When it comes to working with files (reading or writing their content, copying) or folders (copying their content, deleting them), the Apache FileUtils library offers a large number of methods for easily performing these tasks. Some of these are depicted below, together with their usage. For the full reference, check out this page: http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/FileUtils.html.

Importing the library into the project you are working on has to be done by importing the latest org.apache.commons.io package, in which FileUtils is included. The latest version ca be found here: http://commons.apache.org/proper/commons-io/.

Below the most useful of these methods are presented, described, and their usage is exemplified.

Working with files

• writing to files:
  • writeStringToFile(File file, String data): write the string ‘data’ into the file ‘file’, by overwriting any content within the file, if it exists. If the file does not exist, it is created at this step. Usage: writeStringToFile(new File(“pathToFiles/firstFile.txt”), “Some text with writeStringToFile that overwrites file”);
  • writeStringToFile(File file, String data, Charset encoding, boolean append): write the string ‘data’ into the ‘file’ file. The string copied uses the encoding specified as the parameter in the method. Also, the string will be copied at the end of the file if ‘append’ is true(it will be appended to the existing file content, nothing will be erased), or it will erase all the file’s content – if ‘append’ is false. If the file does not exist, it is created at this step. Usage: writeStringToFile(new File(“pathToFiles/firstFile.txt”), “\nSome text with encodȊng, appended and with spacing\n”, Charset.defaultCharset(), true);
  • writeLines(File file, Collection<?> lines, boolean append): write into the specified file ‘file’, the items from the ‘lines’ collection, by appending them to the existing content (if ‘append’ is true) or by overwriting the existing content (if ‘append’ is false). The default separator between the items of the collection will be the new line (each item of the collection will appear on a new line in the file). Usage (writing a list of strings into the file, appending them to the existing content):         writeLines(new File(“pathToFiles/firstFile.txt”), listOfStrings, true); where listOfStrings is, for example: List<String> listOfStrings = ImmutableList.of(“Element 1”, “Element 2”, “Element 3”);
  • writeLines(File file, Collection<?> lines, String lineEnding, boolean append): write into the specified file ‘file’, the items from the ‘lines’ collection, by appending them to the existing content (if ‘append’ is true) or by overwriting the existing content (if ‘append’ is false). The separator between each item will be the one specified by the string parameter ‘lineEnding’. Usage: writeLines(new File(“pathToFiles/firstFile.txt”), listOfStrings, “|”, true); where listOfStrings is, for example: List<String> listOfStrings = ImmutableList.of(“Element 1”, “Element 2”, “Element 3”);
• reading from files:
  • readFileToString(File file): read all the content from the ‘file’, keeping the new line separators (the ‘\n’ ones). Usage: String fileToString = readFileToString(new File(“pathToFiles/copyFile.txt”)); – where the string ‘fileToString’ will be assigned all the content of the file.
  • readLines(File file): read all the content from the file and place each separate line into an element of a string list. Usage:         List<String> fileToListOfStrings = readLines(new File(“pathToFiles/copyFile.txt”));
• comparing two files:
  • contentEquals(File file1, File file2): returns true if two files have the same size and content. Usage: assertTrue(contentEquals(new File(“pathToFiles/firstFile.txt”), new File(“pathToFiles/copyFile.txt”)));

Working with folders

• copying stuff:
  • copyFile(File src, File destination): copy the content of the ‘src’ file into the ‘destination’ file. If the latter does not exist, it will be created at this step. Usage:         copyFile(new File(“pathToFiles/firstFile.txt”), new File(“pathToFiles/copyFile.txt”));  –> ‘copyFile.txt’ will have identical content to ‘firstFile.text’
  • copyDirectory(File srcDir, File destinationDir): copy all the content from folder ‘srcDir’ directly under ‘destinationDir’. Usage:         copyDirectory(new File(“pathToFiles/randomFolder”), new File(“pathToFiles/Test”)); –>’randomFolder’ and ‘Test’ folder will have identical structure and content
  • copyFileToDirectory(File file, File destinationDir): copy the file ‘file’ to the file with the same name from the ‘destinationDir’ folder. If it does not exist, create a new file with the same name and put the content inside it. Usage:        copyFileToDirectory(new File(“pathToFiles/firstFile.txt”), new File(“pathToFiles/thirdOne”)); –> the ‘thirdOne’ folder will hold a ‘firstFile.txt’ file whose content is identical to the file from the ‘pathToFiles/firstFile.txt’ path
  • copyDirectoryToDirectory(File srcDir, File destinationDir): copies the content from the ‘srcDir’ folder into the folder with the same name from the ‘destinationDir’ folder, if it exists. Otherwise it creates the folder with the same name, and then replicates the content into the new folder. Usage:         copyDirectoryToDirectory(new File(“pathToFiles/thirdOne”), new File(“pathToFiles/4thOne”));
• deleting folders
  • deleteDirectory(File srcDir): delete the ‘srcDir’ and all its’ content. Usage:  deleteDirectory(new File(“pathToFiles/Test”));

Example

List listOfStrings = ImmutableList.of("Element 1", "Element 2", "Element 3");
//overwrite content of existing file
writeStringToFile(new File("pathToFiles/firstFile.txt"), "Some text with writeStringToFile that overwrites file");
//append string to existing content, with specified encoding
writeStringToFile(new File("pathToFiles/firstFile.txt"), "\nSome text with encodȊng, appended and with spacing\n", Charset.defaultCharset(), true);
//append a list of strings to the file, each string ends with a new line character; if append=false, boolean parameter can be removed
writeLines(new File("pathToFiles/firstFile.txt"), listOfStrings, true);
//append a list of strings to the file, each string ends with a specified character (| in this case) ; if append=false, boolean parameter can be removed
writeLines(new File("pathToFiles/firstFile.txt"), listOfStrings, "|", true);
//check that the content of two files is identical
copyFile(new File("pathToFiles/firstFile.txt"), new File("pathToFiles/copyFile.txt"));
assertTrue(contentEquals(new File("pathToFiles/firstFile.txt"), new File("pathToFiles/copyFile.txt")));
//copy a file to within a directory
copyFileToDirectory(new File("pathToFiles/firstFile.txt"), new File("pathToFiles/thirdOne"));
//copies a directory's content to another directory
copyDirectory(new File("pathToFiles/thirdOne"), new File("pathToFiles/4thOne"));
//copy directory into a directory with the same name, within the destination directory
copyDirectoryToDirectory(new File("pathToFiles/thirdOne"), new File("pathToFiles/4thOne"));
//read content from a file into a String
String fileToString = readFileToString(new File("pathToFiles/firstFile.txt"));
System.out.println("File to string: " + fileToString);
//read content from a file into a List of Strings
List fileToListOfStrings = readLines(new File("pathToFiles/firstFile.txt"));
System.out.println(fileToListOfStrings.size());
for (int i=0; i<=fileToListOfStrings.size()-1; i++)
System.out.println("The list of strings: " + fileToListOfStrings.get(i));

The resulting structure, in the ‘pathToFiles’ location, is: the ‘firstFile.text’ and ‘copyFile.txt’ files, alongisde the ‘thirdOne’ folder whose content is a ‘firstFile.txt’ file, and a ‘4thOne’ folder, comprising of a ‘firstFile.txt’ file and a ‘thirdOne’ folder (this folder also containing a ‘firstFile.txt’ file). The content of the all the .txt files is identical, as it was copied from one to the other.