1 /*
   2  * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.io.IOException;
  29 import java.nio.CharBuffer;
  30 import java.util.Objects;
  31 
  32 /**
  33  * A {@code Readable} is a source of characters. Characters from
  34  * a {@code Readable} are made available to callers of the read
  35  * method via a {@link java.nio.CharBuffer CharBuffer}.
  36  *
  37  * @since 1.5
  38  */
  39 public interface Readable {
  40 
  41     /**
  42      * Attempts to read characters into the specified character buffer.
  43      * The buffer is used as a repository of characters as-is: the only
  44      * changes made are the results of a put operation. No flipping or
  45      * rewinding of the buffer is performed.
  46      *
  47      * @param cb the buffer to read characters into
  48      * @return The number of {@code char} values added to the buffer,
  49      *                 or -1 if this source of characters is at its end
  50      * @throws IOException if an I/O error occurs
  51      * @throws NullPointerException if cb is null
  52      * @throws java.nio.ReadOnlyBufferException if cb is a read only buffer
  53      */
  54     public int read(java.nio.CharBuffer cb) throws IOException;
  55 
  56     /**
  57      * Reads all characters from this source and appends them to a destination
  58      * in the order in which they are read. On return, the source of characters
  59      * will be at its end.
  60      * <p>
  61      * This method may block indefinitely while reading from the source or
  62      * writing to the destination. If the source or destination is
  63      * {@link AutoCloseable closeable}, then the behavior when either is
  64      * <i>asynchronously closed</i>, or the thread is interrupted during the
  65      * transfer, is highly implementation-dependent and therefore unspecified.
  66      * <p>
  67      * If an I/O error occurs during the operation, then not all characters
  68      * might have been transferred and the source or destination could be
  69      * left in an inconsistent state. The caller of this method should therefore
  70      * ensure in such a case that measures are taken to release any resources
  71      * held by the source and destination.
  72      * <p>
  73      * If the destination is capacity bounded and has insufficient capacity to
  74      * append all characters read from the source then the exception may be
  75      * thrown after transferring some characters to the destination.
  76      *
  77      * @implSpec
  78      * The default implementation invokes the read method to read all characters
  79      * from this source and invokes the {@link Appendable#append(CharSequence, int, int)}
  80      * method to write all characters to the appendable.
  81      *
  82      * The default implementation behaves as if:
  83      * <pre>{@code
  84      *     long transferred = 0;
  85      *     CharBuffer buffer = CharBuffer.allocate(8192);
  86      *     int read;
  87      *     while ((read = this.read(buffer)) >= 0) {
  88      *         buffer.rewind();
  89      *         out.append(buffer, 0, read);
  90      *         transferred += read;
  91      *     }
  92      *     return transferred;
  93      * }</pre>
  94      *
  95      * @implNote
  96      * The default implementation should usually be overridden in cases where
  97      * the implementer is already a {@link CharSequence} or its data is already
  98      * available in the internal representation to avoid the extra overhead of
  99      * a buffer in order to transfer its data to the destination.
 100      *
 101      * @param  out the appendable, non-null
 102      * @return the number of characters transferred
 103      * @throws IOException if an I/O error occurs when reading or writing
 104      * @throws NullPointerException if {@code out} is {@code null}
 105      *
 106      * @since 10
 107      */
 108     public default long transferTo(Appendable out) throws IOException {
 109         Objects.requireNonNull(out, "out");
 110         long transferred = 0;
 111         CharBuffer buffer = CharBuffer.allocate(8192);
 112         int read;
 113         while ((read = this.read(buffer)) >= 0) {
 114             buffer.rewind();
 115             out.append(buffer, 0, read);
 116             transferred += read;
 117         }
 118         return transferred;
 119     }
 120 }