Spring Boot rejects large file upload / content in REST endpoint

Omar Rharbi — Thu, 20 Nov 2025 11:15:24 +0000

// Source - https://stackoverflow.com/q/79825415
// Posted by omar rharbu
// Retrieved 2025-11-20, License - CC BY-SA 4.0

HttpMessageNotReadableException: JSON parse error:
String value length (20048537) exceeds the maximum allowed
(20000000, from StreamReadConstraints.getMaxStringLength())

It looks like Jackson is blocking the request because the JSON string is too large. I'm not trying to catch this exception — I just want to understand:

Why this limit exists

Whether I'm uploading the file in the wrong way

What the correct approach is for handling large file uploads in Spring Boot

Has anyone dealt with the StreamReadConstraints max string length issue? What is the recommended way to upload large files without hitting this JSON size restriction?

Thanks!

The Hard Truth About Learning Spring Boot (And How to Actually Master It)

Omar Rharbi — Tue, 18 Nov 2025 16:43:53 +0000

Everyone says learning Spring Boot is “easy” if you know Java.

They talk about “building REST APIs,” “connecting to a database,” and “deploying microservices.”

But here’s the hard truth:

Most days, it’s confusing, frustrating, and full of small errors you can’t figure out.

And that’s completely normal.

Learning Spring Boot isn’t just about memorizing annotations or following tutorials.

It’s about understanding how the pieces fit together, and learning by building and breaking things.

Step 1: Master Core Java First

Before diving into Spring Boot, make sure you’re comfortable with:

OOP concepts (classes, inheritance, interfaces)
Collections, Streams, and Lambdas
Exception handling and debugging

Spring Boot builds on these fundamentals, so they are non-negotiable.

Step 2: Understand Spring Basics

Spring Boot is just Spring made easier. Learn:

Dependency Injection / IoC
Bean lifecycle and scopes
Annotations like @Component, @Service, @Repository

Once you understand these, Spring Boot’s magic makes sense.

Step 3: Build a Simple REST API

Start small:

Create a Spring Boot project with Spring Initializr
Build a simple controller: @RestController + @GetMapping
Test endpoints with Postman or curl

This helps you understand request → controller → response flow.

This diagram shows how an HTTP request travels through Spring MVC from DispatcherServlet to Controller.

Step 4: Connect to a Database

Learn Spring Data JPA:

Create an Entity and Repository
Save, fetch, and update data
Understand transactions and lazy loading

Overview of Spring MVC architecture showing DispatcherServlet, HandlerMapping, and ViewResolver.

Step 5: Handle Advanced Features

Once comfortable with the basics:

Add authentication (JWT, Spring Security)
Use filters and interceptors
Build a full CRUD app
Experiment with caching, async tasks, or messaging

Modern Spring MVC request flow showing filters, controllers, and responses.

Step 6: Deploy and Iterate

Deploy locally or on cloud platforms (Heroku, AWS, etc.)
Read logs, debug issues
Refactor and improve your code

Learning Spring Boot is a step-by-step journey, not a sprint.

You’ll break things, Google errors endlessly, and feel stuck.

That’s okay. That’s growth.

The Front Controller pattern in Spring MVC using DispatcherServlet.

✅ Tip: Build projects, not just tutorials.

Each small project teaches more than any video series ever could.

DEV Community: Omar Rharbi