de.javakaffee.simplequeue

Class BDBQueue

java.lang.Object

de.javakaffee.simplequeue.BDBQueue

public class BDBQueue
extends Object

Fast queue implementation on top of Berkley DB Java Edition. This class is thread-safe.

This is based on .

Created on Jun 27, 2011

Author:

Martin Grotzke (initial creation)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	BDBQueue.CloseableIterator<T>

Constructor Summary

Constructors

Constructor and Description
BDBQueue(String queueEnvPath, String queueName, int cacheSize) Creates instance of persistent queue.
BDBQueue(String queueEnvPath, String queueName, int cacheSize, boolean readOnly, boolean allowCreate) Creates instance of persistent queue.

Method Summary

Methods

Modifier and Type	Method and Description
int	clear()
void	close() Closes this queue and frees up all resources associated to it.
String	getQueueName() Returns this queue name.
boolean	isEmpty() Determines if this queue is empty (equivalent to size() == 0).
BDBQueue.CloseableIterator<byte[]>	iterator() Returns an iterator over the elements in this queue.
static void	mkdir(File dir, boolean createDirectoryIfNotExisting) Asserts that the given directory exists and creates it if necessary.
byte[]	peek() Retrieves element from the head of this queue.
byte[]	poll() Retrieves and and removes element from the head of this queue.
void	push(byte[] element) Pushes element to the tail of this queue.
void	remove() Removes the eldest element.
long	size() Returns the size of this queue.

Methods inherited from class java.lang.Object

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

Constructor Detail

BDBQueue

public BDBQueue(String queueEnvPath,
        String queueName,
        int cacheSize)
         throws IOException

Creates instance of persistent queue.

Parameters:

queueEnvPath - queue database environment directory path

queueName - descriptive queue name

cacheSize - how often to sync the queue to disk

Throws:

IOException - thrown when the given queueEnvPath does not exist and cannot be created.

BDBQueue

public BDBQueue(String queueEnvPath,
        String queueName,
        int cacheSize,
        boolean readOnly,
        boolean allowCreate)
         throws IOException

Creates instance of persistent queue.

Parameters:

queueEnvPath - queue database environment directory path

queueName - descriptive queue name

cacheSize - how often to sync the queue to disk

readOnly - if the db shall be accessed readonly

allowCreate - if true, the db environment is created if it does not exist.

Throws:

IOException - thrown when the given queueEnvPath does not exist and cannot be created.

Method Detail

mkdir

public static void mkdir(@Nonnull
         File dir,
         boolean createDirectoryIfNotExisting)
                  throws IOException

Asserts that the given directory exists and creates it if necessary.

Parameters:

dir - the directory that shall exist

createDirectoryIfNotExisting - specifies if the directory shall be created if it does not exist.

Throws:

IOException - thrown if the directory could not be created.

poll

public byte[] poll()
            throws IOException

Retrieves and and removes element from the head of this queue.

Returns:

element from the head of the queue or null if queue is empty

Throws:

IOException - in case of disk IO failure

iterator

public BDBQueue.CloseableIterator<byte[]> iterator()
                                            throws IOException

Returns an iterator over the elements in this queue.

Returns:

an iterator over elemtns of the queue.

Throws:

IOException - in case of disk IO failure

peek

public byte[] peek()
            throws IOException

Retrieves element from the head of this queue.

Returns:

element from the head of the queue or null if queue is empty

Throws:

IOException - in case of disk IO failure

remove

public void remove()
            throws NoSuchElementException

Removes the eldest element.

Throws:

NoSuchElementException

push

public void push(byte[] element)
          throws IOException

Pushes element to the tail of this queue.

Parameters:

element - element

Throws:

IOException - in case of disk IO failure

clear

public int clear()

size

public long size()

Returns the size of this queue.

Returns:

the size of the queue

isEmpty

public boolean isEmpty()

Determines if this queue is empty (equivalent to size() == 0).

Returns:

true if this queue is empty, otherwise false.

getQueueName

public String getQueueName()

Returns this queue name.

Returns:

this queue name

close

public void close()

Closes this queue and frees up all resources associated to it.