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docs: rewrite IMPLEMENTING_JRES.md for BaseJRE pattern by stokpop · Pull Request #1339 · cloudfoundry/java-buildpack · GitHub
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docs: rewrite IMPLEMENTING_JRES.md for BaseJRE pattern#1339

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stokpop wants to merge 5 commits into
cloudfoundry:mainfrom
stokpop:docs/implementing-jres-basejre
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docs: rewrite IMPLEMENTING_JRES.md for BaseJRE pattern#1339
stokpop wants to merge 5 commits into
cloudfoundry:mainfrom
stokpop:docs/implementing-jres-basejre

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stokpop commented Jun 29, 2026

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Summary

What changed

  • Removed: manual boilerplate implementation guides (OpenJDK/Zulu/IBM step-by-step with full code listings), redundant "Best Practices" and "Common Patterns" sections (now handled by BaseJRE automatically)
  • Added: BaseJRE variation points table, 3-step implementation guide, lean examples for standard/exact-dir/error-hint patterns
  • Updated: Java 21 in all examples; memory calculator config now shows JBP_CONFIG_<JRE>_JRE as preferred (covers stack_threads, class_count, headroom) with a note that MEMORY_CALCULATOR_* env vars override but don't cover class_count
  • Kept lean: helper function reference table, memory calculator runtime output, JVMKill + heap dump volume service, troubleshooting section, summary, See Also cross-references

Related

Follows #1288 (BaseJRE refactor that this doc now describes)

Please review if complete or must be extended.

stokpop added 4 commits June 26, 2026 14:59
docs: rewrite IMPLEMENTING_JRES.md for BaseJRE pattern …
f42c75e
PR cloudfoundry#1288 refactored all standard JREs to embed BaseJRE (14 lines each), but the guide still showed the old 100+ line manual implementation with explicit Supply()/Finalize() boilerplate. Rewrite to document the actual pattern: newBaseJRE() + optional extraFinalizeOpts. Removes sections on manual memory calculator and JVMKill integration (now internal to BaseJRE). Adds variation-point table and examples for all three patterns (standard, exact-dir, error-hint).
docs: restore helper functions, runtime component docs, and troublesh… …
0fddbea
…ooting Rebalances the IMPLEMENTING_JRES.md rewrite — adds back lean sections for: - Helper function reference table (GetJREVersion, WriteJavaOpts, etc.) - profile.d script output example - Memory calculator: runtime output and user customization env vars - JVMKill: purpose, heap dump / volume service binding - Troubleshooting: JAVA_HOME, memory calculator, version resolution
docs: add summary and cross-references to IMPLEMENTING_JRES.md
88bcf93
docs: update JRE examples to Java 21, expand memory calculator config …
358bb87
- Use Java 21 in version examples and profile.d output - Prefer JBP_CONFIG_<JRE>_JRE for memory calculator config (covers stack_threads, class_count, headroom) - Note MEMORY_CALCULATOR_* env vars take precedence but don't cover class_count - Add stack_threads/class_count/headroom descriptions
stokpop requested a review from Copilot July 6, 2026 12:42
Copilot AI reviewed Jul 6, 2026
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Pull request overview

This PR rewrites docs/IMPLEMENTING_JRES.md to document the newer BaseJRE template-method pattern (introduced in #1288) and remove the older long-form “manual boilerplate” JRE provider implementation guidance.

Changes:

  • Replaces large per-provider implementation walkthroughs with a BaseJRE variation-points model and a short 3-step “how to add a JRE” guide.
  • Adds concise examples for standard prefix matching, exact-dir matching, and install-error hints.
  • Updates operational reference sections (memory calculator, JVMKill, troubleshooting) and refreshes examples to Java 21.

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Comment thread docs/IMPLEMENTING_JRES.md Outdated
### Detection

### Version Selection
`BaseJRE.Detect()` calls `DetectJREByEnv(jreKey)` which returns `true` when:
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docs: correct JRE interface, env var, and example accuracy in IMPLEME… …
11837e2
…NTING_JRES.md Addresses PR review: - Add missing MemoryCalculatorCommand() to the jres.JRE interface excerpt. - Add the missing `type MinimalJRE` so the no-extra-opts example compiles. - Correct detection/version docs to match DetectJREByEnv/GetJREVersion: the documented JBP_CONFIG_<NAME>_JRE name (recommended) or the auto-generated JBP_CONFIG_<KEY> alias. JBP_CONFIG_COMPONENTS is deprecated and unused for selection; there is no BP_JAVA_<JREKEY> variable.
stokpop requested a review from Copilot July 6, 2026 14:55
Copilot AI reviewed Jul 6, 2026
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Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

Comment thread docs/IMPLEMENTING_JRES.md
```
-Xmx512M -Xms512M -XX:MaxMetaspaceSize=128M -Xss1M -XX:ReservedCodeCacheSize=32M
```
`stack_threads` — number of user threads (default: 200); affects `-Xss` heap budget.
Comment thread docs/IMPLEMENTING_JRES.md
```bash
cf env myapp | grep JBP_CONFIG_COMPONENTS
```
**Wrong Java version selected** — check resolution order: `BP_JAVA_VERSION` → `JBP_CONFIG_<KEY>_JRE` → manifest default. Enable debug: `cf set-env myapp BP_LOG_LEVEL DEBUG`.
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