Package com.google.common.io

Class 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 Detail

      • CharSource

        protected CharSource()
        Constructor for use by subclasses.

    • Method Detail

      • asByteSource

        @Beta
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(java.nio.charset.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

      • lengthIfKnown

        @Beta
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

        @Beta
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

      • 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

        @CheckForNull
public 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

        @Beta
@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

      • 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))