Jakarta Servlet guide · Java SDK

Servlet rate limiting,one filter, every container.

Register ReqKeyFilter once. Every request is checked against the caller’s key, charged against their credits, and held to their plan’s limit — in Tomcat, Jetty, or Undertow.

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  • Keys issued per customer
  • Credits that refill
  • Limits per plan, not per process

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API requests validated
100M+
Average key validation
<5ms
Average analytics ingest
<5ms
Check and log, end to end
<10ms

The usual Jakarta Servlet rate limiter counts requests. It doesn’t know your customers.

Plain servlet apps usually write a Filter around Bucket4j or Guava’s RateLimiter, holding one limiter per client in a ConcurrentHashMap.

With a hand-written Filtertoday
  • Limiters in a map on one JVM — the next node starts from zero
  • Keyed by IP address by default, not by the customer who is paying
  • No API keys: issuing, hashing, scoping, and revoking them is still yours to build
  • No credit balance: a request can’t cost 5 on one route and 1 on another, or refill each month
  • One limit for everyone — no per-plan limits for Free, Pro, and Enterprise customers
  • No per-customer usage log to answer “why was I blocked?” or bill against
With ReqKey in Jakarta Servletone middleware
  • API keys issued per customer, prefixed, hashed, and revocable from the dashboard
  • A credit balance per customer — price each route, refill every hour, day, week, or month
  • Rate limits set per plan, shared by all of a customer’s keys, from 1 second to 24 hours
  • The same count on every worker, instance, and region — no Redis to run
  • Over the limit? A 429 with Retry-After, and no credits charged
  • Every request logged per customer — status, latency, endpoint — in under 5ms
Servlets read the verdict from the ReqKeyAttributes.DECISION request attribute. See the code

Jakarta Servlet in three steps, one of them code.

ReqKey runs inside your API, not in front of it. Your server asks one question per request and gets an answer in under 5ms.

  1. 1

    Install the SDK

    implementation("com.reqkey:reqkey-servlet:1.0.0")

  2. 2

    Set your project key

    Copy it from the dashboard into REQKEY_PROJECT_KEY. It stays on your server.

  3. 3

    Add the Jakarta Servlet middleware

    Every request is checked, charged, and logged before your handler runs.

AppInitializer.javaimplementation("com.reqkey:reqkey-servlet:1.0.0")
import com.reqkey.ReqKeyConfig;
import com.reqkey.middleware.ReqKeyMiddlewareConfig;
import com.reqkey.servlet.ReqKeyFilter;
import jakarta.servlet.DispatcherType;
import jakarta.servlet.FilterRegistration;
import java.util.EnumSet;
 
ReqKeyMiddlewareConfig middleware = ReqKeyMiddlewareConfig.builder("api_payments")
        .keyName("X-Startup-Key")
        .credits(request -> request.getPath().equals("/reports") ? 5 : 1)
        .excludePath("/health")
        .build();
 
ReqKeyFilter filter = new ReqKeyFilter(ReqKeyConfig.fromEnvironment(), middleware);
FilterRegistration.Dynamic registration = servletContext.addFilter("reqkey", filter);
registration.addMappingForUrlPatterns(
        EnumSet.of(DispatcherType.REQUEST, DispatcherType.ASYNC), false, "/*");
 
// In a handler: (VerificationResult) request.getAttribute(ReqKeyAttributes.DECISION)
Also in Java: Spring Boot, JAX-RSFull Java reference

Every request gets one of these answers

  • 200Valid key, credits charged — your handler runs
  • 402Out of credits
  • 403Key disabled, or not allowed on this API
  • 429Over the rate limit — no credits charged

Where ReqKey sits

Your customer
Your APIReqKey, under 5ms
Your handler

Responses go straight back to your customer. ReqKey sees the key check and the log line, nothing else.

Credits

Charge each route what it costs you.

A lookup can cost 1 credit and a render 5, from the same balance. Excluded paths are never validated, charged, or recorded. In Java:

Per-route credits · Java
ReqKeyMiddlewareConfig.builder("api_images")
        // Exact paths or trailing-* prefixes: never validated, charged, or recorded
        .excludePath("/health")
        .excludePath("/docs/*")
        // Or decide per request with a predicate
        .protectWhen(request -> request.getPath().startsWith("/api/"))
        // Charge endpoints differently — a CreditResolver instead of an int
        .credits(request -> request.getMethod().equals("POST") ? 5 : 1)
        .build();

Rate limits

Set limits on plans, not in code.

Your Jakarta Servlet code never hard-codes a number. Each plan carries its credits, refill, and rate limit; moving a customer to Pro changes all three with no deploy.

PlanCreditsRate limit
Free1,000 / month5 req / s
Pro50,000 / month50 req / s
Scale1,000,000 / month500 req / s
429Over the limit, a call is answered with Retry-After and costs nothing — no credits and no quota.

Example plans. You name them and pick the numbers.

Notes for Jakarta Servlet teams hit in production.

Async dispatch

Map the filter for REQUEST and ASYNC dispatch types so async servlets are covered too.

Per-path credits

.credits(request -> ...) prices each path — 5 for reports, 1 for everything else.

Jakarta Servlet 6

The module targets jakarta.servlet — Tomcat 10.1+, Jetty 12, and Undertow on Jakarta EE 10.

Jakarta Servlet rate limiting: the questions teams ask.

Something else? Ask the team or read the docs.

  • The sample registers it programmatically from a ServletContext, which is the form the docs cover.

  • No — reqkey-servlet has no Spring dependency.

  • On their plan or on the customer (consumer) in ReqKey — a number of requests per window from 1 second to 24 hours, shared by all of that customer’s keys. Your Jakarta Servlet code never hard-codes a limit, so upgrading a customer is a dashboard change, not a deploy.

  • A check averages under 5ms. ReqKey runs inside your app as middleware, not as a gateway in front of it, so responses go straight back to your customer.

  • You choose: fail closed and answer 503, or fail open and let requests through. Invalid keys are denied either way, and a validation is never retried, so no one is charged twice.

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