001/*
002 * Copyright (C) 2012 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.io;
018
019import static com.google.common.base.Preconditions.checkNotNull;
020
021import java.io.BufferedOutputStream;
022import java.io.IOException;
023import java.io.InputStream;
024import java.io.OutputStream;
025import java.io.OutputStreamWriter;
026import java.io.Writer;
027import java.nio.charset.Charset;
028
029/**
030 * A destination to which bytes can be written, such as a file. Unlike an {@link OutputStream}, a
031 * {@code ByteSink} is not an open, stateful stream that can be written to and closed. Instead, it
032 * is an immutable <i>supplier</i> of {@code OutputStream} instances.
033 *
034 * <p>{@code ByteSink} provides two kinds of methods:
035 * <ul>
036 *   <li><b>Methods that return a stream:</b> These methods should return a <i>new</i>, independent
037 *   instance each time they are called. The caller is responsible for ensuring that the returned
038 *   stream is closed.
039 *   <li><b>Convenience methods:</b> These are implementations of common operations that are
040 *   typically implemented by opening a stream using one of the methods in the first category, doing
041 *   something and finally closing the stream or channel that was opened.
042 * </ul>
043 *
044 * @since 14.0
045 * @author Colin Decker
046 */
047public abstract class ByteSink {
048
049  /**
050   * Constructor for use by subclasses.
051   */
052  protected ByteSink() {}
053
054  /**
055   * Returns a {@link CharSink} view of this {@code ByteSink} that writes characters to this sink
056   * as bytes encoded with the given {@link Charset charset}.
057   */
058  public CharSink asCharSink(Charset charset) {
059    return new AsCharSink(charset);
060  }
061
062  /**
063   * Opens a new {@link OutputStream} for writing to this sink. This method should return a new,
064   * independent stream each time it is called.
065   *
066   * <p>The caller is responsible for ensuring that the returned stream is closed.
067   *
068   * @throws IOException if an I/O error occurs in the process of opening the stream
069   */
070  public abstract OutputStream openStream() throws IOException;
071
072  /**
073   * Opens a new buffered {@link OutputStream} for writing to this sink. The returned stream is
074   * not required to be a {@link BufferedOutputStream} in order to allow implementations to simply
075   * delegate to {@link #openStream()} when the stream returned by that method does not benefit
076   * from additional buffering (for example, a {@code ByteArrayOutputStream}). This method should
077   * return a new, independent stream each time it is called.
078   *
079   * <p>The caller is responsible for ensuring that the returned stream is closed.
080   *
081   * @throws IOException if an I/O error occurs in the process of opening the stream
082   * @since 15.0 (in 14.0 with return type {@link BufferedOutputStream})
083   */
084  public OutputStream openBufferedStream() throws IOException {
085    OutputStream out = openStream();
086    return (out instanceof BufferedOutputStream)
087        ? (BufferedOutputStream) out
088        : new BufferedOutputStream(out);
089  }
090
091  /**
092   * Writes all the given bytes to this sink.
093   *
094   * @throws IOException if an I/O occurs in the process of writing to this sink
095   */
096  public void write(byte[] bytes) throws IOException {
097    checkNotNull(bytes);
098
099    Closer closer = Closer.create();
100    try {
101      OutputStream out = closer.register(openStream());
102      out.write(bytes);
103      out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
104    } catch (Throwable e) {
105      throw closer.rethrow(e);
106    } finally {
107      closer.close();
108    }
109  }
110
111  /**
112   * Writes all the bytes from the given {@code InputStream} to this sink. Does not close
113   * {@code input}.
114   *
115   * @throws IOException if an I/O occurs in the process of reading from {@code input} or writing to
116   *     this sink
117   */
118  public long writeFrom(InputStream input) throws IOException {
119    checkNotNull(input);
120
121    Closer closer = Closer.create();
122    try {
123      OutputStream out = closer.register(openStream());
124      long written = ByteStreams.copy(input, out);
125      out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
126      return written;
127    } catch (Throwable e) {
128      throw closer.rethrow(e);
129    } finally {
130      closer.close();
131    }
132  }
133
134  /**
135   * A char sink that encodes written characters with a charset and writes resulting bytes to this
136   * byte sink.
137   */
138  private final class AsCharSink extends CharSink {
139
140    private final Charset charset;
141
142    private AsCharSink(Charset charset) {
143      this.charset = checkNotNull(charset);
144    }
145
146    @Override
147    public Writer openStream() throws IOException {
148      return new OutputStreamWriter(ByteSink.this.openStream(), charset);
149    }
150
151    @Override
152    public String toString() {
153      return ByteSink.this.toString() + ".asCharSink(" + charset + ")";
154    }
155  }
156}