自定义 log 输出

实现往一个文件以追加方式将数据写入到文件中

File f = new File(fileName);

if(!f.exists()){
f.createNewFile();
}
RandomAccessFile raf = new RandomAccessFile(f,"rw");
raf.seek(raf.length());
String msg = str + "\n";
raf.write(msg.getByte("utf-8"));
raf.close();