Java example source code file (CharSource.java)

This example Java source code file (CharSource.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, asbytesource, beta, bufferedreader, charsequencecharsource, charsource, closer, concatenatedcharsource, emptycharsource, ioexception, optional, override, reader, string, throwable, util

The CharSource.java Java example source code

/*
 * 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.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Ascii;
import com.google.common.base.Optional;
import com.google.common.base.Splitter;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.io.Writer;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.List;

import javax.annotation.Nullable;

/**
 * A readable source of characters, such as a text file. Unlike a {@link Reader}, a
 * {@code CharSource} is not an open, stateful stream of characters that can be read and closed.
 * Instead, it is an immutable <i>supplier of {@code Reader} instances.
 *
 * <p>{@code CharSource} provides two kinds of methods:
 * <ul>
 * <li>Methods that return a reader: These methods should return a new, independent
 *     instance each time they are called. The caller is responsible for ensuring that the returned
 *     reader is closed.
 * <li>Convenience methods: These are implementations of common operations that are typically
 *     implemented by opening a reader using one of the methods in the first category, doing
 *     something and finally closing the reader that was opened.
 * </ul>
 *
 * <p>Several methods in this class, such as {@link #readLines()}, break the contents of the source
 * into lines. Like {@link BufferedReader}, these methods break lines on any of {@code \n},
 * {@code \r} or {@code \r\n}, do not include the line separator in each line and do not consider
 * there to be an empty line at the end if the contents are terminated with a line separator.
 *
 * <p>Any {@link ByteSource} containing text encoded with a specific {@linkplain Charset character
 * encoding} may be viewed as a {@code CharSource} using {@link ByteSource#asCharSource(Charset)}.
 *
 * @since 14.0
 * @author Colin Decker
 */
@GwtIncompatible
public abstract class CharSource {

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

  /**
   * Returns a {@link ByteSource} view of this char source that encodes chars read from this source
   * as bytes using the given {@link Charset}.
   *
   * <p>If {@link ByteSource#asCharSource} is called on the returned source with the same charset,
   * the default implementation of this method will ensure that the original {@code CharSource} is
   * returned, rather than round-trip encoding. Subclasses that override this method should behave
   * the same way.
   *
   * @since 20.0
   */
  @Beta
  public ByteSource asByteSource(Charset charset) {
    return new AsByteSource(charset);
  }

  /**
   * Opens a new {@link Reader} for reading from this source. This method should return a new,
   * independent reader each time it is called.
   *
   * <p>The caller is responsible for ensuring that the returned reader is closed.
   *
   * @throws IOException if an I/O error occurs in the process of opening the reader
   */
  public abstract Reader openStream() throws IOException;

  /**
   * Opens a new {@link BufferedReader} for reading from this source. This method should return a
   * new, independent reader each time it is called.
   *
   * <p>The caller is responsible for ensuring that the returned reader is closed.
   *
   * @throws IOException if an I/O error occurs in the process of opening the reader
   */
  public BufferedReader openBufferedStream() throws IOException {
    Reader reader = openStream();
    return (reader instanceof BufferedReader)
        ? (BufferedReader) reader
        : new BufferedReader(reader);
  }

  /**
   * Returns the size of this source in chars, if the size can be easily determined without actually
   * opening the data stream.
   *
   * <p>The default implementation returns {@link Optional#absent}. Some sources, such as a
   * {@code CharSequence}, may return a non-absent value. Note that in such cases, it is
   * <i>possible that this method will return a different number of chars than would be returned
   * by reading all of the chars.
   *
   * <p>Additionally, for mutable sources such as {@code StringBuilder}s, a subsequent read may
   * return a different number of chars if the contents are changed.
   *
   * @since 19.0
   */
  @Beta
  public Optional<Long> lengthIfKnown() {
    return Optional.absent();
  }

  /**
   * Returns the length of this source in chars, even if doing so requires opening and traversing an
   * entire stream. To avoid a potentially expensive operation, see {@link #lengthIfKnown}.
   *
   * <p>The default implementation calls {@link #lengthIfKnown} and returns the value if present. If
   * absent, it will fall back to a heavyweight operation that will open a stream,
   * {@link Reader#skip(long) skip} to the end of the stream, and return the total number of chars
   * that were skipped.
   *
   * <p>Note that for sources that implement {@link #lengthIfKnown} to provide a more efficient
   * implementation, it is <i>possible that this method will return a different number of chars
   * than would be returned by reading all of the chars.
   *
   * <p>In either case, for mutable sources such as files, a subsequent read may return a different
   * number of chars if the contents are changed.
   *
   * @throws IOException if an I/O error occurs in the process of reading the length of this source
   * @since 19.0
   */
  @Beta
  public long length() throws IOException {
    Optional<Long> lengthIfKnown = lengthIfKnown();
    if (lengthIfKnown.isPresent()) {
      return lengthIfKnown.get();
    }

    Closer closer = Closer.create();
    try {
      Reader reader = closer.register(openStream());
      return countBySkipping(reader);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  private long countBySkipping(Reader reader) throws IOException {
    long count = 0;
    long read;
    while ((read = reader.skip(Long.MAX_VALUE)) != 0) {
      count += read;
    }
    return count;
  }

  /**
   * Appends the contents of this source to the given {@link Appendable} (such as a {@link Writer}).
   * Does not close {@code appendable} if it is {@code Closeable}.
   *
   * @return the number of characters copied
   * @throws IOException if an I/O error occurs in the process of reading from this source or
   *     writing to {@code appendable}
   */
  @CanIgnoreReturnValue
  public long copyTo(Appendable appendable) throws IOException {
    checkNotNull(appendable);

    Closer closer = Closer.create();
    try {
      Reader reader = closer.register(openStream());
      return CharStreams.copy(reader, appendable);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Copies the contents of this source to the given sink.
   *
   * @return the number of characters copied
   * @throws IOException if an I/O error occurs in the process of reading from this source or
   *     writing to {@code sink}
   */
  @CanIgnoreReturnValue
  public long copyTo(CharSink sink) throws IOException {
    checkNotNull(sink);

    Closer closer = Closer.create();
    try {
      Reader reader = closer.register(openStream());
      Writer writer = closer.register(sink.openStream());
      return CharStreams.copy(reader, writer);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Reads the contents of this source as a string.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source
   */
  public String read() throws IOException {
    Closer closer = Closer.create();
    try {
      Reader reader = closer.register(openStream());
      return CharStreams.toString(reader);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Reads the first link of this source as a string. Returns {@code null} if this source is empty.
   *
   * <p>Like {@link BufferedReader}, this method breaks lines on any of {@code \n}, {@code \r} or
   * {@code \r\n}, does not include the line separator in the returned line and does not consider
   * there to be an extra empty line at the end if the content is terminated with a line separator.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source
   */
  @Nullable
  public String readFirstLine() throws IOException {
    Closer closer = Closer.create();
    try {
      BufferedReader reader = closer.register(openBufferedStream());
      return reader.readLine();
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Reads all the lines of this source as a list of strings. The returned list will be empty if
   * this source is empty.
   *
   * <p>Like {@link BufferedReader}, this method breaks lines on any of {@code \n}, {@code \r} or
   * {@code \r\n}, does not include the line separator in the returned lines and does not consider
   * there to be an extra empty line at the end if the content is terminated with a line separator.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source
   */
  public ImmutableList<String> readLines() throws IOException {
    Closer closer = Closer.create();
    try {
      BufferedReader reader = closer.register(openBufferedStream());
      List<String> result = Lists.newArrayList();
      String line;
      while ((line = reader.readLine()) != null) {
        result.add(line);
      }
      return ImmutableList.copyOf(result);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Reads lines of text from this source, processing each line as it is read using the given
   * {@link LineProcessor processor}. Stops when all lines have been processed or the processor
   * returns {@code false} and returns the result produced by the processor.
   *
   * <p>Like {@link BufferedReader}, this method breaks lines on any of {@code \n}, {@code \r} or
   * {@code \r\n}, does not include the line separator in the lines passed to the {@code processor}
   * and does not consider there to be an extra empty line at the end if the content is terminated
   * with a line separator.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source or if
   *     {@code processor} throws an {@code IOException}
   * @since 16.0
   */
  @Beta
  @CanIgnoreReturnValue // some processors won't return a useful result
  public <T> T readLines(LineProcessor processor) throws IOException {
    checkNotNull(processor);

    Closer closer = Closer.create();
    try {
      Reader reader = closer.register(openStream());
      return CharStreams.readLines(reader, processor);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Returns whether the source has zero chars. The default implementation returns true if
   * {@link #lengthIfKnown} returns zero, falling back to opening a stream and checking for EOF if
   * the length is not known.
   *
   * <p>Note that, in cases where {@code lengthIfKnown} returns zero, it is possible that
   * chars are actually available for reading. This means that a source may return {@code true} from
   * {@code isEmpty()} despite having readable content.
   *
   * @throws IOException if an I/O error occurs
   * @since 15.0
   */
  public boolean isEmpty() throws IOException {
    Optional<Long> lengthIfKnown = lengthIfKnown();
    if (lengthIfKnown.isPresent() && lengthIfKnown.get() == 0L) {
      return true;
    }
    Closer closer = Closer.create();
    try {
      Reader reader = closer.register(openStream());
      return reader.read() == -1;
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Concatenates multiple {@link CharSource} instances into a single source. Streams returned from
   * the source will contain the concatenated data from the streams of the underlying sources.
   *
   * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will
   * close the open underlying stream.
   *
   * @param sources the sources to concatenate
   * @return a {@code CharSource} containing the concatenated data
   * @since 15.0
   */
  public static CharSource concat(Iterable<? extends CharSource> sources) {
    return new ConcatenatedCharSource(sources);
  }

  /**
   * Concatenates multiple {@link CharSource} instances into a single source. Streams returned from
   * the source will contain the concatenated data from the streams of the underlying sources.
   *
   * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will
   * close the open underlying stream.
   *
   * <p>Note: The input {@code Iterator} will be copied to an {@code ImmutableList} when this method
   * is called. This will fail if the iterator is infinite and may cause problems if the iterator
   * eagerly fetches data for each source when iterated (rather than producing sources that only
   * load data through their streams). Prefer using the {@link #concat(Iterable)} overload if
   * possible.
   *
   * @param sources the sources to concatenate
   * @return a {@code CharSource} containing the concatenated data
   * @throws NullPointerException if any of {@code sources} is {@code null}
   * @since 15.0
   */
  public static CharSource concat(Iterator<? extends CharSource> sources) {
    return concat(ImmutableList.copyOf(sources));
  }

  /**
   * Concatenates multiple {@link CharSource} instances into a single source. Streams returned from
   * the source will contain the concatenated data from the streams of the underlying sources.
   *
   * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will
   * close the open underlying stream.
   *
   * @param sources the sources to concatenate
   * @return a {@code CharSource} containing the concatenated data
   * @throws NullPointerException if any of {@code sources} is {@code null}
   * @since 15.0
   */
  public static CharSource concat(CharSource... sources) {
    return concat(ImmutableList.copyOf(sources));
  }

  /**
   * Returns a view of the given character sequence as a {@link CharSource}. The behavior of the
   * returned {@code CharSource} and any {@code Reader} instances created by it is unspecified if
   * the {@code charSequence} is mutated while it is being read, so don't do that.
   *
   * @since 15.0 (since 14.0 as {@code CharStreams.asCharSource(String)})
   */
  public static CharSource wrap(CharSequence charSequence) {
    return new CharSequenceCharSource(charSequence);
  }

  /**
   * Returns an immutable {@link CharSource} that contains no characters.
   *
   * @since 15.0
   */
  public static CharSource empty() {
    return EmptyCharSource.INSTANCE;
  }

  /**
   * A byte source that reads chars from this source and encodes them as bytes using a charset.
   */
  private final class AsByteSource extends ByteSource {

    final Charset charset;

    AsByteSource(Charset charset) {
      this.charset = checkNotNull(charset);
    }

    @Override
    public CharSource asCharSource(Charset charset) {
      if (charset.equals(this.charset)) {
        return CharSource.this;
      }
      return super.asCharSource(charset);
    }

    @Override
    public InputStream openStream() throws IOException {
      return new ReaderInputStream(CharSource.this.openStream(), charset, 8192);
    }

    @Override
    public String toString() {
      return CharSource.this.toString() + ".asByteSource(" + charset + ")";
    }
  }

  private static class CharSequenceCharSource extends CharSource {

    private static final Splitter LINE_SPLITTER = Splitter.onPattern("\r\n|\n|\r");

    private final CharSequence seq;

    protected CharSequenceCharSource(CharSequence seq) {
      this.seq = checkNotNull(seq);
    }

    @Override
    public Reader openStream() {
      return new CharSequenceReader(seq);
    }

    @Override
    public String read() {
      return seq.toString();
    }

    @Override
    public boolean isEmpty() {
      return seq.length() == 0;
    }

    @Override
    public long length() {
      return seq.length();
    }

    @Override
    public Optional<Long> lengthIfKnown() {
      return Optional.of((long) seq.length());
    }

    /**
     * Returns an iterable over the lines in the string. If the string ends in a newline, a final
     * empty string is not included to match the behavior of BufferedReader/LineReader.readLine().
     */
    private Iterable<String> lines() {
      return new Iterable<String>() {
        @Override
        public Iterator<String> iterator() {
          return new AbstractIterator<String>() {
            Iterator<String> lines = LINE_SPLITTER.split(seq).iterator();

            @Override
            protected String computeNext() {
              if (lines.hasNext()) {
                String next = lines.next();
                // skip last line if it's empty
                if (lines.hasNext() || !next.isEmpty()) {
                  return next;
                }
              }
              return endOfData();
            }
          };
        }
      };
    }

    @Override
    public String readFirstLine() {
      Iterator<String> lines = lines().iterator();
      return lines.hasNext() ? lines.next() : null;
    }

    @Override
    public ImmutableList<String> readLines() {
      return ImmutableList.copyOf(lines());
    }

    @Override
    public <T> T readLines(LineProcessor processor) throws IOException {
      for (String line : lines()) {
        if (!processor.processLine(line)) {
          break;
        }
      }
      return processor.getResult();
    }

    @Override
    public String toString() {
      return "CharSource.wrap(" + Ascii.truncate(seq, 30, "...") + ")";
    }
  }

  private static final class EmptyCharSource extends CharSequenceCharSource {

    private static final EmptyCharSource INSTANCE = new EmptyCharSource();

    private EmptyCharSource() {
      super("");
    }

    @Override
    public String toString() {
      return "CharSource.empty()";
    }
  }

  private static final class ConcatenatedCharSource extends CharSource {

    private final Iterable<? extends CharSource> sources;

    ConcatenatedCharSource(Iterable<? extends CharSource> sources) {
      this.sources = checkNotNull(sources);
    }

    @Override
    public Reader openStream() throws IOException {
      return new MultiReader(sources.iterator());
    }

    @Override
    public boolean isEmpty() throws IOException {
      for (CharSource source : sources) {
        if (!source.isEmpty()) {
          return false;
        }
      }
      return true;
    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }
        result += lengthIfKnown.get();
      }
      return Optional.of(result);
    }

    @Override
    public long length() throws IOException {
      long result = 0L;
      for (CharSource source : sources) {
        result += source.length();
      }
      return result;
    }

    @Override
    public String toString() {
      return "CharSource.concat(" + sources + ")";
    }
  }
}