Java – How to add and remove BOM from UTF-8 file

By mkyong | Updated: April 14, 2021

Viewed: 28,967 (+237 pv/w)

Tags: bom ByteBuffer hex java.io read bytes read file utf-8 write bytes write file

This article shows you how to add, check and remove the byte order mark (BOM) from a UTF-8 file. The UTF-8 representation of the BOM is the byte sequence 0xEF, 0xBB, 0xBF (hexadecimal), at the beginning of the file.

• 1. Add BOM to a UTF-8 file
• 2. Check if a file contains UTF-8 BOM
• 3. Remove BOM from a UTF-8 file
• 4. Copy a file and add BOM
• 5. Download Source Code
• 6. References

P.S The below BOM examples only works for UTF-8 file.

1. Add BOM to a UTF-8 file

To Add BOM to a UTF-8 file, we can directly write Unicode \ufeff or three bytes 0xEF,0xBB,0xBF at the beginning of the UTF-8 file.

1.1 The below example, write a BOM to a UTF-8 file /home/mkyong/file.txt.

package com.mkyong.io.howto;

import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class AddBomToUtf8File {

  public static void main(String[] args) throws IOException {

      Path path = Paths.get("/home/mkyong/file.txt");
      writeBomFile(path, "mkyong");

  }

  private static void writeBomFile(Path path, String content) {
        // Java 8 default UTF-8
        try (BufferedWriter bw = Files.newBufferedWriter(path)) {
            bw.write("\ufeff");
            bw.write(content);
            bw.newLine();
            bw.write(content);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

Output

$ hexdump -C /home/mkyong/file.txt
00000000  ef bb bf 6d 6b 79 6f 6e  67 0a 6d 6b 79 6f 6e 67  |...mkyong.mkyong|
00000010

$ file /home/mkyong/file.txt
file.txt: UTF-8 Unicode (with BOM) text

$ cat /home/mkyong/file.txt
mkyong
mkyong

1.2 Before Java 8, BufferedWriter and OutputStreamWriter examples of writing BOM to a UTF-8 file.

  private static void writeBomFile(Path path, String content) {
      try (BufferedWriter bw = new BufferedWriter(
              new OutputStreamWriter(
                      new FileOutputStream(path.toFile())
                      , StandardCharsets.UTF_8))) {
          bw.write("\ufeff");
          bw.write(content);
          bw.newLine();
          bw.write(content);
      } catch (IOException e) {
          e.printStackTrace();
      }
  }

1.3 PrintWriter and OutputStreamWriter example to write BOM to a UTF-8 file. The 0xfeff is the byte order mark (BOM) codepoint.

  private static void writeBomFile(Path path, String content) {
      try (PrintWriter pw = new PrintWriter(
              new OutputStreamWriter(
                      new FileOutputStream(path.toFile()), StandardCharsets.UTF_8))) {
          //pw.write("\ufeff");
          pw.write(0xfeff); // alternative, codepoint
          pw.write(content);
          pw.write(System.lineSeparator());
          pw.write(content);

      } catch (IOException e) {
          e.printStackTrace();
      }
  }

1.4 Alternatively, we can write the BOM byte sequence 0xEF, 0xBB, and 0xBF directly to a file.

  private static void writeBomFile4(Path path, String content) {
      try (FileOutputStream fos = new FileOutputStream(path.toFile())) {

          byte[] BOM = {(byte) 0xEF, (byte) 0xBB, (byte) 0xBF};

          fos.write(BOM);
          fos.write(content.getBytes(StandardCharsets.UTF_8));
          fos.write(System.lineSeparator().getBytes(StandardCharsets.UTF_8));
          fos.write(content.getBytes(StandardCharsets.UTF_8));

      } catch (IOException e) {
          e.printStackTrace();
      }
  }

2. Check if a file contains UTF-8 BOM

The below example read the first 3 bytes from a file and check if it contains the 0xEF, 0xBB, 0xBF byte sequence.

package com.mkyong.io.howto;

import org.apache.commons.codec.binary.Hex;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class CheckBom {

  public static void main(String[] args) throws IOException {

      Path path = Paths.get("/home/mkyong/file.txt");

      if(isContainBOM(path)){
          System.out.println("Found BOM!");
      }else{
          System.out.println("No BOM.");
      }

  }

  private static boolean isContainBOM(Path path) throws IOException {

      if(Files.notExists(path)){
          throw new IllegalArgumentException("Path: " + path + " does not exists!");
      }

      boolean result = false;

      byte[] bom = new byte[3];
      try(InputStream is = new FileInputStream(path.toFile())){

          // read first 3 bytes of a file.
          is.read(bom);

          // BOM encoded as ef bb bf
          String content = new String(Hex.encodeHex(bom));
          if ("efbbbf".equalsIgnoreCase(content)) {
              result = true;
          }

      }

      return result;
  }

}

Output

Found BOM!

The import org.apache.commons.codec.binary.Hex; is in the below commons-codec library. Or, we can use one of these methods to convert bytes to hex.

  <dependency>
      <groupId>commons-codec</groupId>
      <artifactId>commons-codec</artifactId>
      <version>1.14</version>
  </dependency>

3. Remove BOM from a UTF-8 file

The below example ByteBuffer to remove BOM from a UTF-8 file.

P.S Some XML, JSON, CSV parsers may fail to parse or process the file if it contains BOM in the UTF-8 file; it is common to remove or skip the BOM before parsing the file.

package com.mkyong.io.howto;

import org.apache.commons.codec.binary.Hex;

import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class RemoveBomFromUtf8File {

  public static void main(String[] args) throws IOException {

      Path path = Paths.get("/home/mkyong/file.txt");
      writeBomFile(path, "mkyong");
      removeBom(path);

  }

  private static void writeBomFile(Path path, String content) {
      // Java 8 default UTF-8
      try (BufferedWriter bw = Files.newBufferedWriter(path)) {
          bw.write("\ufeff");
          bw.write(content);
          bw.newLine();
          bw.write(content);
      } catch (IOException e) {
          e.printStackTrace();
      }
  }

  private static boolean isContainBOM(Path path) throws IOException {

      if (Files.notExists(path)) {
          throw new IllegalArgumentException("Path: " + path + " does not exists!");
      }

      boolean result = false;

      byte[] bom = new byte[3];
      try (InputStream is = new FileInputStream(path.toFile())) {

          // read 3 bytes of a file.
          is.read(bom);

          // BOM encoded as ef bb bf
          String content = new String(Hex.encodeHex(bom));
          if ("efbbbf".equalsIgnoreCase(content)) {
              result = true;
          }

      }

      return result;
  }

  private static void removeBom(Path path) throws IOException {

      if (isContainBOM(path)) {

          byte[] bytes = Files.readAllBytes(path);

          ByteBuffer bb = ByteBuffer.wrap(bytes);

          System.out.println("Found BOM!");

          byte[] bom = new byte[3];
          // get the first 3 bytes
          bb.get(bom, 0, bom.length);

          // remaining
          byte[] contentAfterFirst3Bytes = new byte[bytes.length - 3];
          bb.get(contentAfterFirst3Bytes, 0, contentAfterFirst3Bytes.length);

          System.out.println("Remove the first 3 bytes, and overwrite the file!");

          // override the same path
          Files.write(path, contentAfterFirst3Bytes);

      } else {
          System.out.println("This file doesn't contains UTF-8 BOM!");
      }

  }

}

Output

Found BOM!
Remove the first 3 bytes, and overwrite the file!

4. Copy a file and add BOM

The below example copy of a file and add a BOM to the target file.

package com.mkyong.xml.sax;

import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class CopyAndAddBomToXmlFile {

    public static void main(String[] args) {
        Path src = Paths.get("src/main/resources/staff.xml");
        Path dest = Paths.get("src/main/resources/staff-bom.xml");
        writeBomFile(src, dest);
    }

    private static void writeBomFile(Path src, Path dest) {

        try (FileOutputStream fos = new FileOutputStream(dest.toFile())) {

            byte[] BOM = {(byte) 0xEF, (byte) 0xBB, (byte) 0xBF};
            // add BOM
            fos.write(BOM);

            // BOM + src to fos
            Files.copy(src, fos);

        } catch (IOException e) {
            e.printStackTrace();
        }


    }

}

5. Download Source Code

6. References

• Wikipedia – Byte order mark
• Stackoverflow – What’s the difference between UTF-8 and UTF-8 without BOM?
• Java – Create and write a file
• How to write to file in Java – BufferedWriter
• SAX Error – Content is not allowed in prolog
• Java – How to join and split byte arrays, bytes
• Java – How to convert byte arrays to Hex
• BOM : Java Glossary