ObjectOutputStream 乱码,该怎么解决

        FileOutputStream fos = new FileOutputStream(filename);
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(new Date());
        

String defaultCharsetName=Charset.defaultCharset().displayName();   
 System.out.println("defaultCharsetName:"+defaultCharsetName);
 

output: defaultCharsetName:UTF-8

 if v:lang =~ "utf8$" || v:lang =~ "UTF-8$"
     set fileencodings=gbk,utf-8,chinese,latin-1
     set termencoding=utf-8
     set encoding=utf-8
   endif 

 public static void FileWriterTest(String filename) throws IOException {
		String s = "try";
		String s1 = "agin";	
		FileWriter fw = new FileWriter(filename);
		fw.write(s, 0, s.length());
		fw.write(s1,0,s1.length());
		fw.flush();
	}