common/io/CharSink.java

/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.io;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.stream.Stream;

/**
 * A destination to which characters can be written, such as a text file. Unlike a {@link Writer}, a
 * {@code CharSink} is not an open, stateful stream that can be written to and closed. Instead, it
 * is an immutable <i>supplier</i> of {@code Writer} instances.
 *
 * <p>{@code CharSink} provides two kinds of methods:
 *
 * <ul>
 *   <li><b>Methods that return a writer:</b> These methods should return a <i>new</i>, independent
 *       instance each time they are called. The caller is responsible for ensuring that the
 *       returned writer is closed.
 *   <li><b>Convenience methods:</b> These are implementations of common operations that are
 *       typically implemented by opening a writer using one of the methods in the first category,
 *       doing something and finally closing the writer that was opened.
 * </ul>
 *
 * <p>Any {@link ByteSink} may be viewed as a {@code CharSink} with a specific {@linkplain Charset
 * character encoding} using {@link ByteSink#asCharSink(Charset)}. Characters written to the
 * resulting {@code CharSink} will written to the {@code ByteSink} as encoded bytes.
 *
 * @since 14.0
 * @author Colin Decker
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public abstract class CharSink {

  /** Constructor for use by subclasses. */
  protected CharSink() {}

  /**
   * Opens a new {@link Writer} for writing to this sink. This method returns a new, independent
   * writer each time it is called.
   *
   * <p>The caller is responsible for ensuring that the returned writer is closed.
   *
   * @throws IOException if an I/O error occurs while opening the writer
   */
  public abstract Writer openStream() throws IOException;

  /**
   * Opens a new buffered {@link Writer} for writing to this sink. The returned stream is not
   * required to be a {@link BufferedWriter} in order to allow implementations to simply delegate to
   * {@link #openStream()} when the stream returned by that method does not benefit from additional
   * buffering. This method returns a new, independent writer each time it is called.
   *
   * <p>The caller is responsible for ensuring that the returned writer is closed.
   *
   * @throws IOException if an I/O error occurs while opening the writer
   * @since 15.0 (in 14.0 with return type {@link BufferedWriter})
   */
  public Writer openBufferedStream() throws IOException {
    Writer writer = openStream();
    return (writer instanceof BufferedWriter)
        ? (BufferedWriter) writer
        : new BufferedWriter(writer);
  }

  /**
   * Writes the given character sequence to this sink.
   *
   * @throws IOException if an I/O error while writing to this sink
   */
  public void write(CharSequence charSequence) throws IOException {
    checkNotNull(charSequence);

    Closer closer = Closer.create();
    try {
      Writer out = closer.register(openStream());
      out.append(charSequence);
      out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Writes the given lines of text to this sink with each line (including the last) terminated with
   * the operating system's default line separator. This method is equivalent to {@code
   * writeLines(lines, System.getProperty("line.separator"))}.
   *
   * @throws IOException if an I/O error occurs while writing to this sink
   */
  public void writeLines(Iterable<? extends CharSequence> lines) throws IOException {
    writeLines(lines, System.getProperty("line.separator"));
  }

  /**
   * Writes the given lines of text to this sink with each line (including the last) terminated with
   * the given line separator.
   *
   * @throws IOException if an I/O error occurs while writing to this sink
   */
  public void writeLines(Iterable<? extends CharSequence> lines, String lineSeparator)
      throws IOException {
    writeLines(lines.iterator(), lineSeparator);
  }

  /**
   * Writes the given lines of text to this sink with each line (including the last) terminated with
   * the operating system's default line separator. This method is equivalent to {@code
   * writeLines(lines, System.getProperty("line.separator"))}.
   *
   * @throws IOException if an I/O error occurs while writing to this sink
   * @since 22.0
   */
  public void writeLines(Stream<? extends CharSequence> lines) throws IOException {
    writeLines(lines, System.getProperty("line.separator"));
  }

  /**
   * Writes the given lines of text to this sink with each line (including the last) terminated with
   * the given line separator.
   *
   * @throws IOException if an I/O error occurs while writing to this sink
   * @since 22.0
   */
  public void writeLines(Stream<? extends CharSequence> lines, String lineSeparator)
      throws IOException {
    writeLines(lines.iterator(), lineSeparator);
  }

  private void writeLines(Iterator<? extends CharSequence> lines, String lineSeparator)
      throws IOException {
    checkNotNull(lineSeparator);

    try (Writer out = openBufferedStream()) {
      while (lines.hasNext()) {
        out.append(lines.next()).append(lineSeparator);
      }
    }
  }

  /**
   * Writes all the text from the given {@link Readable} (such as a {@link Reader}) to this sink.
   * Does not close {@code readable} if it is {@code Closeable}.
   *
   * @return the number of characters written
   * @throws IOException if an I/O error occurs while reading from {@code readable} or writing to
   *     this sink
   */
  @CanIgnoreReturnValue
  public long writeFrom(Readable readable) throws IOException {
    checkNotNull(readable);

    Closer closer = Closer.create();
    try {
      Writer out = closer.register(openStream());
      long written = CharStreams.copy(readable, out);
      out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
      return written;
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }
}