java写文件UTF-8格式

String fileName = dir + File.separator + date + File.separator + (file.list().length + 1) + ".txt";
File file = new File(fileName);

BufferedWriter writer = null;
FileOutputStream writerStream = new FileOutputStream(file);
writer = new BufferedWriter(new OutputStreamWriter(writerStream, "UTF-8"));

StringBuilder strBuild = new StringBuilder();

writer.write(strBuild.toString());

注意上面的代码最好放在catch中，然后在finally中添加

writer.flush();
writer.close();

参考链接：https://blog.csdn.net/dunceiam/article/details/43190609