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From "B. K. Oxley (binkley)" <>
Subject Re: [vfs] proposal: FileUtils
Date Mon, 31 Jan 2005 23:39:21 GMT
I looked over the problem again and think I'd prefer a command object 

public interface Operation<E extends Exception> {
     void execute() throws E;


public interface IOOperation extends Operation<IOException> { }

(Excess abstraction, I know.  I had a hard time resisting the coolness 
of generic exceptions.)

And some operations:

public class Move implements IOOperation {
     private final FuFile original, newLocation;
     private final IOOperation next;

     public Move(final FuFile original, final FuFile newLocation,
             final IOOperation next) {
         if (null == original) throw new NullPointerException();
         if (null == newLocation) throw new NullPointerException();
         if (null == next) throw new NullPointerException();

         this.original = original;
         this.newLocation = newLocation; = next;

     public void execute()
             throws IOException {

         try {

         } catch (final IOException e) {

             throw e;

And to make a Save operation:

public class Save implements IOOperation {
     private final FuPolicy policy;
     private final InputStream newContents;
     private final FuFile original;

     public Save(final FuPolicy policy, final InputStream newContents,
             final FuFile original) {
         if (null == policy) throw new NullPointerException();
         if (null == newContents) throw new NullPointerException();
         if (null == original) throw new NullPointerException();

         this.policy = policy;
         this.newContents = newContents;
         this.original = original;

     public void execute()
             throws IOException {
         final FuFile backup = policy.createBackup(original);

         new Delete(backup, policy.createScratch(backup),
                 new Move(original, backup,
                         new Write(newContents, original))).execute();

Isn't that nifty?  :-)

I get to use the policy object without interfering with "FuFile" (my 
dummy file object just for proof of concept); I can create complex 
operations by composing simpler operations as building blocks.

In fact, perhaps I should pull "new Delete(...)", "new Move(...)" and 
"new Write(...)" out into fields of Save so that someone could replace 
them with subclassed instances via IoC.

How does that suit you?


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