Handling files in Java

The java.io.File class provides ways to access file and directory information. It also allows file-level operations like rename, delete and move.

Checkout the source here.

/**

* A program to list all files and directories in a given directory.

*

* @author megha birmiwal

*/

public class DirectoryLister {

public void listDirectories(String filepath) {

File topDir = new File(filepath);

if (!topDir.exists()) {

System.out.println("Directory does not exist: " + filepath);

return;

}

if (!topDir.isDirectory()) {

System.out.println("Not a directory: " + filepath);

return;

}

File[] files = topDir.listFiles();

for (File file : files) {

if (file.isHidden()) {

// do not show hidden files

continue;

}

if (file.isDirectory()) {

System.out.println(file.getName() + " - D");

} else {

System.out.println(file.getName() + " - " + file.length());

}

// You can use the File APIs to play around with files, eg. rename or delete etc.

//                      String name = file.getName();

//                      name = name.replace(".png", ".jpg");

//                      name = name + ".txt";

//                  file.renameTo(new File(name));

//          file.delete();

}

}

public static void main(String[] args) {

DirectoryLister lister = new DirectoryLister();

lister.listDirectories("/");

}

}

File IO

An example of how to read/write text files in java.
http://code.google.com/p/java-through-examples/source/browse/src/org/megha/blog/example/io/#io

package org.megha.blog.example.io;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.Reader;

import java.util.ArrayList;

import java.util.List;

/**

* Reads all lines from a {@link Reader}.

* Don't use this to read huge files!

*

* @author megha birmiwal

*/

public class LinesReader {

private Reader reader;

public LinesReader(Reader reader) {

this.reader = reader;

}

/**

* Reads all the lines from the provided {@link Reader}.

*

* @return a list of strings (lines from the file)

* @throws IOException if there was an exception reading from the file

*/

public List<String> readAllLines() throws IOException {

BufferedReader bufferedReader = new BufferedReader(reader);

List<String> lines = new ArrayList<String>();

String line = bufferedReader.readLine();

while (line != null) {

lines.add(line);

line = bufferedReader.readLine();

}

return lines;

}

} package org.megha.blog.example.io; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.Writer; import java.util.HashSet; import java.util.List; import java.util.Set; /**  * Reads a file and writes unique words as output into another.  *  * @author megha birmiwal  */ public class UniqueWords {         public static void main(String args[]) throws IOException {                 if (args.length != 2) {                         System.out.println("please provide two file names: <infile> <outfile>");                         return;                 }                                 FileReader fileReader = null;                 try {                         fileReader = new FileReader(args[0]);                 } catch (FileNotFoundException e) {                         System.out.println("file not found: " + e.getMessage());                         return;                 }                 LinesReader lineReader = new LinesReader(fileReader);                 List<String> readLines = null;                 try {                         readLines = lineReader.readAllLines();                 } catch (IOException e) {                         System.out.println("IOException while reading from file: " + e.getMessage());                         return;                 } finally {                         fileReader.close();                 }                 // Prints all the lines in the file //              for (String line : readLines) { //                      System.out.println(line); //              }                 // Get all the unique words and save in a file                 Set<String> uniquewords = new HashSet<String>();                 for (String line : readLines) {                         String[] words = line.split("[ ;,/\\(\\)\\[\\]\"\\t]");                         for(String word : words) {                                 uniquewords.add(word);                         }                 }                 Writer writer = new FileWriter(args[1]);                 try {                         for(String word : uniquewords) {         //                      System.out.println(word);                                 writer.write(word + "\n");                         }                 } finally {                         writer.close();                 }         } }