Java Applet Caching Issues

I spent the last 3 days in frustration trying to get Java Plug-in cache mechanisms to work.
Since JDK 1.5, the Java Plug-in has advanced caching options using the "cache_archive" and
"cache_version" tags.

One particular vexing issue that I faced was that inspite of adding all the cache directives in the applet's object tag, the jar files were not cached. A quick google showed 2 bugs:
1. Unfortunately, if the servers do not return Last-Modified or Expires in HTTP response headers, it would disable plugin caching for the connection, and plugin would try to redownload the file again without caching. This results in two HTTP GET requests per file.
2. If a running applet makes a call to URLConnection.setDefaultUseCaches(false), then all subsequent loads from this plugin will exhibit the multiple-load-request behaviour.

In our case, the Applet was setting the cache as false in the code. Hence the cache directives were not working as expected. More information on this can be found here and here.

Search functionality in Textpad and EditPlus

A lot of people use text editors such as Textpad and EditPlus. My favourite is Textpad; it can handle large files and also has a very good interface.

Many times we need to search for muliple words in a line. For e.g. in a log file, search for all lines having words 'abc' and 'xyz' on a single line. Using the regular expression search facility available in these editors, this task becomes a piece of cake.

RegEx for the above task: abc.*xyz
We can keep on adding more words - abc.*xyz.*123

A simple feature, but very powerful while analysing logs etc.

Favicon is a bit messy

Recently when I was analysing the log files on the server, I came across many reqeuests for a resource - favicon.ico
This was strange, since I knew that there was no such file on the server - so why were browsers making a request for this file.

I did a quick google and came to know about this interesting things:
- Favicon stands for "Favourites Icon". Its the small image U see in front of the URL on the addressbar.
- The icon looks good, but the problem is that some browsers keep on making a request to this file everytime the page is loaded !

Here are some links having more info:
http://www.favicon.co.uk/
http://www.htmlkit.com/services/favicon/

Cool collection of JS code

Found this link that contains a cool collection of Javascript code. Worth a perusal.

I liked the fee menu javascript code available here:

http://javascriptkit.com/script/cutindex23.shtml

Interpreting 2 digit years

As a good practice, it is always recommended to use 4 digits to specify the year. But a lot of applications may have a front-end that accepts 2 digit year as the input from the user. Or there could be a intergration with a third-party that requires us to parse 2 digit years.

We all understand the ambiguity in parsing 2 digit years. The logic that you would need to use depends on the business requirement. For e.g. if you are accepting birth-year then it cannot be greater than today and we can go 100 yrs back.

So how do different API's handle it?

The SimpleDateFormat class follows the following logic:
"For parsing with the abbreviated year pattern ("y" or "yy"), SimpleDateFormat must interpret the abbreviated year relative to some century. It does this by adjusting dates to be within 80 years before and 20 years after the time the SimpleDateFormat instance is created."

The Joda Time API takes a different approach:
"What is particularly interesting about this format is the two digit year. Since the interpretation of a two digit year is ambiguous, the appendTwoDigitYear takes an extra parameter that defines the 100 year range of the two digits, by specifying the mid point of the range. In this example the range will be (1956 - 50) = 1906, to (1956 + 49) = 2005. Thus 04 will be 2004 but 07 will be 1907. This kind of conversion is not possible with ordinary format strings, highlighting the power of the Joda time formatting architecture"

The default setting in Windows 2000 m/cs:
"Under Windows 98 or Windows 2000, two-digit years for the Year argument are interpreted based on user-defined computer settings. The default settings are that values from 0 through 29 are interpreted as the years 2000–2029, and values from 30 through 99 are interpreted as the years 1930–1999. For all other Year arguments, use a four-digit year; for example, 1924."

The Internet mail standard uses the following:
"Two digit years are treated as valid in the loose translation and are translated up to a 19xx or 20xx figure. By default, following the specification of RFC2822, if the year is greater than '49', it's treated as being in the 20th century (19xx). If lower, or equal, then the 21st (20xx). That is, 50 becomes 1950 while 49 is 2049."

JS library for dates

I was looking for a reusable JS function that would allow me to format and compare dates just the way it is done in Java using classes such as DateFormat, Date etc.

I found this JS file on the web - simple and easy to use. And quite powerful too:
http://www.javascripttoolbox.com/lib/date/

Difference between empty string and null in Oracle Database

In Oracle, when we store a empty string i.e. "" through JDBC, then Oracle stores it as a NULL value. This causes a lot of confusion to Java developers. In Java a null and a "" are 2 different entities.

Hence even if you store an "" string when inserting into the database, when you retrieve the results, you would get the string as null.

If we do a getInt(), getFloat() etc. then we would get 0.

Dynamically making a field as readOnly using Javascript

I was looking for a sleek solution that would make all the fields of my form read-only dynamically - or atleast make them appear to be readonly.

I decided to use the powerful JQuery library to make this happen. Here is the code that can be put in a JSP/ASP page and included in any page that needs to have all fields as readonly.
$(document).ready(function(){
$(":input,checkbox,radio").addClass("readonlytextbox");
$(":input").focus(function() {this.blur();} );
$("input[@type=checkbox]").click(function()
{alert("Cannot change this field.");
return false;} );
$("input[@type=checkbox]").keydown(function()
{return false;} );
$("input[@type=radio]").click(function()
{return false;} );
$("input[@type=radio]").keydown(function()
{return false;} );
$("select").focus(function()
{alert("Cannot change this field.");
return false;} );
//-- end of code
});

ReadOnly and Disabled fields

In HTML, we have two options if we want non-editable fields. Mark the fields as readonly or make them disabled.

The difference between the two is that a diabled field is not send as a HTTP parameter to the server when the form is submitted, whereas a readonly field is send back to the server.
This may be important when you use frameworks such as Struts where the formbeans may expect nested properties to come back to the server.