/**
* 读取最后几行
*
* @param file 文件
* @param charset 编码
* @param n 条数
* @param positive 是否正序
* @return ArrayList<String>
*/
public static ArrayList<String> tail(File file, int n, Charset charset, boolean positive) {
ArrayList<String> arrayList = new ArrayList<>();
RandomAccessFile randomAccessFile = null;
try {
randomAccessFile = new RandomAccessFile(file, "r");
//获取文件长度
long length = randomAccessFile.length();
//如果长度小于1，则说明文件为空
if (length < 1) {
return arrayList;
}
long available = length - 1;
//标记文件最后位置
randomAccessFile.seek(available);
for (int i = 0; i < n && available > 0; i++) {
if (available == length - 1) {
available--;
randomAccessFile.seek(available);
}
int c = randomAccessFile.read();
while (c != '\n' && available > 0) {
available--;
randomAccessFile.seek(available);
c = randomAccessFile.read();
}
//标记当前位置
long nowPointer = randomAccessFile.getFilePointer();
String line = new String(randomAccessFile.readLine().getBytes(), charset);
arrayList.add(line);
if (nowPointer > 1) {
randomAccessFile.seek(nowPointer - 2);
}
}
if (!positive) {
Collections.reverse(arrayList);
}
return arrayList;
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
assert Objects.nonNull(randomAccessFile);
randomAccessFile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return arrayList;
}
网友评论