update while the poll thread sleeps for 3 sec,
In my code for the second void run() method in the Poller class, the outgoing queue is not passed and fed to the messageprocessor class for updating. My flow of execution only just loops back to first run method and am getting Class exception.
Please help me to solve these problems.

I can't sugar coat this, your code is a mess. However, as far as why your message processor code is not being executed, you never actually start the thread you created with this code:
MessageProcessor processor = new MessageProcessor() {
// the run method which should fetch the message processor class.
final public void run() {
MessageProcessor(outgoingQueue).generate(outgoingQueue);
}
};
Ignoring the confusingly named method being called, your code should look more like this:
Message processor = new MessageProcessor() {
// the run method which should fetch the message processor class.
final public void run() {
MessageProcessor(outgoingQueue).generate(outgoingQueue);
}
};
new Thread(processor).start();