Class CharStreams

java.lang.Object
com.google.common.io.CharStreams
@GwtIncompatible public final class CharStreams extends Object
Provides utility methods for working with character streams.
Since:
1.0
Author:
Chris Nokleberg, Bin Zhu, Colin Decker

  • Method Details

    • copy

      @CanIgnoreReturnValue public static long copy(Readable from, Appendable to) throws IOException
      Copies all characters between the Readable and Appendable objects. Does not close or flush either object.
      Parameters:
      from - the object to read from
      to - the object to write to
      Returns:
      the number of characters copied
      Throws:
      IOException - if an I/O error occurs

    • toString

      public static String toString(Readable r) throws IOException
      Reads all characters from a Readable object into a String. Does not close the Readable.

      Java 25+ users: If the input is a Reader, prefer Reader.readAllAsString().

      Parameters:
      r - the object to read from
      Returns:
      a string containing all the characters
      Throws:
      IOException - if an I/O error occurs

    • readLines

      public static List<String> readLines(Readable r) throws IOException
      Reads all of the lines from a Readable object. The lines do not include line-termination characters, but do include other leading and trailing whitespace.

      Does not close the Readable. If reading files or resources you should use the Files.readLines(File, Charset) and Resources.readLines(URL, Charset, LineProcessor) methods.

      This method prioritizes convenience over performance: It reads the entire input into memory immediately. To instead read and process lines individually, use an alternative like BufferedReader.lines().

      Java 25+ users: If the input is a Reader, you may prefer Reader.readAllLines(). The two may have different performance characteristics for different Reader classes and Java versions, but both methods read the entire input into memory immediately, so we discourage use of both when memory usage is a concern.

      Parameters:
      r - the object to read from
      Returns:
      a mutable List containing all the lines
      Throws:
      IOException - if an I/O error occurs

    • readLines

      @CanIgnoreReturnValue public static <T extends @Nullable Object> T readLines(Readable readable, LineProcessor<T> processor) throws IOException
      Streams lines from a Readable object, stopping when the processor returns false or all lines have been read and returning the result produced by the processor. Does not close readable. Note that this method may not fully consume the contents of readable if the processor stops processing early.

      Users who can use Stream: If your input is a Reader, consider wrapping it with a BufferedReader and operating on the Stream of lines returned by BufferedReader.lines().

      Throws:
      IOException - if an I/O error occurs
      Since:
      14.0

    • exhaust

      @CanIgnoreReturnValue public static long exhaust(Readable readable) throws IOException
      Reads and discards data from the given Readable until the end of the stream is reached. Returns the total number of chars read. Does not close the stream.
      Throws:
      IOException
      Since:
      20.0

    • skipFully

      public static void skipFully(Reader reader, long n) throws IOException
      Discards n characters of data from the reader. This method will block until the full amount has been skipped. Does not close the reader.
      Parameters:
      reader - the reader to read from
      n - the number of characters to skip
      Throws:
      EOFException - if this stream reaches the end before skipping all the characters
      IOException - if an I/O error occurs

    • nullWriter

      public static Writer nullWriter()
      Returns a Writer that simply discards written chars.

      Java 11+ users: use Writer.nullWriter() instead. Note that the CharStreams method returns a singleton writer whose close method has no effect, while the Writer.nullWriter() method returns a new instance whose methods throw after the instance is closed.

      Since:
      15.0

    • asWriter

      public static Writer asWriter(Appendable target)
      Returns a Writer that sends all output to the given Appendable target. Closing the writer will close the target if it is Closeable, and flushing the writer will flush the target if it is Flushable.
      Parameters:
      target - the object to which output will be sent
      Returns:
      a new Writer object, unless target is a Writer, in which case the target is returned