Add conditional JDK caching (#1201)

* Add JDK caching

Cache resolved JDK tool-cache entries by exact platform and release identity, with a default-on cache-jdk input and explicit opt-out.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Apply batched suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Fix JDK cache CI validation

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Update brace-expansion security fix

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Refresh brace-expansion license metadata

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Refine JDK cache semantics

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Refine JDK cache documentation

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Simplify JDK cache identity

Use one normalized runner OS dimension, reset the internal cache key schema for the unreleased feature, and align documentation, tests, and bundles.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Align JDK cache OS identity

Use the established RUNNER_OS value directly and retain process.platform only as a non-Actions fallback.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Harden JDK cache saves and document tool-cache reuse

Bind each JDK cache key to the installation identity it was computed for,
keep post-job saves best-effort per entry, and state the real reuse and
verification guarantee in the documentation.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* docs: restructure README caching section

Rename '## Caching dependencies' to '## Caching' and add a what-gets-cached
overview table covering the dependency, wrapper, and JDK caches. Lead with the
common 'cache: maven' example and the dependency-cache material, and demote JDK
caching into its own subsection.

Also corrects the IMPORTANT callout, which implied JDK caching required an
explicit opt-in; it is enabled implicitly whenever 'cache' is set.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* docs: fix caching documentation defects

- Remove pull-request framing that compared behavior to `main`; state the
  tool-cache and `jdkfile` behavior directly and unconditionally.
- Clarify that the JDK cache is a separate cache *entry* from the dependency
  and wrapper caches, while its *enablement* is coupled to `cache`, so the
  opening paragraph agrees with the enablement matrix.
- Cite the actions/setup-java-benchmarks repository instead of an open PR and
  a self-referential PR comment, keeping the measured figures and caveats.
- Keep the `cache`/`cache-jdk` matrix only in docs/advanced-usage.md and
  summarize the rules in prose in README.md to avoid divergence.
- Describe the guarantee that a cache key is only saved with the installation
  it was computed for, instead of documenting inode/size/timestamp internals.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* docs: add V6 what's new entry for JDK caching

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: e2755464-4e83-47b6-ba71-731bb481b418

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Copilot-Session: e2755464-4e83-47b6-ba71-731bb481b418

src/setup-java.ts

@@ -1,6 +1,10 @@
 import fs from 'fs';
 import * as core from '@actions/core';
-import {getBooleanInput, getVersionFromFileContent} from './util.js';
+import {
+  getBooleanInput,
+  getVersionFromFileContent,
+  isJdkCacheEnabled
+} from './util.js';
 import * as constants from './constants.js';
 import * as path from 'path';
 import {fileURLToPath} from 'url';
@@ -17,6 +21,7 @@ export async function run() {
   const packageType = core.getInput(constants.INPUT_JAVA_PACKAGE);
   const jdkFile = getJdkFileInput();
   const cache = core.getInput(constants.INPUT_CACHE);
+  const cacheJdk = isJdkCacheEnabled(cache);
   const cacheDependencyPath = core.getInput(
     constants.INPUT_CACHE_DEPENDENCY_PATH
   );
@@ -80,6 +85,7 @@ export async function run() {
         packageType,
         checkLatest,
         forceDownload,
+        cacheJdk,
         setDefault,
         verifySignature,
         verifySignaturePublicKey,
@@ -105,6 +111,7 @@ export async function run() {
         packageType,
         checkLatest,
         forceDownload,
+        cacheJdk,
         setDefault,
         verifySignature,
         verifySignaturePublicKey,
@@ -183,6 +190,7 @@ async function installVersion(
     packageType,
     checkLatest,
     forceDownload,
+    cacheJdk,
     setDefault,
     verifySignature,
     verifySignaturePublicKey,
@@ -194,6 +202,7 @@ async function installVersion(
     packageType,
     checkLatest,
     forceDownload,
+    cacheJdk,
     setDefault,
     verifySignature,
     verifySignaturePublicKey,
@@ -238,6 +247,7 @@ interface installerInputsOptions {
   packageType: string;
   checkLatest: boolean;
   forceDownload: boolean;
+  cacheJdk: boolean;
   setDefault: boolean;
   verifySignature: boolean;
   verifySignaturePublicKey: string | undefined;