Webservices in Websphere

Webservices support in Web Sphere is enhanced by a service pack as defined in the url (http://www-1.ibm.com/support/docview.wss?rs=180&uid=swg21264563). The benefits it provides as per the extract is

IBM WebSphere Application Server V6.1 Feature Pack for Web Services extends the capabilities of Application Server V6.1 to enable Web Services messages to be sent asynchronously, reliably, and securely, focusing on interoperability with other vendors.

Through support for key Web Services standards, you can send messages:

• Reliably - be confident that your message will reach its destination
• Asynchronously - communicate reliably even if one of the parties is temporarily off-line, busy, or unobtainable
• Securely – rest assured your messages are not vulnerable to attack
• Interoperably – flexibility to interoperate with other vendors’ offerings

The Webservices can be developed with the help of common editors like Eclipse or MyEclipse Blue or AST offered along with the Application Server or RAD. These are excerpts from Websphere sites. Please check the websphere sites for more information.

Class Loader Hierarchy

As per the delegation contract, a class should be attempted to be loaded by the parent class loader. If the parent class loader cannot load the class, the request should then be handed over to the child class loader. The process will continue till the class loader which originally received the request to load the class. Still if the class cannot be located in the classpath, a ClassNotFoundException is thrown. The request will not be transmitted to the child class loaders of the class loader which originally received the request to load the class.

Say we have 4 class loaders with names as shown below. ClassLoaderX, ClassLoaderY, ClassLoaderA, ClassLoaderB. The relations between them are shown below

When the JVM starts, all classes accessible from /x/data can be loaded by the ClassLoaderX. Then the control is transferred to ClassLoaderY, which can load the classes present under /y/data folder. The control is transferred to ClassLoaderA as well as to ClassLoaderB which can load the classes under /a/data and /b/data. The classes loaded by the parent class will not be loaded by the child class loader again as the child class loader will check if the classes are already loaded by any of its parent class loaders.

Now when the ClassLoaderB gets a request to load a class, it will delegate the request to its parent class loader i.e. ClassLoaderY. The ClassLoaderY will delegate the request to its parent classloader ClassLoaderX. Since ClassLoaderX does not have any parent class loader, it will try to load the class from its classpath i.e. /x/data. If the class is present in its classpath, it will load the class. If it cannot find the class in its classpath, the request is delegated to the child classloader i.e. ClassLoaderY. The ClassLoaderY will attempt to load the class from its classpath /y/data. If it finds the class, the class will be loaded by the ClassLoaderY. If it cannot find the class, the request is delegated to the ClassLoaderB. ClassLoaderB will attempt to load the class from its classpath. If it cannot find the class in its classpath, the request cannot be delegated to the child classloader of ClassLoaderB. Instead it will throw a ClassNotFoundException.

Consider a scenario where the following jar packaging is done. Class P is having Class Q as its super class. Class Q refers to Class R. P is packaged in p.jar and placed in /b/data folder. Q is packaged in q.jar file and placed under /x/data folder and R is packaged in r.jar and placed in /b/data folder. Can you guess what happens!

ClassLoaderB will try to load P and it will load the class after ClassLoaderY and X attempts to load it. Since P has Q as the super class, ClassLoaderB will attempt to load it. Q will be loaded by ClassLoaderX as Q is placed in the classpath of ClassLoaderX. Now Q refers to R and hence ClassLoaderX tries to load it. It will give ClassNotFoundException as r.jar is not present in classpath of ClassLoaderX. As per the policy, the loader should not delegate the request to child classloader and hence ClassLoaderB will never be asked to load R.

If a class is already loaded by the parent classloader, the child classloader will not attempt to load the class again. However some application servers have written custom classloaders which override these features. Another point to note is that the same class will be loaded by ClassLoaderA and ClassLoaderB if the class is placed in their classpath. This is because the classloader always checks its parent for loaded classes but not its children or siblings.

Java has got bootstrap classloader, extension classloader and application classloader by default. Bootstrap classloader can be mapped to ClassLoaderX, extension classloader can be mapped to ClassLoaderY and application classloader can be mapped to ClassLoaderB in the example above.

Few pointers

1. Do not place the jars in the bootstrap classpath or the extension classpath just to make the application work. It will create issues which might surface later.
2. Packaging the application is important because it impacts the class loading order too. All related classes should be packaged together or the proper documentation should be provided as to what order the jars should be loaded.
3. Place common utility jars and common files in common classloaders path. However caution should be taken if they are supposed to be used in an independent manner. For e.g.: log4j.properties, if loaded by parent classloader, the properties file present in the child classloader path will never be considered and might give annoying results.

Avoding log4j logger statements in log files

We all have used log4j in multiple scenarios and it serves the purpose. There are cases when we don’t want the logger statements from few classes or few packages to clutter the log files. Some other cases, we want the logger statement to be printed in only one log file and not in all log files. These are 2 different cases and I will explain solution for both of the requirements.

Requirement 1: Don’t print the log statements in any of the configured log files. Consider a scenario where we have configured 4 -5 log files at different levels and for different purposes. If we don’t want the logger statement from the classes in a particular package or particular class to appear in any of these log files, we have to use the following syntax.

log4j.category.=OFF

e.g. log4j.category.com.test.welcome=OFF means that all the statements logged from the classes present in com.test.welcome package will not be logged in any of the configured log files.

Requirement 2: Don’t print the same log statements in all of the configured log files. It should be printed in the more specific log file only. Consider the scenario like this

log4j.category.com.pack1.pack2 = INFO, appender1

log4j.category.com.pack1 = INFO, appender2

The statements logged from the classes present in the package com.pack1 will be printed in the appender2 as well as appender1 log files as both of them satisfy the category. Now if we don’t want the logger statements from the pack2 not to print in appender1, then we can use the additivity clause.

# set additivity to false to ensure that the parent appenders do not log these statements
log4j.additivity.pack2 =false

The above line means that the logger statement from pack2 will be present only in appender1 log file and not in appender2 log file. This is because the logger file is configured for appender2 as well as appender1. That means the logger statement got printed only in the specific log file and not in its parent appenders.

Identifying Services

Currently the direction is towards Services. This push is seen primarily in smaller and growing companies. If you look at bigger corporations who already have their business process developed, are they changing their entire application to make it as a service? Not really!!. In these corporations, still there are projects happening in the services part. If the mainframe application (few of them developed long back) need to make its core business process available to the company, Service would help here. The service that exposes business functionality can be exposed as a Service.

The important task is to find out what services are to be created and at what level do we expose it? The service should do a functionality that has business significance. We need to contextualize to the business scenario and then evaluate if the service does business function or not? Let’s take a scenario. A Web Dealer wants to allow users to buy the items from the user’s shopping cart. This can be exposed as a Service. This service however needs many other related services like removing items from the cart, charging the credit card, placing order in shipping system etc. For the Web Dealer, exposing a payment service doesn’t make business sense as it doesn’t perform valid business functionality. Similarly exposing a service to update the shipping system also doesn’t make sense as the user cannot request to ship the items directly. But for a payment company, making the payment against a credit card will be valid functionality. The point that I’m trying to make is that it’s based on the business functionality that the services need to be decided. Food for one can be poison for the other. In the above scenario, the Web Dealer exposes a service to buy items taking the user details, credit card details and payment details as input, perform the entire business operation and return the response back to the client. The Payment Company will expose the Payment Service. The Service of the Web Dealer can make finer calls to the Payment Service and achieve the functionality. The shipping service might be designed as a bean call or a service that is not exposed to external users which will be used by the Web Dealer Service. From a web dealer user perspective, it just made a call to Web Dealer Service and not multiple fine grained calls to multiple services to complete the transaction.

While identifying and designing the services, attempt can be made to make many fine grained services. This gives more reusability. But these fine grained services should not be exposed. These fine grained services should be composed together to a coarse grained service and exposed as a valid service. Exposing too many fine grained services causes too many issues, performance security and network load being few of them.

Every attempt should be made to make the service asynchronous in nature. This means the client should not be forced to wait till the service completes its execution. After the processing is complete, the Service can provide some means to tell the client about the status of the execution.

These are my view points. If you disagree or would like to suggest or debate, please leave your comments.

Daily Shopping

You can get anything from US and believe me its easy. If you walk into some super markets like Wal-Mart or Meyers, you can get anything, from ball to bed. House hold articles are not very expensive but you can get really expensive ones too. A dinner set (4 dinner plates, 4 small plates, 4 cups and few more dishes) will cost around 60USD. An air bed will cost around 50USD while a spring bed will cost around 300USD. A bottle of milk (3 litres) will be around 2USD.

Indian Shops

Almost every city, you will find Indian shops. If you go to Chicago or Boston, you might find it a lot and if you go to some smaller cities, you might have to travel to the nearest city to find one. But, you will get everything over there from Cereals, Masala (Everest masala, Grandma masala and many more…), DVD’s for rent, Indian rice varieties, spices. So point is, you really don’t have to carry anything from India thinking that you won’t get it there. But yes, it might be a little more expensive than the normal super markets. Almost all Indian spices can be bought from super markets like Wal-Mart, Fred-Meyers and it will be cheaper compared to an Indian shop.

Driving in US

Driving and moving around is US is different from that of our contry. You cannot walk from one place to another (of course major metro’s and cities, walking in the busy areas are common. If you walk around in Newyork city, it reminds you of Bombay ;-) ). For the small cities, the hotels will be present mostly near a free way exit. You might have to travel to the next exit to get food or sometimes you will get at the same exit. So a car is required for all travel purpose. If you don’t have a license handy, you can always rely on cabs which can be booked over the phone. They normally takes 20 -40 mins to show up after your booking.

Rental Cars

If you want to book a rental car, you need a credit card. Some of the car rentals are www.hertz.com; www.enterprisecar.com; www.nationalcar.com;. The average rent will be around 20-30 USD per day for a small car like Toyota Corolla which does not include the Insurance. Car Insurance needs to be bought separately and I strongly advise you to buy it for first few days at least. I will write a separate blog on various insurances that you can buy for car rental. The rental cars will have automatic gear shift. So you don’t have to worry about the gear shifts. The next major difference. The cars are all left hand drive. If you have never driven in US, I would strongly advise you NOT to drive in US. You have to follow rules and rules are much different in US, major being there are rules for freeways.

Freeways

Freeways are like highways in India. I should be crazy to do such a comparison. Well, the point that I want to make is that the free ways normally connect cities, sometimes states and sometimes multiple states. I-75 goes all the way from Michigan to Florida, roughly 700 miles. Now let me tell the major rules. You are not supposed to stop your car on a freeway, unless it’s an emergency. In case of emergency, you should pull your car to the right side (if present, some places it will be left side) shoulder and never stop on the road. If you want to stop the car for taking rest, you should take the car through the nearest exit and stop at a safe place like Gas Station, Eat outs etc. Yes, there will nothing on the freeways; you should take the exit roads to fill gas, to eat out, to take rest and to stop the vehicle for driver changing and for anything that involves stopping the car. Every exit will have a number like Exit 169. Before the exit, all the facilities available at the exit will be posted on the freeways. Normally, for every exit, there will be an adjacent entry where you can get back to the freeway. Some places it may not be the case and it will be mentioned at the exit. So the general flow is, take an exit, do whatever you want and then join back the freeway at the entry.

There are speed limits posted on the road and it should be followed. You will be ticketed by the cops if you exceed the speed limit and sometimes if you don’t maintain the minimum speed limit. There are some rules specific to states and you should read the rules before travelling in that state. You will be ticketed by the cops if you don’t follow rules, whether you are aware or not. The freeways will have multiple lanes and shifting between the lanes should be done carefully. So please do read the rules, it’s important and it’s very much different from driving in our country.

Landing Stay & House Lease

It’s pretty easy to get a stay arranged in US. All the reservation to the Hotel can be done through online reservation systems. You will have to use your credit card to do the reservation. Few of the hotels are www.marriot.com; www.choicehotels.com; Please do the reservation in advance. The reservation can be canceled in most of the places till 24 hours before the start date of the stay. However check the policies before doing the reservation. Having said that, you should probably try to get a stay arranged at your friends place because that makes it more comfortable stay J. Another point to remember is that most of the hotels will have only breakfast (some of them give it free). This information will be available in the website itself and it changes from hotel to hotel. For other times in the day, you will have to go to near by places for food.

House for Rent

Houses are available for lease. The duration of lease will be anywhere up from 6 months. This means that you sign a contract with the leasing company for a stipulated period of stay. The rent will be fixed while signing the contract for the contract period. For smaller cities, the rent will be 700 USD for single bed room apartments and for bigger cities it can go higher. If you know that you are going to stay there for a longer duration , you can think of signing lease for longer duration to lock down the rent. The leasing company increases the rent every time you renew the lease. You can break the lease by paying a lease breakage fee. This should be mention in the contract. It can be amount equaling to a month or 2 month rent. Mostly the houses or apartments will be owned by a leasing company. You can search for lease availability in your area in www.rent.com. Whenever you get into lease agreements, look out for discounts, some places have move in specials like first month rent free, few amount off from first month rental etc. You can expect partially furnished apartments in most cases which might include a fridge, dishwasher, washing machine and a dryer, microwave, heater and air conditioner. But, this varies from apartment to apartment. Some places will have laundry unit as part of your apartment while some will have it as a common place. If you are going to cold areas like Michigan, check if you have a good heater in the unit. The temperature can go as low as -20F outside and you need good heaters to maintain the room temperature. Some apartments give heating power as free and it’s really worth if you can get this offer. Also check with your colleagues if they can help, the leasing contracts are flexible and it can be changed, but once signed, it cannot be changed. After completing a fixed lease term, you can either extend the lease for another lease term or go for a month to month contract.