org.apache.commons.io
Class CopyUtils

java.lang.Object
  org.apache.commons.io.CopyUtils

public class CopyUtils
extends Object

This class provides static utility methods for buffered copying between sources (InputStream, Reader, String and byte[]) and destinations (OutputStream, Writer, String and byte[]).

Unless otherwise noted, these copy methods do not flush or close the streams. Often doing so would require making non-portable assumptions about the streams' origin and further use. This means that both streams' close() methods must be called after copying. if one omits this step, then the stream resources (sockets, file descriptors) are released when the associated Stream is garbage-collected. It is not a good idea to rely on this mechanism. For a good overview of the distinction between "memory management" and "resource management", see this UnixReview article.

For byte-to-char methods, a copy variant allows the encoding to be selected (otherwise the platform default is used). We would like to encourage you to always specify the encoding because relying on the platform default can lead to unexpected results.

We don't provide special variants for the copy methods that let you specify the buffer size because in modern VMs the impact on speed seems to be minimal. We're using a default buffer size of 4 KB.

The copy methods use an internal buffer when copying. It is therefore advisable not to deliberately wrap the stream arguments to the copy methods in Buffered* streams. For example, don't do the following:

copy( new BufferedInputStream( in ), new BufferedOutputStream( out ) );

The rationale is as follows:

Imagine that an InputStream's read() is a very expensive operation, which would usually suggest wrapping in a BufferedInputStream. The BufferedInputStream works by issuing infrequent InputStream.read(byte[] b, int off, int len) requests on the underlying InputStream, to fill an internal buffer, from which further read requests can inexpensively get their data (until the buffer runs out).

However, the copy methods do the same thing, keeping an internal buffer, populated by InputStream.read(byte[] b, int off, int len) requests. Having two buffers (or three if the destination stream is also buffered) is pointless, and the unnecessary buffer management hurts performance slightly (about 3%, according to some simple experiments).

Behold, intrepid explorers; a map of this class:

       Method      Input               Output          Dependency
       ------      -----               ------          -------
 1     copy        InputStream         OutputStream    (primitive)
 2     copy        Reader              Writer          (primitive)

 3     copy        InputStream         Writer          2

 4     copy        Reader              OutputStream    2

 5     copy        String              OutputStream    2
 6     copy        String              Writer          (trivial)

 7     copy        byte[]              Writer          3
 8     copy        byte[]              OutputStream    (trivial)
 

Note that only the first two methods shuffle bytes; the rest use these two, or (if possible) copy using native Java copy methods. As there are method variants to specify the encoding, each row may correspond to up to 2 methods.

Origin of code: Apache Avalon (Excalibur)

Version:

$Id: CopyUtils.java 140571 2004-04-24 23:49:25Z bayard $

Author:

Peter Donald, Jeff Turner, Matthew Hawthorne

Constructor Summary

CopyUtils()
Instances should NOT be constructed in standard programming.

Method Summary

static void	copy(byte[] input, OutputStream output) Copy bytes from a byte[] to an OutputStream.
static void	copy(byte[] input, Writer output) Copy and convert bytes from a byte[] to chars on a Writer.
static void	copy(byte[] input, Writer output, String encoding) Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.
static int	copy(InputStream input, OutputStream output) Copy bytes from an InputStream to an OutputStream.
static void	copy(InputStream input, Writer output) Copy and convert bytes from an InputStream to chars on a Writer.
static void	copy(InputStream input, Writer output, String encoding) Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.
static void	copy(Reader input, OutputStream output) Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.
static int	copy(Reader input, Writer output) Copy chars from a Reader to a Writer.
static void	copy(String input, OutputStream output) Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.
static void	copy(String input, Writer output) Copy chars from a String to a Writer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CopyUtils

public CopyUtils()

Instances should NOT be constructed in standard programming.

Method Detail

copy

public static void copy(byte[] input,
                        OutputStream output)
                 throws IOException

Copy bytes from a byte[] to an OutputStream.

Parameters:

input - the byte array to read from

output - the OutputStream to write to

Throws:

IOException - In case of an I/O problem

copy

public static void copy(byte[] input,
                        Writer output)
                 throws IOException

Copy and convert bytes from a byte[] to chars on a Writer. The platform's default encoding is used for the byte-to-char conversion.

Parameters:

input - the byte array to read from

output - the Writer to write to

Throws:

IOException - In case of an I/O problem

copy

public static void copy(byte[] input,
                        Writer output,
                        String encoding)
                 throws IOException

Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.

Parameters:

input - the byte array to read from

output - the Writer to write to

encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.

Throws:

IOException - In case of an I/O problem

copy

public static int copy(InputStream input,
                       OutputStream output)
                throws IOException

Copy bytes from an InputStream to an OutputStream.

Parameters:

input - the InputStream to read from

output - the OutputStream to write to

Returns:

the number of bytes copied

Throws:

IOException - In case of an I/O problem

copy

public static int copy(Reader input,
                       Writer output)
                throws IOException

Copy chars from a Reader to a Writer.

Parameters:

input - the Reader to read from

output - the Writer to write to

Returns:

the number of characters copied

Throws:

IOException - In case of an I/O problem

copy

public static void copy(InputStream input,
                        Writer output)
                 throws IOException

Copy and convert bytes from an InputStream to chars on a Writer. The platform's default encoding is used for the byte-to-char conversion.

Parameters:

input - the InputStream to read from

output - the Writer to write to

Throws:

IOException - In case of an I/O problem

copy

public static void copy(InputStream input,
                        Writer output,
                        String encoding)
                 throws IOException

Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.

Parameters:

input - the InputStream to read from

output - the Writer to write to

encoding - The name of a supported character encoding. See the IANA Charset Registry for a list of valid encoding types.

Throws:

IOException - In case of an I/O problem

copy

public static void copy(Reader input,
                        OutputStream output)
                 throws IOException

Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.

Parameters:

input - the Reader to read from

output - the OutputStream to write to

Throws:

IOException - In case of an I/O problem

copy

public static void copy(String input,
                        OutputStream output)
                 throws IOException

Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.

Parameters:

input - the String to read from

output - the OutputStream to write to

Throws:

IOException - In case of an I/O problem

copy

public static void copy(String input,
                        Writer output)
                 throws IOException

Copy chars from a String to a Writer.

Parameters:

input - the String to read from

output - the Writer to write to

Throws:

IOException - In case of an I/O problem