Writing to file in UTF-8 encoding in FSDataOutputStream (Hadoop)?

I am trying to write a csv to a file in a MapReduce reducer function. Here is my code:

public class DataSet311Reducer extends Reducer<Text, Text, Text, Text> {

  @Override
  public void reduce(Text key, Iterable<Text> values, Context context)
      throws IOException, InterruptedException {
    Configuration conf = new Configuration();
    FileSystem fs = FileSystem.get(conf);
    Path path = new Path(key.toString().toLowerCase() + ".csv");
    FSDataOutputStream os = fs.create(path);
    os.writeChars("KEY,DATE,AGENCY,DESCRIPTOR,LOCATIONTYPE,INCIDENTZIP,INCIDENTADDRESS,LATITUDE,LONGITUDE\n");
    StringBuilder sb = new StringBuilder();
    for (Text value : values) {
      sb.append(value.toString());
      sb.append("|");
      os.writeUTF(value.toString());
      os.writeUTF("\n");
    }
    os.close();
    context.write(key, new Text(sb.toString()));
  }
}

      

        
        
        
      

    

I need to save a file in UTF-8 encoding for use with CartoDB. When checking the file file, it shows me

unspecified.csv: application/octet-stream; charset=binary

How to save content with correct encoding and header content?