Add environment variable KOTLIN_JUPYTER_JAVA_EXECUTABLE to set java e…

…xecutable for running kernel

Sometimes Java executable is not inside bin subfolder of java_home. It can lead to the issues like #405. This commit allows to avoid this situation by simply setting additional environment variable.

Fixes #405

distrib/kotlin_kernel/env_names.py

@@ -15,3 +15,6 @@
 
 # specific JDK location environment variable
 KERNEL_JAVA_HOME = "KOTLIN_JUPYTER_JAVA_HOME"
+
+# java executable path. If set, has greater priority than KOTLIN_JUPYTER_JAVA_HOME
+KERNEL_JAVA_EXECUTABLE = "KOTLIN_JUPYTER_JAVA_EXECUTABLE"

distrib/run_kotlin_kernel/run_kernel.py

@@ -55,12 +55,15 @@ def run_kernel_impl(connection_file: str, jar_args_file: str = None, executables
         class_path_arg = os.pathsep.join([os.path.join(jars_dir, jar_name) for jar_name in cp])
         main_jar_path = os.path.join(jars_dir, main_jar)
 
+        java_exec = os.getenv(env_names.KERNEL_JAVA_EXECUTABLE)
         java_home = os.getenv(env_names.KERNEL_JAVA_HOME) or os.getenv(env_names.JAVA_HOME)
 
-        if java_home is None:
-            java = "java"
-        else:
+        if java_exec is not None:
+            java = java_exec
+        elif java_home is not None:
             java = os.path.join(java_home, "bin", "java")
+        else:
+            java = "java"
 
         jvm_arg_str = os.getenv(env_names.KERNEL_JAVA_OPTS) or os.getenv(env_names.JAVA_OPTS) or ""
         extra_args = os.getenv(env_names.KERNEL_EXTRA_JAVA_OPTS)