Author : Exel

Date : 18 Apr 2025

Note : This is just for my own personal learning of SpringBatch, I am going to use my Expense CSV File
to learn how to process CSV Files and

Folder Structure :

src/main/java/com/example/expense/
├── ExpenseApplication.java                   # Main Spring Boot application entry point
│
├── config/
│   └── BatchConfig.java                      # Core Batch config: defines Job, Step, Reader/Processor/Writer wiring
│
├── controller/
│   └── FileUploadController.java             # Handles file upload requests and triggers batch job via JobLauncher
│
├── dto/                                      # Optional DTOs for response or input (currently unused)
│
├── entity/
│   └── Expense.java                          # JPA entity representing a row in the 'expenses' table
│
├── jobs/                                     # All logic related to the Spring Batch job
   ├── listener/                             # Optional: listeners that run on job start/finish (e.g., logging, auditing)
   ├── processor/
   │   └── ExpenseProcessor.java             # Cleans and transforms the Expense data (e.g., lowercase category)
   ├── reader/
   │   └── ExpenseCSVReader.java             # Reads and maps CSV data into Expense objects
   └── writer/
       └── ExpenseWriter.java                # Writes Expense objects to DB using a JPA repository

Sequence Diagram of Import Job :

sequenceDiagram
    autonumber
    participant Client
    participant Controller
    participant JobLauncher
    participant Job
    participant Step
    participant Reader
    participant Processor
    participant Writer
    participant Database

    Client->>Controller: POST /upload-expenses (CSV)
    Controller->>JobLauncher: jobLauncher.run(importJob, JobParameters)
    JobLauncher->>Job: importJob.run()
    Job->>Step: Execute step1
    loop for each chunk (e.g. 1000 records)
        Step->>Reader: expenseReader.read()
        Reader->>Step: Expense[]
        Step->>Processor: process(expense)
        Processor->>Step: processedExpense
        Step->>Writer: write(List<processedExpense>)
        Writer->>Database: JPA bulk insert
    end
    Step->>Job: Step complete
    Job->>JobLauncher: Job complete
    Controller-->>Client: 200 OK: Batch job started

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---

Sequence Diagram of Convert Job :

sequenceDiagram
    participant Client
    participant Controller
    participant JobLauncher
    participant convertJob
    participant convertStep
    participant DBReader
    participant GSTProcessor
    participant CSVWriter
    participant EmailListener

    Client->>Controller: POST /[email protected]
    Controller->>JobLauncher: run(convertJob, jobParams)
    JobLauncher->>convertJob: start()
    convertJob->>convertStep: execute()
    loop For each chunk
        convertStep->>DBReader: read()
        DBReader-->>convertStep: Expense
        convertStep->>GSTProcessor: process(Expense)
        GSTProcessor-->>convertStep: ExpenseWithGST
        convertStep->>CSVWriter: write(ExpenseWithGST)
    end
    convertStep-->>convertJob: step completed
    convertJob->>EmailListener: afterJob()
    EmailListener->>SMTP Server: send email with CSV
    EmailListener-->>Client: Email Sent

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To test via MANUAL Curl for import Job :

curl -X POST -F "[email protected]" http://localhost:8444/upload-expenses curl -X POST -F "[email protected]" http://localhost:8444/upload-minio-batch