Java based web frameworks

A quick rant on the state of web based frameworks in the J2EE world
a. Imposing Maven on me is not nice.
b. If your "web" based framework cannot support clean URL's you are in the wrong business when you are writing frameworks
c. A J2EE standard doesn't mean its a good standard (JSF - Im looking at you)
d. When you want a view technology please please use JSP. Its mature and it works. It is as good or as bad as you want it to be. Making your own template language which is either inflexible or just as bad as JSP is just plain silly. Reinventing JSTL with a different archaic syntax is silly. Doing it in the guise of "no java in JSP" is silly - There isn't a framework that I can't write bad code in.
e. Make simple things simpler and make hard things easier if possible and it's ok if hard things remain hard. But do not make simple things simpler(oh look how quickly I can do CRUD) and hard things harder(because lets face it , every application does have corner cases).  Do not make hard thing's simpler and simple things harder (I have to set up how many files for Hello World?) - because lets face it not everything in a web application is Rocket Science.
f. Who would have thought Spring would turn out to be more heavyweight than EJB.
g. Who would have thought that Struts 1 would still be so heavily used
h. Who would have thought that I would now prefer to code in ASP.net than identify which Web Framework I should use.

java memory leaks

One of my colleagues asked how I diagnosed a memory leak that was impacting his application , so this is what i said. Maybe Ill write it tutorial form some time


The version of java we are running doesnt make this easy so this is what I did on dev (its hard to make this a coherent narrative).

Almost any memory leak debugging takes the following form(Im assuming the Out of Memory says the HEAP is out of memory)
a. Run your application steps that are causing the memory leak (detecting this is actually the biggest problem but if you dont know what step is causing the leak , you basically have to access all the functionality of your application). This ensures that all statics/caches/classes are loaded. Then force a garbage collection. Then check the memory for the Java VM and take a heap dump (this is a binary form of all the objects on the heap including the allocation graph)
b. Now repeat the step causing the problem. make sure that the step ends correctly (for e.g. if the step is a user goes and saves the quote, ensure that you logout and invalidate his session otherwise you get false readings). Now run a full GC again. Take another heap dump.
c. Compare the two heap dumps. if there is a difference that means you have a leak - ideally there shouldnt be a difference. In practice on a server like tomcat there are a lot of things happening in the background even if no user is accessing the site so even after a full gc , you might still see some tomcat classes or objects that appear to be new. The way around this is that you have to loop the step in b so that you will get to see significant differences for your classes rather than the app server classes.

For our env however taking a heap dump seems problematic because of the version of JDK seems really old(1.5 _07) and I wasnt able to load the taken heap dump in any tool.

Heap Dump
To take a heap dump you have the following options
a. Some JVM's support -XX:+HeapDumpOnCtrlBreak (kill -3 pid on linux). However our version doesnt
b. Some profilers(e.g. Jprobe) allow you to take heap dump - You have to pay for this but there are some free ones like NetBeans. however all of them need you to run some install steps so I didnt use this
c. use jmap . This is a utility that Java provides. Later versions let you say JAVA_BIN/jmap -dump processid. For our version we have to say jmap -heap:format=b processid . however this isnt working correctly since i couldnt load this dump into any tool. what I finally used was jmap -histo processid. This is a poor mans heap dump . it shows the classes and the number and the size they occupy, but it doesn't show who allocated the classes (so for e.g. I knew it was the concurrency related classes that were leaking , but I didnt know who was creating them - that was thanks to Google)

d. +XX:HeapDumpOnOutOfMemory - This will automatically take a heap dump when you run out of memory but debugging with this is slightly harder because you have live objects
e. use HPROF (this is an earlier version of the tool) when you start up java but it will slow the process.

Monitoring
To look at how much memory is being used, and to force GC you have the following options
a. Look at the probe we installed (specific to tomcat) - lambda/psi probe . Click System information . under overview you can see the memory being used and you can Force GC as well. You can also click Memory Utilization and it will show you the breakup. I had to add some JMX parameters to startup. This is tomcat specific.
It also lets you see sessions and their footprints (sometimes the leak isnt actually a leak. Code puts too much data in session , the user doesnt log out , the session remains active for say 30 minutes , then that much memory is used up for 30 minutes. technically this isnt aleak , when the session times out , the objects will get collected , but it looks like a leak because the memory keeps getting used , but doesnt get reclaimed)
b. use JConsole . This is in the bin directory of your java. When you start it on your machine you can add a remote connection
These are the settings I added on dev
export JAVA_OPTS="-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/usr/local/apache-tomcat-5.5.30/logs -XX:PermSize=256m -XX:MaxPermSize=256m -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=12345 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Dfile.encoding=UTF8"
This will also let you see some things that the probe does.
Using this I could find out
a. That it wasnt the sessions causing the problem (since the probe showed that only 1 MB was being used in sessions).
b. I also used it to check and see whether threads were causing issues , not the case.

Testing
I used JMeter to simulate a web user going and approving a quote and simply looped that 4000 times. I couldnt not use say SOAPUI because we needed to simulate a stub being created whereas SOAP acts as the client so it wouldnt have shown the problem. Ordinarily you would not know the Stub causes the problem , but the histograph had shown such a large number of the concurrent objects on the heap , that a google search showed that other people had faced this problem with axis 1.4.1. If I didnt have this I would have had to write a script that would have placed a quote, gone and approved it , saved it , modified it etc.

The histographs are in /root/histbeftest and /root/hist92per and are easily compared to verify.

Analysis
The histograph files are plain text and can be compared in a text editor. If I had a heap dump we could use
a. JHat - this comes in the bin directory of java (1.6 onwards and some update of 1.5 onwards but it can read 1.5 dumps). This will let you browse the heap and even compare them
b. Profilers like JProbe
c. Other tools like VisualVM, HPJmeter NetBeans, extensions in eclipse all let you load heap dumps.
One of the issues you might run into is that the Heap Dump file is quite large and your client tool may not have enough memory. To verify a memory leak you usually reduce the amount of memory you give to the JVM so that you get smaller heap dump files (so for e.g. the iquote app once it is running and all the classes are loaded takes about 20 to 30% of 512MB which is about 150 MB. So I could reduce the memory to 256MB instead of 512 and run the tests to create a much smaller heap dump)

a memory leak in sample code and then trying to detect it using tools is usually the best way to learn.

Updated JEE Interview Questions - Draft

JSP
What are the various way's to handle exceptions in a web application. What would you use when. Demonstrate with examples from any project you have worked on
What are the various way's you have implemented security in your web application. Also mention alternatives that can be used
Which framework have you used. Please describe the shortcomings in the framework and the ways to work around them
What is the difference between a static include, jsp:include, jsp:forward and redirect. Please give one example of each.
Describe some Tag Libraries you have written. What are advantages / disadvantages of tag library. If possible give an example of a badly written open source JSP tag library(or any of your own) and how you would improve it.
Give one example of when you would use a filter. How do you execute a filter after the request?
Give one example of when you would use a listener. Which listeners have you used in your project?
Besides defining servlets , name one feature that can be specified in the web deployment descriptor
Name JSP implicit object. Give one example of the use of each implicit object. Is exception an implicit object? If so can i write exception.printStackTrace in any JSP? what will it print?
Comment whether a JSP web application works with cookies disabled.
Which web container did you use. Please describe how to use a container specific feature.
Describe some JSTL tags you have used and what they are useful for
How do you use a datasource in a JSP?
How do you internationalize a web application. What all do you need to take care of

EJB
How do you implement security in an EJB . Why does the framework provided security not work in most real world scenarios? (or does it?)
If an MDB throws an Exception what happens to the message?
If an EJB has two methods M1 and M2 both with RequiresNew and M1 makes a call to M2 by calling it (because M2 is a method in the same class) how many transactions are there?
What limitations are

JDBC
Lets say you want to execute a query and show some data. Walk through the steps to do this in Raw JDBC.
What do you prefer using of the following and why? CMP/JDO/ORMs (like hibernate/toplink)/SQL helpers (like Spring/iBatis)/Raw SQL?
In the context of ORM what is lazy loading/eager load. What do you use in your project? Why? What factors determine what is to be used.
Your ORM based system is slow. How would you diagnose the problem?
Why is pessimistic locking not useful in a web-application (or is it?)

JMS
Say you have a queue. The Producer can produce messages much faster than the consumer can consume. What are your options?


JMX
Give any example where you have used JMX

WEB
Given a large data set , what options do you have for displaying this dataset. Which one do you prefer and why?
Suppose you are tasked to implement an AJAX based system where the user types in a word in a search box and you want to show him possible queries (e.,g. in Google if you type dee you get deepak chopra or deepika padukone)in a drop down , what considerations would you have in implementing the AJAX parts of the client (Assume that you have a server side component that can give you the results)
If you want Google to search your site easily , what do you need to take care of in your web app

Misc
You have a clustered J2EE web application. You need to batch process a file which has a billion records. Each record is independent . How do you do it?
You have a table which has UserID (primary key) and UserName. The requirement is to display this in a drop down box on a page so that the user will select the name but the value posted to the next page will be the userid. The data displayed must be sorted by username. The DB developer asks you what data structure he needs to return the results in. What is your answer? Assuming that you get this data structure , is there any comment you wish to make on your implementation?
Name a few design patterns that you see being used in the Java API with examples.

JSP Interview questions

1. What are the various way's to handle exceptions in a web application. What would you use when. Demonstrate with examples from any project you have worked on
2. What are the various way's you have implemented security in your web application. Also mention alternatives that can be used
3. When would you use servlets. name one thing you can do with a servlet that you cannot do with a JSP.
4. Which framework have you used. Please describe the shortcomings in the framework and the ways to work around them
5. What is the difference between a static include, jsp:include, jsp:forward and redirect. Please give one example of each.
6 Describe some Tag Libraries you have written. What are advantages / disadvantages of tag library. If possible give an example of a badly written open source JSP tag library(or any of your own) and how you would improve it.
7. Give one example of when you would use a filter. How do you execute a filter after the request?
8. Give one example of when you would use a listener. Which listeners have you used in your project?
9. Besides defining servlets , name one feature that can be specified in the web deployment descriptor
10. Name JSP implicit object. Give one example of the use of each implicit object. Is exception an implicit object? If so can i write exception.printStackTrace in any JSP? what will it print?
11. Comment whether a JSP web application works with cookies disabled.
12. Which web container did you use. Please describe how to use a container specific feature.
13. Describe some JSTL tags you have used and what they are useful for
14. How do you use a datasource in a JSP?
15. How do you internationalize a web application. What all do you need to take care of

Data DrivenTesting(from a database)

Motivation
Data to a test needs to be varied , however the input needs to be constrained to a set of values(normally in some database table). E.g. check the prices of the top 10 items. Here we need to provide 10 item ids , however if these values are kept in a CSV file , then the file needs to be repeatedly updated. There needs to be a way to get these values to the test at runtime

Solution
Use the JDBC Request Sampler to fetch the data at runtime. Use either the Save Responses to a file or a BeanShell post processor to write the data to a file. Finally use the CSV Data Set Config to read this data.

Sample

Varying the data to the test

Motivation
The same test's need to be run, but the data we pass to it must be varied.
In addition further tests may need to change their behavior depending on the data. E.g. A user registering may provide different data , and subsequent screens may change depending on what the user has entered or may be skipped altogether. A common scenario is when a user registers to a site has various options he can choose from , and we need to test the behavior of the site for different combinations

Solution
JMeter provides multiple ways to vary the data
a. Use of User Parameters [1]
b. Use of Variables [2]
c. CSV Data Set Config [3]
The solution we will use is Option c.

The advantage of using CSV Data Set Config is that the data is externalised from the test , and can be updated by any user including a non technical business person. By making the assertion a part of the data, users can add more tests without needing the test itself to be modified. The other advantage of a CSV Data Set Config over a User Parameters pre processor is that the number of items that will be tested is fixed independent of the number of threads you will run (assuming you write the test in that fashion) OR can be made dependent on the number of threads. User Parameters is more closely tied to the number of threads.
e.g. If you wanted to create 10 distinct users , you'd only have 10 rows in your CSV data set config and you could use 1 to 10 threads. But if you needed to do this with User Parameters you'd probably need to specify exactly 10 threads.

So the solution takes the form of
a. Create a CSV Data Set Config element and point it to the CSV files.
b. Create your tests to use this data
If you want as many tests as you have rows in your CSV file, then you can either end the thread or use a Loop Controller an check for the special value ''<EOF>"


Sample

References
[1] User Parameters
[2] Variables
[3] CSV Data Set Config

Testing multiple environments with JMeter

Motivation
Most projects have a number of environments through which the code moves. e.g. A Development environment, A Test environment, A User Acceptance test environment, A reference environment and finally the Production environment. Hence the same test script is to be targeted to multiple environments. In theory all of this is automated , and anything that succeeds/fails in one environment would succeed/fail consistently in all other environments. However environmental differences and human errors almost always cause one to hear "But it works on my machine"
Whats needed is a way to run the same test against different environments easily
Solution
An assumption we are going to make here is that these tests are automated and would be run from the command line, in our case using ANT.
The solution has to address two basic requirements
a. Parameterization of the various environments
b. You should still be able to run the test in GUI mode (when you are modifying/extending the test)
To implement this we will use JMeter properties[1] and use normal ANT [2],[3] features.

While writing the HTTP tests, add an HTTP Request Default element

If the Server name or IP is to be varied then enter
${__property(run.server,,yourdevserver.com)}
This will look for a property named run.server , but will use yourdevserver.com if no property is specified. For the third parameter, use the server against which you want to run the test while running in GUI mode.

Finally in your Build Script that you use to run Jmeter

<jmeter jmeterhome=".." testplan="${run.test.plan}"

resultlog="${report.dir}/${run.test.report}-${run.env}-${DSTAMP}${TSTAMP}.jtl">

<property name="jmeter.save.saveservice.output_format" value="xml"/>

<property name="run.server" value="${run.server}" />

</jmeter>

where the ANT property run.server can be varied to run this against different environment.

Sample

TODO attach ant and jmx file.

References
[1] JMeter Properties
[2] JMeter Ant task
[3] Ant Manual

JMeter Prologue

I've been testing my existing work application using JMeter for the last 6 months , so what follows are a series of posts that I think isn't covered in most documentation or available online easily or in the same place (I had to figure out these solutions myself). However there is a caveat to that, the solution may not be the best possible one , may not be efficient and there may be more elegant ways to do what the solution does. In which case please inform me. However the solutions do have one thing in common, they worked for me. Your mileage may vary.

The rest of the post is a rant , feel free to move on
A few observations on a Friday(with a tip of the hat to BusyBee)


That people who keep asking for Unit Tests don't have a clue about testing web based applications.

That data driven integration testing between multiple systems is damn hard to do , but boy is it satisfying when you actually find a defect due to it, and boy is it worth your time to develop these tests.

That open source tools are so much better than some of the paid commercial tools. Except when it comes to presentation of the reports. Which surprisingly is also the difference between a Techie and a Manager.

That there still is no tool to truly perform visual tests on a website.
And That someone who could develop such a tool could make a lot of money.
And that someone wont be me.

That there is no time to test all the normal cases, much less the weird corner ones. and that there would always have been plenty of time in hindsight, if we had just gotten our act together earlier

That a successful test is the one that fails in local,development, test, QA , UAT environments. That a test thats succeeds in the above environments but fails on the production environment is a pain.

That a web based test should never underestimate the ignorance of a user.

That developers do not make good testers. And that most developers are better testers than the official testing team, especially when we test other developers code. And that scares me.