CODEWITHSUNDEEP
javaspring-bootrestrestful-url
AMagic
AMagic

Reputation: 2810

Keep calling a rest API until server completes the task

I am calling a REST API synchronously from a Spring boot app (in JAVA 11) to download a file.

This is how the REST API looks like:

@GetMapping("/download/{userId}/{fileName}")
public String download(final int userId, final String fileName) {
        if(requested file is available) {
             return {file location URL}
        } else {
             Begin generating a new file (takes 5 seconds to more than 5 minutes)
             return "file generation in progress" 
        } 
    }

The API returns two things, either it returns the status of the file if it is generating the file (which takes anywhere from 5 seconds to 5 minutes or more), or the file location URL itself if the file is generated.

The problem I am trying to solve is, I need to call this "/download" API every 5 seconds and check if the file is ready or not.

Something like this:

Is there a way I can achieve this? I tried looking CompletableFuture & @Scheduled but I am so new to both of these options and couldn't find any way to implement them in my code. Any help would be appreciated!

Upvotes: 1

Views: 970

Answers (1)

Ramachandran Murugaian
Ramachandran Murugaian

Reputation: 651

You can make use of the Java Failsafe Library. Refer the answer from [Retry a method based on result (instead of exception). I have modified the code from the answer to match your scenario.

private String downloadFileWithRetry() {
    final RetryPolicy<String> retryPolicy = new RetryPolicy<String>()
        .withMaxAttempts(-1)
        .handleResultIf("file generation in progress"::equalsIgnoreCase);

    return Failsafe
        .with(retryPolicy)
        .onSuccess(response -> System.out.println("Generated file Url is ".concat(response.getResult())))
        .get(this::downloadFile);
}

private String downloadFile() {
    return "file generation in progress";
}

Upvotes: 1

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