Tutorial Java : File Read and Write

Useful Java file I/O class

Studying Java is an exciting thing. I really love coding and I am really happy to share that. After writing the Devilish Children, I was confused when writing the next game. One thing that is so important is File Input and Output. I mean, I need to know the easiest way to read and write text file using Java. After searching for the sollution, I found some easy way to do that. I just have to create a FileUtil class that has static method to read and write file. Actually, I get this code from a Game Engine called GTGE. Because GTGE is an open source project, I modified it to fulfill my requirement, added some comments, and write it to this blog.

Here is the source code of FileUtil.java class:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;

/**
 * This class has been written by Haqqi. You can
 * freely use, modify, and distribute it.
 * @author Haqqi
 */
public class FileUtil {
  /**
   * Private constructor to prevent the object creation
   */
  private FileUtil() {}
  /**
   * Set the file based on relative path
   * @param filePath Path of the file
   * @return Generated file
   */
  public static File setFile(String filePath) {
    // create new file object
    File file = null;
    // getting the path from working directory
    // you can check the directory by printing it
    String path = System.getProperty("user.dir")
        + File.separatorChar + filePath;
    try {
      // construct the file based on the path
      file = new File(path);
    }
    catch(Exception e) {
      e.printStackTrace();
    }
    // if file is not found, then throw exception
    if (file == null) {
      throw new RuntimeException();
    }
    return file;
  }
  /**
   * Write an Array of String into a file. The written
   * file will be just like a text file.
   * @param text Array of String that want to be written
   * @param file File
   * @return true if success and false if not
   */
  public static boolean fileWrite(String[] text,
      File file) {
    try {
      // create buffer
      BufferedWriter out = new BufferedWriter(
          new FileWriter(file));
      PrintWriter writeOut = new PrintWriter(out);
      // writing text to file
      for (int i = 0; i < text.length; i++) {
        writeOut.println(text[i]);
      }
      // close the writer
      writeOut.close();
      return true;
    }
    catch (IOException e) {
      e.printStackTrace();
      return false;
    }
  }
  /**
   * Read file from a file
   * @param file
   * @return
   */
  public static String[] fileRead(File file) {
    try {
      // buffered reader
      BufferedReader readIn = new BufferedReader(
          new FileReader(file));
      // ArrayList to store the string each line
      ArrayList list = new ArrayList();
      // Temporarily object
      String data;
      // Read each line until end of line
      while ((data = readIn.readLine()) != null) {
      list.add(data);
      }
      // closing reader
      readIn.close();
      // return as Array of String
      return (String[])list.toArray(new String[0]);
    }
    catch (IOException e) {
      e.printStackTrace();
      return null;
    }
  }
}

The constructor is modified to be private to prevent the object creation, since all the methods is static method. Before you use fileWrite and fileRead method, you can easily set the file by using setFile method. You just need to set the relative path of the file from working directory. For example, if your woring directory is "D:\\My Java Project\TheProject", and your file is inside folder "data" and titled "My Files.my", so you just call setFile("data/My Files.my"); to get the file. Use the set file in method fileRead and FileWrite. Remember that fileRead returns an Array of String. Each index for 1 line in the file.

Ok, I hope this post will be very helpful for you. Please be free to leave a comment.