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="copy
" methods="methods" that="that" let="let" you="you" specify="specify" the="the" buffer="buffer" size="size" because="because" in="in" modern="modern" VMs="VMs" the="the" impact="impact" on="on" speed="speed" seems="seems" to="to" be="be" minimal.="minimal." We're="We're" using="using" a="a" default="default" buffer="buffer" size="size" of="of" 4="4"/>
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.
copy
public static int copy(InputStream input,
OutputStream output)
throws IOException
Copy bytes from an InputStream
to an
OutputStream
.
input
- the InputStream
to read fromoutput
- the OutputStream
to write to
- the number of bytes copied
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.
input
- the InputStream
to read fromoutput
- the Writer
to write to
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.
input
- the InputStream
to read fromoutput
- the Writer
to write toencoding
- The name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.
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
.
input
- the Reader
to read fromoutput
- the OutputStream
to write to
copy
public static int copy(Reader input,
Writer output)
throws IOException
Copy chars from a Reader
to a Writer
.
input
- the Reader
to read fromoutput
- the Writer
to write to
- the number of characters copied
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
.
input
- the String
to read fromoutput
- the OutputStream
to write to
copy
public static void copy(String input,
Writer output)
throws IOException
Copy chars from a String
to a Writer
.
input
- the String
to read fromoutput
- the Writer
to write to
copy
public static void copy(byte[] input,
OutputStream output)
throws IOException
Copy bytes from a byte[]
to an OutputStream
.
input
- the byte array to read fromoutput
- the OutputStream
to write to
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.
input
- the byte array to read fromoutput
- the Writer
to write to
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.
input
- the byte array to read fromoutput
- the Writer
to write toencoding
- The name of a supported character encoding. See the
IANA
Charset Registry for a list of valid encoding types.