Snippet IT » Tips and Tricks

Java: Use ByteBuffer As InputStream

szehau — Mon, 11 Jan 2010 17:05:38 +0000

Sometime, your program may need to read data from a ByteBuffer buffer into a InputStream object. There is no class in Java library that provide the facility to do the conversion.

Anyway, to use a ByteBuffer object as an InputStream is pretty simple. What you need to do is to write a class wrapper that inherit InputStream and override the read() function in InputStream.

Here is the example:


public class ByteBufferInputStream extends InputStream {

  private int bbisInitPos;
  private int bbisLimit;
  private ByteBuffer bbisBuffer;

  public ByteBufferInputStream(ByteBuffer buffer) {
    this(buffer, buffer.limit() - buffer.position());
  }

  public ByteBufferInputStream(ByteBuffer buffer, int limit) {
    bbisBuffer = buffer;
    bbisLimit = limit;
    bbisInitPos = bbisBuffer.position();
  }

  @Override
  public int read() throws IOException {
    if (bbisBuffer.position() - bbisInitPos > bbisLimit)
      return -1;
    return bbisBuffer.get();
  }
}

In this class, ByteBufferInputStream, you can specify the limit to read from the ByteBuffer so that you can use the data in ByteBuffer later for other purposes. The read behavior is same as other InputStream class, where when there is no more data to read (or reached the preset limit), the read() function returns negative one.

Java: Format Integer Into Fixed Width String

szehau — Mon, 04 Jan 2010 17:36:47 +0000

Sometime, you may want to format an integer or a long value into a fixed width String. You need to display the value in fixed width especially in reports where you want to keep the numbers in aligned (e.g. 3456 as 0003456 and 1234 as 0001234).

Other than that, you may also want to format the integer value for a better visibility. For example, to display integer value as a document number (e.g. 12345678 as 00-01234-5678), for example an account number.

The Java.format() is not flexible enough to solve my problem. At least it cannot be used to format a fixed length document number in the format I want: XX-XXXX-XXXX. Therefore I decide write my own format function.

The following function format a integer value into a fixed length String.


public class IntegerUtil {
    public static String formatFixedWidth(int value, int width) {
        char[] chars;
        int i;
        int c;

        chars = new char[width];
        for (i = 0; i < width; i++) {
            c = value % 10;
            chars[width-i-1] = (char)('0' + c);
            value = value / 10;
        }
        return new String(chars);
    }
}

To format the document number like the one I said above, you simply modify the source code above to add one or two lines code to append a "-" to the String when the loop iterate to the place where you want to put the "-". Remember to increase the characters buffer as well.

The following function shows a sample implementation of my document number format.


public class IntegerUtil {
  public static String formatDocumentNumber(int value) {
    char[] chars;
    int i;
    int c;
    int size;

    size = 10+2;
    chars = new char[size];
    for (i = 0; i < size; i++) {
      if (i == 4 || i == 9) {
        chars[width-i-1] = '-';
        continue;
      }
      c = value % 10;
      chars[width-i-1] = (char)('0' + c);
      value = value / 10;
    }
    return new String(chars);
  }
}

Java: Continuously Read Data From FileChannel Without MappedByteBuffer

szehau — Thu, 17 Dec 2009 11:46:01 +0000

When programmer writes a program to read data from a file continuously and sequentially with a fixed data type reading sequence (e.g. to read three integers then 2 doubles repeatedly), he or she may find the MappedByteBuffer from Java library is useful.

MappedByteBuffer is pretty useful because its content is a memory-mapped region of a file. Program can access to the position of the file it wants directly. It also does some optimization on loading data from file, where part of the content are loaded into memory before the read action is actually performed. But when the data will be load? It remains unknown and it is operating system dependent. This is the first problem when using MappedByteBuffer - are the data buffered?

The second problem arises when programmer uses MappedByteBuffer to read a big file. MappedByteBuffer only allows data reading up to the maximum value of an integer (2,147,483,648 bytes). If the program needs to read further from that, it will need to re-map the file by calling the FileChannle.map function by parsing in the correct file position. The programmer will need to be very careful in passing the correct file position because some time it can be very confusing.

To overcome these two problems, we can introduce, design and write a new class that ensures the data reading action is buffered for the best performance and also allows continuous of reading without the need of re-mapping the FileChannle. First, let's write out the pseudo code for the read file action:


get data (e.g. get integer)
  ensure the memory buffer has enough data for the requested data type
    if not enough, read data from file
read the data from buffer and return them in the requested data type

Below is the example of implementation:


public class FileChannelReader {

  private final static int BUFFER_SIZE = 64 * 1024; // 64k

  private ByteBuffer readerBuffer;
  private FileChannel readerFileChannel;

  public FileChannelReader(FileChannel fileChannel) {
    readerBuffer = ByteBuffer.allocate(PAGE_SIZE);
    readerFileChannel = fileChannel;
    readerBuffer.clear();
    readerBuffer.flip();
  }

  // Ensure the buffer has enough data
  private void ensureData(int size) throws IOException  {
    if (readerBuffer.remaining() < size) {
      readerBuffer.compact();
      if (readerFileChannel.read(readerBuffer) <= 0)
        throw new IOException("Unexpected end-of-stream");
      readerBuffer.flip();
    }
  }

  // Get current position
  public long position() throws IOException {
    return readerFileChannel.position() - readerBuffer.remaining();
  }

  // Set current position
  public void position(long position) throws IOException {
    readerFileChannel.position(position);
    readerBuffer.clear();
    readerBuffer.flip();
  }

  // Get integer
  public int getInt() throws IOException {
    ensureData(Integer.SIZE/8);
    return readerBuffer.getInt();
  }

  // Get long
  public long getLong() throws IOException {
    ensureData(Long.SIZE/8);
    return readerBuffer.getLong();
  }

  // And so on ...
}

I'm using this technique in my programming projects and it performs pretty well. The data to be read is always ensured to be buffered and it also reduces complexity in writing a program to read data sequentially.

Wordpress: Catch A Spam Comment With Statcounter

szehau — Fri, 11 Dec 2009 17:21:59 +0000

Sometime your Wordpress' anti spam software (e.g. Akismet) may not able to stop all the comment spam because the comment looks too real to it and to human too. In this case, you will need to identify the comment whether it is actually a real comment or it is automatically submitted by software.

Someone who made a comment must have visited your site. That's it, if he or she has not visited your site but his or her comment is posted on one of your post. Then it is very high possibility that the comment is a spam comment.

How do you ensure someone who left a comment on your blog actually visited your site? The best way to do it is by looking at the IP address where the computer submitted the comment.

In Wordpress, when someone has made a comment, his computer's IP address is recorded. With the IP address, you can check the IP address against the IP address recorded in your website's stats counter.

One of the stats counter software that allows you to look up an IP address is Statcounter. After you have logged in into Statcounter, select your blog website's statistic and then click on the "Look Up IP address" link on the left.

Key in the IP address where your Wordpress comment entry came from and click "Search!". If an entry is matched, that means he or she who submitted the comment has actually visited your website before.

Wordpress: How To Add Table Into A Post

szehau — Wed, 25 Nov 2009 16:23:41 +0000

Wordpress' WYSIWYG post editor does not come with the functionality that allows user to create table when editing a post (like what you can do in Microsoft word).

However, putting a table into a post in Wordpress editor is not as hard as writing a software codes. What you need to know is to familiar yourself with some HTML tags.

To create a table in post, you will need to switch your editor to HTML mode. Simply click on the HTML tab on the top-right of your Wordpress editor and then insert the table codes into the position where you want the table appear.

Here is a simple table:





Column 1
Column 2


Data 1
Data 2

And it looks like this:

Column 1	Column 2
Data 1	Data 2

You can change the table width by changing the width parameter to a certain value, either in pixels (without unit) or percentage (with %). You can also change the border size (border), cell's padding (cellpadding) and cell's spacing (cellspacing). Border size, cell's padding and cell's spacing are in unit pixels.

After you have put the code, change back to visual mode to preview your table. At that time, you can apply format (e.g. color, bold, link and etc) to your text in the table.

Another table with 2 columns in a row are merged:





2 Columns merged


Data 1
Data 2

And it looks like this:

2 Columns merged
Data 1	Data 2

Another table with 2 rows in a column are merged:





Column 1
Column 2


Data 2

And it looks like this:

Column 1	Column 2
	Data 2

It is easy and fun, right? You always have to trial and error to create the table you want. Once you have understood the basic, you can easily create tables with the design you want.

Have fun!;

JavaScript: Overcome Slow Loading JavaScript On A Web Page

szehau — Thu, 19 Nov 2009 11:37:34 +0000

Sometime a web page may load slowly due to loading a third party JavaScript source file from other domain. Most of the time, a web site comes with advertisement scripts or scripts for keep tracking visitors and these scripts are normally provided by third parties like Google Adsense, Statcounter, Amazon and etc. When these scripts' loading speed is extremely slow, it blocks the whole page from loading.

One of the way to overcome the slow loading of JavaScript problems is to move the code that load the JavaScript file to the end of the website before the body tag. For example, . This is so that the browser can load and render the whole page and then only load and run the script.

But this does not actually solve most of the problem. This is because in most time, in most JavaScript, the programmers will use the document.write() method to render the HTML code at the position where the JavaScript is loaded. For example, if you move the source line that load a advertisement to the bottom of the page and left the parameters on top, the advertisement will be loaded at the bottom of the page.

To solve this problem, we can implement a simple tricks with little JavaScript code. The idea is like this:

Put a empty div place holder at the place where you originally want to put and give it a unique name, let's say ads1_ori.
Put a hidden div place holder at the bottom, put the scripts that load slowly inside the place hold and give it a unique name, let's say ads1_new.
At bottom of the page, right before the body tag, write a few line of JavaScript code to load the HTML content from ads1_ori to ads1_new.

Example of implementation:



  Some Web Site
  

  ....

  

  ...

Adobe Acrobat Reader: Possible Security Vulnerability When Acrobat JavaScript Is Enabled

Wordpress: Rename Permalink URL with Ease in Administrator Page

szehau — Wed, 18 Nov 2009 11:48:09 +0000

It is quite troublesome every time when blogger wants to rename a post's permalink URL after he or she has renamed the post's title in Wordpress's administrator page. Blogger needs to click the Edit button next to the permalink URL and modify the text accordingly.

Blogger now can do it with a easier way with this simple trick. After you have changed the post title, click the Edit button next to permalink's URL, empty the text inside and click Save. Wordpress will automatically write the full permalink URL again for you.

That's all what you need to do to rename the whole permalink URL. Simple right? Have fun!

Wordpress: Schedule to Publish a Post

szehau — Tue, 17 Nov 2009 12:00:55 +0000

To publish a post doesn't mean you always need to be in front in your computer. Using Wordpress, you can simply write a post, schedule it and forget it. Wordpress will then publish your scheduled post at the right time!

Here is how you schedule Wordpress to publish your post in future:

Write your post as usual.
On your right hand side, find the words Publish immediately.
Click on the Edit link and change the date and time to any date and time in future.
Make sure you click the OK button.
Then you will see the blue color Publish button has been changed to Schedule.
Press Schedule button once you have done editing your post.

That's it. Your post will be published at the date and time you have set.

Youtube: Stop Youtube From Loading

szehau — Sun, 06 Sep 2009 14:46:14 +0000

Previously, I wrote a "how to" article on How to stop Youtube loading data from the Internet using Google Chrome. Now you can do it at any browser using this simple trick.

To stop Youtube from loading immediately, simply drag the progress button at the progress bar (at the bottom of the video) to the end (to the right hand side) and Youtube will assume the video has ended and stop loading data from the Internet. That's all what you need to do!

BigDump: Alternative to phpMyAdmin to Import/Restore Large Database

szehau — Tue, 07 Jul 2009 15:15:29 +0000

Recently I was facing problem on restoring database with a lot of data into MYSQL using phpMyAdmin. The restoring process keeps interrupted due to the connection between browser and server time's timeout and also due to the timeout in PHP script. Only partial data is restored and I kept dropping the database, increase PHP timeout, increased memory limit, and tried to restore again. But it still failed.

Then, I found a very useful, free script BigDump which helps me to solve my problem. The way it work is pretty simple. It simply split the dump data into a few parts and execute it one by one. The script remembers where is the point it ups to in session, execute a portion of data, and then restart itself to continue to process the un-process data.

If you are having problems importing or restoring huge data into MYSQL using phpMyAdmin, you can try using this script. You can either upload your MYSQL dumps from the script page or point it to the MYSQL dumps located in your server.

Download BigDump (about 10kb)

Gmail: Drag and Drop, Hiding and More

szehau — Thu, 02 Jul 2009 15:53:37 +0000

Gmail developers make more enhancement to the Gmail labeling. Previously, Gmail has the new label menu added with shortcut keys, now it comes with drag and drop, hiding and more features.

New location for labels

The new labels are now located at your left sidebar (or on the right, for those of you using the Arabic, Hebrew, or Urdu versions of Gmail). The labels are grouped together with other system labels such as inbox and spam.

Label hiding and showing

Instead of showing a long list of labels (if you have a long long list as what I have), Gmail now show only a few labels and you can access to the rest by click the more link.

You may have named your label ++somthing to make it on top previously. Now the control is on yours. You can simple drag and drop to reorder the labels.

Drag and Drop

This is the coolest feature I like the most. You can now drap messages and drop to label or drag label and drop to messages. Drag and drop messages to label is just like using the "Move to" label function. While drag and drop label to messages is just like using the "Label" message function.

Google Adsense: Can I place small images next to my Google ads?

szehau — Wed, 17 Jun 2009 08:30:10 +0000

You may have seen people to put small images next to Google ads with size Medium Rectangle (300 x 250) and Large Rectangle (336 x 280) to gain more clicks and to get higher click thru rate.

Can you actually do that? The answer is no.

According to Google Adsense, the way you put the images will mislead the visitor that that the images and the ads are directly associated, or that the advertiser is offering the exact item found in the neighboring image.

They may click the ad expecting to find something that isn't actually being offered. That's not a good experience for users or advertisers.

Google Chrome: How to Stop Youtube Loading Data from the Internet

szehau — Mon, 25 May 2009 17:36:27 +0000

I love Youtube and I believe many people love it too. Many people like to embed the Youtube video into their websites or blogs so they can write something about the video and share with friends.

Sometimes, after I have clicked the play button on the embedded video in somebody's blog but I would like to stop it because I found that the video is not interested to me at all. I can only pause the video and I can't stop it from loading data from Internet because there is no stop button at the embed video.

At the same time, I also feel don't want to leave the page because I haven't finished reading the post content or comments left on the page. But to stop the video from loading, I have to navigate to other page and back to the page again.

It's quite useful to have a stop button at the video because I don't want the Youtube application to keep consuming my network's bandwidth (which is pretty slow in my country). A typical video can have size from a few mega bytes to hundreds of mega bytes.

To solve the problem, I found a really simple trick to stop the Youtube video from loading in Google Chrome browser. I'm not sure whether you can perform it on other browser or not.

Google Chrome runs plug-in in other process. A Youtube video is a Shockwave application which is a plug-in to Google Chrome browser. So to stop the video from loading, you simply kill the Shockwave plug-in process. Please note that killing the process may cause applications (e.g. flash animation) at other tabs in Google Chrome browse not working.

To kill the process, right click on Google Chrome at your windows task bar (or right click Google Chrome Windows' title) and select "Task manager". This is the task manager for Google Chrome only and not for the whole Windows Operating System. After that find the process with name "Plug-in: Shockwave Flash" and click on it. Then click "End process" button to end the process. To reload the video again, simply refresh the page.

Again, please note that killing the process may cause plug-ins / applications (e.g. flash animation) at other tabs in Google Chrome browse not working.

Wordpress Theme: How to Enable Gravatar in Wordpress Theme

szehau — Thu, 07 May 2009 16:33:13 +0000

Gravatars are Globally Recognized Avatars. An avatar or gravatar is an icon, or representation, of a user in a shared virtual reality, such as a forum, chat, website, or any other form of online community in which the user(s) wish to have something to distinguish themselves from other users.

To enable Gravatar in your Wordpress theme's comments, you will need to have some knowledge on editing PHP code and a little bit knowledge on Wordpress architecture. The minimum requirement to allow Gravatar to work on your theme is to have Wordpress running at version at least 2.5.

Open and edit the file that contains the code to generate comments (normally comments.php) in your Wordpress theme folder. Find the portion of code where all comments are looped and printed out. For example:



  ......

Put the following code in the portion of code above:

Depending on how large is the Gravatar image you want to display on your page, you can adjust the $size = '64' to other value (pixels). The default size if 92 pixels if you don't specified the size value.

Read Wordpress Codex for more on using Gravatar.

Gmail: How to Search Your Email Quickly in Gmail

szehau — Thu, 07 May 2009 15:15:23 +0000

If your are using Gmail as you email client, how do you search all your emails from your girl friends with keywords "I love your" for a certain date range for the received emails?

You can use the advanced search options by clicking the "Show search option" next to the search box in Gmail or use Gmail's built-in command. You may not notice there are actually a few short comands that let you search your desire emails quickly and these "commands" have been used when you perform an advanced search.

I have discovered a few pretty useful commands by playing around with the advanced search functions in Gmail. The commands are pretty simple and pretty "human" friendly. Link the Google Search, the commands are in action:value format.

There maybe more, but below at those that I have discovered:

in:folder - The search result will include all the emails in the selected folder. Some of the valid folder name are inbox (Gmail inbox), drafts (Drafts folder), chats (all chat messages), spam (Spam folder), trash (Trash folder) and anywhere (Inbox, Spam and Trash folders).
For example to search all emails in Trash folder with keyword "hello", simply key in in:trash hello in Gmail search box.
is:status - The search result will include all the emails in the selected status. Some of the valid status are sent (sent emails), starred (emails that marked with star), read (already read emails) and unread (unread emails).
For example to search all unread emails with keyword "hello", simply key in is:unread hello in Gmail search box.
label:label-name - The search result will include all the emails with the specified label. Spaces in label must replaced with dashes(-).
For example to search all emails labeled with "My Girlfriend" with keyword "I love you", simply key in label:My-Girlfriend I love you in Gmail search box.
from:name-or-email - The search result will include all the emails sent by the specified name.
For example to search all emails from Kent or kent@example.com with keyword "hello", simply key in from:kent hello or from:kent@example.com hello in Gmail search box.
to:name-or-email - The search result will include all the emails sent to the specified name.
For example to search all emails sent to Kent or kent@example.com with keyword "hello", simply key in to:kent hello or to:kent@example.com hello in Gmail search box.
subject:(keywords) - The search result will include all the emails with the specified keywords.
For example to search all emails with subject "please return my money", simply key in subject:(please return my money) in Gmail search box.
has:attachment - The search result will include all the emails with attachment.
after:date - The search result will include all the emails after the specified date. The date format is in yyyy/m/d.
For example to search all emails after the date 2009/5/7, simply key in after:2009/5/7 in Gmail search box.
before:date - The search result will include all the emails before the specified date. The date format is in yyyy/m/d.
For example to search all emails after the date 2009/5/7, simply key in after:2009/5/7 in Gmail search box.
To seach emails without specific keywords, simply put a minus infront of the keyword.
For example to search all emails with keyword "hello" but not "world", in:trash hello -world.

Have fun with your Gmail search!

Snippet IT » Tips and Tricks

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