GCube ResultSet (gRS)

ResultSet Framework

Introduction

The ResultSet Framework provides the enabling mechanism to pass by reference data between components and / or services that can be hosted in the same or remote nodes. It utilizes the gCore Framework for keeping state and offers value adding operations for encapsulating remote and local calls, paging of content, data movement, remote processing and more described in available code documentation.

Implementation Overview

The framework consists of 4 sub components :

1. the ResultSet library
2. the ResultSet Service
3. the ResultSet Client
4. the ResultSet Garbage Collector

• The ResultSet is the enabling element that creates a linked list of pages holding the records that are part of the specific result set. It can iterate over the created parts and perform various operations on the structure of the list and the contents themselves. Its operations are mostly part specific but they can also affect the entire result chain. Once a page of content has been created and the next in line has been initialized the part cannot be altered. Once it has been declared that the authoring of a result set has finished, the entire chain of it is immutable.
• The ResultSet Service is merely a WS front-end to the ResultSet library. It creates and manages WS-Resources holding references to instances of the ResultSet components. These instances are responsible to hold state regarding the iteration over the chain of pages and for accessing / modifying / querying the data held.
• The ResultSet Client is a library giving access to both high and low level operations that can be performed on a specific ResultSet component instance and its underlying data. It enables handling of ResultSets that are both wrapped through a WS front-end and that are locally manipulated though direct java invocations (within JVM).
• The ResultSet Garbage Collector is a thread that clears up resources used by the ResultSet Framework (removing file-system resources and destroying created gCore-Resources)

Dependencies

• ResultSetLibrary
  • jdk 1.5
  • gCore
• ResultSetService
  • jdk 1.5
  • gCore
  • ResultSetLibrary
• ResultSetClient
  • jdk 1.5
  • gCore
  • ResultSetLibrary
  • ResultSetService
• ResultSetGarbageCollector
  • jdk 1.5
  • gCore
  • ResultSetLibrary
  • ResultSetService stubs

Usage Example

The ResultSets that can be created are content independent but depending on the content inserted different operations can be performed. So different readers and writers have been implemented to offer different levels of versatility depending on the content. Here he will mainly focus on the XML authoring and retrieving which is most commonly used and thoroughly tested up to this point. As more types of readers / writers become popular additional documentation will be made available

The code examples are not exhaustive in error checking and should only be considered as usage templates

Creating an RS

  /*A method that creates a new RSXMLWriter and populates it with some results*/
  public static RSXMLWriter createRSWriter() throws Exception{
     /*Create a new writer with the default parametrizable values*/ 
     RSXMLWriter writer=RSXMLWriter.getRSXMLWriter(); 
     /*Create a new writer which should have as a condition for paging inserted results either having 
     30 records per page or having a total size surpasing 1024 bytes */ 
     //writer=RSXMLWriter.getRSXMLWriter(30,1024); 
     /*Create a new writer and set a lifetime property of 1000 millisecs. Also set that the paging 
     condition will be having 10 records per page or a total size surpasing teh default value*/ 
     //writer=RSXMLWriter.getRSXMLWriter(new PropertyElementBase[]{new PropertyElementLifeSpanGC(1000)}); 
     //writer.setRecsPerPart(10); 
     /*Add a new result with the given id, collection, rank and payload*/ 
     writer.addResults(new ResultElementGeneric("id1","collection1","rank1","payload")); 
     /*Add a new result with the given id, collection, rank and payload*/ 
     writer.addResults(new ResultElementGeneric("id2","collection1","rank2","payload")); 
     /*Add an array of results with the given id, collection, rank and payload*/ 
     writer.addResults(new ResultElementBase[]{new ResultElementGeneric("id3","collection1","rank3","payload"),
        new ResultElementGeneric("id4","collection1","rank4","payload")}); 
     /*Give back the writer*/ 
     /*One should ALWAYS close the RS he is creating in order to make the full payload available to readers*/ 
     writer.close(); 
     return writer; 
  }

Retrieving a locator

From a writer

  /*This method retrieves an instance of an RSLocator capable of identifying a ResultSet authored by the provided RSXMLWriter. Depending on the type of 
  resource requested, this identifier can either be an identifier pointing to the local node (filesystem) or an idenitfier capable of pinpointing the RS 
  through a web service using the WS-Resource pattern. One can create many locators (of the same or different) type for the same authored RS*/
  public static RSLocator getLocator(RSXMLWriter writer) throws Exception{
     RSLocator locator=null; 
     /*Retrieves a locator identifying the RS in the local node*/ 
     //locator=writer.getRSLocator(new RSResourceLocalType()); 
     /*Retrieves a locator identifying the RS through WS-Resource pattern accesible from any node. The 
     The service pointed to must be in the localhost. This method can be used when manipulating the RSXMLWriter 
     outside container context. Otherwise the following method can be used*/ 
     //locator=writer.getRSLocator(new RSResourceWSRFType("http://localhost:8080/wsrf/services/gcube/searchservice/ResultSetService")); 
     /*Retrieves a locator identifying the RS through WS-Resource pattern accessible from any node. The 
     default constructor utilizes the container context (which must be available) to compose the locally hosted 
     ResultSetService that must be deployed*/ 
     locator=writer.getRSLocator(new RSResourceWSRFType()); 
     return locator; 
  }

From a reader

  /*This method retrieves an instance of an RSLocator capable of identifying the ResultSet read by the provided RSXMLReader. Everythime the method is called    
  the same resource is identified. Both types  of locators can be serialized to string and utilized to initialize a new RSLocator*/
  public static RSLocator getLocator(RSXMLReader reader) throws Exception{
     RSLocator locator=null; 
     /*Retrieves a locator identifying the RS. The type is the same as the one used to initialize the RSXMLReader*/ 
     locator=reader.getRSLocator(); 
     return new RSLocator(locator.getLocator()); 
  }

Reading an RS

Page by Page

  /*This method instantiates a new RSXMLReader to point to the RS identified by the provided

RSLocator and iterates over each page retrieving the contents*/

  public static void readRS(RSLocator locator) throws Exception {
     PropertyElementBase []props=reader.getProperties(PropertyElementEstimationCount.class,PropertyElementEstimationCount.propertyType);
     System.out.println(((PropertyElementEstimationCount)props[0]).toXML());
     RSXMLReader reader=RSXMLReader.getRSXMLReader(locator); 
     while(!reader.isLast()){
        reader.getNumberOfResults(); 
        /*Retrieve the records in the current page as instances of the provided class that extends the ResultElementBase*/ 
        ResultElementBase []res=reader.getResults(ResultElementGeneric.class); 
        reader.getNextPart(); 
     } 
     reader.getFirstPart(); 
     do{
        reader.getFullPayload(); 
     }while(reader.getNextPart()); 
  }

Iterating

  /*This method instantiates a new RSXMLReader to point to the RS identified by the provided RSLocator and iterates over each record retrieving the    
  contents*/
  public static void iterateRS(RSLocator locator) throws Exception {
     RSXMLIterator iter=RSXMLReader.getRSXMLReader(locator).getRSIterator(); 
     while(iter.hasNext()){
        ResultElementGeneric elem=(ResultElementGeneric)iter.next(ResultElementGeneric.class); 
        /*Retrieve the DocID of the retrieved record*/ 
        if(elem!=null) elem.getRecordAttributes(ResultElementGeneric.RECORD_ID_NAME); 
     } 
  }

Extending Base elements

Two types of elements are currently extendable in the context of the Framework.

• PropertyElementBase - Which is used to add / retrieve property elements describing the authored RSs
• ResultElementBase - Which is used to add / retrieve records from the RS

These elements must be available to both the producer and the consumer as library elements in order to be used. of course this is not mandatory and a consumer can ustilize a differnt element to retrieve the records that a consumer inserted using some other element. It is in the repsonsibility of the producer / consumer to synchronize the elements they use. These elements serve mainly as containers for the actual payload that should be inserted / retrieved possibly adding some common handling functionality on top of that payload.

Extending PropertyElementBase

  /*This is ane example of extending the PropertyElementBase to derive Property Element that is used to add WSRF EndpointReferenceType serializations to 
  the RS head page*/
  public class PropertyElementWSEPR extends PropertyElementBase{
     /* The Type of the Property this Property element produces*/ 
     public static String propertyType="WS-EPR"; 
     private String epr=null; 
     /* Default contructor required by the PropertyElementBase in order to instantiate the class using reflection*/ 
     public PropertyElementWSEPR(){} 
     /* Initializes a new PropertyElementWSEPR with the given EndpointReferenceType serialization */ 
     public PropertyElementWSEPR(String epr) throws Exception{
        this.epr=epr; 
        setType(PropertyElementWSEPR.propertyType); 
     } 
     /* The usefull property payload from the PropertyElementWSEPR point of view as valid xml */ 
     public String toXML() throws Exception{ 
        return this.epr; 
     } 
     /* The usefull property payload from the PropertyElementWSEPR point of view as returned by 
     PropertyElementWSEPR.fromXML */ 
     public void fromXML(String xml) throws Exception{
        this.epr=xml; 
     } 
  }

Extending ResultElementBase

  /* A Result element that extends the ResultElementBase and can be used to insert and retrieve xml records from an RS*/
  public class ResultElementFoo extends ResultElementBase{
     /* The name of the attribute holding a desired record attribute */ 
     public static final String RECORD_FOO_NAME="Foo"; 
     private String payload; 
     /* Default contructor nessecary for the framework to instantiate the ResultElementFoo though reflection */ 
     public ResultElementFoo(){} 
     /* Creates a new link ResultElementFoo with the provided Foo attribute value and payload */ 
     public ResultElementFoo(String foo,String payload) throws Exception{
        Vector<RecordAttribute> at=new Vector<RecordAttribute>(); 
        at.add(new RecordAttribute(ResultElementFoo.RECORD_FOO_NAME,foo)); 
        setRecordAttributes(at.toArray(new RecordAttribute[0])); 
        this.payload=payload; 
     } 
     private void setPayload(String payload){
        this.payload=payload; 
     } 
     public String getPayload(){
        return this.payload; 
     } 
     /* The Attributes that can be defined for a record are handled internally by the ResultElementBase and can be 
     set / accessed using the Base elements respective methods*/ 
     public String getFooValue(){
        return getRecordAttributes(ResultElementFoo.RECORD_FOO_NAME)[0].getAttrValue(); 
     } 
     /* The xml representation of the record payload */ 
     public String toXML() throws Exception{
        return payload; 
     } 
     /* The payload of the result element as returned by the ResultElementFoo.toXML */ 
     public void fromXML(String xml) throws Exception{
        setPayload(xml); 
     } 
  }

Complex Operations

RS creation within Workflows

In the context of a workflow it might be desirable to send to the asking component a locator capable of identifying the RS that the producer will be populating. This is best done in a non blocking manner in a background thread.

  /*This method creates an RS and starts a background thread populating the RS. It then returns the locator to the RS that is beeing populated*/
  public static RSLocator populateRS() throws Exception{
     RSXMLWriter writer=RSXMLWriter.getRSXMLWriter(); 
     BackgroundPopulating rst=new BackgroundPopulating(writer); 
     rst.start(); 
     return writer.getRSLocator(new RSResourceLocalType()); 
  }

  /*This extends Thread in order to enable populating of the RS the RSXMLWriters it is initialized with points to*/
  public class BackgroundPopulating extends Thread{
     RSXMLWriter writer=null; 
     /*The RSXMLWriter to use for populating the RS*/
     public BackgroundPopulating(RSXMLWriter writer){
        this.writer=writer; 
     } 
     /*Populate the RS*/
     public void run(){
        try{
           writer.addResults(new ResultElementGeneric("id1","collection1","rank1","payload")); 
           writer.addResults(new ResultElementGeneric("id2","collection1","rank2","payload")); 
           writer.addResults(new ResultElementBase[]{new ResultElementGeneric("id3","collection1","rank3","payload"),
               new ResultElementGeneric("id4","collection1","rank4","payload")}); 
           writer.close(); 
        }catch(Exception e){
           e.printStackTrace(); 
        } 
     } 
  }

Partial Localization

  /*This method localizes a ResultSet keeping the top count records of the identified throught the RSLocator RS. The localization is in terms
of the node that hosts the RS content and not the Resource type. This can be further defined by the RSResourceType*/
  public static RSLocator localizePart(RSLocator locator,int count) throws Exception {
     RSXMLReader reader=RSXMLReader.getRSXMLReader(locator); 
     reader.isLocal(); //false 
     //RSXMLReader readerTop=reader.keepTop(count); 
     //readerTop.isLocal(); //false 
     //RSXMLReader readerLocalJVM=readerTop.makeLocal(new RSResourceLocalType()); 
     //readerLocalJVM.isLocal(); //true 
     //RSXMLReader readerLocalWS=readerTop.makeLocal(new RSResourceWSRFType()); 
     //readerLocalWS.isLocal(); //true 
     RSXMLReader readerLocalTop=reader.makeLocal(new RSResourceLocalType(),count); 
     readerLocalTop.isLocal(); //true 
     return readerLocalTop.getRSLocator(); 
  }

RS xPath filtering

  /*This method scans through every record of the RS and evaluates the provided xPath expression against each. If the evaluation returns
some result, the record is inserted in a new RS. A new RSXMLReader is created holding the matching record. The xPath expression must
start with a reference to the current node (eg .//[..])*/
  public static RSLocator filterRS(RSLocator locator,String xPath) throws Exception {
     RSXMLReader reader=RSXMLReader.getRSXMLReader(locator); 
     return reader.filter(xPath).getRSLocator(); 
  }

RS as Flow Control Mechanism

The ResultSet Framework offers the additional functionality of synchronizing result production with result consumption. This functionality is simulated in the following attached code

ResultSet as Flow Contol Mechanism Example code

Pool Of RS Writers

Another feature that is available for usage is a pool of pre-created writers with already created locators. In cases of container heavy load and of WS based locators, this pool can save a significant amount of time in the creation of a writer. In the context of a service for example on can staticly define a factory of writers that include a configurable pool of precreated writers and use this factory to retrieve the writers to use. The code below shows this in sudo-code.

import org.gcube.searchservice.searchlibrary.rsclient.elements.pool.PoolConfig;
import org.gcube.searchservice.searchlibrary.rsclient.elements.pool.PoolObjectConfig;
import org.gcube.searchservice.searchlibrary.rsclient.elements.pool.RSPoolObject;
import org.gcube.searchservice.searchlibrary.rswriter.RSWriterFactory;
import org.gcube.searchservice.searchlibrary.rswriter.RSXMLWriter;

public class ExampleService {
/**
* Factory of rs writers
*/
  private static RSWriterFactory factory=null; //the factory that will be used and include the pool
  static{
     PoolConfig config=new PoolConfig(); //the pool configuration
     PoolObjectConfig oConf=new PoolObjectConfig(); //configuration item
     try{
        oConf.FlowControl=false; //the specific writers should not allow flow control
        oConf.MaxSize=20; //the maximum size of the specific writer pool
        oConf.MinSize=8; //the minimum size (threshlod to repopulate)
        oConf.ObjectType=RSPoolObject.PoolObjectType.WriterXML; //the type of writer
        oConf.ResourceType=RSPoolObject.PoolObjectResourceType.WSRFType; //the type of locator to pre-contsruct
        oConf.ServiceEndPoint=null; //not staticly created but in service context
        config.add(oConf); //add this object in the pool
     }catch(Exception e){
        log.error("Could not initialize factory pool. Continuing",e);
     }
     factory=new RSWriterFactory(config);
  }
  public String doWork(DoWork params) throws SomeBaseFault{
     Vector<String> results=MyLibrary.search(params.getQuery);
     //background add records
     PropertyElementBase [] props=new PropertyElementBase []{
        new PropertyElementEstimationCount(results.size(),results.size(),results.size())};
     // without the factory this call would have been RSXMLWriter.getRSXMLWriter(props)
     return writer=factory.getRSXMLWriter(props).getRSLocator(new RSResourceWSRFType();
  }
}

ResultSet Extentions

ResultSet Leasing

Freeing resources hold by a ResultSet(RS) in currently takes place in the vicinity of the GarbageCollector. The policy implemented thus far is that the GarbageCollector wakes up periodically and if it finds an RS that has not been modified for too long it removes it. This removing results in freeing two types of resources:a) The disk storage resources and b) the WS resources. The former resources are freed by removing the RS files from the file system while the latter are freed by calling the destroy function on the RS WSRF resource.

Leasing aims to be a mechanism to enhance the resource feeing mechanism of the ResultSet. When creating a new RS the author is able to chose up until when the RS will be available. As a consequence the internal mechanisms of the RS will be able to free the resources hold at a convenient point in time. As of now we identify two leasing policies/types:

• Time leasing. When the RS author creates a resource he will be able to set a life time during which the ResultSet will be available. This essentially means that after this period the resultset will not be accessible. Extension is also possible in case it is requested.

• Access leasing. When RS author creates a resource he will be allowed to set the number of reads that are allowed. In case the number of reads is exceeded the resource will not be available, anymore.

Implementation Details

There are two types of resources to be managed. Disk and WSRF resources. Freeing them is essential in the success of the resultset. In the case of the GC of the RS will be running in the background in order to “sweep” RSs that have not been created with any type of leasing. Time leasing In case an RS is created with a time leasing then it can be freed by the GC if two conditions hold:

• The leasing has expired
• There has been no-one reading the RS for a certain period of time

To handle the second requirement we automatically extend the time leasing of a RS upon a getFirstPart request of an RS (indicating that there is going to be a read) if the the already existing leasing is sorter than the constant time limit assigned for reading the RS.

For supporting time leasing we have to add an xml element in the header of the RS. This will hold the the expiration time. This expiration time is touched:

 Created: Upon RS creation
 Read: Upon RS read connection
 Possibly Altered: Upon getFirstPart
 Read: from GC so as to remove or not the RS

Note: the RS lifetime could have been partially implemented to work in tandem with the WSRF lifetime but we need the leasing mechanism inside the RS core as an extra feature not coupled with a specific technology (WSRF). We must investigate if we are able to extract the the expiration time from the WSRF mechanism.

Access leasing

Access leasing is more straight forward. The author of an RS defines the number of reads that this RS is available for. To implement this also an extra element at the header of the RS is required. This element will essentially be a counter. Upon the counter become 0 successive reads of a part will result in removing the part thus feeing up the disk space reserved. The RS resource will ultimately be picked up by the GC. If the counter reaches 0 the RS will also be unavailable.

The forward counter element in the xml RS header will be touched:

 Created: Upon RS creation
 Altered: Upon getFirstPart call of the RS reader, indicating that a read starts.
 Read: Upon RS read initiation.

Notification for the garbage collected resources

Using the RSEPRCache component a service/component can store the EPR of a RS, in this cache, and use it again without having to wait for the execution of the query that produced the given RS. A RSEPRCache instance needs to be notified when the Garbage Collector collects an RS WS-resource, in order to update its content.

For this purpose, each deployed ResultSetService will register as a notifier, in the service's initialisation phase, to a unique topic for all the ResultSetServices and RSEPRCache instances of the infrastructure. In each period of the garbage collection procedure, the Collector aggregates all the RS WS-resources that are being garbage collected, and sends a batch notification message with the corresponding RS EPRs to the unique topic. When a RSEPRCache instance is created, it subscribes as a notification receiver to the unique topic, and it is able to receive notification messages with the EPRs of garbage-collected RSs, during its lifetime.

ResultSet Security

The ResultSet framework will offer a for of security in the context of content encryption and authorization. The author of a RS will be able to request for content encryption and/or authorization.

Upon RS creation a private public key will be created. Using these two keys the production of an encryption key will take place. The a) encryption key and b) the private key will be placed in the header of the RS and the header will be encrypted using the private RS key. The rest of the content of the RS will be encrypted with the encryption key. The public key will be returned to the RS author. It is the job of the RS author to pass the public key to the RS clients.

Upon reading the RS the client also indirectly has access to the private key so as to alter the RS header (for forward RS etc) but it is never actually reviled.

Interface

We propose a number of RS initialization attributes. Those attributes along with the already existing ones will have to be packed in a initialization properties structure (RSCreationProperties). These properties will include:

 1.Flow control (enable/disable)
 2.Scope
 3.Time leasing (leasing period)
 4.Forward leasing (number of reads allowed)
 5.Security features (enable/disable)
 6.Cached (yes/no)

We will have default values and function overload to achieve backward compatibility and usage ease.

ResultSet Cache

The Result Set Cache is a component that caches Result Set EndPointReferences(EPRs) and communicates with the Result Set service instances that are deployed in the infrastructure, to be informed about the Result Set EPRs that are being reclaimed.

Internal Structure

A ResultSet Cache can be used by every component(even if this component is not a web-service deployed in gCube infrastructure), that needs to store EPRs of Result Sets that were once obtained, in order to use them again in the future. For example a component that forms a query Q, which returns results that are contained in a Result Set with EPR A, can add A in a RSEPRCache object with the Q as a key. When this component needs the results for the same query Q in the future, it can get the corresponding ResultSet EPR A through the Cache object, without having to wait for the execution of the query again. In order to add a new ResultSet EPR in a RSEPRCache object, a add method is provided that takes two arguments, an java.lang.String object which is the EPR to be added and a java.lang.Object object which is the key that can be used to retrieve this EPR. In order to get a previously added ResultSet EPR from a Cache object, a get method is provided that takes a java.lang.Object object as an argument, and returns the java.lang.String EPR with a corresponding key equal to the argument, using the equals() method that is defined in the actual class of the argument. The EPR to be added using the add method must be expressed as a java.lang.String, in a serialized form. The EPR returned by the get method is also expressed as a java.lang.String, in a serialized form i.e:

<ns1:ResultSetResourceReference xmlns:ns1="http://gcube.org/namespaces/searchservice/ResultSetService">
  <ns2:Address xmlns:ns2="http://schemas.xmlsoap.org/ws/2004/03/addressing">
    http://ariadni.di.uoa.gr:8080/wsrf/services/gcube/searchservice/ResultSet
  </ns2:Address>
  <ns3:ReferenceProperties xmlns:ns3="http://schemas.xmlsoap.org/ws/2004/03/addressing">
    <ns1:ResourceKey>287f4870-e7b5-11dd-bf93-8bbaa734be44</ns1:ResourceKey>
  </ns3:ReferenceProperties>
  <ns4:ReferenceParameters xmlns:ns4="http://schemas.xmlsoap.org/ws/2004/03/addressing"/>
</ns1:ResultSetResourceReference>

A ResultSet Cache object receives notifications, from every ResultSet service that is deployed in the infrastructure, for ResultSet EPRs that were reclaimed and can't be accessed any more. Using gCube IS-Notification mechanism each ResultSet Cache object subscribes to a global topic for notifying about reclaimed ResultSet EPRs, receives batch messages that contain the EPRs of the reclaimed ResultSets and deletes the contents that are related to them(see also Notification_for_the_garbage_collected_resources). This operation is performed in the background, and the contents of a Cache object remain valid without any action needed from the component that uses the Cache object.

Usage Examples

//construct a new RSEPRCache using the default settings. myEpr will be used to register to
//the notifications' topic used for notifying when a ResultSet is removed from RS garbage collector
String myEpr = ServiceHost.getBaseURL().toString() + ServiceContext.getContext().getJNDIName();
RSEPRCache rseprCache = new RSEPRCache(new EndpointReferenceType(new AttributedURI(myEpr)), ServiceContext.getContext());
 
...
 
//get the epr of the Result Set that answers to queryQ
String epr = searchMaster.search(queryQ);
//add this epr to the cache with the queryQ as a key
rseprCache.add(queryQ, epr);
 
//perform some actions with the results obtained
...
 
//perform some other actions
...
 
//if you want results for the same queryQ, get the epr for the corresponding Result Set
//get it from the cache.
epr = rseprCache.get(queryQ);
 
RSLocator rsLocator = null;
RSXMLReader reader = null;
//there is always a possibility that the retrieved EPR refers to a Result Set that was 
//reclaimed. A try-catch statement should be used when using the EPR.
try{
	rsLocator = new RSLocator(epr);
	reader = RSXMLReader.getRSXMLReader(rsLocator);
}catch(Exception e){
	//execute the query again in case of failure
        epr = searchMaster.search(queryQ);
        rsLocator = new RSLocator(epr);
	reader = RSXMLReader.getRSXMLReader(rsLocator);
}				 
 
//perform actions to the retrieved results
...

When retrieving an EPR from a RSEPRCache object, there is always a small possibility that the Result Set that this EPR refers to, has been reclaimed but the corresponding notification has never arrived to the RSEPRCache object, due to a network failure. Another smaller possibility is that the notification arrives to the RSEPRCache object between invocations:

epr = rseprCache.get(queryQ);

and

rsLocator = new RSLocator(epr);
reader = RSXMLReader.getRSXMLReader(rsLocator);

So creating a RSXMLReader from the EPR retrieved should be performed inside a try-catch statement.

A second constructor is provided, for creating caches with different settings than default:

/**
 * Constructor of RSEPRCache that takes configuration parameters and creates a new cache with 
 * this configuration.
 * 
 * @param notificationConsumerEPR the EPR of the service that will be used to register to
 * the notifications topic used for notifying when a ResultSet is removed from RS garbage collector
 * @param sctx the context of the service that will be used to register to the notifications topic
 * @param ttl the default amount of time to live for an element from its creation date
 * @param tti the default amount of time to live for an element from its last accessed date
 * @param maxElementsInMemory the maximum number of elements in memory, before they are evicted
 * @param overflowToDisk whether to use the disk store when there is overflow of the memory used
 * @throws Exception
 */
public RSEPRCache(EndpointReferenceType notificationConsumerEPR, 
GCUBEServiceContext sctx, long ttl, long tti, int maxElementsInMemory, boolean overflowToDisk)

A third constructor is provided, for the creation of caches by components that are not gCube services(i.e. portlets):

/**
 * Default constructor of RSEPRCache that should be used by gCube components that are not exposed as services. 
 * It returns a new RSEPRCache object.
 * 
 * @param notificationConsumerEPR the caller's URI expressed as an EPR, that will be used to register 
 * to the notifications topic used for notifying when a ResultSet is removed from RS garbage collector
 * @param sman a security manager that will be used to register to the notifications topic
 * @param sc the infrastructure scope of this scope will be used for subscribing to the topic
 * @throws Exception
 */
public RSEPRCache(EndpointReferenceType notificationConsumerEPR, GCUBESecurityManager sman, GCUBEScope sc)

The first argument for the last constructor can be the address of the machine where the component runs, i.e:

EndpointReferenceType consEpr = new EndpointReferenceType();
consEpr.setAddress(new Address("http://ariadni.di.uoa.gr"));
RSEPRCache cache = new RSEPRCache(consEpr, sman, sc);

Dependencies

• Result Set Service Stubs

The Notification message types are defined in the wsdl of the Result Set Service.

• EHCACHE

Ehcache is used internally to implement the caching mechanisms.

• gCore