feat: Add set-default option (#1017)

* Add set-default option

This option allows to install an additional JDK without making it the
default one.

I have wanted this for quite a long time as I'm running custom GitHub
Actions with Java, which might require a specific JDK and I don't want
to pollute the JDK that is used by the overall workflow calling the
action.
And I'm apparently not alone as there was a preexisting issue.

Fixes #560

* 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>

* test: fix Prettier formatting in base-installer test

Resolves the failing 'Basic validation / build' format-check on
__tests__/distributors/base-installer.test.ts (line exceeded print width).

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

---------

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

src/distributions/base-installer.ts

@@ -20,6 +20,7 @@ export abstract class JavaBase {
   protected packageType: string;
   protected stable: boolean;
   protected checkLatest: boolean;
+  protected setDefault: boolean;
   protected verifySignature: boolean;
   protected verifySignaturePublicKey: string | undefined;
 
@@ -38,6 +39,10 @@ export abstract class JavaBase {
     this.architecture = installerOptions.architecture || os.arch();
     this.packageType = installerOptions.packageType;
     this.checkLatest = installerOptions.checkLatest;
+    this.setDefault =
+      installerOptions.setDefault !== undefined
+        ? installerOptions.setDefault
+        : true;
     this.verifySignature = installerOptions.verifySignature ?? false;
     this.verifySignaturePublicKey = installerOptions.verifySignaturePublicKey;
   }
@@ -179,8 +184,15 @@ export abstract class JavaBase {
       foundJava.path = macOSPostfixPath;
     }
 
-    core.info(`Setting Java ${foundJava.version} as the default`);
-    this.setJavaDefault(foundJava.version, foundJava.path);
+    if (this.setDefault) {
+      core.info(`Setting Java ${foundJava.version} as the default`);
+      this.setJavaDefault(foundJava.version, foundJava.path);
+    } else {
+      core.info(
+        `Installing Java ${foundJava.version} (not setting as default)`
+      );
+      this.setJavaEnvironment(foundJava.version, foundJava.path);
+    }
 
     return foundJava;
   }
@@ -312,9 +324,13 @@ 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'));
+    this.setJavaEnvironment(version, toolPath);
+  }
+
+  protected setJavaEnvironment(version: string, toolPath: string) {
+    const majorVersion = version.split('.')[0];
     core.setOutput('distribution', this.distribution);
     core.setOutput('path', toolPath);
     core.setOutput('version', version);