怎么实现一个tail，一开始的想法是在本地或者内存记录下当前读取到的文件的位置，然后每隔一定时间检测下看看是否有更新，想好了之后就准备开始写，但是按照习惯，能偷懒绝对不动手的原则首先google了一把，果不其然，网上已经有实现方案了，二话不说，拷贝过来进行修改。

思路就是我刚才的思路，但是接下来这个思路有个问题，就是轮询的效率并不高，而且读取不是实时的，因为我要做远程的这种文件同步，延迟性的tail肯定不可取，所以加入jdk7的新特性，进行文件监控，这样每次文件有更新，将会第一时间被通知到，然后进行相关的tail操作，核心代码如下：

public void run() {long filePointer = 0;if (this.startAtBeginning) {filePointer = 0;} else {filePointer = this.targetFile.length();}try {this.tailing = true;RandomAccessFile file = new RandomAccessFile(targetFile, "r");while (this.tailing) {WatchKey key = watchService.take();for (WatchEvent<?> event : key.pollEvents()) {System.out.println("[Tail monitor ] " + event.context() + "  " + event.kind() + " was triggered");}long fileLength = this.targetFile.length();System.out.println("fileLength : " + fileLength);if (fileLength == 0) {System.out.println("fileLength : " + fileLength);Thread.sleep(sampleInterval);System.out.println("Sleep : " + sampleInterval);key.reset();continue;}if (fileLength < filePointer && fileLength != 0) {file = new RandomAccessFile(targetFile, "r");filePointer = 0;}if (fileLength > filePointer) {file.seek(filePointer);String line = file.readLine();while (line != null) {line = new String(line.getBytes("8859_1"), tailFileCharSet);this.fireNewLogFileLine(targetFile.getName(), line);line = file.readLine();}filePointer = file.getFilePointer();}key.reset();}file.close();} catch (IOException e) {e.printStackTrace();} catch (InterruptedException e) {e.printStackTrace();}}

具体的远程tail，请移步

http://git.oschina.net/grom/rainy

然后在测试的时候发觉到一个很坑爹的问题，读取出来的日志居然有乱码，经过排查，RandomAccessFile有下面的一句

 switch (c = read()) {

C是个char类型，这不是坑爹么，不读成byte，读成char，那你使用的什么编码？算了，按理说应该是8859-1，直接转下试试，果然成功

line = new String(line.getBytes("8859_1"), tailFileCharSet);