Java and XML: putting SAX to work

Why use XML?

XML is becoming increasingly popular. Why is that? After all XML is just a data format, isn't it? To get an understanding of XML's popularity, take a look at this file:

458345-3456,4367.12,6.5
436122-3456,18.30,5
419023-4523,-43218.45,9.5

What do you think it is? Let's take another file--with the same numbers:

<banking>
<account>
  <number>458345-3456</number>
  <balance>4367.12</balance>
  <interest>6.5</interest>
</account>
<account>
  <number>436122-3456</number>
  <balance>18.30</balance>
  <interest>5</interest>
</account>
<account>
  <number>419023-4523</number>
  <balance>-43218.45</balance>
  <interest>9.5</interest>
</account>
</banking>

Suddenly the numbers make more sense, right? So XML is not just a data format, it may also add some kind of information to your data. You might argue that these files are probably read by a computer program, which really doesn't prefer one format over the other, and you'll of course need to know what "number", "balance", and "interest" really mean in order to use the data in a real application. You're right, but programmers still use a lot of time looking at data files--especially when their programs aren't working--and most humans would prefer the last file format.

But the real power in XML is that it is a standardized format. If you give the above XML-file to Internet Explorer for example it'll actually understand it and show it in a nice format:

In the olden days when computing was done on mainframes (if you don't know what a mainframe is then just think of it as a very large server), every program used its own hand-made file formats--often for good reasons. If you compare the sizes of the two files above then the second one contains more than four times as many characters as the first one. If you have slow network connections and expensive storage medias then a factor four means a lot. Numbers can also be packed much more economically in binary formats. For example four bytes for a Java "int" compared with up to ten bytes when the number is in text format.

But today disk storage is cheap, and networks are fast, so unless you have very large data amounts you can afford the XML-format. Again, the important factor which makes XML a good choice is its standardized format. Especially when one considers the nature of the vast global communication network we have today--which includes an array of computer brands and multiple geographical dialects--it becomes imperative to have a common language/method to tie everything together or to allow that communication. Thus, XML simplifies the client-server world we live in.

But without backup from users and vendors no standard will survive. XML is backed by lots of tools, API's, and committees.

We'll start our journey into the XML world by solving a simple task.