org.apache.commons.io

Class CopyUtils

public class CopyUtils extends Object

Deprecated: Use IOUtils. Will be removed in 2.0. Methods renamed to IOUtils.write() or IOUtils.copy(). Null handling behaviour changed in IOUtils (null data does not throw NullPointerException).

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.

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 java.io.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: Excalibur.

Version: $Id: CopyUtils.java 437680 2006-08-28 11:57:00Z scolebourne $

Author: Peter Donald Jeff Turner Matthew Hawthorne

Field Summary
static intDEFAULT_BUFFER_SIZE
The default size of the buffer.
Constructor Summary
CopyUtils()
Instances should NOT be constructed in standard programming.
Method Summary
static voidcopy(byte[] input, OutputStream output)
Copy bytes from a byte[] to an OutputStream.
static voidcopy(byte[] input, Writer output)
Copy and convert bytes from a byte[] to chars on a Writer.
static voidcopy(byte[] input, Writer output, String encoding)
Copy and convert bytes from a byte[] to chars on a Writer, using the specified encoding.
static intcopy(InputStream input, OutputStream output)
Copy bytes from an InputStream to an OutputStream.
static intcopy(Reader input, Writer output)
Copy chars from a Reader to a Writer.
static voidcopy(InputStream input, Writer output)
Copy and convert bytes from an InputStream to chars on a Writer.
static voidcopy(InputStream input, Writer output, String encoding)
Copy and convert bytes from an InputStream to chars on a Writer, using the specified encoding.
static voidcopy(Reader input, OutputStream output)
Serialize chars from a Reader to bytes on an OutputStream, and flush the OutputStream.
static voidcopy(String input, OutputStream output)
Serialize chars from a String to bytes on an OutputStream, and flush the OutputStream.
static voidcopy(String input, Writer output)
Copy chars from a String to a Writer.

Field Detail

DEFAULT_BUFFER_SIZE

private static final int DEFAULT_BUFFER_SIZE
The default size of the buffer.

Constructor Detail

CopyUtils

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

Method Detail

copy

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

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