[jira] [Resolved] (STRATOS-110) Topology Event Message Processors should follow 'chain of responsibility' design pattern

["Nirmal Fernando (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/STRATOS-110?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Nirmal Fernando resolved STRATOS-110.
-------------------------------------

    Resolution: Fixed

> Topology Event Message Processors should follow 'chain of responsibility' design pattern
> ----------------------------------------------------------------------------------------
>
>                 Key: STRATOS-110
>                 URL: https://issues.apache.org/jira/browse/STRATOS-110
>             Project: Stratos
>          Issue Type: Improvement
>    Affects Versions: 4.0.0 M1
>            Reporter: Nirmal Fernando
>            Assignee: Nirmal Fernando
>            Priority: Critical
>             Fix For: 4.0.0 M1
>
>
> Following is the MessageProcessor interface with this change.
> package org.apache.stratos.messaging.message.processor;
> import org.apache.stratos.messaging.domain.topology.Topology;
> /**
>  * Message processor interface. Every Message Processor should implement this.
>  */
> public interface MessageProcessor {
>    
>     /**
>      * Link a message processor and its successor, if there's any.
>      * @param nextProcessor
>      */
>     public abstract void setNext(MessageProcessor nextProcessor);
>     /**
>      * Message processing and delegating logic.
>      * @param type type of the message.
>      * @param message real message body.
>      * @param topology Topology that will get updated.
>      * @return whether the processing was successful or not.
>      */
>     public abstract boolean process(String type, String message, Topology topology);
> }
> I've implemented initial Message Processors:
> ├── ClusterCreatedEventProcessor.java
> ├── ClusterRemovedEventProcessor.java
> ├── CompleteTopologyEventProcessor.java
> ├── MemberActivatedEventProcessor.java
> ├── MemberStartedEventProcessor.java
> ├── MemberSuspendedEventProcessor.java
> ├── MemberTerminatedEventProcessor.java
> ├── ServiceCreatedEventProcessor.java
> └── ServiceRemovedEventProcessor.java
> Now, it is up to the Message Processor Delegator to build the Message processor chain.
>         // instantiate all the relevant processors
>         ServiceCreatedEventProcessor processor1 = new ServiceCreatedEventProcessor();
>         ServiceRemovedEventProcessor processor2 = new ServiceRemovedEventProcessor();
>         ClusterCreatedEventProcessor processor3 = new ClusterCreatedEventProcessor();
>       
>        
>         // link all the relevant processors in the required order
>         processor1.setNext(processor2);
>         processor2.setNext(processor3);
>         processor3.setNext(processor4);
> and also it's a duty of the deligator to start the flow:
> boolean hasProcessed = processor1.process(type, json, TopologyManager.getTopology());
> After the flow started, Processor who is capable of handling the message would eventually receive it and will process the message and other Processors will simply delegate the message to its successor.



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