Working with Deleting/Updating a Set In Hibernate

If a hibernate mapping object contains contains a Set of objects, it's usually configured with the attribute 'set'. If you want hibernate to take care of updating/deleting those objects in the set from the database table, the set attribute cascade must have the value "all-delete-orphan" and properly handled in the code that tries to update it.

Say our parent object is Car and child objects are of type Part. Our set mapping would be of the form below

In order to make the changes to the set elements which are of Part type, the order of the update statements must be of this sequence.

Car car = manufacturer.getCar();

//we want to reduce the number of parts say from 10 to 8.

//If the two parts have the ids 9 and 10, then let's remove it

Set parts = car.getParts()

//iterate through the set and grab the objects with ids 9 and 10

Part part9 = (Part)iter.next();//assuming this is the 9th object in the set

Part part10 = (Part)iter.next();//assuming this is the 10th object in the set

parts.remove(part9);

parts.remove(part10);

//persist to database to update the records

saveOrUpdate(car); //this will merge the differences. the database record will //now have 8 rows instead of 10 for the parts. Also, you can use the merge(car) //method and it will work the same way.

//if you want to delete all parts since its no longer produced, just do this

parts.clear();

saveOrUpdate(car); //then there will be zero entries for the parts in the database table

//When it comes to adding a new part, just add the new part object and persist.

Part part11 = new Part();

//...fill properties

parts.add(part11);

saveOrUpdate(car);

JFreeChart LegendTitle Font Change

I've been trying to search the whole day yesterday on how to change the Font for a chart's legend title. JFreeChart doesn't have any good free reference documentation about this use case but I was finally able to figure it out by playing with LegendTitle's methods. The code below works for changing the Font of the current LegendTitle object.

LegendTitle legendTitle = chart.getLegend();

legendTitle.setItemFont(font);

legendTitle.setNotify(true);

The setNotify() method somehow alerts the different objects dependent on the LegentTitle and update it's state. If that is not called, nothing happens. If that method is set to true that means, the current change on the chart, specifically the LegentTitle, call all dependent objects and notify of this change and properly act on it.

iPhone Mobile Camp Atlanta

Last Saturday, July 18th, I went to attend the Mobile Camp Atlanta in Marietta the whole morning. There were alot of presentations to choose from crossing iPhone, Android, Palm-Pre, Windows Mobile, Blackberry development. But I mainly focus my interest in the iPhone seminars. The iPhone Development presentations covered best practices user interface design, Parsing XML, Core Data, JSON, Facebook and Analytics, Push Notification. I've attended all of them except for the last one.

I am not an iPhone developer but I'm looking into getting converted before the end of the year. After the end of the presentations, I'm decided to add in my skills Objective C Language which apparently iPhone is using. I believe phones in the not so distant future will become a critical part of the IT Enterprise Infrastructure in terms of delivering important, well formatted content to the business user or customer. I'm sure iPhone will become a great tool to realize this need.

Here's what I've taken for each presentations.

iPhone App Design Best Practices

1. Be true to the device. Know the capabilities of the hardware and what the API can provide.

2. Read the Human Interface Guidelines provided by Apple.

3. Start designing your app after item 2 & 3 are done.

4. Use DataObjects metaphor.

5. Start button design to 324x80 pixels and load it to a temporary button album in iPhone just to see how it fits.

6. Use a third party tool like iView for viewing prototypes of the interface design. You can also use iPhone Stencil created by Design Commission.

7. Remember that 3G S has warmer color that its predecessors.

8. Perform Paper Prototyping to understand the flow of the application.

9. Native apps are more comfortable with users than browser based ones. Native in this context is Objective C.

10. Do not hardcode the screensize, iPhone itself might change the lcd screensize in the future plus if you are developing on iPod as well.

11. Let the app be customizable by users to make it their own. User experience is a need.

12. Pixel density of iPhone is much higher than what you have in a laptop or desktop. The prototype from the laptop/desktop will look different when viewed from iPhone.

13. As a rule of thumb, always design apps both for iPhone and iPod.

Parsing XML using NSXMLParser

The NSXMLParser is SAX based parser. It rides on top of Cocoa. This goes hand-in-hand with NSDictionary and NSArray. NSDictionary allows you to store key/value pair. Like a Map in Java. To manage multiple occurence of same key, which are basically the xml nodes that you are trying to get onto, turn it into an array. This is only true for one level node. For deep level nodes, give the parser a hint then build the array.

Introduction to Core Data

Core Data in iPhone sense means Persistent Objects. All apps have a delegate. iPhone uses managed object model and context. There are 3 main APIs suitable to perform manipulating persistent objects - NSString, NSArray and NSDictionary.

JSON in iPhone

Use the JSON documentation from iPhone Noob. The only thing to do to deserialize JSON objects are to turn them into Dictionaries and Arrays. By the way, the debugging in XCode looks really cool.

FaceBook Connect in iPhone

I'm not really intested in developing applications via FaceBook. But if you do, all you have to do is download t FaceBook Connect Dev and apply to obtain "API Key" and "API Secret".

Analytics for iPhone

This was mainly a discussion about a product called Flurry, which is a better version of iTunes analytics. This comes close to Google Analytics. The presenter just basically showed us on the web his product he created and it does have much more meaningful data than iTunes does.

Integrating Author It Compiled Documents with Strutsonlin

Integrating the end product of a content management tool with a web application is painful. Even if the web application is built on top of an MVC framework. Author It is a CMS tool that will let you build an html based documentation. The focus on this discussion is integrating an end product which is an online help documentation with Struts. 

The documentation will allow users to view the help page regarding the current page by clicking on the Help button from the menu bar of the application. The user can also search for any specific help pages she/he wants to view. 

The integration effort requires several files to be created/edited as listed below

1. onlinehelp-config.xml

2. onlinehelp.jsp

3. common.js

4. mainMenuBar.jsp

5. web.xml

6. OnlineHelpProcessor class

and several classes as shown below from the diagram

onlinehelp-config.xml

This file contains the mapping between struts/tiles and the online help html documentation page through its numeric code which is the prefix to the file name of the help page (i.e. 207.htm). There are two parent nodes in it - nonupdate and update. 

nonupdate node contains mapping for help pages that are "only" non-editable web pages while the update node maps help pages to editable web pages.

The element is the tiles definition name attribute. This configuration is read and cached when the application starts up. Think of the element as the help page file name appended with .htm.

onlinehelp.jsp

This is the original index.htm file generated by Author It tool, the entry point for all help documentation pages. There are three modifications to this file - import of the taglib struts-bean.tld, bean definition of the onlineHelpCode and the SRC attribute value of the frame element. 

The import of the bean taglib is needed to extract the SessionData bean which lives in the session and get the onlineHelpCode string value from it and plop it to the SRC element. It is important that this file is located where the jsp files are.

common.js

Of course we want the help page to be in a new window. This is where we add a new function that will open a pop-up window when the help page is invoked.

mainMenuBar.jsp

This is where the Help button is located and a javascript function to invoke the online help documentation in a new window is identified. This jsp file contains all the buttons necessary to provide functionality for the user.

web.xml

We don't want the onlinehelp-config.xml file to be read each time we invoked the help pages. There's 3 ways to handle this file

1. Read this file, convert it to Java Bean/Map and put it in session.

2. Read this file, convert it to Java Bean/Map and put it in cache.

3. Read this file, put attributes in a Map and put it in a singleton object.

I prefer the latter for simplicity and less coupling though all of them promotes efficiency. If the bean is put in session we are introducing a tight coupling with the container's session implementation. If a third party caching mechanism is used then we are tied to that implementation.

In this example I used the third option and have a servlet intialize the class that reads this file which is called OnlineHelpProcessor (Singleton). The method called for initialization from this class is initializeOnlineHelpCodes(). Its just basically reading the file and putting attributes in a Map.

When the application starts up, the singleton class is initialized and all the elements from the config file is put into a Map ready for access anytime.

OnlineHelpProcessor

This class reads the onlinehelp-config.xml file and converts the elements into a key/value pair in a Map and provides a method that takes in a struts forward name argument and returns the onlinehelpcode value which is later used to load the right help page.

Using Chain of Responsibility Pattern

More than a year ago I was presented with a business requirement that has an accompanying process flow chart. The requirement  was basically validating an Insurance Agent. The following information were used to perform business rules/validation on a specific agent and see if he/she can do business at a certain area, or is able to use current authorization or if his/her current contract is valid. 

1. Authorization

2. Profile

3. Contract

4. Managing Agent

Looking from the document, there were sets of processes that contains business rules that needs to be performed but each process completion can lead to one or more possible processes to be run. This scenario is depicted below.

I chose a pattern to basically build the framework that will allow for easy integration of new processes into the mix and not complicate the validation implementation. If this is to be implemented without a framework, deeply nested if - else statements arises and increases cyclomatic complexity issues. The Chain of Responsibility Pattern seem to perfectly fit this requirement. This pattern comprise of several chains all link together and each chain is aware of if the request coming in is intended for it or not. If it is then it applies whatever process is needed on that request data. If not then it just passes the request to the next chain in the link. The process in the figure above is represented as a chain. In this case we have 9 chains in the link. 

Each of the 9 chains contains thick business logic validation implemetation that takes in an input and redirects the output to a different chain for further request validation. The process continues until one of the chains mark the validation process as completed and package the output data to whatever format the requester is expecting. 

This is the Class Diagram that reflects this design. In addition to the chain pattern, the Template Method Pattern was also used as can be seen from the hierarchy relationship of Chain interface, AbstractChain and its subclasses.

There are four things to consider from this diagram - Chain interface, ChainManager, AbstractChain and its implementation(chains).

Chain Interface

Defines the contract for implementing the methods add(Chain chain), processNext() and isLast(). The latter identifies a chain if its the last one to be executed. 

ChainManager

It is responsible for creating the chains, linking them altogether and kicking off the first chain. The pseudo code below shows this implementation.

Chain process1Chain = new Process1Chain();

Chain process2Chain = new Process2Chain();

Chain process3Chain = new Process3Chain();

Chain process4Chain = new Process4Chain();

Chain process5Chain = new Process5Chain();

Chain process6Chain = new Process6Chain();

Chain process7Chain = new Process7Chain();

Chain process8Chain = new Process8Chain();

Chain process9Chain = new Process9Chain();

DefaultChain defaultChain = new DefaultChain();

process1Chain.add(process2Chain);

process2Chain.add(process3Chain);

process3Chain.add(process4Chain);

process4Chain.add(process5Chain);

process5Chain.add(process6Chain);

process6Chain.add(process7Chain);

process7Chain.add(process8Chain);

process8Chain.add(process9Chain);

process9Chain.add(defaultChain);

// Assign the point of entry chain,

Chain entryPointChain = process1Chain;

//Kick of the first chain

entryPointChain.processNext();

AbstractChain

The process() method of this class reflects the Template Method Pattern. The power of polymorphism lies here. Its subclasses plugin the right logic at run time and these chains are decoupled from each other. 

As you notice the DefaultChain is included in the diagram. If you want to do some post-processing cleanup, provide the logic here.  

The beauty of this chain pattern is its extensible. From our example above, if we need to add another set of validation logic, all we have to do is create another chain and add it in the link and provide the business logic in its process() method. If a validation is no longer needed, just remove that chain from the link that implements the validation and the application should still run without any side effects.

When do we say its the right tecnology to use?

When is a technology the right tool to use? Do we influence the feature we want in an application from what is available from the technology or from what is required from the business requirement?

It's always a challenge to marry the right technology with the right requirement that would produce a fluid, solid application. One-Stop-Shop approach of resolving business issues is no longer becoming relevant in the global IT market. You pay so much that without realizing only a fraction of the features provided by that technology is only essential to what the business requires. A lot of companies now are resorting to only "get what you need" and "pay what you only need" mentality. This is where customization comes in. The beauty of customization is it delivers the solution that the problem it exactly expects. This strategy relieves companies from paying too much.

When the curse of overengineering starts to sink in, its a manifestation of wrong implementation. But what is overengineering? It's a combination of technology misuse and irrelevant complex implementation. If the implementation looks simple and it solves a business need then we just answered the first question above.

The danger comes when technology features molds how the application should behave. This deviates the application from concentrating into its prioritized functionalities and might deliver features not needed at all. Scope creep is the twin evil of this situation. Looking at it at the brighter side, this is the best opportunity to step back and review the requirements and correct and refine the implementation.

Implementing User Sessions for Crystal Reports Java SDK

If you are submitting requests for batch processing in Crystal Reports via its Java SDK, never login to the server per request. I've seen this implemented and it's just creating an unnecessary overhead. Here are the steps to create a session that would serve multiple requests.

1. Log on to Crystal Report Server

You call the metod CrystalEnterprise.getSessionMgr() which returns you an object of type ISessionMgr. From there call the method of the returned object below which returns an object of type IEnterpriseSession.

logon(String userName, String password, String ceServerName, String secEnterprise);

2. Create Logon Token

The IEnterpriseSession has a method getLogonTokenMgr() that returns ILogonTokenMgr. Call the method below to get the logon token string.

createWCAToken(String clientServerName, int validMinutes, int validNumLogon);

The validMinutes parameter represents how long do you want to maintain the session and the validNumLogon represents how many logons the client can perform in one session within the given valid minutes.

3. Logon to Crystal Server with Token

Call the method below from the class ISessionMgr and pass the logon token string that was previously generated. This returns to you a new IEnterpriseSession that has the token. All transactions will then use this session object until the minutes or log on counts are exhausted.

logonWithToken(logonTokenString);

Of course, somehow this session will expire later on and the client application need to reconnect. The good news is you just have to follow the same steps. On the other hand, if the session is still valid and somehow the application needs to reset the connection, always check for the session if it already expired. If it is, release the token and logoff with the following sequence then proceed to steps 1 through 3 again.

releaseToken(logonTokenString); // called from ILogonTokenMgr
ceSessionWithToken.logoff(); // called from IEnterpriseSession with token
ceSession.logoff(); // called from IEnterpriseSession without token

This approach will be very useful for batch processing. You want to keep the pipe full while the report server is processing. With on demand request report processing, you don't want to keep a session open for a long time.