Long end,long num,File file,String charset
4個參數說明
end 相當於座標，tail 向上的起點，num是讀取的行數,file 目標檔charset字元集預設UTF8
end 為null 代表從檔案最末端向上取得。
Map m=FileUtil.tail(null,10,file,null)//讀取檔案最後10行，結果在m.get(FileUtil.ARR) 裡
FileUtil.tail(m.get(FileUtil.POINT),3,file,null)//讀取檔案倒數11行到13行，其實就是接著上邊的第10行再向上讀3行
複製代碼代碼如下:
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){//取得的行數不夠，且沒有到達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;
}
}