Java создать новый файл

Создание файла — очень распространенная операция ввода-вывода. Сегодня мы рассмотрим различные способы создания файла в java.

Java создать файл

1. File.createNewFile()

   java.io.File class can be used to create a new File in Java. When we initialize File object, we provide the file name and then we can call createNewFile() method to create new file in Java. File createNewFile() method returns true if new file is created and false if file already exists. This method also throws java.io.IOException when it’s not able to create the file. The files created is empty and of zero bytes. When we create the File object by passing the file name, it can be with absolute path, or we can only provide the file name or we can provide the relative path. For a non-absolute path, File object tries to locate files in the project root directory. If we run the program from command line, for the non-absolute path, File object tries to locate files from the current directory. While creating the file path, we should use System property file.separator to make our program platform independent. Let’s see different scenarios with a simple java program to create a new file in java.

   package com.journaldev.files;
   
   import java.io.File;
   import java.io.IOException;
   
   public class CreateNewFile {
   
       /**
        * This class shows how to create a File in Java
        * @param args
        * @throws IOException 
        */
       public static void main(String[] args) throws IOException {
           String fileSeparator = System.getProperty("file.separator");
           
           //absolute file name with path
           String absoluteFilePath = fileSeparator+"Users"+fileSeparator+"pankaj"+fileSeparator+"file.txt";
           File file = new File(absoluteFilePath);
           if(file.createNewFile()){
               System.out.println(absoluteFilePath+" File Created");
           }else System.out.println("File "+absoluteFilePath+" already exists");
           
           //file name only
           file = new File("file.txt");
           if(file.createNewFile()){
               System.out.println("file.txt File Created in Project root directory");
           }else System.out.println("File file.txt already exists in the project root directory");
           
           //relative path
           String relativePath = "tmp"+fileSeparator+"file.txt";
           file = new File(relativePath);
           if(file.createNewFile()){
               System.out.println(relativePath+" File Created in Project root directory");
           }else System.out.println("File "+relativePath+" already exists in the project root directory");
       }
   
   }
   

   When we execute the above program from Eclipse IDE for the first time, the below output is produced.

   /Users/pankaj/file.txt File Created
   file.txt File Created in Project root directory
   Exception in thread "main" 
   java.io.IOException: No such file or directory
   	at java.io.UnixFileSystem.createFileExclusively(Native Method)
   	at java.io.File.createNewFile(File.java:947)
   	at com.journaldev.files.CreateNewFile.main(CreateNewFile.java:32)
   

   For the relative path, it throws IOException because tmp directory is not present in the project root folder. So it’s clear that createNewFile() just tries to create the file and any directory either absolute or relative should be present already, else it throws IOException. So I created “tmp” directory in the project root and executed the program again, here is the output.

   File /Users/pankaj/file.txt already exists
   File file.txt already exists in the project root directory
   tmp/file.txt File Created in Project root directory
   

   First two files were already present, so createNewFile() returns false, third file was created in tmp directory and returns true. Any subsequent execution results in the following output:

   File /Users/pankaj/file.txt already exists
   File file.txt already exists in the project root directory
   File tmp/file.txt already exists in the project root directory
   

   If you run the same program from terminal classes directory, here is the output.

   //first execution from classes output directory	
   pankaj:~/CODE/JavaFiles/bin$ java com/journaldev/files/CreateNewFile
   File /Users/pankaj/file.txt already exists
   file.txt File Created in Project root directory
   Exception in thread "main" java.io.IOException: No such file or directory
   	at java.io.UnixFileSystem.createFileExclusively(Native Method)
   	at java.io.File.createNewFile(File.java:947)
   	at com.journaldev.files.CreateNewFile.main(CreateNewFile.java:32)
   
   //tmp directory doesn't exist, let's create it
   pankaj:~/CODE/JavaFiles/bin$ mkdir tmp
   
   //second time execution
   pankaj:~/CODE/JavaFiles/bin$ java com/journaldev/files/CreateNewFile
   File /Users/pankaj/file.txt already exists
   File file.txt already exists in the project root directory
   tmp/file.txt File Created in Project root directory
   
   //third and subsequent execution
   pankaj:~/CODE/JavaFiles/bin$ java com/journaldev/files/CreateNewFile
   File /Users/pankaj/file.txt already exists
   File file.txt already exists in project root directory
   File tmp/file.txt already exists in project root directory
   

2. FileOutputStream.write(byte[] b)

   If you want to create a new file and at the same time write some data into it, you can use FileOutputStream write method. Below is a simple code snippet to show it’s usage. The rules for absolute path and relative path discussed above is applicable in this case too.

   String fileData = "Pankaj Kumar";
   FileOutputStream fos = new FileOutputStream("name.txt");
   fos.write(fileData.getBytes());
   fos.flush();
   fos.close();
   

3. Java NIO Files.write()

   We can use Java NIO Files class to create a new file and write some data into it. This is a good option because we don’t have to worry about closing IO resources.

   String fileData = "Pankaj Kumar";
   Files.write(Paths.get("name.txt"), fileData.getBytes());
   

Вот и все, что нужно для создания нового файла в java-программе.

Вы можете проверить больше основных примеров Java из нашего репозитория GitHub.