Creates a new java.io.Writer that wraps around a java.lang.Appendable. It properly flushes and closes appendables that happened to also be java.io.Flushables and/or java.io.Closeables. This uses instanceof only in the constructor, and a (Java 1.5) delta in flush() and close(), which avoids having to use any logic or reflection after object const…

NewWriterForAppendable.java

/*
   XBN-Java is released under the LGPL 2.1

   XBN-Java is a collection of generically-useful non-GUI programming utilities, featuring shareable self-returning method chains, "Listify"-ers, regular expression convenience classes, ValidateValue and AlterValue, highly-configurable output for strings and lists, and unit-testing example code.

   Copyright (C) 2013 Jeff Epstein

   This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA*)
 */
   import  java.io.Closeable;
   import  java.io.Flushable;
   import  java.io.IOException;
   import  java.io.Writer;
/**
   <P>{@code java NewWriterForAppendable}.</P>

   @author  Copyright (C) 2013 Jeff Epstein, with asistance by Marc Baumbach for {@code newWriterForAppendable(apbl)}. Released under the LPGL 2.1. <CODE><A HREF="http://xbnjava.jeffyepstein.com">http://xbnjava.jeffyepstein.com</A></CODE>, <CODE><A HREF="https://github.com/aliteralmind/xbnjava">https://github.com/aliteralmind/xbnjava</A></CODE>
 **/
public class NewWriterForAppendable  {
   /**
      <P>Demonstrates {@code newWriterForAppendable(apbl)} for creating a new {@code Writer} that wraps around {@code System.out} (writes to the console).</P>
    **/
   public static final void main(String[] igno_red)  {
      try  {
         NewWriterForAppendable.newWriterForAppendable(System.out).write("hello");
      }  catch(IOException iox)  {
         throw  new RuntimeException("WriterForAppendableXmpl", iox);
      }
   }
   /**
      <P>A {@code Flushable} whose {@code flush()} function does nothing. This is used by {@link #newWriterForAppendable(Appendable ap_bl) newWriterForAppendable}{@code (apbl)} as a (Java 1.5) delta.</P>

      @see  #newWriterForAppendable(Appendable) newWriterForAppendable(apbl)
    **/
   public static final Flushable FLUSHABLE_DO_NOTHING = new Flushable()  {
      public void flush()  {
      }
   };
   /**
      <P>A {@code Closeable} whose {@code close()} function does nothing. This is used by {@link #newWriterForAppendable(Appendable ap_bl) newWriterForAppendable}{@code (apbl)} as a (Java 1.5) delta.</P>

      @see  #newWriterForAppendable(Appendable) newWriterForAppendable(apbl)
    **/
   public static final Closeable CLOSEABLE_DO_NOTHING = new Closeable()  {
      public void close()  {
      }
   };
   /**
      <P>Creates a new {@code java.io.Writer} that wraps around a {@code java.lang.Appendable}. It properly {@link java.io.Writer#flush() flush}es and {@link java.io.Writer#close() close}s appendables that happened to also be {@link java.io.Flushable}s and/or {@link java.io.Closeable Closeable}s. This uses {@code instanceof} only in the constructor, and a (Java 1.5) delta in {@code flush()} and {@code close()}, which avoids having to use any logic or reflection after object construction.</P>

      <P>This function is released as a <A HREF="https://gist.github.com/aliteralmind/8494917">gist</A>, and is an example of the <A HREF="http://en.wikipedia.org/wiki/Adapter_pattern#Object_Adapter_pattern">Object Adapter pattern</A>. Thanks to <A HREF="http://stackoverflow.com/users/1211906/marc-baumbach">Marc Baumbach</A> on <A HREF="http://stackoverflow.com">{@code stackoverflow}</A> for the assistance. See (viewed 1/18/2014)
      <BR> &nbsp; &nbsp; <CODE><A HREF="http://stackoverflow.com/questions/21200421/how-to-wrap-a-java-lang-appendable-into-a-java-io-writer">http://stackoverflow.com/questions/21200421/how-to-wrap-a-java-lang-appendable-into-a-java-io-writer</A></CODE></P>

      @return  A new writer that uses an appendable to do its output.
      @see  #FLUSHABLE_DO_NOTHING
      @see  #CLOSEABLE_DO_NOTHING
    **/
   public static final Writer newWriterForAppendable(Appendable ap_bl)  {
      return  (new WFA(ap_bl));
   }
   private NewWriterForAppendable()  {
      throw  new IllegalStateException("constructor: Do not instantiate.");
   }
}
class WFA extends Writer  {
   private final Appendable apbl;
   private final Flushable  flbl;
   private final Closeable  clbl;
   public WFA(Appendable ap_bl)  {
      if(ap_bl == null)  {
         throw  new NullPointerException("newWriterForAppendable: ap_bl");
      }
      apbl = ap_bl;

      //Avoids instanceof at every call to flush() and close()
      flbl = (Flushable)((ap_bl instanceof Flushable) ? ap_bl
         :  NewWriterForAppendable.FLUSHABLE_DO_NOTHING);
      clbl = (Closeable)((ap_bl instanceof Closeable) ? ap_bl
         :  NewWriterForAppendable.CLOSEABLE_DO_NOTHING);
   }
   @Override
   public void write(char[] a_c, int i_ndexStart, int i_ndexEndX) throws IOException {
      apbl.append(String.valueOf(a_c), i_ndexStart, i_ndexEndX);
   }
   @Override
   public Writer append(char c_c) throws IOException {
      apbl.append(c_c);
      return  this;
   }
   @Override
   public Writer append(CharSequence c_q) throws IOException {
      apbl.append(c_q);
      return  this;
   }
   @Override
   public Writer append(CharSequence c_q, int i_ndexStart, int i_ndexEndX) throws IOException  {
      apbl.append(c_q, i_ndexStart, i_ndexEndX);
      return  this;
   }
   @Override
   public void flush() throws IOException {
      flbl.flush();
   }
   @Override
   public void close() throws IOException {
      flush();
      clbl.close();
   }

}