java i/o BufferedWriter 出现漏读数据的问题

Question

public void Writerdemo(){

double startime = System.currentTimeMillis();

String s1="F:/tt.txt";

String  str = "imooc";

File file =new File(s1);

if(file.exists()){

}else{

try {

file.createNewFile();

} catch (IOException e) {

e.printStackTrace();

}

}

String id=null;

int n=1;

try {

FileWriter fw = new FileWriter(file,true);

BufferedWriter bufw = new BufferedWriter(fw);

for(int i=1;i<1000;i++){

if(i%99==0){

s1="F:/tt"+n+".txt";

bufw = new BufferedWriter(new FileWriter(new File(s1),true));

n++;

}

id= "ID:"+i+"\t";

String s = id+str;

bufw.write(s);

bufw.newLine();//换行

}

bufw.close();

fw.close();

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

double endtime = System.currentTimeMillis();

System.out.println("程序运行时间："+(endtime-startime)/1000+"秒");

}

程序运行后每个文件之间总有十几条或几十条数据没有了，不知道什么出问题了 ，求指教！！