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Jakarta Commons IO
1.1 has been released. Commons IO provides low level utilities, file filters and
streams that probably should be in the JDK.
This release fixes all open bugs and adds various enhancements. These include
FileSystemUtils, which allows you to obtain the free space on a drive, and
FilenameUtils which allows you to manipulate filenames without using File
objects.
Commons IO is a library of utilities to assist with developing IO functionality.
There are three main areas included:
- Utility classes - with static methods to perform common tasks
- Filters - various implementations of file filters
- Streams - useful stream, reader and writer implementations
IOUtils contains utility methods dealing with reading, writing and
copying. The methods work on InputStream, OutputStream, Reader and Writer.
As an example, consider the task of reading bytes from a URL, and printing them.
This would typically done like this:
InputStream in = new URL( "http://jakarta.apache.org" ).openStream();
try {
InputStreamReader inR = new InputStreamReader( in );
BufferedReader buf = new BufferedReader( inR );
String line;
while ( ( line = buf.readLine() ) != null ) {
System.out.println( line );
}
} finally {
in.close();
}
With the IOUtils class, that could be done with:
InputStream in = new URL( "http://jakarta.apache.org" ).openStream();
try {
System.out.println( IOUtils.toString( in ) );
} finally {
IOUtils.closeQuietly(in);
}
In certain application domains, such IO operations are common, and this class
can save a great deal of time. And you can rely on well-tested code.
For utility code such as this, flexibility and speed are of primary importance.
However you should also understand the limitations of this approach. Using the
above technique to read a 1GB file would result in an attempt to create a 1GB
String object!
The FileUtils class contains utility methods for working with File
objects. These include reading, writing, copying and comparing files.
For example to read an entire file line by line you could use:
File file = new File("/commons/io/project.properties");
List lines = FileUtils.readLines(file, "UTF-8");
The FilenameUtils class contains utility methods for working with
filenames without using File objects. The class aims to be consistent
between Unix and Windows, to aid transitions between these environments (such as
moving from development to production).
For example to normalize a filename removing double dot segments:
String filename = "C:/commons/io/../lang/project.xml";
String normalized = FilenameUtils.normalize(filename);
// result is "C:/commons/lang/project.xml"
The FileSystemUtils class contains utility methods for working with
the file system to access functionality not supported by the JDK. Currently, the
only method is to get the free space on a drive. Note that this uses the command
line, not native code.
For example to find the free space on a drive:
long freeSpace = FileSystemUtils.freeSpace("C:/");
Different computer architectures adopt different conventions for byte
ordering. In so-called "Little Endian" architectures (eg Intel), the
low-order byte is stored in memory at the lowest address, and subsequent bytes
at higher addresses. For "Big Endian" architectures (eg Motorola), the
situation is reversed.
There are two classes in this package of relevance:
- The EndianUtils class contains static methods for swapping the
Endian-ness of Java primitives and streams.
- The SwappedDataInputStream class is an implementation of the DataInput
interface. With this, one can read data from files of non-native
Endian-ness.
For more information, see http://www.cs.umass.edu/~verts/cs32/endian.html
The org.apache.commons.io.filefilter package defines an
interface (IOFileFilter) that combines both java.io.FileFilter
and java.io.FilenameFilter. Besides that the package offers a
series of ready-to-use implementations of the IOFileFilter
interface including implementation that allow you to combine other such filters.
These filters can be used to list files or in FileDialog, for example.
See the filefilter package javadoc for more details.
The org.apache.commons.io.input and org.apache.commons.io.output
packages contain various useful implementations of streams. These include:
- Null output stream - that silently absorbs all data sent to it
- Tee output stream - that sends output data to two streams instead of one
- Byte array output stream - that is a faster version of the JDK class
- Counting streams - that count the number of bytes passed
- Proxy streams - that delegate to the correct method in the proxy
- Lockable writer - that provides synchronization of writes using a lock
file
See the input or output package javadoc for more details.
This information is from http://jakarta.apache.org/commons/io/
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