Dedupe setJavaDefault and document multi-version/toolchain behavior

- Refactor setJavaDefault to delegate shared output/env logic to
  setJavaEnvironment, avoiding duplication between the two.
- Document that set-default applies to all JDKs in a multiline
  java-version, and that installed JDKs remain registered in Maven
  toolchains regardless of set-default.

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

dist/setup/index.js

@@ -78309,7 +78309,6 @@ const constants_1 = __nccwpck_require__(27242);
 const os_1 = __importDefault(__nccwpck_require__(70857));
 class JavaBase {
     constructor(distribution, installerOptions) {
-        var _a;
         this.distribution = distribution;
         this.http = new httpm.HttpClient('actions/setup-java', undefined, {
             allowRetries: true,
@@ -78319,7 +78318,10 @@ class JavaBase {
         this.architecture = installerOptions.architecture || os_1.default.arch();
         this.packageType = installerOptions.packageType;
         this.checkLatest = installerOptions.checkLatest;
-        this.setDefault = (_a = installerOptions.setDefault) !== null && _a !== void 0 ? _a : true;
+        this.setDefault =
+            installerOptions.setDefault !== undefined
+                ? installerOptions.setDefault
+                : true;
     }
     setupJava() {
         var _a, _b;
@@ -78540,13 +78542,9 @@ class JavaBase {
         return error;
     }
     setJavaDefault(version, toolPath) {
-        const majorVersion = version.split('.')[0];
         core.exportVariable('JAVA_HOME', toolPath);
         core.addPath(path_1.default.join(toolPath, 'bin'));
-        core.setOutput('distribution', this.distribution);
-        core.setOutput('path', toolPath);
-        core.setOutput('version', version);
-        core.exportVariable(`JAVA_HOME_${majorVersion}_${this.architecture.toUpperCase()}`, toolPath);
+        this.setJavaEnvironment(version, toolPath);
     }
     setJavaEnvironment(version, toolPath) {
         const majorVersion = version.split('.')[0];

docs/advanced-usage.md

@@ -294,6 +294,8 @@ steps:
 
 In this example, `JAVA_HOME` and `java` on `PATH` point to Java 17, while Java 21 is available via `JAVA_HOME_21_X64` or the step output `path`.
 
+> **Note:** When a single step installs multiple JDKs via a multiline `java-version`, the `set-default` value applies to all of them. With `set-default: false`, none of those JDKs become the default; each remains discoverable through its `JAVA_HOME_<major>_<arch>` variable. Regardless of `set-default`, installed JDKs are still registered in the Maven toolchains file, so they can be selected via Maven toolchains.
+
 ## Installing Java from local file
 If your use-case requires a custom distribution or a version that is not provided by setup-java, you can download it manually and setup-java will take care of the installation and caching on the VM:
 

src/distributions/base-installer.ts

@@ -310,16 +310,9 @@ export abstract class JavaBase {
   }
 
   protected setJavaDefault(version: string, toolPath: string) {
-    const majorVersion = version.split('.')[0];
     core.exportVariable('JAVA_HOME', toolPath);
     core.addPath(path.join(toolPath, 'bin'));
-    core.setOutput('distribution', this.distribution);
-    core.setOutput('path', toolPath);
-    core.setOutput('version', version);
-    core.exportVariable(
-      `JAVA_HOME_${majorVersion}_${this.architecture.toUpperCase()}`,
-      toolPath
-    );
+    this.setJavaEnvironment(version, toolPath);
   }
 
   protected setJavaEnvironment(version: string, toolPath: string) {