Frequently Asked Questions

General

1. What does bpm4struts stand for ?
2. What tools can I use to model ?
3. Where is the online documentation ?
4. I still have more questions! What now ?

1. When I try to run AndroMDA on my model I get an exception, what's going on ?
2. I am using MagicDraw, and I am getting NullPointerExceptions in .getForwardPath(), although my UML model seem to be correct.
3. Do I really need to tag elements with stereotypes ?
4. Do I need to tag elements with tagged values ?
5. What kind of work is involved in making a very simple bpm4struts model ?
6. The session-scoped forms are cleaned on each subsequent entry of that same use-case, how can I transfer data between use-cases ?
7. I've noticed that sometimes my Controller implementation is generated and sometimes not, what's going on?

1. I am not happy with the generated code, can I change it ?
2. I want to precompile my JSP pages, can it be done ?
3. I am precompiling my JSP pages, but I got an error ?
4. How can I define in the UML model that the form-based authentication is used for bpm4struts applications ?

1. I don't want a Struts application, I like Webwork better ... is bpm4struts for me ?
2. Can bpm4struts generate Java Server Faces too ?
3. If you use JSP, TagLibs, it could be worth it to use the UML modeling as you cannot directly "run" the JSP pages as they are within the web browser (especially if you put Java codes in your JSP files ;-)). You always need to run the web container to see the flow, etc.
   
   But if you use XMLC (you just put "id" on the part you want to change in the runtime), you can have the flow, lookfeel, sample data, etc. directly without needing to run the web container. So you just build the HTML files, add the flow directly as they would work within the web container. You can directly show the "story board" to your customer without any implementation and any web container, just use web browser ;-) Very easy. In this case it's not worth it, IMO, to use the flow modeling (activity diagram) in UML, as the story board would be a lot more easier to understand for the customer.
   
   I agree that the class diagram (structure) is always good to use, also for the presentation layer, as we can model the structure of the servlet part. But this would be already the PSM and not PIM anymore.

General

What does bpm4struts stand for ?

Bpm4Struts stands for: Business Modeling for Struts. It means you will be able to create your Struts web application by modeling business processes. Business processes in a Struts application typically involve displaying JSP pages and sending requests to the server by means of actions performed on those pages, such as button clicks or navigating using hyperlinks. These actions mostly result in code being executed on the server (in the action itself, or better yet: delegated to the business layer), it is this code which contains the business logic.

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What tools can I use to model ?

Currently only MagicDraw has been extensively tested, unfortunately this is commercial software and requires a licence to run. Support for a free tool such as Poseidon is underway.

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Where is the online documentation ?

There is the general documentation Bpm4Struts, there is a user-guide and there is the how-to which serves as a small tutorial describing an example application. All of this is hosted here.

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I still have more questions! What now ?

Subscribe to our forum, Go here: AndroMDA forum

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Using bpm4struts

When I try to run AndroMDA on my model I get an exception, what's going on ?

You have to make sure your model complies with the constraints as documented in the user guide. Failing to do so will confuse the cartridge and might have unpredicatable behavior such as exceptions or undeployable Struts code.

Here are some common exceptions with a description and their resolution

Exception	Description	Resolution
NullPointerException at StrutsActionLogicImpl.getPackageName(StrutsActionLogicImpl.java)	The cartridge tried to resolve the package for an action by trying to look for the controller, the controller was not found.	Make sure all activity graphs have a controller assigned to them.
ClassCastException at StrutsActivityGraphLogic.getController(StrutsActivityGraphLogic.java)	A controller was found but does not seem suited for bpm4struts.
MethodInvocationException at class StrutsTriggerLogicImpl	A method was called on one of the triggers, but some of the required information was not found, such as the name.	Make sure all triggers on transitions going out of a jsp page (action states with the FrontEndView stereotype) have a suitable name, it may not be empty.

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I am using MagicDraw, and I am getting NullPointerExceptions in .getForwardPath(), although my UML model seem to be correct.

Did you make sure your action states all have names ? in magicdraw you really need to click 'open specification...' in order to e nter the name, if you typed the name in the diagram directly you have not entered the name, rather a label. So click 'open specification...' (right-click -- context menu) on all your action states to make sure their names are not-empty.

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Do I really need to tag elements with stereotypes ?

Yes, and the reason is very simple: the cartridge maps stereotypes to templates. This is a way of telling which files should be generated from what elements.

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Do I need to tag elements with tagged values ?

No, but failing to do so will not enable some of the more interesting cartridge features. Using tagged values you can enable the validation of form input fields, for example. It depends on the context of the specific model element whether or not a tagged value would be needed. All tagged values have a default value, so if you don't add one it' value will be implied.

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What kind of work is involved in making a very simple bpm4struts model ?

Let's get over the things to do for a single use-case with a single page:

1. create a use-case
2. give this use-case the FrontEndApplication stereotype
3. create an activity graph in this use-case
4. add an initial state
5. add an action state "Action1"
6. add a transition from the initial state into this action state
7. add another action state "Action2"
8. add a transition from "Action1" into "Action2"
9. add the FrontEndView stereotype to "Action2" (doing this will make it a JSP page)
10. add a final state and give it the name of the use-case to forward to (case-insensitive)
11. add a transition from "Action2" into this final state
12. because this transition is going out of an action state with the FrontEndView stereotype it needs a trigger with a name and optionally with some parameters (this will be rendered as a submittable form)
13. Create a controller class, "ActionController"
14. "assign" this controller class to the activity graph created in step 3. (using MagicDraw you can do that easily)
15. optionally you can add operations to this controller and have an action state defer to any of these operations

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The session-scoped forms are cleaned on each subsequent entry of that same use-case, how can I transfer data between use-cases ?

Since the forms are stored in the session scope it is possible to have stale data in different instances of the same use-case. In order to avoid this we must make sure the data is removed from the form whenever we re-enter that use-case. But in doing so we make it more difficult to send data between use-cases, sometimes it is needed to send an ID or semething to the next use-case, how can we make sure the form cleaning does not dispose this data ?

The solution is in fact very simple: do not use the forms when transporting values to another use-case. In fact it is a better idea to simple use HttpServletRequest.setAttribute(String,Object), this will put the value as a request scope variable that is available in the target use-case.

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I've noticed that sometimes my Controller implementation is generated and sometimes not, what's going on?

Controllers are not generated (the implementation that is) until you give it at least one operation (since it would be pointless otherwise).

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Tuning bpm4struts

I am not happy with the generated code, can I change it ?

Sure you can, openup the cartridge and go into the 'templates' directory. You will find a bunch of templates, how they map onto files can be found in the deployment-descriptor in the 'META-INF' subdirectory (next to 'templates'). You can override cartridge resources, this is all explained here.

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I want to precompile my JSP pages, can it be done ?

Sure it can, just put the compiled JSPs in your WAR bundle under WEB-INF/classes.

If you have set up your environment using the andromdapp:generate plugin you can go into the 'web' component and open the project.properties file. In this file make sure you have the following property set: precompileJsps=true. Doing so will enable precompilation.

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I am precompiling my JSP pages, but I got an error ?

It is possible AndroMDA generates servlets with a path that is too long for the Windows filesystem when it is read from the ear bundle. In that case it is sufficient to explode you ear or war when you deploy, this will cause the path to the file to be shortened. This problem manifests itself by means of a java.lang.ClassNotFoundException.

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How can I define in the UML model that the form-based authentication is used for bpm4struts applications ?

You don't specify that in the UML model directly

You should consider the bpm4struts cartridge just as an example ,... customization can be done in the templates .. so you would like to change one of them .. more particular the one called 'StrutsXDocletMergeWebSecurity.vsl', you will understand it when you open it.

Anyway, form based authentication is configured by default, but the security is disabled by default too .. so you need to enable it.

You will need to open up andromda.xml and in the bpm4struts namespace give the 'securityRealm' the value of your security realm. other ${app.root.dir}/${web.dir}/${jsp.src.dir} ${app.root.dir}/${web.dir}/${mda.build.dir} ${app.root.dir}/${web.dir}/${mda.build.dir} ${app.root.dir}/${web.dir}/${mda.build.dir} ${app.root.dir}/${web.dir}/${java.src.dir} ${app.root.dir}/${web.dir}/${properties.src.dir} ${app.root.dir}/${web.dir}/${mda.build.dir} ]]>

Security is disabled by default because it requires you to configure your container too (i.e. users/roles).

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Other technologies

I don't want a Struts application, I like Webwork better ... is bpm4struts for me ?

Not really, at this point there is no cartridge for Webwork, but it can easily be written. Taking a look at how bpm4struts is designed will make it straightforward to implement the same thing for Webwork. This new cartridge could be called bpm4webwork ...

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Can bpm4struts generate Java Server Faces too ?

No, JSF is not Struts. For more information go here: Apache Struts JSF Faq. If you'd like to use JSF instead, check out the JSF cartridge.

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If you use JSP, TagLibs, it could be worth it to use the UML modeling as you cannot directly "run" the JSP pages as they are within the web browser (especially if you put Java codes in your JSP files ;-)). You always need to run the web container to see the flow, etc.

But if you use XMLC (you just put "id" on the part you want to change in the runtime), you can have the flow, lookfeel, sample data, etc. directly without needing to run the web container. So you just build the HTML files, add the flow directly as they would work within the web container. You can directly show the "story board" to your customer without any implementation and any web container, just use web browser ;-) Very easy. In this case it's not worth it, IMO, to use the flow modeling (activity diagram) in UML, as the story board would be a lot more easier to understand for the customer.

I agree that the class diagram (structure) is always good to use, also for the presentation layer, as we can model the structure of the servlet part. But this would be already the PSM and not PIM anymore.

The bpm4struts cartridge for AndroMDA has mainly been created out of a general discomfort with working with JSP/Servlets or even Struts directly. The problem was that I would find myself spending too much time on details related to the underlying technology, rather than on the core business of the application.

More concretely:

1. Client-side/server-side input validation: Changing the type of a field, or adding a new one, would require me to update code at several locations. Granted, XDoclet can solve this problem.
2. Exception handling: It's a known problem, and I was not unaffected by it neither. Exceptions are underestimated and therefore mostly added too late, which can be hard to do. I would like to have a default behavior in pages: "whenever something goes wrong, go back the previous page and display the error message". If you change the page flow often you'll find yourself updating struts-config.xml all the times.
3. Page flow transition (actions -- pages): Error prone, although struts-config.xml is pretty clear and straightforward it is too easy to make a mistake. Repositioning transitions can be a nightmare if your pages rely on the parameters in your requests etc... you get the picture. Before you know it people are starting to put stuff in the 'session' (UGH).
4. Security: I wanted a way to bundle resources together in web.xml, but I am too lazy to keep updating that file all the time.
5. I18N Resources: Or you lock your application into a single language, or you take the time to use the i18n features available. But in doing so you'll need to maintain a bundle for each language, wouldn't it be nice if the file would be created for you (at least in one language) ?
   ... I guess there is more, but you get the picture ...
   Anyway, I chose Struts as a presentation layer, so subsequently I wrote an AndroMDA cartridge for Struts. There's no magic involved, the cartridge only takes over those tasks that are too boring and I was too lazy to do myself, this allows me to keep focus on what the application should be doing, not on how it should be doing it.
   If I understand correctly you build static pages using XMLC, for a POC. This is perhaps very interesting for short demos and presentations, but it is not the target of bpm4struts, as you briefly pointed out. I aimed for stable and production-ready dynamic web pages, I hope there will be enough users to give it a try, that way I am sure we'll get there eventually.
   Mind you, with QVT coming (soon?) we would have a standardized way of modeling our tiers, this would allow to generate different presentation layers using a single UML model. For now you would simply need to write a cartridge for WebWork/Swing/.Net/... and you could generate your code for that specific technology - still from the same UML.
   With bpm4struts you do not model for a specific technology, it is just that the cartridge outputs Struts code. You could easily share the model with a bpm4swing cartridge and have it generate Java Swing code.
   And you're right of course, everything has its own domain on which it is applicable, I am sure other technologies such as XMLC are better suited for specific tasks.

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