读取特定文件，替换第一行内容

private static void replaceTxtFirstLineByStr(String path, String replaceStr) throws Exception {
String temp = "";
try {
File file = new File(path);
FileInputStream fis = new FileInputStream(file);
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader br = new BufferedReader(isr);
StringBuffer buf = new StringBuffer();
//要替换第一行，所以先读取第一行
String firstLineStr = br.readLine();
// 将内容插入
buf = buf.append(replaceStr);
// 保存该行后面的内容
while ((temp = br.readLine()) != null) {
buf = buf.append(System.getProperty("line.separator"));
buf = buf.append(temp);
}
br.close();
isr.close();
fis.close();
FileOutputStream fos = new FileOutputStream(file);
PrintWriter pw = new PrintWriter(fos);
pw.write(buf.toString().toCharArray());
pw.flush();
pw.close();
fos.close();
} catch (IOException e) {

throw new Exception();
}
}