java快速读取文本文件最后一行数据内容，文本文件非常大

java快速读取文本文件最后一行数据内容，文本文件非常大

[code="java"]
public static void main(String[] args) throws Exception {
File file = new File("E:/a.txt"); // 100M
long start = System.currentTimeMillis();
String lastLine = readLastLine(file, "gbk");
long delt = System.currentTimeMillis() - start;
System.out.println(lastLine);
System.out.println("读取时间(毫秒):" + delt);

file = new File("E:/b.txt");// 仅一行文字
start = System.currentTimeMillis();
lastLine = readLastLine(file, "gbk");
delt = System.currentTimeMillis() - start;
System.out.println(lastLine);
System.out.println("读取时间(毫秒):" + delt);
}

public static String readLastLine(File file, String charset) throws IOException {
if (!file.exists() || file.isDirectory() || !file.canRead()) {
return null;
}
RandomAccessFile raf = null;
try {
raf = new RandomAccessFile(file, "r");
long len = raf.length();
if (len == 0L) {
return "";
} else {
long pos = len - 1;
while (pos > 0) {
pos--;
raf.seek(pos);
if (raf.readByte() == '\n') {
break;
}
}
if (pos == 0) {
raf.seek(0);
}
byte[] bytes = new byte[(int) (len - pos)];
raf.read(bytes);
if (charset == null) {
return new String(bytes);
} else {
return new String(bytes, charset);
}
}
} catch (FileNotFoundException e) {
} finally {
if (raf != null) {
try {
raf.close();
} catch (Exception e2) {
}
}
}
return null;
}

[/code]

[code="java"]
// 使用RandomAccessFile , 从后找最后一行数据
RandomAccessFile raf = new RandomAccessFile("E:/demo/data.dat", "r");
long len = raf.length();
String lastLine = "";
if (len != 0L) {
long pos = len - 1;
while (pos > 0) {
pos--;
raf.seek(pos);
if (raf.readByte() == '\n') {
lastLine = raf.readLine();
break;
}
}
}
raf.close();
System.out.println(lastLine);[/code]

也可以使用内存映射文件, 和上面的处理类似, 都是从后面向前找回车, 然后获得最后一行数据

使用RandomAccessFile吧，这个类似c语言中的文件指针，可以快速的偏移