Class CharSource

java.lang.Object
com.google.common.io.CharSource
@GwtIncompatible public abstract class CharSource extends Object
A readable source of characters, such as a text file. Unlike a Reader, a CharSource is not an open, stateful stream of characters that can be read and closed. Instead, it is an immutable supplier of Reader instances.

CharSource provides two kinds of methods:

  • 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.
  • 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.

Several methods in this class, such as readLines(), break the contents of the source into lines. Like BufferedReader, these methods break lines on any of \n, \r or \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.

Any ByteSource containing text encoded with a specific character encoding may be viewed as a CharSource using ByteSource.asCharSource(Charset).

Note: In general, CharSource is intended to be used for "file-like" sources that provide readers that are:

  • Finite: Many operations, such as length() and read(), will either block indefinitely or fail if the source creates an infinite reader.
  • Non-destructive: A destructive reader will consume or otherwise alter the source as they are read from it. A source that provides such readers will not be reusable, and operations that read from the stream (including length(), in some implementations) will prevent further operations from completing as expected.
Since:
14.0
Author:
Colin Decker

  • Constructor Details

    • CharSource

      protected CharSource()
      Constructor for use by subclasses.

  • Method Details

    • asByteSource

      public ByteSource asByteSource(Charset charset)
      Returns a ByteSource view of this char source that encodes chars read from this source as bytes using the given Charset.

      If ByteSource.asCharSource(Charset) is called on the returned source with the same charset, the default implementation of this method will ensure that the original CharSource is returned, rather than round-trip encoding. Subclasses that override this method should behave the same way.

      Since:
      20.0

    • openStream

      public abstract Reader openStream() throws IOException
      Opens a new Reader for reading from this source. This method returns a new, independent reader each time it is called.

      The caller is responsible for ensuring that the returned reader is closed.

      Throws:
      IOException - if an I/O error occurs while opening the reader

    • openBufferedStream

      public BufferedReader openBufferedStream() throws IOException
      Opens a new BufferedReader for reading from this source. This method returns a new, independent reader each time it is called.

      The caller is responsible for ensuring that the returned reader is closed.

      Throws:
      IOException - if an I/O error occurs while of opening the reader

    • lines

      @MustBeClosed public Stream<String> lines() throws IOException
      Opens a new Stream for reading text one line at a time from this source. This method returns a new, independent stream each time it is called.

      The returned stream is lazy and only reads from the source in the terminal operation. If an I/O error occurs while the stream is reading from the source or when the stream is closed, an UncheckedIOException is thrown.

      Like BufferedReader.readLine(), this method considers a line to be a sequence of text that is terminated by (but does not include) one of \r\n, \r or \n. If the source's content does not end in a line termination sequence, it is treated as if it does.

      The caller is responsible for ensuring that the returned stream is closed. For example: 

      try (Stream<String> lines = source.lines()) {
  lines.map(...)
     .filter(...)
     .forEach(...);
}
      Throws:
      IOException - if an I/O error occurs while opening the stream
      Since:
      22.0 (but only since 33.4.0 in the Android flavor)

    • lengthIfKnown

      public Optional<Long> lengthIfKnown()
      Returns the size of this source in chars, if the size can be easily determined without actually opening the data stream.

      The default implementation returns Optional.absent(). Some sources, such as a CharSequence, may return a non-absent value. Note that in such cases, it is possible that this method will return a different number of chars than would be returned by reading all of the chars.

      Additionally, for mutable sources such as StringBuilders, a subsequent read may return a different number of chars if the contents are changed.

      Since:
      19.0

    • length

      public long length() throws IOException
      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 lengthIfKnown().

      The default implementation calls lengthIfKnown() and returns the value if present. If absent, it will fall back to a heavyweight operation that will open a stream, skip to the end of the stream, and return the total number of chars that were skipped.

      Note that for sources that implement lengthIfKnown() to provide a more efficient implementation, it is possible that this method will return a different number of chars than would be returned by reading all of the chars.

      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 while reading the length of this source
      Since:
      19.0

    • copyTo

      @CanIgnoreReturnValue public long copyTo(Appendable appendable) throws IOException
      Appends the contents of this source to the given Appendable (such as a Writer). Does not close appendable if it is Closeable.
      Returns:
      the number of characters copied
      Throws:
      IOException - if an I/O error occurs while reading from this source or writing to appendable

    • copyTo

      @CanIgnoreReturnValue public long copyTo(CharSink sink) throws IOException
      Copies the contents of this source to the given sink.
      Returns:
      the number of characters copied
      Throws:
      IOException - if an I/O error occurs while reading from this source or writing to sink

    • read

      public String read() throws IOException
      Reads the contents of this source as a string.
      Throws:
      IOException - if an I/O error occurs while reading from this source

    • readFirstLine

      public @Nullable String readFirstLine() throws IOException
      Reads the first line of this source as a string. Returns null if this source is empty.

      Like BufferedReader.readLine(), this method considers a line to be a sequence of text that is terminated by (but does not include) one of \r\n, \r or \n. If the source's content does not end in a line termination sequence, it is treated as if it does.

      Throws:
      IOException - if an I/O error occurs while reading from this source

    • readLines

      public ImmutableList<String> readLines() throws IOException
      Reads all the lines of this source as a list of strings. The returned list will be empty if this source is empty.

      Like BufferedReader.readLine(), this method considers a line to be a sequence of text that is terminated by (but does not include) one of \r\n, \r or \n. If the source's content does not end in a line termination sequence, it is treated as if it does.

      Throws:
      IOException - if an I/O error occurs while reading from this source

    • readLines

      @CanIgnoreReturnValue public <T extends @Nullable Object> T readLines(LineProcessor<T> processor) throws IOException
      Reads lines of text from this source, processing each line as it is read using the given processor. Stops when all lines have been processed or the processor returns false and returns the result produced by the processor.

      Like BufferedReader.readLine(), this method considers a line to be a sequence of text that is terminated by (but does not include) one of \r\n, \r or \n. If the source's content does not end in a line termination sequence, it is treated as if it does.

      Throws:
      IOException - if an I/O error occurs while reading from this source or if processor throws an IOException
      Since:
      16.0

    • forEachLine

      public void forEachLine(Consumer<? super String> action) throws IOException
      Reads all lines of text from this source, running the given action for each line as it is read.

      Like BufferedReader.readLine(), this method considers a line to be a sequence of text that is terminated by (but does not include) one of \r\n, \r or \n. If the source's content does not end in a line termination sequence, it is treated as if it does.

      Throws:
      IOException - if an I/O error occurs while reading from this source or if action throws an UncheckedIOException
      Since:
      22.0 (but only since 33.4.0 in the Android flavor)

    • isEmpty

      public boolean isEmpty() throws IOException
      Returns whether the source has zero chars. The default implementation first checks lengthIfKnown(), returning true if it's known to be zero and false if it's known to be non-zero. If the length is not known, it falls back to opening a stream and checking for EOF.

      Note that, in cases where lengthIfKnown returns zero, it is possible that chars are actually available for reading. This means that a source may return true from isEmpty() despite having readable content.

      Throws:
      IOException - if an I/O error occurs
      Since:
      15.0

    • concat

      public static CharSource concat(Iterable<? extends CharSource> sources)
      Concatenates multiple CharSource instances into a single source. Streams returned from the source will contain the concatenated data from the streams of the underlying sources.

      Only one underlying stream will be open at a time. Closing the concatenated stream will close the open underlying stream.

      Parameters:
      sources - the sources to concatenate
      Returns:
      a CharSource containing the concatenated data
      Since:
      15.0

    • concat

      public static CharSource concat(Iterator<? extends CharSource> sources)
      Concatenates multiple CharSource instances into a single source. Streams returned from the source will contain the concatenated data from the streams of the underlying sources.

      Only one underlying stream will be open at a time. Closing the concatenated stream will close the open underlying stream.

      Note: The input Iterator will be copied to an 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 concat(Iterable) overload if possible.

      Parameters:
      sources - the sources to concatenate
      Returns:
      a CharSource containing the concatenated data
      Throws:
      NullPointerException - if any of sources is null
      Since:
      15.0

    • concat

      public static CharSource concat(CharSource... sources)
      Concatenates multiple CharSource instances into a single source. Streams returned from the source will contain the concatenated data from the streams of the underlying sources.

      Only one underlying stream will be open at a time. Closing the concatenated stream will close the open underlying stream.

      Parameters:
      sources - the sources to concatenate
      Returns:
      a CharSource containing the concatenated data
      Throws:
      NullPointerException - if any of sources is null
      Since:
      15.0

    • wrap

      public static CharSource wrap(CharSequence charSequence)
      Returns a view of the given character sequence as a CharSource. The behavior of the returned CharSource and any Reader instances created by it is unspecified if the charSequence is mutated while it is being read, so don't do that.
      Since:
      15.0 (since 14.0 as CharStreams.asCharSource(String))

    • empty

      public static CharSource empty()
      Returns an immutable CharSource that contains no characters.
      Since:
      15.0