Comprehensive Guide to Upgrading from JDK8/11 to JDK17: Performance Gains, New Language Features, and Migration Steps

If you are still using JDK8, you may have encountered OutOfMemoryError or JVM tuning challenges; this guide introduces a garbage collector that can deliver up to a hundred‑fold performance improvement, potentially solving those issues.

1. Why Upgrade to JDK17

JDK17, released on 2021‑09‑14, is a long‑term support (LTS) version offering stable updates and improved reliability. Performance benchmarks show that moving from Java 8 to 11 improves G1GC speed by 16.1% (ParallelGC 4.5%), and from 11 to 17 further improves G1GC by 8.66% (ParallelGC 6.54%). The standout feature is the stable ZGC garbage collector with sub‑millisecond pause times.

Additional benefits include new syntax such as switch expressions, text blocks, pattern‑matching instanceof, records, sealed classes, and better NullPointerException messages, as well as framework support: Spring Framework 6 and Spring Boot 3 require Java 17 as a minimum.

2. Performance Test Results

Using JDOS with machines of various configurations (2C4G, 4C8G, 8C16G), we deployed JDK8, JDK11, and JDK17 and ran a 60‑minute load test with 180 virtual users creating 512 KB payloads per request. The results (see chart) demonstrate that all garbage collectors perform better on JDK17, especially ZGC, which offers the lowest pause times and high throughput.

3. Oracle JDK vs OpenJDK

Oracle JDK 17 became free for commercial use in September 2021, with continued GPL‑based OpenJDK releases. Starting September 2023, Oracle JDK 21 is the new LTS, and Oracle JDK 17 will require a license after September 2024. Functionally, Oracle JDK and OpenJDK are identical since JDK 11, so using OpenJDK 17 or other community builds (AdoptOpenJDK, RedHat OpenJDK) is recommended.

4. New Language Features from JDK11 to JDK17

Switch expressions simplify branching with the -> syntax.

Text blocks ( """ ) reduce escaping and improve readability.

Records provide concise immutable data carriers.

Pattern‑matching instanceof removes the need for explicit casts.

Sealed classes/interfaces restrict subclassing.

5. Migration Steps

5.1 JDK Selection

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

5.2 Maven Compiler Configuration

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

5.3 Spring Boot Upgrade

Upgrade to Spring Boot 2.7.15 (Spring 5.3.29) because Spring Boot 3 requires Java 17 and many internal libraries still target 2.x.

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

Alternatively, use dependencyManagement to set versions:

<properties>
    <!-- Framework version configuration -->
    <springboot-version>2.7.15</springboot-version>
    <springframework.version>5.3.29</springframework.version>
</properties>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>${springboot-version}</version>
            <scope>import</scope>
            <type>pom</type>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-framework-bom</artifactId>
            <version>${springframework.version}</version>
            <scope>import</scope>
            <type>pom</type>
        </dependency>
    </dependencies>
</dependencyManagement>

5.4 Circular Dependency Issue

Spring Boot 2.7.15 may raise a circular‑dependency error at startup. Resolve by refactoring bean dependencies or, if necessary, enable the legacy behavior:

spring.main.allow-circular-references=true

5.5 JVM Arguments

Enable ZGC with -XX:+UseZGC . For libraries that need deep reflection, add appropriate --add-opens or --add-exports flags (examples for SGM, R2M, Ducc, AKS are listed in the source).

6. Verification After Upgrade

Upgrade first to JDK 11, then to JDK 17, validating after each step.

Monitor logs for startup exceptions related to module access or reflection.

Check monitoring tools (SGM, UMP, etc.) for normal operation.

Perform staged traffic rollout with load testing to ensure business stability.

Run full end‑to‑end functional tests after the upgrade.

7. Conclusion

Upgrading to JDK 17 not only unlocks new language features but, more importantly, provides sub‑millisecond pause times with the ZGC garbage collector, delivering dramatic GC performance gains. The migration is straightforward, involving framework version updates and JVM argument adjustments, and is strongly recommended for production systems.