Java provides a standard way of reading from and writing to files. The java.io package contains classes which can be used to read and write files and other sources.

Java will read all input as a stream of bytes. The InputStream class is the superclass of all classes representing an input stream of bytes.

Classes from the java.io package can be chained, e.g. certain classes handle the reading and writing of an input stream of bytes while others provide a higher level of abstraction, e.g. to read a line of a file.

In general the classes in this package can be divided into the following classes:

You can access files relative to the current execution directory of your Java program. To print the current directory in which your Java program is running, you can use the following statement.

System.out.println(System.getProperty("user.dir")); 

To read a text file you can use the following method:

public String readTextFile(String fileName) {
  
  String returnValue = "";
  FileReader file = null;
  
  try {
    file = new FileReader(fileName);
    BufferedReader reader = new BufferedReader(file);
    String line = "";
    while ((line = reader.readLine()) != null) {
      returnValue += line + "\n";
    }
  } catch (Exception e) {
      throw new RuntimeException(e);
  } finally {
    if (file != null) {
      try {
        file.close();
      } catch (IOException e) {
        // Ignore issues during closing 
      }
    }
  }
  return returnValue;
} 

To write a file you can use the following method:

public void writeTextFile(String fileName, String s) {
    FileWriter output = null;
    try {
      output = new FileWriter(fileName);
      BufferedWriter writer = new BufferedWriter(output);
      writer.write(s);
    } catch (Exception e) {
      throw new RuntimeException(e);
    } finally {
      if (output != null) {
        try {
          output.close();
        } catch (IOException e) {
          // Ignore issues during closing
        }
      }
    }

  } 

You can also create the directories automatically for a given file path. The following code shows an example.

File file = new File("foo/bar/test.txt");
File parent = file.getParentFile();

if(!parent.exists() && !parent.mkdirs()){
    throw new IllegalStateException("Couldn't create dir: " + parent);
}