Update URLs and remove broken links (#574)

* update URLs and remove broken links

* link to volatile

Author: elharo

src/main/java/org/apache/commons/io/DirectoryWalker.java

@@ -186,11 +186,11 @@
  *
  * <p>
  * This example provides a public {@code cancel()} method that can be called by another thread to stop the
- * processing. A typical example use-case would be a cancel button on a GUI. Calling this method sets a
- * <a href="https://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#36930"> volatile</a> flag to ensure
- * it will work properly in a multi-threaded environment. The flag is returned by the {@code handleIsCancelled()}
- * method, which will cause the walk to stop immediately. The {@code handleCancelled()} method will be the next,
- * and last, callback method received once cancellation has occurred.
+ * processing. A typical example use-case is a cancel button on a GUI. Calling this method sets a
+ * <a href='https://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#d5e12277'>(@code volatile}</a>
+ * flag to ensure it works properly in a multi-threaded environment.
+ * The flag is returned by the {@code handleIsCancelled()} method, which causes the walk to stop
+ * immediately. The {@code handleCancelled()} method will be the next, and last, callback method received once cancellation has occurred.
  * </p>
  *
  * <pre>

src/main/java/org/apache/commons/io/FileSystemUtils.java

@@ -473,11 +473,10 @@ List<String> performCommand(final String[] cmdAttribs, final int max, final Dura
         //
         // This method does what it can to avoid the 'Too many open files' error
         // based on trial and error and these links:
-        // https://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4784692
-        // https://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4801027
-        // https://forum.java.sun.com/thread.jspa?threadID=533029&messageID=2572018
-        // however, it's still not perfect as the JDK support is so poor
-        // (see commons-exec or Ant for a better multithreaded multi-OS solution)
+        // https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4784692
+        // https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4801027
+        // However, it's still not perfect as the JDK support is so poor.
+        // (See commons-exec or Ant for a better multithreaded multi-OS solution.)
         //
         final Process proc = openProcess(cmdAttribs);
         final Thread monitor = ThreadMonitor.start(timeout);

src/main/java/org/apache/commons/io/IOUtils.java

@@ -1164,7 +1164,7 @@ public static void copy(final InputStream input, final Writer writer, final Char
      * </p>
      * <p>
      * Character encoding names can be found at
-     * <a href="http://www.iana.org/assignments/character-sets">IANA</a>.
+     * <a href="https://www.iana.org/assignments/character-sets">IANA</a>.
      * </p>
      * <p>
      * This method uses {@link InputStreamReader}.