How to scan Java source texts?

  I'd like to scan Java source texts, printing one token per line.

  I thought it might be possible with the compiler API, and
  have read that it can return an AST, but I do not know how
  to just obtain the tokens from the source code AST.

  I am able to write a scanner for Java myself, but this would
  take days. So I would like to shortcut it by using a Java SE
  (with JDK) call. (I would not like to use a third-party
  library, because when I use the Java SE compiler API, I can
  be sure that this will be up-to-date with future Java-Versions.)

  So, the best solution would be a short program getting this
  information out of the Java compiler API. But I cannot find
  an example for this in the web.

  What does not seem to work is:

public class Main
{ public static void main( final java.lang.String[] args )throws java.io.IOException
  { final java.io.File javaFile = new java.io.File( "Main.java" );
    final java.io.FileReader file = new java.io.FileReader( javaFile );
    final java.io.StreamTokenizer streamTokenizer = new java.io.StreamTokenizer( file );
    for( int i; true; )
    { i = streamTokenizer.nextToken();
      if( i == java.io.StreamTokenizer.TT_EOF )break;
      java.lang.System.out.println( streamTokenizer.sval ); }}}

  Still, this gives the idea of what I want to accomplish.

  For example, the scanner should decompose:

a+=b +"c\"d/*e"/*f*/
                                    +g;

  into

a
+=
b
+
"c\"d/*e"
/*f*/
+
g
;

  (the comment ?/*f*/? can as well be deleted; also, there is
  no need for any further information, such as token types.)