org.hypergraphdb

Class HGEnvironment

java.lang.Object

org.hypergraphdb.HGEnvironment

public class HGEnvironment
extends Object

This class provides some facilities to manage several open HyperGraph databases within a single virtual machine. This is useful when one needs to access a currently open database by its location.

The class essentially implements a static map of currently open databases. The general name HGEnvironment reflects the intent to eventually put JVM-wide operations here.

Author:

Borislav Iordanov

Constructor Summary

Constructors

Constructor and Description
HGEnvironment()

Method Summary

Methods

Modifier and Type	Method and Description
static void	closeAll() Close all currently open HyperGraph instances.
static void	configure(String location, HGConfiguration config) Configure a HyperGraphDB instance before it is actually opened.
static void	disableShutdownHook() Disable the HyperGraph JVM shutdown hook.
static ExecutorService	executor() Return the environment-wide ExecutorService.
static boolean	exists(String location) Return true if there is a HyperGraph database at the given location and false otherwise.
static HyperGraph	get(String location) Retrieve an already opened or open a HyperGraph instance.
static HyperGraph	get(String location, HGConfiguration config) Retrieve the HyperGraphDB instance at the specified location and open it (if not already opened) with the given configuration.
static HGConfiguration	getConfiguration(String location) Retrieve the configuration of a HyperGraphDB instance.
static HyperGraph	getExistingOnly(String location) Same as get, but will return null if there is no database at that location.
static MemoryWarningSystem	getMemoryWarningSystem() Return the singleton MemoryWarningSystem attached to this JVM.
static HGDatabaseVersionFile	getVersions(String location) Return the HGDatabaseVersionFile containing version information for the various components on the database instance at the directory specified by the location parameter.
static boolean	isOpen(String location) Return true if the database at the given location is already open and false otherwise.

Methods inherited from class java.lang.Object

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

Constructor Detail

HGEnvironment

public HGEnvironment()

Method Detail

getMemoryWarningSystem

public static MemoryWarningSystem getMemoryWarningSystem()

Return the singleton MemoryWarningSystem attached to this JVM.

get

public static HyperGraph get(String location)

Retrieve an already opened or open a HyperGraph instance. Note that a new database instance will potentially be created via new HyperGraph(location) if it doesn't already exist.

Parameters:

location - The location of the HyperGraph instance.

Returns:

The HyperGraph database instance.

get

public static HyperGraph get(String location,
             HGConfiguration config)

Retrieve the HyperGraphDB instance at the specified location and open it (if not already opened) with the given configuration. If the instance has already been opened, the configuration parameter is ignored.

Parameters:

location - The filesystem path of the database instance.

config - The set of configuration parameters.

Returns:

getExistingOnly

public static HyperGraph getExistingOnly(String location)

Same as get, but will return null if there is no database at that location.

exists

public static boolean exists(String location)

Return true if there is a HyperGraph database at the given location and false otherwise.

isOpen

public static boolean isOpen(String location)

Return true if the database at the given location is already open and false otherwise.

configure

public static void configure(String location,
             HGConfiguration config)

Configure a HyperGraphDB instance before it is actually opened. If the instance at that location is already opened, the new configuration will only take effect if you close and re-open the instance.

Parameters:

location - The filesystem path to the database instance.

config - A HGConfiguration with the desired parameters set.

getConfiguration

public static HGConfiguration getConfiguration(String location)

Retrieve the configuration of a HyperGraphDB instance. If no configuration was previously defined, a new one will be created.

Parameters:

location - The filesystem path to the HyperGraphDB instance.

getVersions

public static HGDatabaseVersionFile getVersions(String location)

Return the HGDatabaseVersionFile containing version information for the various components on the database instance at the directory specified by the location parameter.

Since:

1.3

closeAll

public static void closeAll()

Close all currently open HyperGraph instances. This is generally done by a HyperGraphDB internal shutdown hook registered with the JVM. But if you need more control over the shutdown sequence, this method will gracefully do so.

disableShutdownHook

public static void disableShutdownHook()

Disable the HyperGraph JVM shutdown hook. The role of the shutdown hook is the close all open databases gracefully. If you disable, no such process is triggered upon JVM shutdown. If you have your own shutdown hook that must take upon that task, you can call the closeAll method.

executor

public static ExecutorService executor()

Return the environment-wide ExecutorService. The executor service is shared between all opened databases. It is used to submit long running tasks such as queries and wait for them to complete.