Windows hard links

For a very long time I don't know that in Windows OS, there is a technology called 'hard link'. One of the reason is that I usually just use FAT file system and only the NTFS support hard link.

The first time I know about hard link is when looking for information about winsxs folders. All the dll files in System32 are actually hard links point to winsxs folders.

The first time I know about hard link is when looking for information about winsxs folders. All the dll files in .

Using php record visitor information

Its very useful to record the site visitor information like ip address, search keywords, visit url...

Today I will write a simple php script to achieve that. First we need a database table to store the information. Here is the table:

Java traverse a directory and zoom image files

In this example, the code list all the files in a directory and zoom the images into fixed width.

You need these jars:

Java generics Wildcards

The syntax <? extends T> is "any type that is subtype of T".

The list might might be any list that contains subtype of Number. So next code would be wrong.

Java Generics Introduction

The Java Generics is much like the C++ template. But they are also very different from each other.

A simple exampe:

PHP Zoom image, code example

How to zoom image in php? Here is a quick recipe.

 
 
<?php
 
list($image_width, $image_height) = @getimagesize('xx.jpg');
$imgsrc = imagecreatefromjpeg('xx.jpg');
$towidth = 565;
$newwidth = $towidth ;
$newheight = ($image_height * $towidth )/$image_width;
$imgdst = imagecreatetruecolor($newwidth , $newheight );
 
$copy = @imagecopyresized($imgdst, $imgsrc, 0, 0, 0,0, $newwidth , $newheight , $image_width, $image_height );
 
imagejpeg($imgdst, 'yy.jpg');
imagedestroy($imgsrc);
imagedestroy($imgdst);
?>
 

Python dictionaries dict() and {} performance

Dictionary is unordered collection. Python using hash to location element location in dictionary, its very fast to add or remove from dictionary .

Declare a dictionary, there are a lot of different to create dictionary:

How to download gziped web pages with Java

The common way to do this is detect Content-Encoding Http header field, if it exist and value is "gzip", using GZIPInputStream to wrap the InputStream.

But the Content-Encoding is not always reliable, some pages output gzip compressed data without Content-Encoding field set.

Java Mysql Example

MySQL is an Open Source database system, its fast and light weight. MySQL is a very good choice for small to medium size project. It can work with all kinds of platform and languages. This tutorial shows how to work with MySQL in Java.

To use MySQL in Java, we have to get the JDBC driver for MySQL. JDBC is a specification of how to generally access a database. Different database vendor should provide a bridge that connect the specific database implementation and JDBC API. Such a bridge is also called driver or connector.

To use MySQL in Java, we have to get the JDBC driver for MySQL. JDBC is .

Java Volatile keywords

When multiple thread access the same object concurrently , there are two methods to do it: access the original object every time or keep a local private copy of the object. The second way surely faster because access shared memory need some extra works.

But there is a problem: what if the original object changed? In other words, the second method may cause shared variable inconsistent. But for some shared variables , we only read it, never change it or occasionally change it, under this circumstance , its safe to use private local copy and gain the performance.

But there is a problem: what if the original object changed? In other words, the second method .

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