com.gridsystems.innergrid.kernel.genericutils
Class PagedRequest<E>

java.lang.Object
  java.lang.Thread
      com.gridsystems.innergrid.kernel.genericutils.PagedRequest<E>

Type Parameters:

E - Object type to be paged.

All Implemented Interfaces:

java.lang.Runnable

public abstract class PagedRequest<E>
extends java.lang.Thread

Base class for asynchronous paged requests.

Subclassing

Subclasses must implement the run() method, and do it fill the results list.

The implementation should correctly (and regularly) check for interruption condition, as it is the mechanism used by PagedRequestManager to cancel request executions.

Usage

A typical iteration loop over a paged request that gets the results, concurrently to the request execution, will have the following layout:

PageRequestManager<MyBean> myManager = new PageRequestManager<MyBean>(); ... PagedRequest<MyBean> req = myManager.getPagedRequest(id);

while (true) {
try {
MyBean items[] = req.getResults(results.size(), N);
if (items == null) break; // No more items
// do something whith items
}
catch (PagedRequestTimeoutException e) {
// do nothing
}
catch (PagedRequestNoDataException e) {
// sleep some time
}
}

Or, if we just want to wait until the request execution is finished, and get all its results in one operation, we can do:

PagedRequest req = ...;
req.join();

int count = req.getResultsCount();
Object results[] = (count == 0) ? new Object[0] : req.getResults(0, count);

Version:

1.0

Author:

lgaspart, rruiz, Xmas (generics)

Nested Class Summary

Nested classes/interfaces inherited from class java.lang.Thread

java.lang.Thread.State, java.lang.Thread.UncaughtExceptionHandler

Field Summary

protected com.gridsystems.innergrid.kernel.server.KernelContext	originalContext Request user information.
protected java.util.ArrayList<E>	results Results of the request.
protected java.lang.Class<E>	theClass Class of type E.

Fields inherited from class java.lang.Thread

MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY

Constructor Summary

PagedRequest(com.gridsystems.innergrid.kernel.server.KernelContext context, java.lang.Class<E> theClass, boolean blockRequest)
Creates a new instance.

Method Summary

void	clear() Clears the Paged request.
long	getId() Gets the identifier of the paged request.
long	getLastAccessTime() Gets the time of the last access to this request data.
E[]	getResults(int from, int count) Calls getResultsTimeout() with an appropriate timeout value depending on the 'block' flag specified at construction time.
int	getResultsCount() Gets the number of results of the paged request.
E[]	getResultsTimeout(int from, int count, long timeout) Asks for 'count' results, starting at offset 'from'.
long	getTime() Gets the hour of the paged request.
java.lang.String	getUser() Gets the user of the paged request.
abstract void	run() Subclasses must implement the request in this method.

Methods inherited from class java.lang.Thread

activeCount, checkAccess, countStackFrames, currentThread, destroy, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, stop, suspend, toString, yield

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

originalContext

protected com.gridsystems.innergrid.kernel.server.KernelContext originalContext

Request user information.

results

protected java.util.ArrayList<E> results

Results of the request.

theClass

protected final java.lang.Class<E> theClass

Class of type E.

Constructor Detail

PagedRequest

public PagedRequest(com.gridsystems.innergrid.kernel.server.KernelContext context,
                    java.lang.Class<E> theClass,
                    boolean blockRequest)

Creates a new instance.

Parameters:

theClass - Class of type E

context - The request context

blockRequest - true if the request must be blocking

Method Detail

run

public abstract void run()

Subclasses must implement the request in this method.

Specified by:

run in interface java.lang.Runnable

Overrides:

run in class java.lang.Thread

getId

public long getId()

Gets the identifier of the paged request.

Overrides:

getId in class java.lang.Thread

Returns:

this paged request identifier

getUser

public java.lang.String getUser()

Gets the user of the paged request.

Returns:

the user of this paged request

getTime

public long getTime()

Gets the hour of the paged request.

Returns:

the hour of this paged request

getResultsCount

public int getResultsCount()

Gets the number of results of the paged request.

Returns:

the number of results in this request

getLastAccessTime

public long getLastAccessTime()

Gets the time of the last access to this request data.

Returns:

the last access time

getResultsTimeout

public E[] getResultsTimeout(int from,
                             int count,
                             long timeout)
                      throws PagedRequestNoDataException

Asks for 'count' results, starting at offset 'from'. If not enough data is initially available, it will block during at most 'timeout' milliseconds.

The returned value depends on the following rules:

• If, after the timeout interval, there are no available results, but the request execution is still in progress, a PagedRequestNoDataException will be thrown.
• The same exception will be thrown if the current thread is interrupted.
• If, after the timeout interval, there are one or more results, they will be returned in an array, even if there are less items than requested.
• If the request execution has finished, and there are no results in the specified range, null will be returned. This marks the end condition for a retrieval loop.

Parameters:

from - The offset of the first result to get

count - The number of results to get

timeout - The max blocking time

Returns:

An array with the obtained results, or null if the request is finished and 'from' is out of the results bounds.

Throws:

PagedRequestNoDataException - In case of timeout

getResults

public E[] getResults(int from,
                      int count)
               throws PagedRequestNoDataException

Calls getResultsTimeout() with an appropriate timeout value depending on the 'block' flag specified at construction time.

Parameters:

from - The initial offset

count - The number of results to retrieve

Returns:

An array with the results (either all, or a partial subset), or null if the request execution has finished and 'from' is out of bounds

Throws:

PagedRequestNoDataException - if no results are available yet

clear

public void clear()

Clears the Paged request.