User guideCommons-IO contains utility classes, endian classes, line iterator, file filters, file comparators and stream implementations. For a more detailed descriptions, take a look at the Javadocs. Utility classesIOUtilsIOUtils 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 be done like this: InputStream in = new URL( "https://commons.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( "https://commons.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! FileUtilsThe 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"); FilenameUtilsThe 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" FileSystemUtilsThe 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:/"); Endian classesDifferent 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:
For more information, see http://www.cs.umass.edu/~verts/cs32/endian.html Line iterator
The LineIterator it = FileUtils.lineIterator(file, "UTF-8"); try { while (it.hasNext()) { String line = it.nextLine(); /// do something with line } } finally { LineIterator.closeQuietly(iterator); } File filters
The See the filefilter package Javadoc for more details. File comparators
The See the comparator package Javadoc for more details. Safe DeserializationYou can safely deserialize any input using a ValidatingObjectInputStream.
Here is the only way to safely read a ValidatingObjectInputStream vois = ValidatingObjectInputStream.builder() .setPath(Paths.get("MyFile.ser")) .get(); vois.accept(HashMap.class, Number.class, Integer.class); HashMap<String, Integer> map2 = (HashMap<String, Integer>) vois.readObject(); Here is an example that performs a roundtrip: // Data final HashMap<String, Integer> map1 = new HashMap<>(); map1.put("1", 1); // Write final byte[] byteArray; try (ByteArrayOutputStream baos = new ByteArrayOutputStream(); final ObjectOutputStream oos = new ObjectOutputStream(baos)) { oos.writeObject(map1); oos.flush(); byteArray = baos.toByteArray(); } // Read try (ByteArrayInputStream bais = new ByteArrayInputStream(byteArray); ValidatingObjectInputStream vois = ValidatingObjectInputStream.builder().setInputStream(bais).get()) { // String.class is automatically accepted vois.accept(HashMap.class, Number.class, Integer.class); final HashMap<String, Integer< map2 = (HashMap<String, Integer>) vois.readObject(); assertEquals(map1, map2); } // Reusing a configuration final ObjectStreamClassPredicate predicate = new ObjectStreamClassPredicate() .accept(HashMap.class, Number.class, Integer.class); try (ByteArrayInputStream bais = new ByteArrayInputStream(byteArray); ValidatingObjectInputStream vois = ValidatingObjectInputStream.builder() .setPredicate(predicate) .setInputStream(bais) .get()) { // String.class is automatically accepted final HashMap<String, Integer< map2 = (HashMap<String, Integer<) vois.readObject(); assertEquals(map1, map2); } Streams
The
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