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apavithraa/springboot-architecture
Skills for creating, testing, reviewing, migrating and guarding Spring Boot 4 projects with Java 25: project scaffolding with architecture patterns, Boot 4 test templates, code review, Boot 3 to 4 migration, and a team harness of build gates and agent hooks.
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java-version-policy.mdskills/creating-springboot-projects/references/
Java Version Policy (Spring Boot 4)
Single source for Java version advice. Other skills link here. Update this file when a new JDK ships.
Last checked: 2026-10-17.
Policy
| Use | Java version |
|---|---|
| Default for new projects | 25 (current LTS) |
| Accept when the user asks | 21 (previous LTS) or 17 (Boot 4 minimum) |
| Newest release | 27 (GA 2026-09-15, non-LTS) |
| Next LTS | 29 (expected September 2027) |
Rules:
- Default to Java 25. Do not pick a non-LTS release unless the project already tracks non-LTS releases.
- Do not flag Java 17 or 21 as "too old". Both are valid Boot 4 baselines.
- Before you pick Java 27, check the Spring Boot system requirements page. On 2026-10-17, Boot 4.1.1 lists support "up to and including Java 26".
- Read the Java version from
pom.xmlorbuild.gradlebefore you give version-specific advice.
Preview APIs change between releases
Code compiled with --enable-preview runs only on the same JDK feature release. Preview APIs also change shape. Do not copy a preview sample to a different JDK.
| API | JDK 25 | JDK 26 | JDK 27 |
|---|---|---|---|
| Lazy init | StableValue.of() + orElseSet(...) (JEP 502) | LazyConstant.of(supplier) (JEP 526) | LazyConstant.of(supplier); isInitialized/orElse removed; Set.ofLazy added (JEP 531) |
| Structured concurrency | StructuredTaskScope.open(Joiner) (JEP 505) | Sixth preview (JEP 525) | join() throws ExecutionException; third type parameter for the exception; Joiner.awaitAll() removed (JEP 533) |
| Primitive patterns | JEP 507 | JEP 530 | JEP 532 (unchanged from 26) |
Runtime changes when you move past Java 25
JDK 26
- Final field mutation warns (JEP 500). Deep reflection that writes
finalfields prints a warning. A future release will deny it. Serialization, mocking, and some injection libraries do this. Test with--illegal-final-field-mutation=denyto find them early. Prefer constructor injection. - AOT object caching works with any GC (JEP 516). This can improve Boot startup.
- HTTP/3 in
java.net.http.HttpClient(JEP 517).
JDK 27
- G1 is the default in all environments (JEP 523). Before, the JVM picked Serial GC with 1 CPU or less than 1792 MB of memory. Small containers now get G1. Measure memory and latency in small pods. To keep Serial, set
-XX:+UseSerialGC. - Compact object headers are on by default (JEP 534). Headers shrink from 96 to 64 bits, so heap use drops. To turn them off, set
-XX:-UseCompactObjectHeaders. - Post-quantum hybrid key exchange for TLS 1.3 (JEP 527). Test outbound HTTPS calls through your proxies before rollout.
- JFR in-process data redaction (JEP 536). Use it when JFR recordings leave the host.