Java implementation of backward reading file function sample sharing

Long end, Long num,File File,String charset
Four parameters
End corresponds to the coordinate, tail up the starting point, num is the number of lines read,file charset character set default UTF8
Null end means to fetch from the end of the file up.

Map m=FileUtil. Tail (null,10,file,null)// read the last 10 lines of the file and the result is in m. et(fileutil.arr)
FileUtil. Tail (m.get(fileutil.point),3,file,null

public class FileUtil {
    private static final long step=5000;
    public static final String ARR="arr";
    public static final String POINT="point";
    public static Map tail(Long end,long num,File file,String charset)throws Exception{
        if(num<=0||(end!=null&&end<0)){
            throw new IllegalArgumentException();
        }
        Map map=new HashMap();
        RandomAccessFile acc=null;
        try {
            acc = new RandomAccessFile(file, "r");
            long temp_end = (end == null ? acc.length() : end);
            long my_point = temp_end > step ? (temp_end-step) : 0;
            acc.seek(my_point);
            LinkedList<Object[]> queue = new LinkedList<Object[]>();
            String temp;
            int n=0;
            while((temp=acc.readLine())!=null){
                if(++n==1&&my_point!=0){
                    continue;
                }
                Object[]  objects=new Object[2];
                long point = acc.getFilePointer();
                if(point>=temp_end&&end!=null){break;}
                objects[0]=point;
                objects[1]=new String(temp.getBytes("8859_1"),charset);
                if(queue.size()==num){
                    queue.poll();
                }
                queue.offer(objects);
            }
            if(queue.size()<num&&my_point>0){
                long last_num=num-queue.size();
                Object[] header = queue.peek();
                if(header==null){throw new RuntimeException("FileUtil step:"+step+" not enough long");}
                Map m = tail((Long)header[0], last_num, file,charset);
                map.put(POINT,m.get(POINT));
                map.put(ARR,ArrayUtils.addAll((Object[])m.get(ARR),queue.toArray()));
            }else if(queue.size()>0){//I didn't get enough rows, and I didn't get to TOP
                map.put(POINT,queue.peek()[0]);
                map.put(ARR,queue.toArray());
            }
        }finally {
            if(acc!=null){
                try {
                    acc.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return map;
    }

}