You’ve seen the ticket a hundred times. It lands in the sprint board, marked “High Priority,” but the description is anything but.
“Hey, can we get a new endpoint? We just need to get a customer’s `firstName` and `city` by sending their `email`.”
We’ve all been there. It’s another simple data-fetching API, almost identical to the last one we built. The work isn’t difficult, but it’s repetitive. Each one of these “quick” tasks pulls you out of the deep, focused work you were doing on a truly complex problem. The context-switching alone is a productivity killer.
It’s not just boring; it’s slow for the whole company. Every time a new request like this comes in, it has to wait in line with bigger, more important features. The mobile team is blocked, and the analytics team can’t get their data. Everyone is waiting on a developer to spend an hour on a copy-paste job.
This gets you thinking: what if we could automate the automation? What if we could build one final system that could handle all of these requests? What if we could build a dynamic API that could build other APIs at runtime?
It sounds like magic, but it’s not. It’s a very real pattern, and this blog will show you how it works.
The Core Idea: Describe Your API as Data
The breakthrough comes when you stop hardcoding the rules of your API—the path, the inputs, the outputs—and start treating them as data.
Instead of a new controller class in our project, imagine a new row in a database table. This row holds what we can call an “API Recipe” in a simple JSON format.
{
"endpointPath": "/v1/users/by-email",
"requestFields": {
"email": "String"
},
"responseFields": {
"firstName": "String",
"city": "String"
}
}
That’s it. This JSON is our new API.
endpointPath: This is simply where the API lives, its unique address on the server.
requestFields: This is the list of ingredients the user must provide. It’s our contract for the request, and we’ll also use it for automatic validation.
responseFields: This is what the final dish will look like. It’s the exact list of fields the API will return.
Why is Dynamic API a Game-Changer?
By treating our API definitions as data, we unlock some incredible benefits. A product manager, through a simple admin UI, could configure and launch a new data endpoint themselves without ever filing a ticket. A new API is live the moment the data is saved—no build pipeline, no deployment window, just instant availability. Every API generated by this system will also be consistent, using the same error formats and standards, which makes life easier for the developers consuming them.
We just need an engine that can read these recipes and bring them to life.
The Engine: Three Key Techniques
So, how do we build an engine that can read these recipes and handle requests on the fly? It comes down to three clever techniques.
1. The Universal Endpoint (The "Catch-All")
Your first question should be: “How can my app know about a URL that’s just sitting in a database?” You’re right, it can’t. An application only knows the URLs you write in your code when it starts up.
So, we create one single URL in our code that acts as a front door for all our new APIs.
@RestController
public class DynamicApiRouter {
@PostMapping("/api/**") // This is our front door
public Object routeRequest(HttpServletRequest request, ...) {
// Inside this method, we read the full URL the user called...
String dynamicPath = request.getRequestURI().substring(...); // e.g., "/v1/users/by-email"
// ...then we use that path to find the right recipe in our database.
}
}
That `/` wildcard is the key. It tells Spring, “Any `POST` request that starts with `/api/`, just send it to this one method. I’ll handle it.” It’s our universal mailbox. The code then just reads the rest of the address from the request to know which recipe to look up.
2. The Internal Query Builder (GraphQL)
Okay, we’ve found our recipe. It says we only need to return `firstName` and `city`. How do we query our data layer for just those fields without a mess of `if/else` logic? Without this, you might fetch the entire `Customer` object with all 50 fields from the database, only to throw away 48 of them. That’s incredibly wasteful.
The secret is to use GraphQL as an internal tool.
Instead of exposing GraphQL directly to the end user, our service becomes its own client. It programmatically builds a query string based on the recipe it just fetched. It looks at the `responseFields` from our recipe and builds a simple question for GraphQL, like: “Hey, for this customer, just give me the `firstName` and `city`.”
The code actually builds a text query that looks like this:
query {
findCustomers(criteria: [{field: "email", value: "test@user.com"}]) {
firstName
city
}
}
We then give this query to a GraphQL engine running right inside our own service. This gives us incredible flexibility to shape the data exactly as needed for each dynamic API, and it’s far cleaner than trying to build a dynamic SQL `SELECT` clause with strings.
3. The Safe Database Bridge (JPA Specifications)
The final step is to translate that GraphQL query into a real, safe database query. For this, we use a tool called JPA Specifications.
A Specification is simply a way to build a database `WHERE` clause using pure Java code. It’s like snapping together LEGO bricks to build your query. The big bad wolf of database programming is “SQL Injection,” where a hacker tricks your code into running a malicious command. By building our query with JPA’s “LEGO bricks,” we’re building a wall that makes SQL injection impossible.
// Simplified example of building a spec
Specification<Customer> spec = (root, query, builder) -> {
// This creates a safe "WHERE email = ?" condition
return builder.equal(root.get("email"), "test@user.com");
};
// Use the spec to find the data. Spring Data JPA handles the rest.
List<Customer> customers = customerRepository.findAll(spec);
It’s a clean, safe, and powerful way to talk to our database, and it can even be extended to handle complex queries, like searching inside JSON data.
How to Build a Dynamic API That Creates Multiple APIs on Demand
Think about the flow now:
- An administrator saves a new JSON recipe to the database.
- Instantly—with zero code changes and no redeployment—a new API like `/api/v1/users/by-email` is live. The running application is completely unaware that a new API has just been born; its job is just to execute any recipe it’s given.
- A client app calls it. Our universal endpoint catches it, finds the recipe, builds a GraphQL query for the exact fields needed, and uses a safe JPA query to get the data.
You haven’t just solved one ticket. You’ve created a system that solves an entire category of future problems. You’ve stopped being an assembly-line worker and become the person who designs the factory. And that’s the kind of engineering that gives us back our time to focus on the truly hard, interesting challenges.
Wrapping Up
What we’ve built here isn’t just another clever backend trick—it’s a mindset shift. Instead of writing an endless boilerplate for every new request, we’ve built a system that writes it for us. One API that can create others, instantly, safely, and without redeployment.
It’s the kind of solution that quietly changes how a team works. Product managers don’t wait in queues. Developers don’t lose focus on repetitive tickets. The system just grows with the needs of the business.
And that’s the real power of it—you stop being the person who builds endpoints and start being the person who builds possibilities.
Curious how this approach could streamline your APIs and backend systems? Partner with Xcelore for Custom AI Solutions and API experts that can help you build dynamic, scalable solutions tailored to your business.
FAQs
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1. How do I secure dynamically generated APIs?
All requests go through the universal endpoint, so you can apply the same authentication, authorization, and rate limits as regular APIs. Each recipe defines required fields, preventing unexpected or malicious input. Dynamic doesn’t mean insecure; it just automates API creation while keeping your safety checks in place.
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2. Can a dynamic API system replace an API gateway?
No, it can’t replace an API gateway. A dynamic API system is designed to create APIs instantly, but an API gateway handles routing, security, rate limiting, and monitoring for all APIs. The dynamic API system is like a factory that builds APIs, and the gateway is the traffic manager that keeps everything running safely. Together, they complement each other perfectly.
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3. Can this system work with existing API ecosystems and tools?
Yes! The dynamic API system fits right into your existing infrastructure. It works alongside your current APIs, gateways, and monitoring tools. Think of it as an add-on layer—creating new endpoints on the fly, while your ecosystem handles routing, security, and analytics.
