File file = new File(filepath);

BufferedInputStream fis = new BufferedInputStream(new FileInputStream(file));

BufferedReader reader = new BufferedReader(new InputStreamReader(fis,"utf-8"),10*1024*1024);// 用10M的缓冲读取文本文件  

String line = "";

while((line = reader.readLine()) != null){

   //TODO: write your business

}

String path = "你要读的文件的路径";

        RandomAccessFile br = new RandomAccessFile(path, "rw");

        String str = null, app = null;

        int i = 0;

        while ((str = br.readLine()) != null) {

            i++;

            app = app + str;

            if (i >= 100) {// 假设读取100行

                i = 0;

                // 这里你先对这100行操作，然后继续读

                app = null;

            }

        }

        br.close();