How to Open a File in Java

There are following ways to open a file in Java:

Java Desktop class
Java FileInputStream class
Java BufferedReader class
Java FileReader class
Java Scanner class
Java nio package

Java Desktop class

Java Desktop class provide an open() method to open a file. It belongs to a java.awt package. Desktop implementation is platform-dependent, so it is necessary to check the operating system supports Desktop or not. The Desktop class looks for an associated application registered on the native desktop to handle a file. If there is no associated application or application is fails to be launched, it throws the FileNotFoundException. Launches the user default browser to show a specified URI.

Launches the user default mail client with an optional mail-to URI.
Launches the registered application to open, edit, or print a specified file.

The open() method of Desktop class launches the associated application to open a file. It takes a file as an argument. The signature of the method is:

The method throws the following exceptions:

NullPointerException: If the file is null.
IllegalArgumentException: It is thrown when the file does not exist.
IOException: It is thrown when there is no application associated with the given file type.
UnsupportedOperationExecution: If the current platform does not support the Desktop.Action.Open action.

Example

  import java.awt.Desktop;  import java.io.*;  public class OpenFileExample1   {  public static void main(String[] args)   {  try  {  //constructor of file class having file as argument  File file = new File(“C:\demo\demofile.txt”);   if(!Desktop.isDesktopSupported())//check if Desktop is supported by Platform or not  {  System.out.println(“not supported”);  return;  }  Desktop desktop = Desktop.getDesktop();  if(file.exists())    //checks file exists or not  desktop.open(file);             //opens the specified file  }  catch(Exception e)  {  e.printStackTrace();  }  }  }  

When we run the above program, it opens the specified text file in the default text editor. We can also open the .docx, .pdf, and .jpg file.

Output:

How to Open a File in Java

Java FileInputStream class

Java FileInputStream class is used to open and read a file. We can open and read a file by using the constructor of the FileInputStream class. The signature of the constructor is:

It accepts a file as an argument. It throws FileNotFoundException if the file does not exist or file name is a directory.

Example

  import java.io.*;  import java.util.Scanner;  public class OpenFileExample2  {  public static void main(String args[])  {  try  {  //constructor of file class having file as argument  File file=new File(“C:\demo\demofile.txt”);   FileInputStream fis=new FileInputStream(file);     //opens a connection to an actual file  System.out.println(“file content: “);  int r=0;  while((r=fis.read())!=-1)  {  System.out.print((char)r);//prints the content of the file  }  }  catch(Exception e)  {  e.printStackTrace();  }  }  }  

Output:

How to Open a File in Java

Java BufferedReader class

Java BufferedReader class reads text from a character input stream. It belongs to a java.io package. We use the constructor of the BufferedReader class to open or read a file. The signature of the constructor is:

It creates a buffering character-input stream that uses a default?sized input buffer. It uses a default size input buffer.

Example

  import java.io.*;  import java.util.Scanner;  public class OpenFileExample3  {  public static void main(String args[])  {  try  {  //constructor of File class having file as argument  File file=new File(“C:\demo\demofile.txt”);   //creates a buffer reader input stream  BufferedReader br=new BufferedReader(new FileReader(file));  System.out.println(“file content: “);  int r=0;  while((r=br.read())!=-1)  {  System.out.print((char)r);  }  }  catch(Exception e)  {  e.printStackTrace();  }  }  }   

Output:

How to Open a File in Java

Java FileReader class

Java FileReader class is also used for opening and reading a file. It belongs to a java.io package. It is a convenience for reading characters of the files. It is used for reading raw bytes using the FileInputStream class. We use the constructor of the FileInputStream class to open and read a file. The signature of the constructor is:

It accepts a file as an argument. It throws the FileNotFoundException if the specified file does not exist or the file name is a directory.

Example

  import java.io.*;  public class OpenFileExample4  {  public static void main(String args[])  {  try  {  //constructor of the File class having file as an argument  FileReader fr=new FileReader(“C:\demo\demofile.txt”);   System.out.println(“file content: “);  int r=0;  while((r=fr.read())!=-1)  {  System.out.print((char)r);//prints the content of the file   }  }  catch(Exception e)  {  e.printStackTrace();  }  }  }  

Output:

How to Open a File in Java

Java Scanner class

Java Scanner class is also used for opening and reading a file. The Scanner class belongs to java.util package. The constructor of Scanner class is used for opening and reading a file. The signature of the constructor is:

It accepts a file (to be scanned) as an argument. It also throws FileNotFoundException, if the source of the file is not found.

Example

  import java.io.File;   import java.util.Scanner;   public class OpenFileExample5  {   public static void main(String[] args)   {   try  {  File file=new File(“C:\demo\demofile.txt”);   Scanner sc = new Scanner(file); //file to be scanned  while (sc.hasNextLine()) //returns true if and only if scanner has another token  System.out.println(sc.nextLine());   }  catch(Exception e)  {  e.printStackTrace();  }  }   }  

Output:

How to Open a File in Java

Java nio package

readAllLines() method: The readAllLines() method is the method of File class. It reads all lines from a file and bytes from the file are decoded into characters using UTF-8 charset. It returns the lines from the file as a list. The signature of the method is:

Where path is the file path.

Above method is equivalent to invoking the following:

Collections.emptyList(): The emptyList() method is the method of Collection class which belong to java.util package. It is used to obtain an empty list. The signature of the method is:

Example

  import java.util.*;   import java.nio.charset.StandardCharsets;   import java.nio.file.*;   import java.io.*;   public class OpenFileExample6  {   public static List readFileInList(String fileName)   {   List lines = Collections.emptyList();   try  {   lines=Files.readAllLines(Paths.get(fileName), StandardCharsets.UTF_8);   }   catch (IOException e)   {   e.printStackTrace();   }   return lines;   }   public static void main(String[] args)   {   List l = readFileInList(“C:\demo\demofile.txt”);   Iterator itr = l.iterator();   //access the elements  while (itr.hasNext()) //returns true if and only if scanner has another token  System.out.println(itr.next());      //prints the content of the file  }   }  

Output:

How to Open a File in Java

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How to Open a File in Java

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