In the following snippet you can find out how to use the InetAddress class to obtain the ip of the server where a domain is hosted along with the DNS information. Using this class you’ll obtain only the technical DNS details(name server, SOA & MX records), not the emails or the names of the domain owners.
Read the rest of this entry »

(No Ratings Yet)

 Loading ...

There are 2 useful classes in java to manipulate dates: java.util.Date and java.util.Calendar. Another useful class to format and parse string dates is java.text.SimpleDateFormat. Read the rest of this entry »

(No Ratings Yet)

 Loading ...

When you have to deal with a large amount of data to be operated on mySQL databases, the performance can be dramatically improved using a few simple tweaks.

First of all you have to use Statement.addBatch/executeBatch instead of simple execute methods. For each added batch, the jdbc driver will store in local memory and when the executeBatch is invoked, all the batches are sent at once to the database. This will result in an huge speed improvement.
Read the rest of this entry »

(No Ratings Yet)

 Loading ...

Here is a snippet that shows how to download a file in java. The snippet is tested and works just fine:

	static public void download(String address, String localFileName)
											throws MalformedURLException
												 , FileNotFoundException
												 , IOException
	{

		URL url = new URL(address);

		OutputStream out = new BufferedOutputStream(
								new FileOutputStream(localFileName));
		URLConnection conn = url.openConnection();
		InputStream in = conn.getInputStream();

		byte[] buffer = new byte[1024];
		int numRead;
		int progress = 0;
		while ((numRead = in.read(buffer)) != -1) {
			out.write(buffer, 0, numRead);
			progress += 1024;
			System.out.print("\r" + (int)(progress / 1000)+ "kb");
		}            

		in.close();
		out.close();
	}

(No Ratings Yet)

 Loading ...

HttpClient is an apache java library that can be used to read pages over http. It can be used mainly for webpages and provide a well defined API that can handle Cookies, Sessions,… It offers support for both Get and Post methods, so it’s very useful for writing http java clients that can login and perform different actions on webpages.

Starting with the version 4 the classes were drastically changed. Old tutorials don’t works anymore and the class names and methods were changed to some degree which makes old code pretty useless if you want to switch to a version 4.
Read the rest of this entry »

(No Ratings Yet)

 Loading ...

Sometimes I feel there are too many classes in java to work with streams and files. InputStream is the base class of all the classes in Java IO API. The input stream class is intended to be used to read the data from different sources in chunks. This is useful for large streams that don’t fit in memory.

Lots of libraries returns objects of type InputStream and sometimes you know the stream small and you just need the data as a simple String. Here is the snippet written as a static method to transfer the data from a InputStream to a String.
Read the rest of this entry »

(No Ratings Yet)

 Loading ...

Method chaining is a simple programming technique that can be implemented in almost any programming language. In simple words, it means that a method performs some operations on “this” object and then returns it so it can be used further more. It allows us to invoke several methods one after another, on one or different objects, usually written in the same line.

For example we can build a rectangle class using using the Method Chaining for setters. You can see the setters are a little bit different than regular setters:

class ChainedRectangle
{
    protected int x;
    public ChainedRectangle setX(int x) { this.x = x; return this; }

    protected int y;
    public ChainedRectangle setY(int y) { this.y = y; return this; }

    protected int width;
    public ChainedRectangle setWidth(int width) { this.width = width; return this; }

    protected int height;
    public ChainedRectangle setHeight(int height) { this.height = height; return this; }

    protected String color;
    public ChainedRectangle setColor(String color) { this.color = color; return this; }
}

Then if we need to build a rectangle we can write a single line for setting all the required values:

new         Rectangle().setX(10).setY(10).setWidth(13).setHeight(15).setColor("red");

Along with autocomplete option in most of todays IDEs method chaining might provide a suggestive way of doing some actions in less code.
Read the rest of this entry »

(No Ratings Yet)

 Loading ...

I was starting today to look on different approaches and techniques that are used in scalable web or non web applications. One technique used in many large systems is simply called “memory cache”. It means that data are cached in memory so the data will not be queried again.

Cache and memory cache exists for a long time; even the hardware parts link hard disks cd units have some sort of memory cache.

Why memory cache becomes so important when we talk about web applications? It’s simple. Because web applications happens to fulfill thousands of requests simultaneously. Or sometimes they have to. It’s obvious that keeping the data into memory and reuse it the next time you need it it will improve the performance. And it looks very simple. At the first view simple hashmap would do the job, unless…

There a few facts we need to be consider in real world:

• What happens when the database is updated?
• In most cases a web application create a thread for each http request. The same thing happens in java of php or other languages. The creation of the threads is handled by the web server, web container, and not by the code we write.
• The scalable applications run distributed on multiple servers. If one application change the database, the cache system should be informed on all the machines.

Read the rest of this entry »

(No Ratings Yet)

 Loading ...

Using Google Guice in web applications can raise some issues. First of all when we talk about web applications we talk about servlets and we talk about managed environments. The creation of servlets in not controlled by us, when we write the application, it is controlled by the web application container. This generates some problems:
- Because we can not control the servlet creation we can not use Guice to inject servlet members in the classic way.
- Bootstrapping: we need a mechanism to bootstrap Guice into the application. The best way is to do it at start up before any http request will be invoked.
Read the rest of this entry »

(2 votes, average: 4 out of 5)

 Loading ...

I use windows and I hate when I have to switch on another computer, or when I have to do any change related to windows especially changing the environment variables. I like to download the tool, framework, … I use as a zip and then to do minimal operations to install it. The thing I hate the most is setting environment variables, and path in that small dialog window. I have all my java applications and frameworks in one single directory so the configuration depends only on the thing I hate most: thats right, environment variables.
Read the rest of this entry »

(No Ratings Yet)

 Loading ...