Comparing Non Blocking Progressive Server-Side Rendering (PSSR)

This project builds upon previous work comparing Java template engines for Spring WebFlux and Spring MVC, originally presented in "Shoot-out! Template engines for the JVM" by Jeroen Reijn.

We benchmark multiple Java template engines across three frameworks — Quarkus, Spring MVC, and Spring WebFlux, focusing on Progressive Server-Side Rendering (PSSR), scalability under load, and modern Java features like virtual threads.

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Template Engines

The following engines are included in the benchmark:

Engine	Version
Thymeleaf	3.1.3
HtmlFlow	4.7
kotlinx.html	0.12.0
Rocker	2.2.1
JStachio	1.3.7
Pebble	3.2.4
Freemarker	2.3.34
Trimou	2.5.1.Final
Velocity	2.3

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Changes from Previous Work

• Added Quarkus and Spring MVC support, alongside Spring WebFlux.
• Integrated virtual threads, enabling non-blocking behavior in traditionally blocking engines.
• Replaced Dispatchers.Default with Dispatchers.IO in Spring WebFlux for blocking routes to measure performance with a dedicated I/O dispatcher.
• Enabled progressive rendering for engines without asynchronous data model support using Observable.blockingIterable().
• Changed engine configs to allow template caching.

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Progressive Rendering Support

Framework	Supported	Notes
Spring WebFlux	✅	Uses Flux<String> and reactive adapters.
Spring MVC	⚠️ Partially	StreamingResponseBody supported, but early buffering prevents complete streaming.
Quarkus	✅	Uses Multi<String> for reactive routes and StreamingOutput with configurable output buffer (quarkus.rest.output-buffer-size) for synchronous routes.

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Available Routes

Each framework exposes routes under /presentations and /stocks, rendered by different engines and threading models.

Spring WebFlux Routes

Presentations:

• /presentations/thymeleaf - reactive
• /presentations/thymeleaf/sync - synchronous, blocking
• /presentations/thymeleaf/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/htmlFlow - reactive
• /presentations/htmlFlow/suspending - suspending, non-blocking
• /presentations/htmlFlow/sync - synchronous, blocking
• /presentations/htmlFlow/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/kotlinx - reactive (malformed HTML)
• /presentations/kotlinx/sync - synchronous, blocking
• /presentations/kotlinx/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/rocker/sync - synchronous, blocking
• /presentations/rocker/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/jstachio/sync - synchronous, blocking
• /presentations/jstachio/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/pebble/sync - synchronous, blocking
• /presentations/pebble/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/freemarker/sync - synchronous, blocking
• /presentations/freemarker/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/trimou/sync - synchronous, blocking
• /presentations/trimou/virtualSync - synchronous, non-blocking with virtual threads
• /presentations/velocity/sync - synchronous, blocking
• /presentations/velocity/virtualSync - synchronous, non-blocking with virtual threads

Stocks:

• /stocks/thymeleaf - reactive
• /stocks/thymeleaf/sync - synchronous, blocking
• /stocks/thymeleaf/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/htmlFlow - reactive
• /stocks/htmlFlow/suspending - suspending, non-blocking
• /stocks/htmlFlow/sync - synchronous, blocking
• /stocks/htmlFlow/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/kotlinx - reactive (malformed HTML)
• /stocks/kotlinx/sync - synchronous, blocking
• /stocks/kotlinx/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/rocker/sync - synchronous, blocking
• /stocks/rocker/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/jstachio/sync - synchronous, blocking
• /stocks/jstachio/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/pebble/sync - synchronous, blocking
• /stocks/pebble/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/freemarker/sync - synchronous, blocking
• /stocks/freemarker/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/trimou/sync - synchronous, blocking
• /stocks/trimou/virtualSync - synchronous, non-blocking with virtual threads
• /stocks/velocity/sync - synchronous, blocking
• /stocks/velocity/virtualSync - synchronous, non-blocking with virtual threads

Spring MVC Routes

All routes are blocking, with optional support for virtual threads if the spring.threads.virtual.enabled property is set to true.

Presentations:

• /presentations/thymeleaf
• /presentations/htmlFlow
• /presentations/kotlinx
• /presentations/rocker
• /presentations/jstachio
• /presentations/pebble
• /presentations/freemarker
• /presentations/trimou
• /presentations/velocity

Stocks:

• /stocks/thymeleaf
• /stocks/htmlFlow
• /stocks/kotlinx
• /stocks/rocker
• /stocks/jstachio
• /stocks/pebble
• /stocks/freemarker
• /stocks/trimou
• /stocks/velocity

Quarkus Routes

All engines are blocking and support virtual threads if the quarkus.threads.virtual.enabled property is set to true. Also includes a reactive route with HtmlFlow.

Presentations:

• /presentations/thymeleaf
• /presentations/htmlFlow
• /presentations/kotlinx
• /presentations/rocker
• /presentations/jstachio
• /presentations/pebble
• /presentations/freemarker
• /presentations/trimou
• /presentations/velocity
• /presentations/reactive/htmlFlow

Stocks:

• /stocks/thymeleaf
• /stocks/htmlFlow
• /stocks/kotlinx
• /stocks/rocker
• /stocks/jstachio
• /stocks/pebble
• /stocks/freemarker
• /stocks/trimou
• /stocks/velocity
• /stocks/reactive/htmlFlow

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Build & Run

Prerequisites

• Java 21
• Gradle 7+

Build All Modules

./gradlew build

Run by Framework

Spring WebFlux

# JAR
java -jar pssr-benchmark-spring-webflux/build/libs/pssr-benchmark-spring-webflux-1.0-SNAPSHOT.jar

# Gradle
./gradlew runWebflux

Spring MVC

# JAR
java -jar pssr-benchmark-spring-mvc/build/libs/pssr-benchmark-spring-mvc-1.0-SNAPSHOT.jar

# Gradle
./gradlew runMVC           # Traditional threads
./gradlew runMVCVirtual    # Virtual threads

Quarkus

# JAR
java -jar pssr-benchmark-quarkus/build/quarkus-app/quarkus-run.jar

# Gradle
./gradlew runQuarkus        # Traditional threads
./gradlew runQuarkusVirtual # Virtual threads

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Running Benchmarks

Apache Benchmark (ab)

cd benches/ab
./bench-webflux.sh
./bench-mvc.sh
./bench-quarkus.sh

JMeter

cd benches/jmeter
./bench-webflux.sh
./bench-mvc.sh
./bench-quarkus.sh

JMH (Java Microbenchmark Harness)

cd benches/jmh
./bench-jmh.sh

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Benchmark Results

All tests were run on a GitHub-hosted Ubuntu 22.04 VM with 4 cores, 16GB RAM, and OpenJDK 21.

Performance (JMH)

The performance results show the throughput (number of renders per millisecond) for each template engine. The goal is to measure how well each engine performs in template rendering.

Presentations	Stocks

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Scalability

The scalability results depict the throughput (number of requests per second) for each template engine, with concurrent requests ranging from 1 to 2500 users. The goal is to observe how well each engine/approach scales with increasing server load. To simulate I/O operations and enable progressive rendering, we interleaved Observable<T> elements with a 5-millisecond delay in each route.

Spring WebFlux Highlights

• HtmlFlow-Susp (suspendable templates)
• Thymeleaf-Rx (reactive)
• Jstachio-Virtual (virtual threads)
• Aggregated: Blocking

Presentations	Stocks

Spring MVC Highlights

• Aggregated: Blocking, Virtual

Presentations	Stocks

Quarkus Highlights

• HtmlFlow-Rx (reactive)
• Aggregated: Blocking, Virtual

Presentations	Stocks