Java/File Input Output/Files

Change a file attribute to read only

   
import java.io.File;
public class Main {
  public static void main(String[] args) throws Exception {
    File file = new File("ReadOnly.txt");
    file.createNewFile();
    file.setReadOnly();
    if (file.canWrite()) {
      System.out.println("writable!");
    } else {
      System.out.println("read only!");
    }
  }
}

Change a file attribute to writable

   
 
import java.io.File;
public class Main {
  public static void main(String[] args) throws Exception {
    File file = new File("Writable.txt");
    file.createNewFile();
    file.setReadOnly();
    if (file.canWrite()) {
      System.out.println("File is writable!");
    } else {
      System.out.println("File is in read only mode!");
    }
    file.setWritable(true);
    if (file.canWrite()) {
      System.out.println("File is writable!");
    } else {
      System.out.println("File is in read only mode!");
    }
  }
}

Change last modified time of a file or directory

   
import java.io.File;
import java.util.Date;
public class Main {
  public static void main(String[] args) throws Exception {
    File fileToChange = new File("C:/myfile.txt");
    Date filetime = new Date(fileToChange.lastModified());
    System.out.println(filetime.toString());
    System.out.println(fileToChange.setLastModified(System.currentTimeMillis()));
    filetime = new Date(fileToChange.lastModified());
    System.out.println(filetime.toString());
  }
}

Choose a File

  
import java.io.File;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
public class FileFilterDemo {
  public FileFilterDemo() {
  }
  public static void main(String[] args) {
    JFileChooser chooser = new JFileChooser();
    chooser.setCurrentDirectory(new File("."));
    chooser.setFileFilter(new javax.swing.filechooser.FileFilter() {
      public boolean accept(File f) {
        return f.getName().toLowerCase().endsWith(".gif")
            || f.isDirectory();
      }
      public String getDescription() {
        return "GIF Images";
      }
    });
    int r = chooser.showOpenDialog(new JFrame());
    if (r == JFileChooser.APPROVE_OPTION) {
      String name = chooser.getSelectedFile().getName();
      System.out.println(name);
    }
  }
}

Compare File Dates

  
import java.io.File;
public class CompareFileDates {
  public static void main(String[] args) {
    // Get the timestamp from file 1
    String f1 = "run.bat";
    long d1 = new File(f1).lastModified();
    // Get the timestamp from file 2
    String f2 = "build.xml";
    long d2 = new File(f2).lastModified();
    String relation;
    if (d1 == d2)
      relation = "the same age as";
    else if (d1 < d2)
      relation = "older than";
    else
      relation = "newer than";
    System.out.println(f1 + " is " + relation + " " + f2);
  }
}

Compare two file paths

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file1 = new File("C:/File/demo1.txt");
    File file2 = new File("C:/FileIO/demo1.txt");
    if (file1.rupareTo(file2) == 0) {
      System.out.println("Both paths are same!");
    } else {
      System.out.println("Paths are not same!");
    }
  }
}

Construct file path

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    String filePath = File.separator + "Java" + File.separator + "IO";
    File file = new File(filePath);
    System.out.println(file.getPath());
  }
}
// \Java\IO

Copy File

  
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class CopyBytes {
  public static void main(String[] args) throws IOException {
    File inputFile = new File("input.txt");
    File outputFile = new File("output.txt");
    FileInputStream in = new FileInputStream(inputFile);
    FileOutputStream out = new FileOutputStream(outputFile);
    int c;
    while ((c = in.read()) != -1)
      out.write(c);
    in.close();
    out.close();
  }
}

Create a directory; all ancestor directories must exist

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    boolean success = (new File("directoryName")).mkdir();
    if (!success) {
      System.out.println("Directory creation failed"); 
    }
  }
}

Create a directory; all non-existent ancestor directories are automatically created

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    boolean success = (new File("directoryName")).mkdirs();
    if (!success) {
      System.out.println("Directory creation failed");
    }
  }
}

Create a directory (or several directories)

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File directory = new File("C:/temp/temp1/temp2/temp3");
    if (directory.mkdir()) {
      System.out.println("Success mkdir");
    } else {
      if (directory.mkdirs()) {
        System.out.println("Success mkdirs");
      } else {
        System.out.println("Failed");
      }
    }
  }
}

Create a human-readable file size

   
import org.apache.rumons.io.FileUtils;
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("c:\\java.exe");
    long size = file.length();
    String display = FileUtils.byteCountToDisplaySize(size);
    System.out.println("Name    = " + file.getName());
    System.out.println("size    = " + size);
    System.out.println("Display = " + display);
  }
}

Create a temporary file

   
import java.io.File;
public class Main{
  public static void main(String[] args) throws Exception{
    File f = File.createTempFile("temp_", null);
    
    System.out.println(f.getAbsolutePath());
    
    f.deleteOnExit();
  }
}

Create file

   
import java.io.File;
import java.io.IOException;
public class Main {
  public static void main(String[] args) {
    try {
      File file = new File("myfile.txt");
      if (file.createNewFile())
        System.out.println("Success!");
      else
        System.out.println("Error, file already exists.");
    } catch (IOException ioe) {
      ioe.printStackTrace();
    }
  }
}

Create new empty file

   
import java.io.File;
public class Main {
  public static void main(String[] args) throws Exception {
    File file = new File("C://demo.txt");
    boolean blnCreated = false;
    blnCreated = file.createNewFile();
    System.out.println(blnCreated);
  }
}

Create temporary file in specified directory

   
import java.io.File;
public class Main {
  public static void main(String[] args) throws Exception {
    File file = null;
    File dir = new File("C:/");
    file = File.createTempFile("JavaTemp", ".javatemp", dir);
    System.out.println(file.getPath());
  }
}
//C:\JavaTemp5893283162648915021.javatemp

Create temporary file with specified extension suffix

   
import java.io.File;
public class Main {
  public static void main(String[] args) throws Exception {
    File file1 = null;
    File file2 = null;
    file1 = File.createTempFile("JavaTemp", null);
    file2 = File.createTempFile("JavaTemp", ".java");
    System.out.println(file1.getPath());
    System.out.println(file2.getPath());
  }
}

Creating a Temporary File and delete it on exit

   
 import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
public class Main {
  public static void main(String[] argv) throws Exception {
    File temp = File.createTempFile("pattern", ".dat");
    temp.deleteOnExit();
    BufferedWriter out = new BufferedWriter(new FileWriter(temp));
    out.write("asdf");
    out.close();
  }
}

Data file

  
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.StringTokenizer;
public class DataFileTest {
  static void writeData(Employee e, PrintWriter out) throws IOException {
    e.writeData(out);
  }
  static Employee readData(BufferedReader in) throws IOException {
    Employee e = new Employee();
    e.readData(in);
    return e;
  }
  public static void main(String[] args) {
    Employee staff = new Employee("Java Source", 35500);
    staff.raiseSalary(5.25);
    try {
      PrintWriter out = new PrintWriter(new FileWriter("employee.dat"));
      writeData(staff, out);
      out.close();
    } catch (IOException e) {
      System.out.print("Error: " + e);
      System.exit(1);
    }
    try {
      BufferedReader in = new BufferedReader(new FileReader(
          "employee.dat"));
      Employee e = readData(in);
      e.print();
      in.close();
    } catch (IOException e) {
      System.out.print("Error: " + e);
      System.exit(1);
    }
  }
}
class Employee {
  private String name;
  private double salary;
  public Employee(String n, double s) {
    name = n;
    salary = s;
  }
  public Employee() {
  }
  public void print() {
    System.out.println(name + " " + salary );
  }
  public void raiseSalary(double byPercent) {
    salary *= 1 + byPercent / 100;
  }
  public void writeData(PrintWriter out) throws IOException {
    out.println(name + "|" + salary);
  }
  public void readData(BufferedReader in) throws IOException {
    String s = in.readLine();
    StringTokenizer t = new StringTokenizer(s, "|");
    
    name = t.nextToken();
    
    salary = Double.parseDouble(t.nextToken());
  }
}

Delete a file

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("yourFile.txt");
    System.out.println(file.delete());
  }
}

Delete a file from within Java

  
/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
import java.io.File;
import java.io.IOException;
/**
 * Delete a file from within Java
 * 
 * @author Ian F. Darwin, http://www.darwinsys.ru/
 * @version $Id: Delete.java,v 1.5 2004/02/09 03:33:47 ian Exp $
 */
public class Delete {
  public static void main(String[] argv) throws IOException {
    // Construct a File object for the backup created by editing
    // this source file. The file probably already exists.
    // My editor creates backups by putting ~ at the end of the name.
    File bkup = new File("Delete.java~");
    // Quick, now, delete it immediately:
    bkup.delete();
  }
}

Delete file or directory

   
import java.io.File;
public class Main {
  public static void main(String[] args) throws Exception {
    File file = new File("C:/Demo.txt");
    System.out.println(file.delete());
  }
}

Delete file or directory when virtual machine terminates

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C:/Demo.txt");
    file.deleteOnExit();
  }
}

Deleting a Directory (an empty directory)

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    boolean success = (new File("directoryName")).delete();
    if (!success) {
      System.out.println("Deletion failed");
    }
  }
}

Demonstrate File.

   
import java.io.File;
   
class FileDemo {
  public static void main(String args[]) {
    File f1 = new File("/java/COPYRIGHT");
    System.out.println("File Name: " + f1.getName());
    System.out.println("Path: " + f1.getPath());
    System.out.println("Abs Path: " + f1.getAbsolutePath());
    System.out.println("Parent: " + f1.getParent());
    System.out.println(f1.exists() ? "exists" : "does not exist");
    System.out.println(f1.canWrite() ? "is writeable" : "is not writeable");
    System.out.println(f1.canRead() ? "is readable" : "is not readable");
    System.out.println("is " + (f1.isDirectory() ? "" : "not" + " a directory"));
    System.out.println(f1.isFile() ? "is normal file" : "might be a named pipe");
    System.out.println(f1.isAbsolute() ? "is absolute" : "is not absolute");
    System.out.println("File last modified: " + f1.lastModified());
    System.out.println("File size: " + f1.length() + " Bytes");
  }
}

Determine File or Directory

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C://FileIO");
    boolean isFile = file.isFile();
    if (isFile){
      System.out.println("a file.");
    }else{
      System.out.println("not a file.");
    }
    boolean isDirectory = file.isDirectory();
    if (isDirectory){
      System.out.println("a directory.");
    }else{
      System.out.println("not a directory.");
    }
  }
}

Determine if a file can be read

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    String filePath = "C:/Text.txt";
    File file = new File(filePath);
    if (file.canRead()) {
      System.out.println("readable");
    } else {
      System.out.println("not readable");
    }
  }
}

Determine if a file can be written

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    String filePath = "C:/Text.txt";
    File file = new File(filePath);
    if (file.canWrite()) {
      System.out.println("writable");
    } else {
      System.out.println("not writable");
    }
  }
}

Determine if file or directory exists

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C:/Demo.txt");
    System.out.println(file.exists());
  }
}

Determine if File or Directory is hidden

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C:/Demo.txt");
    System.out.println(file.isHidden());
  }
}

File.getCanonicalFile() converts a filename path to a unique canonical form suitable for comparisons.

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file1 = new File("./filename");
    File file2 = new File("filename");
    System.out.println(file1.equals(file2));
    file1 = file1.getCanonicalFile();
    file2 = file2.getCanonicalFile();
    System.out.println(file1.equals(file2));
  }
}

Find out the directory

  
import java.io.File;
import java.io.IOException;
public class FindDirectories {
  public static void main(String[] args) {
    try {
      File pathName = new File("c:\\");
      String[] fileNames = pathName.list();
      for (int i = 0; i < fileNames.length; i++) {
        File tf = new File(pathName.getPath(), fileNames[i]);
        if (tf.isDirectory()) {
          System.out.println(tf.getCanonicalPath());
        }
      }
    } catch (IOException e) {
      System.out.println("Error: " + e);
    }
  }
}

Forcing Updates to a File to the Disk

   
import java.io.FileDescriptor;
import java.io.FileOutputStream;
public class Main {
  public static void main(String[] argv) throws Exception {
    FileOutputStream os = new FileOutputStream("outfilename");
    FileDescriptor fd = os.getFD();
    os.write(1);
    os.flush();
    fd.sync();
  }
}

Format file length in string

   

public class Utils {
  public static final String format(long l) {
    String s = String.valueOf(l);
    int digits = 0;
    while (s.length() > 3) {
        s = s.substring(0, s.length() - 3);
        digits++;
    }
    StringBuffer buffer = new StringBuffer();
    buffer.append(s);
    if ((s.length() == 1) && (String.valueOf(l).length() >= 3)) {
        buffer.append(".");
        buffer.append(String.valueOf(l).substring(1, 3));
    } else if ((s.length() == 2) && (String.valueOf(l).length() >= 3)) {
        buffer.append(".");
        buffer.append(String.valueOf(l).substring(2, 3));
    }
    if (digits == 0) {
        buffer.append(" B");
    } else if (digits == 1) {
        buffer.append(" KB");
    } else if (digits == 2) {
        buffer.append(" MB");
    } else if (digits == 3) {
        buffer.append(" GB");
    } else if (digits == 4) {
        buffer.append(" TB");
    }
    return buffer.toString();
}
    
  
}

Get Absolute path of the file

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File(File.separator + "Java" + File.separator + "folder");
    System.out.println(file.getPath());
    System.out.println(file.getAbsolutePath());
  }
}

Get a file last modification date

   
 
import java.io.File;
import java.util.Date;
public class Main {
  public static void main(String[] args) {
    File file = new File("Main.java");
    Long lastModified = file.lastModified();
    Date date = new Date(lastModified);
    System.out.println(date);
  }
}

Get a list of files, and check if any files are missing

  
/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
/**
 * Get a list of files, and check if any files are missing.
 * 
 * @author Ian F. Darwin, http://www.darwinsys.ru/
 * @version $Id: CheckFiles.java,v 1.3 2004/02/09 03:33:46 ian Exp $
 */
public class CheckFiles {
  public static void main(String[] argv) {
    CheckFiles cf = new CheckFiles();
    System.out.println("CheckFiles starting.");
    cf.getListFromFile();
    cf.getListFromDirectory();
    cf.reportMissingFiles();
    System.out.println("CheckFiles done.");
  }
  public String FILENAME = "filelist.txt";
  protected ArrayList listFromFile;
  protected ArrayList listFromDir = new ArrayList();
  protected void getListFromFile() {
    listFromFile = new ArrayList();
    BufferedReader is;
    try {
      is = new BufferedReader(new FileReader(FILENAME));
      String line;
      while ((line = is.readLine()) != null)
        listFromFile.add(line);
    } catch (FileNotFoundException e) {
      System.err.println("Can"t open file list file.");
      return;
    } catch (IOException e) {
      System.err.println("Error reading file list");
      return;
    }
  }
  /** Get list of names from the directory */
  protected void getListFromDirectory() {
    listFromDir = new ArrayList();
    String[] l = new java.io.File(".").list();
    for (int i = 0; i < l.length; i++)
      listFromDir.add(l[i]);
  }
  protected void reportMissingFiles() {
    for (int i = 0; i < listFromFile.size(); i++)
      if (!listFromDir.contains(listFromFile.get(i)))
        System.err.println("File " + listFromFile.get(i) + " missing.");
  }
}

Get all path information from java.io.File

  
import java.io.File;
import java.io.IOException;
class PathInfo {
  public static void main(String[] args) throws IOException {
    File f = new File(args[0]);
    System.out.println("Absolute path = " + f.getAbsolutePath());
    System.out.println("Canonical path = " + f.getCanonicalPath());
    System.out.println("Name = " + f.getName());
    System.out.println("Parent = " + f.getParent());
    System.out.println("Path = " + f.getPath());
    System.out.println("Absolute? = " + f.isAbsolute());
  }
}

Get all xml files by file extension

   
import java.io.File;
import java.util.ArrayList;
import java.util.List;
public class Main {
  public static void main(String[] argv) {
    getXMLFiles(new File("c:\\a"));
  }
  public static File[] getXMLFiles(File folder) {
    List<File> aList = new ArrayList<File>();
    File[] files = folder.listFiles();
    for (File pf : files) {
      if (pf.isFile() && getFileExtensionName(pf).indexOf("xml") != -1) {
        aList.add(pf);
      }
    }
    return aList.toArray(new File[aList.size()]);
  }
  public static String getFileExtensionName(File f) {
    if (f.getName().indexOf(".") == -1) {
      return "";
    } else {
      return f.getName().substring(f.getName().length() - 3, f.getName().length());
    }
  }
}

Get extension, path and file name

  
/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
public class FilenameDemo {
  public static void main(String[] args) {
    final String FPATH = "/home/mem/index.html";
    Filename myHomePage = new Filename(FPATH, "/", ".");
    System.out.println("Extension = " + myHomePage.extension());
    System.out.println("Filename = " + myHomePage.filename());
    System.out.println("Path = " + myHomePage.path());
  }
}
/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *  - Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *  - Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *  - Neither the name of Sun Microsystems nor the names of its contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
/**
 * This class assumes that the string used to initialize fullPath has a
 * directory path, filename, and extension. The methods won"t work if it
 * doesn"t.
 */
class Filename {
  private String fullPath;
  private char pathSeparator, extensionSeparator;
  public Filename(String str, char sep, char ext) {
    fullPath = str;
    pathSeparator = sep;
    extensionSeparator = ext;
  }
  public String extension() {
    int dot = fullPath.lastIndexOf(extensionSeparator);
    return fullPath.substring(dot + 1);
  }
  public String filename() { // gets filename without extension
    int dot = fullPath.lastIndexOf(extensionSeparator);
    int sep = fullPath.lastIndexOf(pathSeparator);
    return fullPath.substring(sep + 1, dot);
  }
  public String path() {
    int sep = fullPath.lastIndexOf(pathSeparator);
    return fullPath.substring(0, sep);
  }
}

Get file extension name

   
import java.io.File;
public class Main {
  public static void main(String[] argv) {
    getFileExtensionName(new File("a.txt"));
  }
  public static String getFileExtensionName(File f) {
    if (f.getName().indexOf(".") == -1) {
      return "";
    } else {
      return f.getName().substring(f.getName().length() - 3, f.getName().length());
    }
  }
}

Get file size

   
import java.io.File;
public class Main {
  public static long getFileSize(String filename) {
    File file = new File(filename);
    if (!file.exists() || !file.isFile()) {
      System.out.println("File doesn\"t exist");
      return -1;
    }
    return file.length();
  }
  public static void main(String[] args) {
    long size = getFileSize("c:/my.txt");
    System.out.println("Filesize in bytes: " + size);
  }
}

Get File size in bytes

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C:/demo.txt");
    long fileSize = file.length();
    System.out.println(fileSize + " bytes");
    System.out.println((double) fileSize / 1024 + " KB");
    System.out.println((double) fileSize / (1024 * 1024) + "MB");
  }
}

Get icon for file type

   
import java.io.File;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class Main {
  public static void main(String[] args) throws Exception {
    File file = new File(args[0]);
    sun.awt.shell.ShellFolder sf = sun.awt.shell.ShellFolder.getShellFolder(file);
    Icon icon = new ImageIcon(sf.getIcon(true));
    System.out.println("type = " + sf.getFolderType());
    JLabel label = new JLabel(icon);
    JFrame frame = new JFrame();
    frame.getContentPane().add(label);
    frame.pack();
    frame.setVisible(true);
  }
}

Get parent directory as a File object

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C:/demo.txt");
    File fileParent = file.getParentFile();
    System.out.println("Parent directory: " + fileParent.getPath());
  }
}

Get the parents of an absolute filename path

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("D:\\test\\test.java");
    String parentPath = file.getParent();
    System.out.println(parentPath);
    File parentDir = file.getParentFile();
    System.out.println(parentDir);
    parentPath = parentDir.getParent();
    System.out.println(parentPath);
    parentDir = parentDir.getParentFile();
    System.out.println(parentDir);
    parentPath = parentDir.getParent();
    System.out.println(parentPath);
    parentDir = parentDir.getParentFile();
    System.out.println(parentDir);
  }
}

Getting an Absolute Filename Path from a Relative Filename parent Path

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File(".." + File.separatorChar + "filename.txt");
    file = file.getAbsoluteFile();
  }
}

Getting an Absolute Filename Path from a Relative Filename Path

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("filename.txt");
    file = file.getAbsoluteFile();
  }
}

Getting an Absolute Filename Path from a Relative Filename with Path

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("dir" + File.separatorChar + "filename.txt");
    file = file.getAbsoluteFile();
  }
}

Getting and Setting the Modification Time of a File or Directory

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("filename");
    long modifiedTime = file.lastModified();
    // 0L is returned if the file does not exist
    long newModifiedTime = System.currentTimeMillis();
    boolean success = file.setLastModified(newModifiedTime);
    if (!success) {
      // operation failed.
    }
  }
}

Getting the Current Working Directory

   
public class Main {
  public static void main(String[] argv) throws Exception {
    String curDir = System.getProperty("user.dir");
  }
}

Getting the Parents of a Filename Path

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("test.java");
    String parentPath = file.getParent();
    System.out.println(parentPath);
    File parentDir = file.getParentFile();
    
    System.out.println(parentDir);
  }
}

List drives

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File[] drives = File.listRoots();
    for (int i = 0; i < drives.length; i++) {
      System.out.println(drives[i]);
    }
  }
}

List Filesystem roots

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File[] rootDirectories = File.listRoots();
    System.out.println("Available root directories:");
    for (int i = 0; i < rootDirectories.length; i++) {
      System.out.println(rootDirectories[i]);
    }
  }
}

Listing the Directory Contents

  
import java.io.File;
import java.util.Arrays;
public class Dir {
  static int indentLevel = -1;
  static void listPath(File path) {
    File files[]; 
    indentLevel++; 
    files = path.listFiles();
    Arrays.sort(files);
    for (int i = 0, n = files.length; i < n; i++) {
      for (int indent = 0; indent < indentLevel; indent++) {
        System.out.print("  ");
      }
      System.out.println(files[i].toString());
      if (files[i].isDirectory()) {
        listPath(files[i]);
      }
    }
    indentLevel--; 
  }
  public static void main(String args[]) {
    listPath(new File("c:\\"));
  }
}

Mark file or directory Read Only

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File file = new File("C:/demo.txt");
    System.out.println(file.setReadOnly());
    System.out.println(file.canWrite());
  }
}

Moving a File or Directory to Another Directory

   
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("filename");
    File dir = new File("directoryname");
    boolean success = file.renameTo(new File(dir, file.getName()));
    if (!success) {
      System.out.println("File was not successfully moved");
    }
  }
}

Output to a text File

  
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;
import java.util.Vector;
public class ListOfNumbersDeclared {
  public static void main(String[] a) {
    Vector victor;
    int size = 10;
    victor = new Vector(size);
    for (int i = 0; i < size; i++)
      victor.addElement(new Integer(i));
    try {
      PrintStream out = new PrintStream(new FileOutputStream(
          "OutFile.txt"));
      for (int i = 0; i < size; i++)
        out.println("Value at: " + i + " = " + victor.elementAt(i));
      out.close();
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    }
  }
}

Querying a File for Information

  
import java.io.File;
public class Attr {
  public static void main(String args[]) {
    File path = new File(args[0]); // grab command-line argument
    String exists = getYesNo(path.exists());
    String canRead = getYesNo(path.canRead());
    String canWrite = getYesNo(path.canWrite());
    String isFile = getYesNo(path.isFile());
    String isHid = getYesNo(path.isHidden());
    String isDir = getYesNo(path.isDirectory());
    String isAbs = getYesNo(path.isAbsolute());
    System.out.println("File attributes for "" + args[0] + """);
    System.out.println("Exists    : " + exists);
    if (path.exists()) {
      System.out.println("Readable   : " + canRead);
      System.out.println("Writable   : " + canWrite);
      System.out.println("Is directory : " + isDir);
      System.out.println("Is file    : " + isFile);
      System.out.println("Is hidden   : " + isHid);
      System.out.println("Absolute path : " + isAbs);
    }
  }
  private static String getYesNo(boolean b) {
    return (b ? "Yes" : "No");
  }
}

Random File

  
import java.io.DataInput;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
public class RandomFileTest {
  public static void main(String[] args) {
    Employee[] staff = new Employee[3];
    staff[0] = new Employee("Harry Hacker", 35000);
    staff[1] = new Employee("Carl Cracker", 75000);
    staff[2] = new Employee("Tony Tester", 38000);
    try {
      DataOutputStream out = new DataOutputStream(new FileOutputStream(
          "employee.dat"));
      for (int i = 0; i < staff.length; i++)
        staff[i].writeData(out);
      out.close();
    } catch (IOException e) {
      System.out.print("Error: " + e);
      System.exit(1);
    }
    try {
      RandomAccessFile in = new RandomAccessFile("employee.dat", "r");
      int count = (int) (in.length() / Employee.RECORD_SIZE);
      Employee[] newStaff = new Employee[count];
      for (int i = count - 1; i >= 0; i--) {
        newStaff[i] = new Employee();
        in.seek(i * Employee.RECORD_SIZE);
        newStaff[i].readData(in);
      }
      for (int i = 0; i < newStaff.length; i++)
        newStaff[i].print();
    } catch (IOException e) {
      System.out.print("Error: " + e);
      System.exit(1);
    }
  }
}
class Employee {
  public static final int NAME_SIZE = 40;
  public static final int RECORD_SIZE = 2 * NAME_SIZE + 8 + 4 + 4 + 4;
  private String name;
  private double salary;
  public Employee(String n, double s) {
    name = n;
    salary = s;
  }
  public Employee() {
  }
  public void print() {
    System.out.println(name + " " + salary);
  }
  public void writeData(DataOutput out) throws IOException {
    DataIO.writeFixedString(name, NAME_SIZE, out);
    out.writeDouble(salary);
  }
  public void readData(DataInput in) throws IOException {
    name = DataIO.readFixedString(NAME_SIZE, in);
    salary = in.readDouble();
  }
}
class DataIO {
  public static String readFixedString(int size, DataInput dataInput)
      throws IOException {
    StringBuffer strBuffer = new StringBuffer(size);
    int count = 0;
    boolean more = true;
    while (more && count < size) {
      char aChar = dataInput.readChar();
      count++;
      if (aChar == 0)
        more = false;
      else
        strBuffer.append(aChar);
    }
    dataInput.skipBytes(2 * (size - count));
    return strBuffer.toString();
  }
  public static void writeFixedString(String str, int size, DataOutput dataOutput)
      throws IOException {
    for (int i = 0; i < size; i++) {
      char aChar = 0;
      if (i < str.length())
        aChar = str.charAt(i);
      dataOutput.writeChar(aChar);
    }
  }
}

Read data from text file

  
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class InputFileDeclared {
  private FileInputStream in;
  public InputFileDeclared(String filename) throws FileNotFoundException {
    in = new FileInputStream(filename);
  }
  public String getWord() throws IOException {
    int c;
    StringBuffer buf = new StringBuffer();
    do {
      c = in.read();
      if (Character.isSpace((char) c))
        return buf.toString();
      else
        buf.append((char) c);
    } while (c != -1);
    return buf.toString();
  }
  public static void main(String[] args) throws java.io.IOException {
    InputFileDeclared file = new InputFileDeclared("testing.txt");
    System.out.println(file.getWord());
    System.out.println(file.getWord());
    System.out.println(file.getWord());
  }
}

Read file contents to string using commons-io?

   

import org.apache.rumons.io.FileUtils;
 
import java.io.File;
import java.io.IOException;
 
public class Main
{
    public static void main(String[] args)
    {
        File file = new File("sample.txt");
 
            String content = FileUtils.readFileToString(file);
 
            System.out.println("File content: " + content);
    }
}

Rename file or directory

   
import java.io.File;
public class Main {
  public static void main(String[] args) {
    File oldName = new File("C:/s.txt");
    File newName = new File("C:/d.txt");
    if (oldName.renameTo(newName)) {
      System.out.println("renamed");
    } else {
      System.out.println("Error");
    }
  }
}

Return a file with the given filename creating the necessary directories if not present.

 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import java.io.File;

public class Main {
  /**
   * Return a file with the given filename creating the necessary directories
   * if not present.
   * 
   * @param filename
   *            The file
   * @return The created File instance
   */
  public static File createFile(File destDir, String filename) {
      File file = new File(destDir, filename);
      File parent = file.getParentFile();
      if (parent != null)
          parent.mkdirs();
      return file;
  }
}

Search for files recursively

   
import org.apache.rumons.io.FileUtils;
import java.io.File;
import java.util.Collection;
import java.util.Iterator;
public class Main {
  public static void main(String[] args) throws Exception {
    File root = new File("c:\\");
    String[] extensions = { "xml", "java", "dat" };
    boolean recursive = true;
    Collection files = FileUtils.listFiles(root, extensions, recursive);
    for (Iterator iterator = files.iterator(); iterator.hasNext();) {
      File file = (File) iterator.next();
      System.out.println("File = " + file.getAbsolutePath());
    }
  }
}

Set file attributes.

   
import java.io.File;
import java.util.Calendar;
import java.util.Date;
public class Main {
  public static void main(String[] argv) throws Exception {
    File f = new File("name.txt");
    if (!f.exists()) {
      System.out.println("File not found.");
      return;
    }
    if (f.canRead())
      System.out.println("  Readable");
    else
      System.out.println("  Not Readable");
    if (f.canWrite())
      System.out.println("  Writable");
    else
      System.out.println("  Not Writable");
    System.out.println("  Last modified on " + new Date(f.lastModified()));
    long t = Calendar.getInstance().getTimeInMillis();
    if (!f.setLastModified(t))
      System.out.println("Can"t set time.");
    if (!f.setReadOnly())
      System.out.println("Can"t set to read-only.");
    if (f.canRead())
      System.out.println("  Readable");
    else
      System.out.println("  Not Readable");
    if (f.canWrite())
      System.out.println("  Writable");
    else
      System.out.println("  Not Writable");
    System.out.println("  Last modified on " + new Date(f.lastModified()));
    if (!f.setWritable(true, false))
      System.out.println("Can"t return to read/write.");
    if (f.canRead())
      System.out.println("  Readable");
    else
      System.out.println("  Not Readable");
    if (f.canWrite())
      System.out.println("  Writable");
    else
      System.out.println("  Not Writable");
  }
}

Sort files base on their last modified date

   
import org.apache.rumons.io.ruparator.LastModifiedFileComparator;
 
import java.io.File;
import java.util.Arrays;
 
public class Main {
    public static void main(String[] args) {
        File dir = new File("c:\\");
        File[] files = dir.listFiles();
 
        Arrays.sort(files, LastModifiedFileComparator.LASTMODIFIED_COMPARATOR);
        for (int i = 0; i < files.length; i++) {
            File file = files[i];
            System.out.printf("File %s - %2$tm %2$te,%2$tY%n= ", file.getName(),
                    file.lastModified());
        }
 
        Arrays.sort(files, LastModifiedFileComparator.LASTMODIFIED_REVERSE);
        for (int i = 0; i < files.length; i++) {
            File file = files[i];
            System.out.printf("File %s - %2$tm %2$te,%2$tY%n= ", file.getName(),
                    file.lastModified());
        }
    }
}

Strings -- extract printable strings from binary file

  
/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
/**
 * Strings -- extract printable strings from binary file
 * 
 * @author Ian F. Darwin, http://www.darwinsys.ru/
 * @version $Id: Strings.java,v 1.3 2004/02/08 23:57:29 ian Exp $
 */
public class Strings {
  protected int minLength = 4;
  /**
   * Return true if the character is printable IN ASCII. Not using
   * Character.isLetterOrDigit(); applies to all unicode ranges
   */
  protected boolean isStringChar(char ch) {
    if (ch >= "a" && ch <= "z")
      return true;
    if (ch >= "A" && ch <= "Z")
      return true;
    if (ch >= "0" && ch <= "9")
      return true;
    switch (ch) {
    case "/":
    case "-":
    case ":":
    case ".":
    case ",":
    case "_":
    case "$":
    case "%":
    case "\"":
    case "(":
    case ")":
    case "[":
    case "]":
    case "<":
    case ">":
      return true;
    }
    return false;
  }
  /** Process one file */
  protected void process(String fileName, InputStream inStream) {
    try {
      int i;
      char ch;
      // This line alone cuts the runtime by about 66% on large files.
      BufferedInputStream is = new BufferedInputStream(inStream);
      StringBuffer sb = new StringBuffer();
      // Read a byte, cast it to char, check if part of printable string.
      while ((i = is.read()) != -1) {
        ch = (char) i;
        if (isStringChar(ch) || (sb.length() > 0 && ch == " "))
          // If so, build up string.
          sb.append(ch);
        else {
          // if not, see if anything to output.
          if (sb.length() == 0)
            continue;
          if (sb.length() >= minLength) {
            report(fileName, sb);
          }
          sb.setLength(0);
        }
      }
      is.close();
    } catch (IOException e) {
      System.out.println("IOException: " + e);
    }
  }
  /**
   * This simple main program looks after filenames and opening files and such
   * like for you.
   */
  public static void main(String[] av) {
    Strings o = new Strings();
    if (av.length == 0) {
      o.process("standard input", System.in);
    } else {
      for (int i = 0; i < av.length; i++)
        try {
          o.process(av[i], new FileInputStream(av[i]));
        } catch (FileNotFoundException e) {
          System.err.println(e);
        }
    }
  }
  /** Output a match. Made a separate method for use by subclassers. */
  protected void report(String fName, StringBuffer theString) {
    System.out.println(fName + ": " + theString);
  }
}

Working with RandomAccessFile

  
import java.io.IOException;
import java.io.RandomAccessFile;
public class Diff {
  public static void main(String args[]) {
    RandomAccessFile fh1 = null;
    RandomAccessFile fh2 = null;
    int bufsize; // size of smallest file
    long filesize1 = -1;
    long filesize2 = -1;
    byte buffer1[]; // the two file caches
    byte buffer2[];
    // check what you get as command-line arguments
    if (args.length == 0 || args[0].equals("?")) {
      System.err.println("USAGE: java Diff <file1> <file2> | ?");
      System.exit(0);
    }
    // open file ONE for reading
    try {
      fh1 = new RandomAccessFile(args[0], "r");
      filesize1 = fh1.length();
    } catch (IOException ioErr) {
      System.err.println("Could not find " + args[0]);
      System.err.println(ioErr);
      System.exit(100);
    }
    // open file TWO for reading
    try {
      fh2 = new RandomAccessFile(args[1], "r");
      filesize2 = fh2.length();
    } catch (IOException ioErr) {
      System.err.println("Could not find " + args[1]);
      System.err.println(ioErr);
      System.exit(100);
    }
    if (filesize1 != filesize2) {
      System.out.println("Files differ in size !");
      System.out.println(""" + args[0] + "" is " + filesize1 + " bytes");
      System.out.println(""" + args[1] + "" is " + filesize2 + " bytes");
    }
    // allocate two buffers large enough to hold entire files
    bufsize = (int) Math.min(filesize1, filesize2);
    buffer1 = new byte[bufsize];
    buffer2 = new byte[bufsize];
    try {
      fh1.readFully(buffer1, 0, bufsize);
      fh2.readFully(buffer2, 0, bufsize);
      for (int i = 0; i < bufsize; i++) {
        if (buffer1[i] != buffer2[i]) {
          System.out.println("Files differ at offset " + i);
          break;
        }
      }
    } catch (IOException ioErr) {
      System.err
          .println("ERROR: An exception occurred while processing the files");
      System.err.println(ioErr);
    } finally {
      try {
        fh1.close();
        fh2.close();
      } catch (IOException ignored) {
      }
    }
  }
}

Work with temporary files in Java

  
/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
import java.io.File;
import java.io.IOException;
/**
 * Work with temporary files in Java.
 * 
 * @author Ian F. Darwin, http://www.darwinsys.ru/
 * @version $Id: TempFiles.java,v 1.3 2004/02/09 03:33:47 ian Exp $
 */
public class TempFiles {
  public static void main(String[] argv) throws IOException {
    // 1. Make an existing file temporary
    // Construct a File object for the backup created by editing
    // this source file. The file probably already exists.
    // My editor creates backups by putting ~ at the end of the name.
    File bkup = new File("Rename.java~");
    // Arrange to have it deleted when the program ends.
    bkup.deleteOnExit();
    // 2. Create a new temporary file.
    // Make a file object for foo.tmp, in the default temp directory
    File tmp = File.createTempFile("foo", "tmp");
    // Report on the filename that it made up for us.
    System.out.println("Your temp file is " + tmp.getCanonicalPath());
    // Arrange for it to be deleted at exit.
    tmp.deleteOnExit();
    // Now do something with the temporary file, without having to
    // worry about deleting it later.
    writeDataInTemp(tmp.getCanonicalPath());
  }
  public static void writeDataInTemp(String tempnam) {
    // This version is dummy. Use your imagination.
  }
}