String path = File.separator + "app" + File.separator + "test.txt";
File file = new File(path);
reader = new FileReader(file);
char[] bb = new char[1024];
StringBuffer allUploadFilePath = new StringBuffer();
// 每次读取到的字符长度
int n;
while ((n = reader.read(bb)) != -1) {
allUploadFilePath.append(new String(bb, 0, n));
}