Hello world, but with persistent memories

  • Updated on Apr 2, 2025
  • 1 minute(s) read
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Goal

We want to add persistence using an S3 Bucket to an Hello World Application already hosted on Poja that exposes the /hello?name=your-name endpoint, for which it :

  • Writes a Hello World message inside a .txt file

  • Uploads the file to an S3 bucket

  • Returns a presigned uri to download the file

How-to in 2 steps

Step 1: Enable file storage for the preprod environment

Select the preprod environment, click on the Edit button on the Poja Configuration section and then:

  • Enable the File Storage

  • Click on the Save button

Once it’s done, wait for the deployment to finish.

/health/bucket

Once the File Storage option is activated, /health/bucket endpoint will be added to the application. It returns a presigned URI which gives you read-only access to tiny files created in the bucket for testing purpose.

Step 2: Code your endpoint

The BucketComponent class

To interact with the S3 Bucket associated to your application, Poja provides the BucketComponent class which has 4 public methods:

  • upload()

  • download() to download a specific file by specifying its name

  • presign()  to get a presigned uri to access a specific file for a specified duration

  • getBucketName()

package com.my.company.service;

import static java.io.File.createTempFile;

import com.my.company.file.bucket.BucketComponent;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.time.Duration;
import lombok.AllArgsConstructor;
import lombok.SneakyThrows;
import org.springframework.stereotype.Service;

@Service
@AllArgsConstructor
public class HelloWorldService {
  private final BucketComponent bucketComponent;

  @SneakyThrows
  public String uploadHelloWorldMessage(String name) {
    var fileSuffix = ".txt";
    var filePrefix = "hello-world-" + name;
    var bucketKey = filePrefix + fileSuffix;
    var fileToUpload = createTempFile(filePrefix, fileSuffix);
    writeMessageIntoFile("Hello World " + name + " !", fileToUpload);
    bucketComponent.upload(fileToUpload, bucketKey);
    return bucketComponent.presign(bucketKey, Duration.ofMinutes(5)).toString();
  }

  private void writeMessageIntoFile(String message, File file) throws IOException {
    FileWriter writer = new FileWriter(file);
    writer.write(message);
    writer.close();
  }
}

package com.my.company.endpoint.rest.controller;

import com.my.company.service.HelloWorldService;
import lombok.AllArgsConstructor;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
@AllArgsConstructor
public class HelloWorldController {
  private final HelloWorldService service;

  @GetMapping("/hello")
  public String helloWorld(@RequestParam String name) {
    return service.uploadHelloWorldMessage(name);
  }
}

To trigger a deployment, just commit and push the code to the preprod branch of the repository. Wait. And voilà!

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