Writing a File in Java

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Different ways to write text files in Java.

BufferedWriter

Use java.io.BufferedWriter to write text to character-output stream. This class buffers characters to provide a more efficient writing.

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public static void writeFile(String filename, String content) {
  try( BufferedWriter writer = new BufferedWriter(new FileWriter(filename))) {
    writer.write(content);
  } catch(IOException e) {
    e.printStackTrace();
  }
}

An easier way to create BufferedWriter is to use Files.newBufferedWriter method

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try( BufferedWriter writer = Files.newBufferedWriter(Path.of(filename), StandardCharsets.UTF_8)) { ... }

If you need to write the file to a directoy that may not be exist yet, then you may need to create nonexistent directories first.

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try {
  Files.createDirectories(Path.of("path/newpath/"));
} catch (IOException e) {
  e.printStackTrace();
}

Append String to existing File

You can append content at the end of the file if you set the append parameter to be true when creating the FileWriter.

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public static void appendFile(String filename, String content) {
  try( BufferedWriter writer = new BufferedWriter(new FileWriter(filename, true))) {
    writer.write(content);
  } catch(IOException e) {
    e.printStackTrace();
  }
}

Append to file using Files.newBufferedWriter method

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public static void appendFile(String filename, String content) {
    try( BufferedWriter writer = Files.newBufferedWriter(Path.of(filename), StandardCharsets.UTF_8, StandardOpenOption.APPEND)) {
        writer.write(content);
    } catch(IOException e) {
        e.printStackTrace();
    }
}

PrintWriter

If you need to print formatted text, then use java.io.PrintWriter

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public static void writeFile(String filename, String content) {
  try( PrintWriter printWriter = new PrintWriter(new FileWriter(filename))) {
    printWriter.println("Hello World");
    printWriter.printf("There are %d apples here", 15);
  } catch(IOException e) {
    e.printStackTrace();
  }
}

Write Uing Files Class

java.nio.file.Files class provides static methods to write files.

use Files.write​(Path path, byte[] bytes, OpenOption... options) method to write bytes.

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public static void writeFile(String filename, String content) {
  try {
    Files.write(Path.of(filename), content.getBytes());
  } catch (IOException e) {
    e.printStackTrace();
  }
}

use writeString​(Path path, CharSequence csq, Charset cs, OpenOption... options) to write string to file

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public static void writeFile(String filename, String content) {
  try {
    Files.writeString(Path.of(filename), content, StandardCharsets.UTF_8);
  } catch (IOException e) {
    e.printStackTrace();
  }
}

Reference