More tweaks to how java homes are detected

src/main/java/com/fizzed/jne/JavaHomes.java

@@ -72,6 +72,18 @@ static public JavaHome fromDirectory(Path javaHomeDir, boolean requireReleaseFil
             throw new FileNotFoundException("Java lib directory " + javaLibDir + " was not found in " + javaHomeDir);
         }
 
+        // Test #3: must also have jmods and/or a jre
+        final Path jmodsDir = javaHomeDir.resolve("jmods");
+        if (!Files.isDirectory(jmodsDir)) {
+            final Path jreDir = javaHomeDir.resolve("jre");
+            if (!Files.isDirectory(jreDir)) {
+                final Path rtJarFile = javaLibDir.resolve("rt.jar");
+                if (!Files.exists(rtJarFile)) {
+                    throw new FileNotFoundException("Java jmods/jre directory not found in " + javaHomeDir);
+                }
+            }
+        }
+
         final String javacExeFileName = NativeTarget.resolveExecutableFileName(thisOs, "javac");
         final Path _javacExeFile = javaHomeDir.resolve("bin").resolve(javacExeFileName);
         final Path javacExeFile;
@@ -98,6 +110,7 @@ static public JavaHome fromDirectory(Path javaHomeDir, boolean requireReleaseFil
             if (requireReleaseFile){
                 throw new FileNotFoundException("Java release file " + releaseFile + " was not found in " + javaHomeDir);
             }
+
             // otherwise, we could do "java -version" to try and detect it
             try {
                 String versionOutput = executeJavaVersion(javaExeFile);