ob-java.el: Allow for more whitespace in java code

* lisp/ob-java.el (org-babel-java--package-re)
(org-babel-java--imports-re, org-babel-java--class-re)
(org-babel-java--main-re, org-babel-java--any-method-re):
Updated regexps to allow for more whitespace in the content of java
code blocks.  Convert regexps to `rx' to improve clarity.
* testing/lisp/test-ob-java.el (ob-java/simple-with-main-whitespace):
Added test case with excessive whitespace.

Reported-by: Jarmo Hurri <jarmo.hurri@iki.fi>
Ref: https://orgmode.org/list/87o8k68w05.fsf@iki.fi

lisp/ob-java.el

@@ -77,15 +77,40 @@ like javac -verbose."
   :package-version '(Org . "9.5")
   :type 'symbol)
 
-(defconst org-babel-java--package-re "^[[:space:]]*package[[:space:]]+\\\([[:alnum:]_\.]+\\\);$"
+(defconst org-babel-java--package-re (rx line-start (0+ space) "package"
+					 (1+ space) (group (1+ (in alnum ?_ ?.))) ; capture the package name
+					 (0+ space) ?\; line-end)
   "Regexp for the package statement.")
-(defconst org-babel-java--imports-re "^[[:space:]]*import[[:space:]]+\\\([[:alnum:]_\.]+\\\);$"
+(defconst org-babel-java--imports-re (rx line-start (0+ space) "import"
+					 (1+ space) (group (1+ (in alnum ?_ ?.))) ; capture the fully qualified class name
+					 (0+ space) ?\; line-end)
   "Regexp for import statements.")
-(defconst org-babel-java--class-re "^[[:space:]]*\\\(?:public[[:space:]]+\\\)?class[[:space:]]+\\\([[:alnum:]_]+\\\)[[:space:]]*\n?[[:space:]]*{"
+(defconst org-babel-java--class-re (rx line-start (0+ space) (opt (seq "public" (1+ space)))
+				       "class" (1+ space)
+				       (group (1+ (in alnum ?_))) ; capture the class name
+				       (0+ space) ?{)
   "Regexp for the class declaration.")
-(defconst org-babel-java--main-re "public static void main(String\\\(?:\\[]\\\)?[[:space:]]+[^ ]+\\\(?:\\[]\\\)?).*\n?[[:space:]]*{"
+(defconst org-babel-java--main-re (rx line-start (0+ space) "public"
+				      (1+ space) "static"
+				      (1+ space) "void"
+				      (1+ space) "main"
+				      (0+ space) ?\(
+				      (0+ space) "String"
+				      (0+ space) (1+ (in alnum ?_ ?\[ ?\] space)) ; "[] args" or "args[]"
+				      (0+ space) ?\)
+				      (0+ space) (opt "throws" (1+ (in alnum ?_ ?, ?. space)))
+				      ?{)
   "Regexp for the main method declaration.")
-(defconst org-babel-java--any-method-re "public .*(.*).*\n?[[:space:]]*{"
+(defconst org-babel-java--any-method-re (rx line-start
+					    (0+ space) (opt (seq (1+ alnum) (1+ space)))   ; visibility
+					    (opt (seq "static" (1+ space)))                ; binding
+					    (1+ (in alnum ?_ ?\[ ?\]))                     ; return type
+                                            (1+ space) (1+ (in alnum ?_))                  ; method name
+					    (0+ space) ?\(
+					    (0+ space) (0+ (in alnum ?_ ?\[ ?\] ?, space)) ; params
+					    (0+ space) ?\)
+					    (0+ space) (opt "throws" (1+ (in alnum ?_ ?, ?. space)))
+					    ?{)
   "Regexp for any method.")
 (defconst org-babel-java--result-wrapper "\n    public static String __toString(Object val) {
         if (val instanceof String) {

testing/lisp/test-ob-java.el

@@ -128,6 +128,24 @@ public static void main(String args[]) {
 #+end_src"
     (should (string= "42" (org-babel-execute-src-block)))))
 
+(ert-deftest ob-java/simple-with-main-whitespace ()
+  "Hello world program that defines a main function with the square brackets after `args'."
+  (org-test-with-temp-text
+      "#+begin_src java :results output silent
+public
+static
+void
+main
+ (
+ String
+ args []
+ )
+{
+    System.out.print(42);
+}
+#+end_src"
+    (should (string= "42" (org-babel-execute-src-block)))))
+
 (ert-deftest ob-java/simple-with-class ()
   "Hello world program that defines a class."
   (org-test-with-temp-text