001/*
002 * Copyright (C) 2012 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.io;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018
019import com.google.common.annotations.GwtIncompatible;
020import com.google.common.annotations.J2ktIncompatible;
021import com.google.errorprone.annotations.CanIgnoreReturnValue;
022import java.io.BufferedOutputStream;
023import java.io.IOException;
024import java.io.InputStream;
025import java.io.OutputStream;
026import java.io.OutputStreamWriter;
027import java.io.Writer;
028import java.nio.charset.Charset;
029
030/**
031 * A destination to which bytes can be written, such as a file. Unlike an {@link OutputStream}, a
032 * {@code ByteSink} is not an open, stateful stream that can be written to and closed. Instead, it
033 * is an immutable <i>supplier</i> of {@code OutputStream} instances.
034 *
035 * <p>{@code ByteSink} provides two kinds of methods:
036 *
037 * <ul>
038 *   <li><b>Methods that return a stream:</b> These methods should return a <i>new</i>, independent
039 *       instance each time they are called. The caller is responsible for ensuring that the
040 *       returned stream is closed.
041 *   <li><b>Convenience methods:</b> These are implementations of common operations that are
042 *       typically implemented by opening a stream using one of the methods in the first category,
043 *       doing something and finally closing the stream or channel that was opened.
044 * </ul>
045 *
046 * @since 14.0
047 * @author Colin Decker
048 */
049@J2ktIncompatible
050@GwtIncompatible
051public abstract class ByteSink {
052
053  /** Constructor for use by subclasses. */
054  protected ByteSink() {}
055
056  /**
057   * Returns a {@link CharSink} view of this {@code ByteSink} that writes characters to this sink as
058   * bytes encoded with the given {@link Charset charset}.
059   */
060  public CharSink asCharSink(Charset charset) {
061    return new AsCharSink(charset);
062  }
063
064  /**
065   * Opens a new {@link OutputStream} for writing to this sink. This method returns a new,
066   * independent stream each time it is called.
067   *
068   * <p>The caller is responsible for ensuring that the returned stream is closed.
069   *
070   * @throws IOException if an I/O error occurs while opening the stream
071   */
072  public abstract OutputStream openStream() throws IOException;
073
074  /**
075   * Opens a new buffered {@link OutputStream} for writing to this sink. The returned stream is not
076   * required to be a {@link BufferedOutputStream} in order to allow implementations to simply
077   * delegate to {@link #openStream()} when the stream returned by that method does not benefit from
078   * additional buffering (for example, a {@code ByteArrayOutputStream}). This method returns a new,
079   * independent stream each time it is called.
080   *
081   * <p>The caller is responsible for ensuring that the returned stream is closed.
082   *
083   * @throws IOException if an I/O error occurs while opening the stream
084   * @since 15.0 (in 14.0 with return type {@link BufferedOutputStream})
085   */
086  public OutputStream openBufferedStream() throws IOException {
087    OutputStream out = openStream();
088    return (out instanceof BufferedOutputStream)
089        ? (BufferedOutputStream) out
090        : new BufferedOutputStream(out);
091  }
092
093  /**
094   * Writes all the given bytes to this sink.
095   *
096   * @throws IOException if an I/O occurs while writing to this sink
097   */
098  public void write(byte[] bytes) throws IOException {
099    checkNotNull(bytes);
100
101    try (OutputStream out = openStream()) {
102      out.write(bytes);
103    }
104  }
105
106  /**
107   * Writes all the bytes from the given {@code InputStream} to this sink. Does not close {@code
108   * input}.
109   *
110   * @return the number of bytes written
111   * @throws IOException if an I/O occurs while reading from {@code input} or writing to this sink
112   */
113  @CanIgnoreReturnValue
114  public long writeFrom(InputStream input) throws IOException {
115    checkNotNull(input);
116
117    try (OutputStream out = openStream()) {
118      return ByteStreams.copy(input, out);
119    }
120  }
121
122  /**
123   * A char sink that encodes written characters with a charset and writes resulting bytes to this
124   * byte sink.
125   */
126  private final class AsCharSink extends CharSink {
127
128    private final Charset charset;
129
130    private AsCharSink(Charset charset) {
131      this.charset = checkNotNull(charset);
132    }
133
134    @Override
135    public Writer openStream() throws IOException {
136      return new OutputStreamWriter(ByteSink.this.openStream(), charset);
137    }
138
139    @Override
140    public String toString() {
141      return ByteSink.this.toString() + ".asCharSink(" + charset + ")";
142    }
143  }
144}