src/java.base/share/classes/java/io/Reader.java

*** 1,7 ****
  /*
!  * Copyright (c) 1996, 2012, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
--- 1,7 ----
  /*
!  * Copyright (c) 1996, 2017, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
*** 24,33 ****
--- 24,35 ----
   */
  
  package java.io;
  
  
+ import java.util.Objects;
+ 
  /**
   * Abstract class for reading character streams.  The only methods that a
   * subclass must implement are read(char[], int, int) and close().  Most
   * subclasses, however, will override some of the methods defined here in order
   * to provide higher efficiency, additional functionality, or both.
*** 48,57 ****
--- 50,61 ----
   * @since       1.1
   */
  
  public abstract class Reader implements Readable, Closeable {
  
+     private static final int TRANSFER_BUFFER_SIZE = 8192;
+ 
      /**
       * The object used to synchronize operations on this stream.  For
       * efficiency, a character-stream object may use an object other than
       * itself to protect critical sections.  A subclass should therefore use
       * the object in this field rather than {@code this} or a synchronized
*** 260,265 ****
--- 264,306 ----
       *
       * @exception  IOException  If an I/O error occurs
       */
       public abstract void close() throws IOException;
  
+     /**
+      * Reads all characters from this reader and writes the characters to the
+      * given writer in the order that they are read. On return, this reader
+      * will be at end of the stream. This method does not close either reader
+      * or writer.
+      * <p>
+      * This method may block indefinitely reading from the reader, or
+      * writing to the writer. The behavior for the case where the reader
+      * and/or writer is <i>asynchronously closed</i>, or the thread
+      * interrupted during the transfer, is highly reader and writer
+      * specific, and therefore not specified.
+      * <p>
+      * If an I/O error occurs reading from the reader or writing to the
+      * writer, then it may do so after some characters have been read or
+      * written. Consequently the reader may not be at end of the stream and
+      * one, or both, streams may be in an inconsistent state. It is strongly
+      * recommended that both streams be promptly closed if an I/O error occurs.
+      *
+      * @param  out the writer, non-null
+      * @return the number of characters transferred
+      * @throws IOException if an I/O error occurs when reading or writing
+      * @throws NullPointerException if {@code out} is {@code null}
+      *
+      * @since 10
+      */
+     public long transferTo(Writer out) throws IOException {
+         Objects.requireNonNull(out, "out");
+         long transferred = 0;
+         char[] buffer = new char[TRANSFER_BUFFER_SIZE];
+         int nRead;
+         while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) {
+             out.write(buffer, 0, nRead);
+             transferred += nRead;
+         }
+         return transferred;
+     }
+ 
  }