import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
public class StringToFile {
    public static void main(String[] args) throws IOException {
        String msg = "hello";
        Files.write(Paths.get("./duke.txt"), msg.getBytes());
    }
}

來源：java把字符串寫入文件里的簡單方法分享-http://www.jb51.net/article/47842.htm