Simple Java-based messaging server with support for message queues and topics
Once the server is started, it listens for incoming clients. It creates a ClientHandler
Runnable for each incoming client and passes to it the unique references to
TopicListInterface and MessageQueueInterface. Clients can connect to
the server and send requests which will be handled in a thread-safe manner.
Since communication is done via
sockets, only text can be sent by the client; the ClientHandler Runnable parses
this text and maps it to the appropiate interface method.
The messaging server can handle two types of objects:
- Topics (may have multiple Posts; anyone can subscribe to a topic);
- Messages (only selected receiver can view a message).
Topics are stored in a TopicList. Because concurrency is needed, TopicList is
wrapped in a TopicListInterface (unique across the application), having all
methods defined as synchronized.
Posts are stored in their associated Topic. They are deleted after they expire.
In order to add a new topic/post, a Client needs to provide the appropiate
headers for the request (ADD_TOPIC/ADD_POST) together with request
arguments, one per line. ClientHandler handles the request by calling the
appropiate method (addTopic/addPost) on TopicListInterface
(automatically assigned when ClientClientHandler is created).
[add Topic]
Client ... ClientHandler -> TopicListInterface -> TopicList -> Topic
[add Post]
Client ... ClientHandler -> TopicListInterface -> TopicList -> Topic -> Post
Messages are stored in a MessageQueue. Because concurrency is needed,
MessageQueue is wrapped in a MessageQueueInterface (unique across the
application), having all methods defined as synchronized.
In order to add/receive a message, a Client needs to provide the appropiate
header for the request (PUSH/POP) together with request
arguments, one per line. ClientHandler handles the request by calling the
appropiate method (push/pop) on MessageQueueInterface
(automatically assigned when ClientHandler is created).
MessageQueue has a limit of Messages that it can store.
Messages are appended to the MessageQueue (at the end) and popped from the
MessageQueue (at the front, the removed) if the given receiver matches the
first Message's receiver.
[add Message]
Client ... ClientHandler -> MessageQueueInterface -> MessageQueue -> Message