Why Upgrade to JDK 17? Full Migration Guide from JDK 11 with Benchmarks

1. Introduction

On September 14, 2021 Oracle released the long‑term support JDK 17. This article explores the new features from JDK 11 to JDK 17, the impact of the sub‑millisecond ZGC garbage collector, and the practical steps for a complete upgrade.

2. Why Upgrade to JDK 17

2.1 Long‑term Support – JDK 17 is an LTS release, receiving extended updates and stability guarantees.

2.2 Performance Improvements – Better garbage collectors: G1GC speed increased by 16.1% (JDK 8→11) and 8.66% (JDK 11→17); ParallelGC improved by 4.5% and 6.54% respectively. The stable ZGC offers sub‑millisecond pause times.

2.3 New Syntax and Features – Switch expressions, Text Blocks, pattern‑matching for instanceof, improved NullPointerException messages, records, sealed classes, and more.

2.4 Framework Support – Spring Framework 6 and Spring Boot 3 require Java 17 as the minimum version.

3. Benchmark Results

Tests on JDOS with machines (2C4G, 4C8G, 8C16G) using JDK 8, JDK 11, and JDK 17 showed that all garbage collectors performed better, especially ZGC, which achieved sub‑millisecond pauses and high throughput.

4. Oracle JDK vs OpenJDK

Oracle JDK 17 became free for commercial use in September 2021, but from September 2024 Oracle JDK 17 will require a license. Functionally, Oracle JDK and OpenJDK are identical since JDK 11; using OpenJDK 17 or other community builds (AdoptOpenJDK, RedHat OpenJDK) is recommended.

5. New Features from JDK 11 to JDK 17

5.1 JVM Improvements

ZGC is now a production‑ready collector; enable with -XX:+UseZGC.

G1GC improvements: abortable mixed collections, NUMA‑aware allocation.

CMS collector removed in JDK 14.

ParallelScavenge and SerialOld GC deprecated.

Biased locking disabled by default ( -XX:+UseBiasedLocking removed).

Enhanced NullPointerException messages that show the exact variable.

5.2 Language Enhancements

Switch expressions with -> syntax.

Text Blocks for multi‑line strings.

Records for immutable data carriers.

Pattern‑matching for instanceof.

Sealed classes and interfaces.

6. Upgrade Steps

6.1 JDK Selection

Download OpenJDK 17 from https://jdk.java.net/archive/ or use the cloud mirror

jdt-base-tomcat/java-jdt-centos7.4-openjdk-17.0.2-tomcat8.0.53

.

6.2 Maven Configuration

<properties>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
</properties>

6.3 Spring Boot Upgrade

Upgrade Spring Boot to 2.7.15 (Spring 5.3.29). Staying on Spring Boot 2 avoids major breaking changes while still supporting Java 17.

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.7.15</version>
</parent>

For circular‑dependency errors, either refactor bean relationships or enable legacy behavior:

spring.main.allow-circular-references=true

6.4 Middleware Adjustments

Lombok version ≥ 1.18.20.

Swagger 3.0.0 incompatibility with Spring Boot 2.7 – add a custom BeanPostProcessor to fix.

For JDK 11+ modules, add appropriate --add-opens or --add-exports JVM arguments (e.g., --add-opens java.base/java.lang=ALL-UNNAMED).

6.5 JVM Startup Parameters

Enable ZGC: -XX:+UseZGC.

Common module‑access flags for various components (SGM, R2M, Ducc, AKS) are listed in the original article.

6.6 Post‑Upgrade Validation

Upgrade incrementally (JDK 11 → JDK 17) and monitor logs.

Check monitoring tools (SGM, UMP) for stability.

Perform gradual traffic rollout and full functional testing.

7. Conclusion

Upgrading to JDK 17 provides new language features and dramatically improves GC performance, especially with ZGC’s sub‑millisecond pauses. The migration is straightforward, mainly involving framework version updates and JVM argument adjustments.