Xamarin adjusts Java version to 1.7 when called from command line MSBUILD

Question

I have JDK 1.8 Path set in Visual Studio and I can compile Android 7.0. application without any problems.

In order to automatically build signed APK I also have a PS1 script which is supposed to compile the same application using command line MSBUILD. I set JAVA_HOME, JDK_HOME to JDK 1.8. but MSBUILD still uses JDK 1.7. and I get error "Unsupported class version number 52..."

Is there a way how to set JDK location when invoking MSBUILD from command line?

What is even more confusing is that the default Java version on this machine is 1.8 (if I type java -version I get JDK 1.8.0_111.)

UPDATE When executing build with detailed login I can confirm that Xamarin sees JDK 1.8

ResolveSdksTask Outputs:
    AndroidApiLevel: 25
    AndroidApiLevelName: 25
    AndroidNdkPath: D:\Users\milan\Documents\Android\ndk\android-ndk-r10e
    AndroidSdkBuildToolsPath: D:\Utilities\android-sdk\build-tools\25.0.0
    AndroidSdkBuildToolsBinPath: D:\Utilities\android-sdk\build-tools\25.0.0
    AndroidSdkPath: D:\Utilities\android-sdk
    JavaSdkPath: C:\Program Files\Java\jdk1.8.0_111
    MonoAndroidBinPath: C:\Program Files (x86)\MSBuild\Xamarin\Android
    MonoAndroidToolsPath: C:\Program Files (x86)\MSBuild\Xamarin\Android
    MonoAndroidIncludePath: 
    TargetFrameworkVersion: v7.0
    ZipAlignPath: D:\Utilities\android-sdk\build-tools\25.0.0
    SupportedApiLevel: 24
    AndroidSequencePointsMode: None
   Found Android SDK. API levels: 10, 15, 19, 21, 22, 23, 24

But then later on Task "AdjustJavacVersionArguments" changes Javac version to 1.7:

Task "AdjustJavacVersionArguments"
  ToolPath: C:\Program Files\Java\jdk1.8.0_111\\bin
  ToolExe: javac.exe
  EnableProguard: False
  EnableMultiDex: True
  Javac TargetVersion adjusted to: 1.7
  Javac SourceVersion adjusted to: 1.7
Done executing task "AdjustJavacVersionArguments".

Any ideas?

Answer 1

This looks like a combination of issues.

1) Multidex fails to create the main list due to API 24(Android 7.0) does not support JDK 1.7.

CREATEMULTIDEXMAINDEXCLASSLIST : error : Can't read [C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\MonoAndroid\v7.0\mono.android.jar] (Can't process class [android/app/ActivityTracker.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7))) [D:\src\anqueto\trunk\que\mikonboard.que.androidClient\mikonboard.que.androidClient.csproj]

Also related: Xamarin.Android Proguard - Unsupported class version number 52.0

2) javac is adjusting to JDK 1.7 (Thus you still have it installed).

Here is the Task decompiled:

  public class AdjustJavacVersionArguments : ToolTask
  {
    [Required]
    public new string ToolPath { get; set; }

    public bool EnableProguard { get; set; }

    public bool EnableMultiDex { get; set; }

    [Output]
    public string TargetVersion { get; set; }

    [Output]
    public string SourceVersion { get; set; }

    protected override string ToolName
    {
      get
      {
        return !OS.IsWindows ? "javac" : "javac.exe";
      }
    }

    public override bool Execute()
    {
      this.Log.LogDebugMessage("ToolPath: {0}", (object) this.ToolPath);
      this.Log.LogDebugMessage("ToolExe: {0}", (object) this.ToolExe);
      this.Log.LogDebugMessage("EnableProguard: {0}", (object) this.EnableProguard);
      this.Log.LogDebugMessage("EnableMultiDex: {0}", (object) this.EnableMultiDex);
      if (!this.EnableProguard && !this.EnableMultiDex)
        return true;
      Process process = Process.Start(new ProcessStartInfo(Path.Combine(this.ToolPath, this.ToolExe ?? this.ToolName), "-version")
      {
        RedirectStandardOutput = true,
        RedirectStandardError = true,
        UseShellExecute = false,
        CreateNoWindow = true,
        WindowStyle = ProcessWindowStyle.Hidden
      });
      process.WaitForExit();
      string str1 = process.StandardError.ReadLine();
      if (!str1.StartsWith("javac ") || !str1.Substring(6).StartsWith("1.8"))
        return true;
      string str2 = "1.7";
      this.SourceVersion = str2;
      this.TargetVersion = str2;
      this.Log.LogDebugMessage("Javac TargetVersion adjusted to: {0}", (object) this.TargetVersion);
      this.Log.LogDebugMessage("Javac SourceVersion adjusted to: {0}", (object) this.SourceVersion);
      return true;
    }

    protected override string GenerateFullPathToTool()
    {
      return Path.Combine(this.ToolPath, this.ToolExe);
    }
  }

It specifically looks like it fails to return true; on these lines:

string str1 = process.StandardError.ReadLine();
if (!str1.StartsWith("javac ") || !str1.Substring(6).StartsWith("1.8"))
        return true;

And thus it adjusts to 1.7:

string str2 = "1.7";
this.SourceVersion = str2;
this.TargetVersion = str2;
this.Log.LogDebugMessage("Javac TargetVersion adjusted to: {0}", (object) this.TargetVersion);
this.Log.LogDebugMessage("Javac SourceVersion adjusted to: {0}", (object) this.SourceVersion);
return true;

I would say it might be easiest to uninstall JDK 1.7 and only have JDK 1.8 installed to see if that resolves your issue.

Otherwise try to ensure the project and your JDK are on the same drive. You seem to have bits and pieces on both your C:\ and D:\ drives. I would keep all of your development tools on one drive.