--jvm tries to find Java executable system-wide.

engine/runner/src/main/java/org/enso/runner/JavaFinder.java

@@ -0,0 +1,64 @@
+package org.enso.runner;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Path;
+import org.enso.distribution.DistributionManager;
+import org.enso.distribution.Environment;
+
+/** Utility class that tries to find installed JDK on the system. */
+final class JavaFinder {
+  private JavaFinder() {}
+
+  /**
+   * Tries to find {@code java} executable on the system. If a system-wide JDK is not found, tries
+   * to find it in the {@link DistributionManager distribution} runtimes.
+   *
+   * @return null if cannot be found. Otherwise, returns the absolute path to the executable, or
+   *     simply {@code java} if it is on the {@code PATH}.
+   */
+  static String findJavaExecutable() {
+    var javaHome = System.getenv("JAVA_HOME");
+    if (javaHome != null) {
+      var java = new File(javaHome, "bin/java").getAbsoluteFile();
+      if (java.exists()) {
+        return java.getAbsolutePath();
+      }
+    }
+    if (isJavaOnPath()) {
+      return "java";
+    }
+    var javaInRuntime = findJavaExecutableInDistributionRuntimes();
+    if (javaInRuntime != null) {
+      return javaInRuntime.toAbsolutePath().toString();
+    }
+    return null;
+  }
+
+  private static Path findJavaExecutableInDistributionRuntimes() {
+    var env = new Environment() {};
+    var dm = new DistributionManager(env);
+    var paths = dm.paths();
+    var files = paths.runtimes().toFile().listFiles();
+    if (files != null) {
+      for (var d : files) {
+        var java = new File(new File(d, "bin"), "java").getAbsoluteFile();
+        if (java.exists()) {
+          return java.toPath();
+        }
+      }
+    }
+    return null;
+  }
+
+  private static boolean isJavaOnPath() {
+    try {
+      ProcessBuilder processBuilder = new ProcessBuilder("java", "-h");
+      Process process = processBuilder.start();
+      int exitCode = process.waitFor();
+      return exitCode == 0;
+    } catch (IOException | InterruptedException e) {
+      return false;
+    }
+  }
+}

engine/runner/src/main/java/org/enso/runner/Main.java

@@ -1337,22 +1337,13 @@ private void launch(String[] args) throws IOException, InterruptedException, URI
         println(JVM_OPTION + " option has no effect - already running in JVM " + current);
       } else {
         var commandAndArgs = new ArrayList<String>();
-        JVM_FOUND:
         if (jvm == null) {
-          var env = new Environment() {};
-          var dm = new DistributionManager(env);
-          var paths = dm.paths();
-          var files = paths.runtimes().toFile().listFiles();
-          if (files != null) {
-            for (var d : files) {
-              var java = new File(new File(d, "bin"), "java").getAbsoluteFile();
-              if (java.exists()) {
-                commandAndArgs.add(java.getPath());
-                break JVM_FOUND;
-              }
-            }
+          var javaExe = JavaFinder.findJavaExecutable();
+          if (javaExe == null) {
+            println("Cannot find java executable");
+            throw exitFail();
           }
-          commandAndArgs.add("java");
+          commandAndArgs.add(javaExe);
         } else {
           commandAndArgs.add(new File(new File(new File(jvm), "bin"), "java").getAbsolutePath());
         }