Important

Coding assignment Messaging application

● We will provide a project template of standard RESTful web service
● The template is using plain SQL strings since wiring up what we have in the backend would be too much effort for this
● Your task is to create database structure and some simple endpoints for an imaginary messaging application
● Imagine, that the service is used by lots of users, so try to optimize database structure for large volumes of data

Requirements:
● User should be able to send messages (like email) to recipients who are other users of the messaging application.
● Message should contain title, message body and timestamp of when it was sent
● Message has a maximum of 5 recipients
● User should have a name
Output
Database
● CREATE TABLE statements for the database structure in the database sql file
● Optionally test data as INSERT statements in the same file
Endpoints implemented in the project template
● Send new message
● Read messages addressed to a specified user
● Statistics endpoint: Top 10 users (by sent message count) sorted by decreasing sent message count for the last 30 days

Cache Control Directives

The cache control directives are being used with CacheControl class provided by JAX-RS. Currently it is under benchmarking to find which scenario fits for this problem. See more about

Response Format

This approach allows for concise and expressive code when building responses for RESTful endpoints with proper status code. This API will return in following format:

Status: Message of occurrence

MessageResource

MessageResource is responsible for handling messages in the system.

Get Messages for User Inbox

This endpoint retrieves messages for a specified user's inbox.

Endpoint

• Path: /messages/{userId}/inbox
• HTTP Method: GET
• Produces: application/json

Parameters

• userId - An integer representing the ID of the user for whom messages are to be retrieved.

Response

Success (HTTP Status: 200 OK)

Returns a list of messages from the inbox of the user. SentAt in format yyyy-MM-dd

Request Body (JSON Example)

[
  {
    "title": "Message Title 1",
    "body": "Message Body 1",
    "sentAt": "2024-02-25",
    "senderId": 2
  },
  {
    "title": "Message Title 2",
    "body": "Message Body 2",
    "sentAt": "2024-02-26",
    "senderId": 3
  },
  // ... other messages
]

Not Found (HTTP Status: 404 Not Found)

Returns an error message when no messages are found for the specified user or User not found from the system.

{
  "Not Found: User not found from the system." or "Not Found: No messages found for the user."
}

Internal Server Error (HTTP Status: 500 Internal Server Error)

Returns an error message for any internal server error during message retrieval.

{
  "Internal Server Error: Error retrieving messages for the user."
}

Example Usage

curl -X GET http://localhost:8080/messages/1/inbox

Send New Message

This endpoint sends a new message in the system.

Endpoint

• Path: /messages/send
• HTTP Method: POST
• Consumes: application/json
• Produces: application/json

Request Body (JSON Example)

{
  "title": "Message Title",
  "body": "Message Body",
  "senderId": 123,
  "receiverIds": [456, 789]
}

Constraints

• The title, body, senderId, and receiverIds fields are required and must not be blank or empty.

• receiverIds should have minimum number of recipients: 1 and maximum number of recipients: 5

Response

HTTP Status: 201 Created

Returns a success message when the message is sent successfully.

{
  "Created: The message was sent successfully."
}

HTTP Status: 404 Not Found

An issue occurred, and the record conflicts with the one in the database.

{
  "Not Found: Sender not found from the system."
}

HTTP Status: 409 Conflict

An issue occurred, and the record conflicts with the one in the database.

{
  "Conflict: The record conflicting with record on the database."
}

Internal Server Error (HTTP Status: 500 Internal Server Error)

Error message when there is a unique constraint violation or SQL error.

{
  "Internal Server Error: Unique constraint violation or SQL error"
}

Notes

Rollbacks are employed in case of errors to ensure that the database remains in a consistent state.

Example Usage

curl -X POST   -H "Content-Type: application/json"   -d '{"Invian": "Hello from deadlines", "body": "This should have done before 1 week, but school and other job happened", "senderId": 1, "receiverIds": [456, 789]}' http://localhost:8080/messages/send

StatisticsResource

StatisticsResource is responsible for handling statistics related reports.

Method

Get Top Users with Message Count

Endpoint

• Method: GET
• Path: /statistics/top-users

Response

• Status: 200 OK - Successful retrieval of top users with message count.
• Status: 404 Not Found - No top users found.
• Status: 500 Internal Server Error - Internal server error during processing.

Example

GET /statistics/top-users

---

Requirements

• Maven
• Docker
• Docker-compose (installed separately from Docker)

Running / redeploying

Linux / macOS

make

Windows

Look at the file named Makefile and run the same commands in the root directory of the project

Accessing

REST server

http://localhost:8080

You should get a congratulation message. If not, try again a few seconds later - the database initialization takes some time. If it still doesn't work, look at the logs.

MariaDB database

localhost:3306

Username is root and password is root_password

Developing

The SQL statements in database.sql are run on every redeploy on the empty database, so evolving the database schema works just like code. Change the statements, redeploy and there it is. No need for ALTER TABLE statements.

Note that it is not possible to run the REST server outside of Docker.

Debugging

REST server

Java remote debug port is at localhost:5005

Logs can be read with docker logs codingassignment

MariaDB database

Logs can be read with docker logs codingassignment-db