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  • JDK7
  • Redis


File Changes are monitored through a Storm topology that propogates the events. Meghaduta Storm Topology

The event gets propagated through each stage where the item is built incrementally and finally the notifier is notified (pluggable).

Getting Started

$ mvn clean package

# To start the storm Topology
$ java -cp target/meghaduta-1.0.0-SNAPSHOT.jar meghaduta.storm.MeghaDutaTopology

# To start the HTTP Service
$java -cp target/meghaduta-1.0.0-SNAPSHOT.jar meghaduta.service.MeghaDutaService -server

The HTTP service runs on port 8080 by default and you can query the data

API Operation
/{id} id - itemId to query for

Sample output JSON would be

    "publisher": "William Morrow",
    "authors": "Levitt & Dubner",
    "title": "freakonomics",
    "list price": "7",
    "release date": "20-09-2011"

Sample notification-file.log

[1442738940456] Notifing subscriber-test about Event{itemId='13579', name='title', value='freakonomics', timestamp=1442738934000} from 
item=Item{itemId='13579', lastUpdated=1442738934000, attributes={publisher=William Morrow, authors=Levitt & Dubner, title=freakonomics}}
[1442738940462] Notifing subscriber1 about Event{itemId='13579', name='release date', value='20-09-2011', timestamp=1442738934000} from 
item=Item{itemId='13579', lastUpdated=1442738934000, attributes={publisher=William Morrow, authors=Levitt & Dubner, title=freakonomics, list price=7, release date=20-09-2011}}
[1442738940463] Notifing subscriber2 about Event{itemId='1248', name='list price', value='10', timestamp=1442738934000} from 
item=Item{itemId='1248', lastUpdated=1442738934000, attributes={title=Effective Java, authors=Joshua Bloch, publisher=Addison-Wesley, list price=10}}

Subscription Configuration

# Add all your subscriptions in here. The format is as follows
#  {
#   notifier = "whom should I notify?"
#   filters = [{
#     name = "attribute name"
#     type = "type of the attribute" # accepted values - int, string, date
#     operator = "eq" # accepted values - eq, gt, lt, ge, le
#     value = "value of the attribute to check"
#   }]
#  }
# You can specify multiple filters and by default we'll always AND them.
# FIXME - Move this to a store so that we can in-corporate updates while the system is running

subscriptions = [{
  notifier = "subscriber-test"
  filters = [{
    name = "title"
    type = "string"
    operator = "eq"
    value = "freakonomics"
}, {
  notifier = "subscriber1"
  filters = [{
    name = "release date"
    type = "date"
    operator = "gt"
    value = "01-01-2000"
}, {
  notifier = "subscriber2"
  filters = [{
    name = "publisher"
    type = "string"
    operator = "eq"
    value = "Addison-Wesley"
  }, {
    name = "list price"
    type = "int"
    operator = "ge"
    value = "10"
# You can specify multiple filters and by default we'll always AND them.


meghaduta {
  # Store implementation - redis, rocksdb (experimental)
  store-type = "redis"
  db-location = "localhost"

  # Relative to the project root - can also be an absolute path
  shared-folder = "shared-folder/IN"

  # Notifier implementation
  notifier-type = "file"
  notify-output-file = "notifications.log"

Problem Description

The goal is to build a configurable notification system, which receives inputs in a CSV file and notifies its subscribers based on the condition set.

System Requirements

  • The system should consume CSV files which are dropped into a shared folder which are of the form item,attribute_name,attribute_value. The CSV files will be dropped into the shared folder at any point in time.
  • The system should be able to notify the attribute changes for items to different subscribers based on different configurable conditions
  • The notifications can be sent on any asynchronous messaging system
  • The system should also be able to support queries to get all the attributes for a given item at any time
  • The system should be scalable to -- accept large number of/large sized CSV files -- support large number of subscriber configurations -- support high throughput and low latency on the get query

Sample Files:


13579,authors,Levitt & Dubner
13579,release date,20-09-2011
13579,list price,7 USD
13579,publisher,William Morrow
1248,title,Effective Java
1248,authors,Joshua Bloch
1248,list price,10 USD


13579, list price,11 USD

Sample Subscriber Configurations

Sample conditions are:

if release date >= 01-01-2000, notify to subscriber1 
if publisher is Addison-Wesley and list price is >= 10, notify to subscriber2

Sample Query

GET 13579
Result Set:
authors=Levitt & Dubner
release date = 20-09-2011
list price=11 USD
publisher=William Morrow


Programming Language: Java, but using C#/ C++ is acceptable

Other Technologies: AWS


Notification system built for Amazon Hackathon (Sept 2015)



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