Install Java on Windows CI

.github/workflows/pull_request.yml

@@ -14,6 +14,45 @@ jobs:
     with:
       enable_windows_checks: true
       windows_swift_versions: '["nightly-main"]'
+      windows_pre_build_command: |
+        $jdkVersion = "21"
+        $msiUrl = "https://aka.ms/download-jdk/microsoft-jdk-$jdkVersion-windows-x64.msi"
+        $installerPath = "$env:TEMP\microsoft-jdk-$jdkVersion.msi"
+        $jdkInstallDir = "C:\Program Files\Microsoft\jdk-$jdkVersion"
+
+        # Download the MSI
+        Write-Host "Downloading Microsoft OpenJDK $jdkVersion..."
+        Invoke-WebRequest -Uri $msiUrl -OutFile $installerPath
+
+        # Install silently
+        Write-Host "Installing Microsoft OpenJDK $jdkVersion..."
+        Start-Process msiexec.exe -ArgumentList "/i `"$installerPath`" /quiet /norestart INSTALLDIR=`"$jdkInstallDir`"" -Wait -NoNewWindow
+
+        # Set JAVA_HOME (system-wide, requires admin)
+        Write-Host "Setting JAVA_HOME..."
+        [System.Environment]::SetEnvironmentVariable("JAVA_HOME", $jdkInstallDir, [System.EnvironmentVariableTarget]::Machine)
+
+        # Add to system PATH if not already present
+        $currentPath = [System.Environment]::GetEnvironmentVariable("PATH", [System.EnvironmentVariableTarget]::Machine)
+        if ($currentPath -notlike "*$jdkInstallDir\bin*") {
+            [System.Environment]::SetEnvironmentVariable("PATH", "$currentPath;$jdkInstallDir\bin", [System.EnvironmentVariableTarget]::Machine)
+            Write-Host "Added JDK bin to system PATH."
+        }
+
+        # Refresh current session
+        $env:JAVA_HOME = $jdkInstallDir
+        $env:PATH = "$env:PATH;$jdkInstallDir\bin"
+
+        # Verify
+        Write-Host "`nVerifying installation..."
+        & "$jdkInstallDir\bin\java.exe" -version
+
+        Write-Host "`nDone! JAVA_HOME = $env:JAVA_HOME"
+
+        # Clean up installer
+        Remove-Item $installerPath -Force
+
+        Get-ChildItem Env:
       enable_macos_checks: true
       macos_pre_build_command: brew install openjdk
       enable_ios_checks: false

Sources/SwiftJavaJNICore/VirtualMachine/JavaVirtualMachine.swift

@@ -480,13 +480,21 @@ private func loadLibJava() throws -> DylibType {
   let javaHomeURL = URL(fileURLWithPath: javaHome, isDirectory: true)
 
   let ext = FileManager.libraryExtension
-  let libjvmPaths = [
+  let libjvmPaths: [URL]
+
+  #if os(Windows)
+  libjvmPaths = [
+    URL(fileURLWithPath: "bin\\server\\jvm.dll", relativeTo: javaHomeURL)
+  ]
+  #else
+  libjvmPaths = [
     // look through some standard locations relative to JAVA_HOME
     URL(fileURLWithPath: "jre/lib/server/libjvm.\(ext)", relativeTo: javaHomeURL),
     URL(fileURLWithPath: "lib/server/libjvm.\(ext)", relativeTo: javaHomeURL),
     URL(fileURLWithPath: "lib/libjvm.\(ext)", relativeTo: javaHomeURL),
     URL(fileURLWithPath: "libexec/openjdk.jdk/Contents/Home/lib/server/libjvm.\(ext)", relativeTo: javaHomeURL),
   ]
+  #endif
 
   guard
     let libjvmPath = libjvmPaths.first(where: {

Tests/SwiftJavaJNICoreTests/JavaVirtualMachineTests.swift

@@ -16,17 +16,25 @@ import Testing
 
 @testable import SwiftJavaJNICore
 
+#if canImport(FoundationEssentials)
+import class FoundationEssentials.ProcessInfo
+#else
+import class Foundation.ProcessInfo
+#endif
 @Suite
 struct JavaVirtualMachineTests {
 
   static var isSupportedPlatform: Bool {
     #if os(Android)
-    // Android tests are not currently run within an .apk and so do not have any ambient JVM
-    return false
+    // Android tests are not currently run within an .apk and so do not have any ambient JVM.
+    // This can be overridden for a test harness that supports running within an .apk, like:
+    // skip android test --apk --env SWIFT_JAVA_JNI_TEST_JVM=1
+    let testSentinel = "0"
     #else
-    // disable test when we cannot find a system Java
-    return systemJavaHome() != nil
+    // tests for every other platform should be run in an environment with Java available unless explicitly disabled
+    let testSentinel = "1"
     #endif
+    return (ProcessInfo.processInfo.environment["SWIFT_JAVA_JNI_TEST_JVM"] ?? testSentinel) != "0"
   }
 
   @Test(.enabled(if: isSupportedPlatform))