Java Reference
In-Depth Information
}
catch
(
IOException
e
)
{
// ...
}
We're making use of the
StandardOpenOption
enum, which provides similar capa‐
bilities to the copy options, but for the case of opening a new file instead.
In this example use case, we have used the
Path
API to:
• Create a
Path
corresponding to a new file
• Use the
Files
class to create that new file
• Open a
Writer
to that file
• Write to that file
• Automatically close it when done
In our next example, we'll build on this to manipulate a
.jar
file as a
FileSystem
in
its own right, modifying it to add an additional file directly into the JAR. JAR files
are just ZIP files, so this technique will also work for
.zip
archives:
Path
tempJar
=
Paths
.
get
(
"sample.jar"
);
try
(
FileSystem
workingFS
=
FileSystems
.
newFileSystem
(
tempJar
,
null
))
{
Path
pathForFile
=
workingFS
.
getPath
(
"/hello.txt"
);
List
<
String
>
ls
=
new
ArrayList
<>();
ls
.
add
(
"Hello World!"
);
Files
.
write
(
pathForFile
,
ls
,
Charset
.
defaultCharset
(),
StandardOpenOption
.
WRITE
,
StandardOpenOption
.
CREATE
);
}
This shows how we use a
FileSystem
to make the
Path
objects inside it, via the
getPath()
method. This enables the developer to effectively treat
FileSystem
objects as black boxes.
One of the criticisms of Java's original I/O APIs was the lack of support for native
and high-performance I/O. A solution was initially added in Java 1.4, the Java New
I/O (NIO) API, and it has been successively refined in successive Java versions.
NIO Channels and Bufers
NIO buffers are a low-level abstraction for high-performance I/O. They provide a
container for a linear sequence of elements of a specific primitive type. We'll work
with the
ByteBuffer
(the most common case) in our examples.
ByteBufer
This is a sequence of bytes, and can conceptually be thought of as a performance-
critical alternative to working with a
byte[]
. To get the best possible performance,
