Java is more beautiful with Lombok

I have been using Lombok for a couple of years now and find it extremely useful. Below is why you should consider it.

Why should I use Lombok?

1. Reduces boilerplate.
   - No need to write getter/setter/toString/equalsAndHashcode methods
   - Makes it easy to spot class behavior instead of boilerplate around the state.
2. Inherent support for Builder design pattern. This means no need for class constructors with lengthy set of arguments.
3. Annotation based - improves code readability
4. Industry-wide acceptance (including e-commerce giants and financial services companies)
5. Intellij Idea v2020.3+ inherently support Lombok. So no need to use any plugin.

What about the not-so-good things?
IDE needs to support Lombok else your code wouldn't compile.
- Intellij Idea v2020.3+ support Lombok inherently. For older versions you would need to use a plugin (available for free).

- For Eclipse and other IDE, download plugin for Lombok website

With most users already on Intellij/Eclipse, I hardly see this as an issue

What do I need to get started ?

1. Add Lombok maven dependent to your project
2. Install Lombok plugin for your IDE (not required for Intellij Idea v2020.3+)

Is there a learning curve?

Yes, but its pretty much flat.

Documentation is very good (https://projectlombok.org/features/) and one can get started in well within 30 mins.

Can I get rid of Lombok if I don't like it ?
Yes ofcourse. Delombokify the classes using below simple command which will replace all lombok annotations with the actual code.

java -jar lombok.jar delombok <src-code-dir> -d <delombok-code-dir>

 Code with Lombok annotations

Code which has been delombok-ified using the library's delombok feature

                                                            .... some more getters and setters

The curious case of incorrect JAVA version

I have both JRE6 and JRE7 on my system. I had set the 'path' System Variable to point to JRE6, but whenever I executed 'java -version' on command prompt, java version was 7. Now this is a bit baffling !

Apparently, there was a java.exe file in my System32 folder. And this file was getting executed instead of the one pointed by 'path' variable. I deleted those files and things now function as expected.

Now, the question arises, what was java.exe file doing in System32 folder. I guess automatic java updates remotely done by the System Administrator in my company could be the reason.

I spent quite some time debugging this issue. This is what happens when somebody else messes with your dev machine without letting you know :-|


Interesting Links:
- http://stackoverflow.com/questions/11063831/what-is-the-difference-between-system32-java-exe-and-program-files-java-jdk1
- http://stackoverflow.com/questions/8223511/how-to-prevent-that-java-exe-is-installed-in-windows-system32

String.split() issue in IE8

String.split() behaves differently in IE8 and Chrome/FF when the delimiter used is a regex. In Chrome/FF this method returns an array of all the tokens and the strings that qualified as delimiters in proper order. In IE8 it returns only an array of tokens (the delimiter strings are omitted)

For example

Input -->
String: The train starts from {%1}{%2n} at {%3} on {%4t, dd-MM-yyyy}
Delimiter Regex: ({.*?})

Output -->
Chrome/FF: ["The train starts from ", "{%1}", "", "{%2n}", " at ", "{%3}", " on ", "{%4t, dd-MM-yyyy}", ""]
IE8: ["The train starts from ", " at ", " on "]

To fix this IE8 anamoly I wrote a custom split method that returns delimiters strings as well. You can find it here:
http://jsfiddle.net/aneezbacker/3hyD8/7/ 

Its good for starters. Additional changes can be made to support regex modifiers.


BONUS: IE8 also doesn't support String.trim().  Add the following to your code to make it work
         
           // adding trim function if its not present (IE8 doesn't support trim)
           if(typeof String.prototype.trim !== 'function') {
                String.prototype.trim = function() {
                    return this.replace(/^\s+|\s+$/g, '');
                }
            }

Hope that helps :)

References:
http://stackoverflow.com/questions/2308134/trim-in-javascript-not-working-in-ie

Garbage Collection in Java

Pulp Fiction:

This post will cover the basics of 'Garbage Collection' which is a part of Java's automated memory management. The matter presented here has been compiled from Oracle/Sun's documentations and various posts available freely on the internet. I have tried to present things here in a simplified manner and have willing left out some intrinsic details. I suggest after going through this post you should, atleast once, hear the story straight from the horse's mouth which can found here

Life is beautiful

One of the major reason I love Java is because of its automated memory management feature. As opposed to languages that do not have an automated memory management system in place, Java relieves the programmer from worrying about freeing allocated memory. This enables the programmer to concentrate on implementing the business logic rather than tracing the causes of those pesky memory leaks. Also, as the programmer is not allowed to fiddle directly with the memory blocks, he cannot accidently (or purposely) crash the system by incorrectly freeing allocated memory. This restriction ensures program integrity. Apart from this, some Garbage collectors also help combat heap fragmentation (not covered in this post).

Pitfalls

One point to note here is that Garbage Collection activities consume the very same system resources that are meant to run the application. This may slow down the application or make it appear unresponsive when garbage collection is in progress. Also, since its automated, we do not have much say in regards to when it should take place. Fortunately, Garbage Collection algorithms have vastly improved overtime and hence slow/unresponsive behavior, if any, can largely be taken care of by appropriate heap space tuning and making use of the Garbage Collector which best suits our needs (more on this later in the post).

Some Definitions

Starting with basic definitions, objects that are no longer needed are called Garbage and the process of collecting and throwing away garbage to make space for new objects is called Garbage Collection. Process that does Garbage Collection is called Garbage Collector.

When does a non-garbage object become a garbage object?

The answer to the above question lies in the following four scenarios:

1) All references of that object is explicitly set to null (e.g. obj = null)

2) Object is created inside a block and reference goes out of scope

3) Parent object is set to null

4) If an object has only live references via WeakHashMap

How to identify garbage objects?

Naive Approach

The naive algorithm is to iterate over every reachable object and use a flag to mark the liveliness of that object. Objects that are left over are considered garbage and removed. This is a straight forward approach, but time taken to finish each cycle of garbage collection is proportional to the number of live objects. Hence, this approach will not scale up in applications that maintain a large set of live data. Can we do any better?

Generational Collection

It has been empirically observed in many programs that that most recently created objects are also those most likely to become unreachable(garbage) quickly. This means that objects have a very high infant mortality. Using this empirical observation, memory is managed in Java in generations i.e. objects of different ages are stored in different memory pools.

For simplicity sake, the memory here is divided into 2 parts. First part is called Young Generation (YG) and it holds newly created objects. Second part is called Tenured Generation (TG) and it holds objects that have been around for a while.

All the newly created objects are placed in the YG. When the YG becomes full, garbage collection takes place in YG. Garbage collection in YG is called Minor Collection. So, during minor collection all garbage objects in YG are removed. The live objects left in YG are then moved to the TG if they are old enough to be in TG else they remain in YG. This process goes on till TG gets filled, upon which Garbage collection in takes place in TG. This is called Major Collection. 

If minor collection takes place, but there is not sufficient space in TG to hold the tenured objects, Full Garbage Collection (FullGC) takes place which is simply minor+major collection.

A bit more about Minor Collection

Now, lets see in detail how minor collection (garbage collection in YG) works. The YG is divided into 3 parts - Eden, Survior1 (S1) and Survior2 (S2). All newly created objects are placed in Eden. Once Eden gets filled, minor collection takes place and garbage objects in Eden are removed. Remaining objects are moved to S1. Now, when the Eden gets filled again, minor collection takes place and all garbage objects in Eden and S1 are removed. Remaining objects from both the pools are moved to S2. Similarly, in the next minor collection live objects in Eden and S2 pools are again moved back to S1. Hence, objects keep oscillating between Survior1 and Survior2 till they come of age. Once they do, they are moved to TG in the next minor collection. Important point to note here is that at any point of time, atleast one of S1 or S2 will always be empty.

Metrics for Performance

There are different algorithms for garbage collection. Their efficacy is measured on the following criteria:

1) Throughput - Percentage of total time not spent in garbage collection

2) Pauses - Times when an application appears unresponsive because garbage collection is happening

3) Footprint - Working set of a process measured in pages and cache lines

4) Promptness - Time between when an object becomes dead and when the memory becomes available.

The desired qualities of a good Garbage Collection algorithm would be high Throughput and Promptness and low Pauses and Footprint. But depending on the use-case, one factor may be traded for the other to achieve desired output. Eg. 
Batch Processing Jobs: Aim is to finish the job in the least possible time even if it requires long pauses to achieve that. So here high throughput is given more preferences than low pauses.

Real Time Processing: Here pauses should low even if overall throughput is not at its optimum best.

Now, lets see if size of different generations can affect the above mentioned metrics (we can set the size of generations using the command line parameter -XX:NewRatio. For example, -XX:NewRatio=3 means YG:TG = 1:3 i.e. size of YG is a quarter of the total heap size).

Size of 'Young Generation' is large:

If size of YG is large, then frequency of minor collections will be less. This will hence increase the throughput but at the expense of footprint, promptness and pause times. Also, if the heap is of fixed size, then a large YG implies a smaller TG. And a smaller TG would lead to an increase in the frequency of major collections.

Size of 'Young Generation' is small:

A small YG will minimize pauses at the expense of throughput.

From the above analysis we can infer that there is no one right way to size the generations! The best possible bet is to let JVM take care of the size or you play around with different generation sizes and see what suits your application the best.

Now that we have covered the basics of Garbage Collectors, we will now briefly look into 3 types of collectors that are shipped with JVM. But before that we need to understand one more important feature called Young Generation Guarantee.

Young Generation Guarantee

Young Generation Guarantee means that TG must have enough free memory to accommodate all the live objects. Let me illustrate this with the help of a simple example. Suppose we run an application that creates objects none of which ever become garbage. After the Eden space is filled, minor collection will oscillate the objects between S1 and S2 till they come of age and are eventually moved to TG. Hence, TG must be large enough to accommodate all the live objects, which means TG must be atleast as large as the combined space occupied by Eden and the larger of the two survivor spaces. Garbage Collectors which provide a Young Generation Guarantee are called Young Generation Collectors.

Different Types of Garbage Collectors

1) Serial Collector

This garbage collector provides Young Generation Guarantee and is hence a Young Generation Collector. Prior to J2SE 5.0, JVM used serial collector by default for both minor and major collections. For the later versions, JVM became smart enough to choose the collectors based on the class of machine on which the application has been started.

2) Throughput Collector

In Throughput Collector, minor collections happens using a parallel version of a Young Generation Collector while the major collection happens using a Serial Collector.

Throughput Collector is a good choice for an application that is running on a large no. of processors since minor collection is done by multiple threads.

3) Concurrent Low Pause Collector

In Concurrent Low Pause Collector, minor collection happens using a parallel version of a Young Generation Copying Collector while most of the major collection happens concurrently with the execution of the application. So, if an application is using 10 processors, during major collection the application can continue using 9 processors, while the remaining one processor can be used for major collection. The point to note here is that Concurrent Low Pause Collector can be used only if application can share processor resources with the garbage collector when the application is running.

Since garbage collection takes place concurrently with the application, Concurrent Low Pause Collector is a good choice for applications that can benefit from shorter garbage collector pauses. e.g. Interactive applications. Also, it makes for a good choice when the application has a relatively large set of long-lived data and is running on a machine with multiple processors.

There are quite a few other Garbage Collector implementations details of which are beyond the scope of this article.

References:

1. Tuning Garbage Collection with the 5.0 Java[tm] Virtual Machine 
2. Java's garbage-collected heap 
3. How Garbage Collection works in Java
4. Taming the Java Garbage Collector
5. Java Garbage Collection Distilled

Deleting MySQL Database log files

We have a master database and its slave database running on different nodes. The master DB is subjected to HUGE no. of inserts/updates because of which the log files written by it grew by enormous proportions (log files at one time occupied more than 80% of the disk space).

Log files are important because using them we can track the changes made to the DB and in case of any DB crash, we can rebuild it again from the scratch. But in our case, we didn't require the log files and had the luxury to get rid of them instead of finding a reliable storage to keep them safe.

We decided to go ahead with deleting the log files. We automated this process by setting a flag in configuration file so that MySQL automatically deleted the log files which are older than 90 days.

This can be done as follows:

1) Stop the Master MySQL server.

2) Add the follwing parameter to the my.cnf file (here the figure on the right hand side is the no. of days after which the log file must be cleared)

expire_logs_days = 90

3) Start the server.

Simple !!!


Incase, you just need to delete the log files without automating the process then it can be done using the following command (use desired date value):

PURGE BINARY LOGS BEFORE '2010-05-03 14:56:23';

Since the replication node uses the log files, we need to make sure we only delete files that were created before the logfile that the slave node is currently reading. We can get this data by using the following command on the slave database:

show slave status;

This command gives the details about the slave. The value of the column 'Master_Log_file' is the name of the log file currently being read by the slave. Once we have the name of this file, we can get its creation date. Lets assume the creation date was '2010-05-03 14:56:23'. All log files created before this time can be deleted with the following command

PURGE BINARY LOGS BEFORE '2010-05-03 14:56:23';

References:
MySQL v5 documentation for purging log files

Move MySQL database location

MySQL DB might using some location as data repository where hard-disk space is limited. This will warrant moving the data from that location to some other location which can provide more room to accomodate the increasing data. Following steps can move this data to the new location:


du -h : will show the memory parition of the current folder

--------------------


-->> Set the password for mysqlmanager (required if password is not set already).
mysqlmanager --passwd >> /etc/mysqlmanager.passwd

--> log into mysql manager
mysql -uroot -psh*pp@r --socket=/tmp/mysqlmanager.sock

-->> kill all instances of mysql
ps afx | grep mysql //get process ids
kill -9 4465 4473 4474 // kill those processes

-->> create the directory where you want to transfer the files
mkdir /mnt/mysql/marketingportal

-->> Give mysql the ownership of the directory and its contents (presently they are owned ny root)
chown -R mysql.mysql /mnt/mysql/ //mysql.mysql : group:user

--> Open the folder where the current data is
cd mysql-marketingportal/

--> Copy this data to the new folder
cp -R * /mnt/mysql/marketingportal/

-->> Give mysql the ownership of the new directory and its contents (presently they are owned ny root)
chown -R mysql.mysql /mnt/mysql/ //mysql.mysql : group:user

-->> Change the name of the old directory (optional - this is done to make sure that it isn't beign used any longer)
mv mysql-marketingportal/ mysql-marketingportal-old/

-->> edit the my.cnf file
change the value of datadir

-->> Start the mysqlmanager
nohup mysqlmanager --user=mysql > mysqlmanager.out &

High Performance Database Tips

Some Database mantras discovered on the basis of practical experience.

• Use the smallest datatype possible. eg. where a integer can take care of all possible states, don't use bigint. Every bit of extra space alloted will make the DB to grow in size without any actual utility, and there by taking toll on the performance
• Choose what to index and how much to index. Indexing is creating a meta data of data. If data is being fetched on the basis of a particular attribute, make that attribute an index. It would will definitely boost-up the reads and updates. Also, keep in mind that indexing increases the insert time and these meta-data information do occupy disk space. Partial Indexing is a good way to create indexes not the on the complete field, but the deciding part of it. eg. Index can be created for the first few character's URLs if data to be fetched is on the basis of host name.
  
• Choose storage engine wisely. eg. If the DB is not relational, go for MyISAM. Read the pros-cons of each engine before choosing one.
  
• Controlled Data Redundancy. Higher the normalisation of a DB, lesser is the redundancy. But, one think to keep in mind is that retrieving data from such a DB might require joining of tables, which is a very expensive operation. If the size of DB is huge or if the data to be fetched is distributed across a significant no. of tables, then performance will take the hit. One has to make a educated choice between space and performance. My experience tells me that a bit of redudancy isn't that bad !
• Fetch only relevant data. If you require some fields of a table(s), retrieve only those fields. Don't do a 'select *'.
• Better programming logic: When programitically accessing DB use reuse connections. eg. If on the same DB schema, we need to fire 2 quries to retrive logical/related set of data, try using the same connection. Creating connection is costly. Also, Make sure to close all connections when use is over.
• Don't run all servers on the same node. If application receives a huge no. of hits, and also tremendous DB operations are taking place in the DB (like huge no. of inserts/read/writes), its better to host the application on a node diffrerent from the DB. There is only so much a single node can handle.
  

Write SQL query output on file

Query into outfile 'filename';

Query - query to be fired
filename - name of the file on which the data is to be written. Full path can also be given. Make sure that the folder is already in existence.


eg. select * from HOTEL_DETAILS into outfile 'C:/datafolder/sqldata.txt';


Further Reading:
http://gilfster.blogspot.com/2005/11/writing-sql-results-to-file.html

MySQL Table and Schema Size

I found these 2 commands for finding the size of a table or whole schema on MySQL mailing list (unable to recollect the URL)


Query To Find the size of a schema

#Query to find the size of a database schema (replace YOUR_SCHEMA_NAME with appropriate name)

#Run this query without selecting any schema

SELECT s.schema_name, CONCAT(IFNULL(ROUND((SUM(t.data_length)+SUM(t.index_length)) /1024/1024,2),0.00),"Mb") total_size, CONCAT(IFNULL(ROUND(((SUM(t.data_length)+SUM(t.index_length))-SUM(t.data_free))/1024/1024,2),0.00),"Mb") data_used, CONCAT(IFNULL(ROUND(SUM(data_free)/1024/1024,2),0.00),"Mb") data_free, IFNULL(ROUND((((SUM(t.data_length)+SUM(t.index_length))-SUM(t.data_free)) /((SUM(t.data_length)+SUM(t.index_length)))*100),2),0) pct_used, COUNT(table_name) total_tables FROM INFORMATION_SCHEMA.SCHEMATA s LEFT JOIN INFORMATION_SCHEMA.TABLES t ON s.schema_name = t.table_schema WHERE s.schema_name = "YOUR_SCHEMA_NAME" GROUP BY s.schema_name ORDER BY pct_used DESC\G;

-------------------------------------------------------

Query To Find the size of a table

# Query to find size of a particular table (replace YOUR_TABLE_NAME with appropriate name)

# Run this after choosing the schema

show table status like 'YOUR_TABLE_NAME'

Get log files from S3 that were generated within a given timeframe

Amazon S3 log files are named as:

TargetPrefix-YYYY-MM-DD-HH-MM-SS-UniqueNumber

TargetPrefix is what we chose
YYYY-MM-DD-HH-MM-SS is the timestamp
UniqueNumber is something we should not care about

S3 returns a list of Objects (files) in S3 bucket if give give them the desired prefix.

Now, to get a list of log files that were created within a specific timeframe, we can use the following Algo:

beginTime : YYYY-MM-DD-10:25:15
endTime 13:00:00

1) get all files with prefix YYYY-MM-DD-10-25-16 to YYYY-MM-DD-10:25:59
2) get all files with prefix YYYY-MM-DD-10-26 to YYYY-MM-DD-10:59
3) get all files with prefix YYYY-MM-DD-12
3) get all files with prefix YYYY-MM-DD-13

One can further optimise the algorith to get files on 'day of the month' basis. But, that would not be a good idea because the list of files received from S# will be very long.

Following is a Java method for the implementation of the above logic

/**
 * Retuns a List of targetprefix. List is from (beginTime + 1 second) to the
 * hour value of endtime. Minute and second value of endTime is ignored.
 * 
 * @param dbLogTime
 * @param beginTime
 * @return
 */
public List getPrefixList(Timestamp beginTime, Timestamp endTime, String targetPrefix) {
 List prefixList = new ArrayList();

 SimpleDateFormat sdfhr = new SimpleDateFormat("yyyy-MM-dd-HH");
 SimpleDateFormat sdfmin = new SimpleDateFormat("yyyy-MM-dd-HH-mm");
 SimpleDateFormat sdfsec = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss");

 Calendar beginCal = Calendar.getInstance();
 beginCal.setTimeInMillis(beginTime.getTime());
 beginCal.set(Calendar.MILLISECOND, 0);

 Calendar endCal = Calendar.getInstance();
 endCal.setTimeInMillis(endTime.getTime());
 endCal.set(Calendar.MINUTE, 0);
 endCal.set(Calendar.SECOND, 0);
 endCal.set(Calendar.MILLISECOND, 0);

 if (endCal.compareTo(beginCal) < 0) {
  logger.error("Error: Current Time cannot be less than the time in LAST_PROCESS_TIME. currentCal: "
    + sdfsec.format(endCal.getTime()) + ". lastProcessTime: " + sdfsec.format(beginCal.getTime()));
  return prefixList;
 }

 beginCal.add(Calendar.SECOND, 1);
 while (!(beginCal.get(Calendar.SECOND) == 0)) {
  prefixList.add(targetPrefix + "-" + sdfsec.format(beginCal.getTime()));
  beginCal.add(Calendar.SECOND, 1);
 }

 if (endCal.compareTo(beginCal) > 0) {
  while (!(beginCal.get(Calendar.MINUTE) == 0)) {
   prefixList.add(targetPrefix + "-" + sdfmin.format(beginCal.getTime()));
   beginCal.add(Calendar.MINUTE, 1);
  }
 }

 while (endCal.compareTo(beginCal) >= 0) {
  prefixList.add(targetPrefix + "-" + sdfhr.format(beginCal.getTime()));
  beginCal.add(Calendar.HOUR_OF_DAY, 1);
 }

 return prefixList;
}

Ignore log4j logger statements for specific classes

We use certain 3rd party libraries and while development, we might want to log statements that has been generated from our application and not the third party library.

To set the log level of log requests from such libraries, put the following snippet in log4j.xml file.

<logger name="org.thirdpartlib">
    <!-- Print only messages of  level warn or above in the package <span style="font-style: italic;">thirdpartlib</span>-->
      <level value="WARN"/>
</logger>

Replace org.thirdpartylib with appropriate value. That should be do the magic.

PS: org.thirdpartlib.* won't work.

MySQL database dump

How to take MySQL database dump:

mysqldump -hhostname-uusername -ppassword schemaname tablename (contents will be printed on the console)

mysqldump -hhostname -uusername -ppassword schemaname tablename> filename (contents will be written on file)

hostname: name of the host. If the db is on your local system, then this might not be needed

schemaname: name of the schema which you want to back up

tablename: name of the table which you want to back up

filename: name of the file which will hold the dump. You can specify the location of the file too. Eg. C:\sql\testsqldump.sql. If 'sql' directory doesn't exist and error will be generated.

eg. mysqldump -uroot -padmin userinfo_schema USER_TABLE > D:\sql\userinfo.sql


If you don't provide the tablename, then the dump of whole schema will be taken.

To take dump of all the schema
mysqldump -uroot -padmin --all-databases > filename


To populate the MySQL database:

mysql -uusername -ppassword schemaname < filename
filename: name of the file that contains the mysqldump

eg. mysql -uroot -padmin userinfo_schema < D:\sql\userinfo.sql

TaF Public release

We are now releasing Tell-A-Friend widget for public use.

One of the features that makes this widget stand apart from rest of the widgets is that, if you wish to change the design of the buttons (be it the color, size or appearance), you don't have to embed a new or modified code in your webpage/blog. This helps save a lot of copy-paste exercise, which is kinda a welcome feature for lazy bums like me. All one has to do it to go to the accounts page, choose the kinda button they like, save the changes and then its all Eureka. All the changes are instantly reflected in the blogsite/webpage where TaF is embedded. Now, isn't this something cool ??

Apart from wiring a few connectors in the TaF widget, I worked on the analytics collection module. This was a pretty good learning exercise. I got to know more about the Apache log4j utility. These Apache guys are real bonds. They write some pretty good stuff.

For analytics collections, I wrote a custom JDBC appender to log all data. This has many advantages.

1) It consumes only a limited database connections.
2) Requests are served on first-come-first-serve basis. So, everything is sequential in nature in accordance to time. (log4j uses a queue)

But then, there are possible pitfalls too !!
Imagine that there are many requests, this will increase the queue size, thus increasing the response time. As of now, we have tested our infrastructure for traffics much more than we are expecting. If anyhow, response time does gets a beating, switching to a distributed system would be a possible solution which I suppose would require a bit of tweaking.

May be I will soon write another post on how to write custom JDBC appender and on analytics collection framework of works.

Tell-a-Friend

Tell-a-Friend or TaF (as we developers call it) is a new product from Pramati Technology, Hyderabad

Its something to aid 'spread the word around the world'. Just click on it and instantly announce things to your near & dear ones. So, you can announce your blog posts, articles, products on sale etc. through IM, Email, Blogs and Social Networks(like Facebook and Twitter) through a single integrated interface. So, its kinda like a single window to multiple channels to make a million announcements. So, it will bring more clicks to your weblog / website and help market your articles/products.

When Sunny showed me the TaF button embedded in Nina's blog (ya...thats our test blog), I could see foretell that this product could actually become a rage. Intel Mashmaker, CatchFlix and BigScreen are already using it/used it. But, now any one can integrate TaF in their website/blog for the following 2 divine reasons:
1) The free version is absolutely free :P (and one day beer shall also be free)
2) All it takes is embedding a code snippet in the page where the TaF icon is to be displayed.

Hope I see the TaF icons weblogs alongside dig.com, stumble upon etc. icons. After all, it always feels nice to see people use and talk about something that has your code :P.

TaF extensively employs JAVA, JAVASCRIPT, DOJO and AJAX. The widget opens up in an iframe and seemlessly gives a web2.0 feel to the page. We are working to further boost its performance by using CSS sprites, decreasing the number of http request/response and fine-tuning the backend. A rework on its look-and-feel is also being undertaken. So, with time, its gonna become all the more difficult to ignore it and impossible to resist not having it on your page :)

JSON and HashMap

DWR is used for easy 'AJAX for JAVA' and is employed to call Java methods from Javascript (version 2.0 + supports reverse-AJAX too).

Working on the ShopprStream(earlier known as WEB122) has helped me get acquainted with many facets of web-development.


Now I have a Java method that returns a generic HashMap object ;
For this example lets consider that the key is of type String
And the elements are instances of the class CustomClass with name (of type String) as instance variable

The DWR call will return a JSON object. This is how we can access the data

for (var key in hashMap)
{
     //if not using Firebug, comment out console.log statements
                        
     //'key' is the key in the HashMap
     console.log("key : "+ key);
          
    //this will give the no. of elements stored corresponding to the 'key'
    console.log("hashMap[key].length: "+ hashMap[key].length);
                 
    //Access individual elements corresponding to the 'key'
    for(var i=0; i<hashMap[key].length; i++)
    {
    console.log("hashMap[key][i].name: " + hashMap[key][i].name);
    }
}

If the HashMap contains custom objects, make sure it has a corresponding converter entry in the dwr.xml file

for example, if my class is called CustomClass, then write as

<convert converter="bean" match="com.pramati.web122.imsupport.ContactDetail"/>

Here, abc.xyz is the package structure

If object returned is hashmap, then values can be accessed as:
hasMap[key]

If object returned is hashmap, then values can be accessed as:
hasMap[key][0], hasMap[key][1], hasMap[key][2] . . . . .

Helpful JavaScripts

To bring focus to a text box / button or any other element

just add this javascript in the HTML code:

<script type="text/javascript">
   document.getElementById("elementId").focus();
</script>

where elementId the id of the element on which the focus is to be set

for example, the following code will bring focus to the textbox that has the id email

<input type="text" id="email" />
<script type="text/javascript">
   document.getElementById("email").focus();
</script>

Fake Mail

One can send mails using JAVA Mail API. It is fairly simple to use this library to send mails.

First download the JAVA Mail API, and add mail.jar to your classpath
Then download, JAF API, and add activation.jar to your classpath

Following is the simple code:

Java Class: TestMail.java

import java.io.*;
import java.util.Properties;
import java.util.Date;
import javax.mail.*;
import javax.mail.internet.*;
import java.net.InetAddress;

class TestMail
{
public static void main(String args[])
{
 try
 {
  //from address
  String from = "fromaddress@somecompany.com";
 
  //receipents of the mail
  String to = "toaddress@someothercompany.com";
 
  /*
  *If there are multiple
  *recepients, then email ids
  *should be stored in a String
  *with a space in between them.
  *eg: String to = "id1@comp1.com id2@comp2.com id3@comp3.com"
  */
    
  //subject of the mail
  String subject = "Test Mail Subject";
 
  //e-mail content
  String text = "This is a test email";
 
  /*SMTP host
  *SMTP host should be correct
  *for this program to work.
  *Also, some SMTP servers
  *are configured to allow
  *messages to be sent from
  *one or a few doamins
  */
  String mailhost = "mail.somecompany.com";
 
  //mailer
  String mailer = "testmailer";
 
  Properties props = System.getProperties();
 
  props.put("mail.smtp.host", mailhost);
 
  Session session = Session.getInstance(props, null);
 
     //construct the message
  Message msg = new MimeMessage(session);
  msg.setFrom(new InternetAddress(from));
  msg.setRecipients(Message.RecipientType.TO,
   InternetAddress.parse(to, false));
  msg.setSubject(subject);
  msg.setText(text);
  msg.setHeader("X-Mailer", mailer);
     msg.setSentDate(new Date());

  //send the mail
  Transport.send(msg);    
 
  System.out.println("\nMail was sent successfully.");
 }
 catch(Exception e)
 {
  e.printStackTrace();
 }
}
}

WARNING:
When full headers are viewed by the recepeint for a mail sent by this program, it mite have an indication that there is something fishy about how the mail was sent !!


Happy Spamming !!!

JavaScript NULL

For JavaScript:

If you want to test whether a String object is NULL , then the following may FAIL

if(someString == "")

if(someString == "null")


The CORRECT way to test would be:

if(someString == null)


---------------------------------------------------------
Resources:

http://lists.evolt.org/archive/Week-of-Mon-20050214/169524.html

Post HTML codes in blogs

If you post articles with html tags on blogspot, it will most probably give an error message as:

ERROR
"Your HTML cannot be accepted: Tag is not allowed: "

The way to get around this is to convert all the mark-ups (eg: '<' , '>') into character-entities (eg: '&lt;' for '<' ; '&gt;' for '>')

One can use online applications that perform this conversion stuff:

http://www.stanford.edu/~bsuter/js/convert.html

If formatting has to be retained, then just enclose the code inside '<pre>' and '</pre>' tags.

Web Browser Compatibility !!!!

Developing on a web application is not easy if you intend to have the product compatible with all the available browsers in the universe for some new browser or its clone comes to life everyday.

This article is about how can one know which browser is being used by the end-user and how one can customize the code in accordance the same, be it IE or Mozilla Firefox or Safari or blah blah blaaaaaaaaaaaah !!!

The end-user browser can be determined by using navigator.appname

The following code illustrates the same:

<html>
    <head>
        <script type="text/javascript">
            function navigatorName()
            {
                alert(navigator.appName);
            }
        </script>
    </head>

    <body onload="navigatorName()">
        <div id="browserContents">
        </div>
    </body>
</html>

When the page gets loaded, the onload feature will call the javascript function navigatorName() which will display the alert box with the name of the browser as the message.

Now, inside the function navigatorName, we can write the logic that would make our code browser specific

<html>
 <head>
  <script type="text/javascript">
   function navigatorName()
   {
    if(navigator.appName == "Netscape")
    {
     document.getElementById("browserContents").innerHTML = "Netscape";
    }
    else if(navigator.appName == "Microsoft Internet Explorer")
    {
     document.getElementById("browserContents").innerHTML = "MS IE";
    }
    else
    {
     document.getElementById("browserContents").innerHTML = "Some Browser";
    }
   }
   </script>
  </head>

 <body onload="navigatorName()">
  <div id="browserContents">
   loading . . .
  </div>
 </body>
</html>

Here, when the body part of the page has been loaded, the browser calls the function navigatorName(). This function checks the browser being used, and in accordance to that, replaces the contents of the div with id browserContents appropriate contents by making use of the function document.getElementById("browserContents").innerHTML.