org.apache.commons.io
Class IOUtils

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

public final class IOUtils

extends java.lang.Object

General IO Stream manipulation.

This class provides static utility methods for input/output operations, particularly 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     toString    InputStream         String          3
 5     toByteArray InputStream         byte[]          1

 6     copy        Reader              OutputStream    2
 7     toString    Reader              String          2
 8     toByteArray Reader              byte[]          6

 9     copy        String              OutputStream    2
 10    copy        String              Writer          (trivial)
 11    toByteArray String              byte[]          9

 12    copy        byte[]              Writer          3
 13    toString    byte[]              String          12
 14    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:

CVS $Revision: 1.12 $ $Date: 2003/12/30 16:35:11 $

Author:

Peter Donald, Jeff Turner

Field Summary

private static int

DEFAULT_BUFFER_SIZE

Constructor Summary

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

Method Summary

static void	closeQuietly(java.io.InputStream input) Unconditionally close an InputStream.
static void	closeQuietly(java.io.OutputStream output) Unconditionally close an OutputStream.
static void	closeQuietly(java.io.Reader input) Unconditionally close an Reader.
static void	closeQuietly(java.io.Writer output) Unconditionally close an Writer.
static boolean	contentEquals(java.io.InputStream input1, java.io.InputStream input2) Compare the contents of two Streams to determine if they are equal or not.
static byte[]	toByteArray(java.io.InputStream input) Get the contents of an InputStream as a byte[].
static byte[]	toByteArray(java.io.Reader input) Get the contents of a Reader as a byte[].
static byte[]	toByteArray(java.lang.String input) Get the contents of a String as a byte[].
static java.lang.String	toString(byte[] input) Get the contents of a byte[] as a String.
static java.lang.String	toString(byte[] input, java.lang.String encoding) Get the contents of a byte[] as a String.
static java.lang.String	toString(java.io.InputStream input) Get the contents of an InputStream as a String.
static java.lang.String	toString(java.io.InputStream input, java.lang.String encoding) Get the contents of an InputStream as a String.
static java.lang.String	toString(java.io.Reader input) Get the contents of a Reader as a String.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_BUFFER_SIZE

private static final int DEFAULT_BUFFER_SIZE

See Also:

Constant Field Values

Constructor Detail

IOUtils

public IOUtils()

Instances should NOT be constructed in standard programming.

Method Detail

closeQuietly

public static void closeQuietly(java.io.Reader input)

Unconditionally close an Reader. Equivalent to Reader.close(), except any exceptions will be ignored.

Parameters:

input - A (possibly null) Reader

closeQuietly

public static void closeQuietly(java.io.Writer output)

Unconditionally close an Writer. Equivalent to Writer.close(), except any exceptions will be ignored.

Parameters:

output - A (possibly null) Writer

closeQuietly

public static void closeQuietly(java.io.OutputStream output)

Unconditionally close an OutputStream. Equivalent to OutputStream.close(), except any exceptions will be ignored.

Parameters:

output - A (possibly null) OutputStream

closeQuietly

public static void closeQuietly(java.io.InputStream input)

Unconditionally close an InputStream. Equivalent to InputStream.close(), except any exceptions will be ignored.

Parameters:

input - A (possibly null) InputStream

toString

public static java.lang.String toString(java.io.InputStream input)
                                 throws java.io.IOException

Get the contents of an InputStream as a String. The platform's default encoding is used for the byte-to-char conversion.

Parameters:

input - the InputStream to read from

Returns:

the requested String

Throws:

java.io.IOException - In case of an I/O problem

toString

public static java.lang.String toString(java.io.InputStream input,
                                        java.lang.String encoding)
                                 throws java.io.IOException

Get the contents of an InputStream as a String.

Parameters:

input - the InputStream to read from

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

Returns:

the requested String

Throws:

java.io.IOException - In case of an I/O problem

toByteArray

public static byte[] toByteArray(java.io.InputStream input)
                          throws java.io.IOException

Get the contents of an InputStream as a byte[].

Parameters:

input - the InputStream to read from

Returns:

the requested byte array

Throws:

java.io.IOException - In case of an I/O problem

toString

public static java.lang.String toString(java.io.Reader input)
                                 throws java.io.IOException

Get the contents of a Reader as a String.

Parameters:

input - the Reader to read from

Returns:

the requested String

Throws:

java.io.IOException - In case of an I/O problem

toByteArray

public static byte[] toByteArray(java.io.Reader input)
                          throws java.io.IOException

Get the contents of a Reader as a byte[].

Parameters:

input - the Reader to read from

Returns:

the requested byte array

Throws:

java.io.IOException - In case of an I/O problem

toByteArray

public static byte[] toByteArray(java.lang.String input)
                          throws java.io.IOException

Get the contents of a String as a byte[].

Parameters:

input - the String to convert

Returns:

the requested byte array

Throws:

java.io.IOException - In case of an I/O problem

toString

public static java.lang.String toString(byte[] input)
                                 throws java.io.IOException

Get the contents of a byte[] as a String. The platform's default encoding is used for the byte-to-char conversion.

Parameters:

input - the byte array to read from

Returns:

the requested String

Throws:

java.io.IOException - In case of an I/O problem

toString

public static java.lang.String toString(byte[] input,
                                        java.lang.String encoding)
                                 throws java.io.IOException

Get the contents of a byte[] as a String.

Parameters:

input - the byte array to read from

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

Returns:

the requested String

Throws:

java.io.IOException - In case of an I/O problem

contentEquals

public static boolean contentEquals(java.io.InputStream input1,
                                    java.io.InputStream input2)
                             throws java.io.IOException

Compare the contents of two Streams to determine if they are equal or not.

Parameters:

input1 - the first stream

input2 - the second stream

Returns:

true if the content of the streams are equal or they both don't exist, false otherwise

Throws:

java.io.IOException - In case of an I/O problem