I am newer to Spring, previously I've worked in PHP and Python. I am having some issues understanding how Spring forms work and are validated. My understanding thus far is that when you are using the your form is backed by a bean, meaning you must provide a bean to the JSP. You can also use the stand HTML forms but then you have to manually retrieve the request parameters in the controller.
Here is the issue I am having. I have a User bean that is using Hibernate Validator, and I have add, edit pages for users. The issue is I don't want the password field to appear on the Edit page, the password is going to be garbage anyway because its using BCrypt. However when the form is submitted validation fails because it expects the password to be present. There doesn't seem to be anyway to do partial bean implementation using Spring Form.
I would like to use Spring Form if possible because it reduces repetitive validation code, and its always nice to work with objects. My thoughts now are do I create an intermediate object and then translate the data from that to my bean. Seems tedious and can lead to the creation of way to many objects. My other thought is to just using plain old HTML forms and pull the params myself and set the values in the object.
I'm not sure what is the best approach or if I'm even thinking on the right track. Spring Forms and the validation is offers seems great, but seems like it isn't particularly flexible. Like I said I'm new to Spring so I may just be missing something or not understanding.
Another issue I have been wrestling with is having multiple objects needed on a form. Lets say I have a User bean, which has the following Properties.
private Role role;
private Country country;
So I need to pass User, List, and List to my JSP. I can get them to display fine, however if the form validation fails when it returns to that page, I lose my role and country objects, unless I re-add them to the model before returning the view name. Am I missing something here or is that the norm. It's a request object so I guess that makes sense but seems tedious to have to re-add them every time.
My understanding thus far is that when you are using the your form is
backed by a bean, meaning you must provide a bean to the JSP.
I'd say mostly true. The form is backed by a bean, but the Spring JSTL tags know how to get to the bean based on the set modelAttribute. The bean is living in what you would consider "page" scope, unless you add set your model attribute to be in session. Either way, if you are using the Spring JSTL tags, they are going to one or the other place to get it.
You can also use the stand HTML forms but then you have to manually
retrieve the request parameters in the controller.
Not true. You can "simulate" the same thing that the Spring JSTL tags are doing. Understand that JSTL tags are very much like macros. They are simply copying in some pre-determined block of code into the output with some very rudimentary conditional statements. The key bit that Spring MVC needs to wire the Model Attribute on the Controller side is the name and value, which are easy to decipher how those get generated/wired together.
However when the form is submitted validation fails because it expects
the password to be present.
You could create a "DTO" or "Data Transmission Object", which is basically a go-between to take the values from the UI and are converted in the Controller/Service layer to the real Model objects on the backend. Or, if you are lazy like me, put the User in session scope, in which case you don't have to post the value as Spring will take the one out of session and just updated the one or two fields you did post. Don't post the password, Spring wont set the password.
My thoughts now are do I create an intermediate object and then
translate the data from that to my bean.
Yes, this is the DTO I referred to. You only need to do it where you need to.
I'm not sure what is the best approach or if I'm even thinking on the
right track.
There are probably thousands of ways to do anything in coding, some more right or wrong than others. I know some developers who are design-Nazi's and would say you should always do it one way or another, but I am not one of those people. I think as long as you are consistent, and you are not doing something completely boneheaded you are on the right track. My #1 concern with all the code I write is maintainability. I
Don't want to spend 20hrs trying to re-learn what I did 6mo ago, so I tend to choose the simpler option
Hate repeating code, so I tend to choose more module designs
Hate having to spend 20hrs trying to re-learn what I did 6mo ago, so tend to make heavy use of JavaDoc and comments where I find the code is tricky (lots of loops, doing something weird, etc)
Another issue I have been wrestling with is having multiple objects
needed on a form.
There are several ways to deal with this too. I have never used it, but you CAN actually have more than one Model Attribute associated with the same form and Controller handler. I think you use a <spring:bind> tag or something. I have seen samples around, so Google it if you think you need that.
My approach is usually to either put something in session or build a DTO to hold all the things I need. The first I use more for things like lists to drive building the view, for instance if I have a drop down of States coming from a table. I would have a List of the States put into session and just use them from there, that way I only go after them once and done.
I use the DTO approach (some might call it a Form Bean) when I have a complex gaggle of things I need to change all at once, but the things are not necessarily connected directly. Just to point out: You can have nested objects in your model attributes and use them in your Spring JSTL tags. You can also have Collections (List, Set, Map) in your Model Attribute and get to those as well, although Spring doesn't handle nested Collections very well.
Hope that helps.
Related
Most of the article's talk about how to work with the forms like <form:form> Spring tags just with one bean(entity), but in my web app I have more then one bean(actually 3 of them, wich is mirror to my data model in DB(MySql)). What I want is to put values for all of the properties in my entities classes from one form(it may be a jsp or xhtml or html, whatever).
So, I'm kinda new in Spring MVC and as far as I know it has backing object which comes with <commandName> tag in <form:form> tag and I suppose to think that it may be just one commandName backing object for each form??
Q: - Could you please tell me how to easily(or direct me to any example's) to fulfil my pleasant headache.
Q: - It also may have something to get attributes in one controller class but by different methods. Do I have to store them in session or request? I'm thinking to have ModelAndView class for store multiple attributes in map and after store them in ModelAndView (in model). What you suggest?
hope you are having a wonderful day!
I'd suggest you investigate the technique detailed here:
http://forum.springsource.org/showthread.php?58993-Need-to-Populate-Form-data-into-multiple-java-beans
Also, I'm wondering if there could be a terminology issue here. Do you mean you actually want to have just one form on your UI, with a lot of inputs, or do you really mean you want it all on one SCREEN or page? I say that as its also possible to have multiple forms on one UI screen and go that route... which in fact might be easier, as you could then break up your processing into multiple controllers.
Another consideration on the above relates to screen design... if you are going to be populating the data for several beans from one screen, potentially that could be a LOT of data and your screen could get very cluttered and hard to read. So from that standpoint it might also be better to consider breaking your input controls up into multiple (related) screens. There is a little more about that at the bottom of the article I linked above.
You can refer: https://stackoverflow.com/a/4986410/1882833
One approach would be to have a seperate class which encapsules the required objects. And then use it as a command to set and get the data.
I have a project where the data-model and business-layer are located in two different modules. Of course, the bussiness-module has a dependency to the model-module. The entity-validation is implemented through java-validation-api annotations.
I'm wondering where I should implement the cross-entity-validation (business validation, where the relations between different entity types are validated). Currently I see the follwing options:
Create custom javax.validation.ConstraintValidators and associated annotations. Problem is, that the validator would need access to the business-services, i.e. to retrieve related entities, but the model-module should not have a dependency to the business-module.
Implement cross-entity-validation in the business-services persist/merge-methods (i.e. by using interceptors). That would be possible, but the cross-entity-validation is seperated from the entity-validation and I would like to have only one place for validation.
Which option is preferable? Are there any better suggestions?
Thanks,
Sebastian
From the ideological point of view approach 1. is better. Bean Validation is working at the level of Model (in Model-View-Controller) and it is nothing wrong if Model part talks to database. So, for instance, you can create DAOs, which can be used both by service leayer and Model validators in order to avoid code duplication.
Interceptors are also good place to validate something, but you will not be able to use full power and automaticity of Bean Validation. Probably you will need to call validate method on your model objects by hand, throw ConstraintViolationException where needed, etc. Doable, but a little bit of work. In addition some validation probably will be left in Model, so, as you've pointed out, there would be more then one place, where validation is going on.
So I would move necessary DB code to separate layer and go with option 1.
I'm really confused by this... still.
I asked a similar question to this a while before, but i'll ask it even simpler now.
I see this in a lot of samples and tutorials. How could you put [Bind(Exclude="ID")] on an entire Model, and expect to do Edits on the model? If you get pack all the properties of a model on a POST but not the ID, then how do you know which ID to edit?
Even if i'm using ViewModels... i'm probably creating them without IDs. So in that case... also... how do I know which ID was updated on an Edit?
Yes, i understand that there is a "security" element to this. People can hijack the ID... so we need to keep people from updating the value during a POST. But... what is the correct way to handle edits then? What's common practice?
I feel like i'm missing something VERY trivial.
In MVC requests are processed by the model binder when the client makes a request. If you include models on your controllers then, as far as I'm aware, you actually have to specify the model you wish to bind to by prefixing your arguments with the model name (unless you only have one argument which is the model)
SomeModel_ID
Now, in some cases you might want to exclude certain properties from being bound to because they pose a security risk, which you seem to be happy with as a concept. We will exclude ID on the model, preventing any client request from posting this value in plain text.
Now why might we exclude an entire model? Well not all controller arguments are pre-processed by a model binder. RedirectToAction for example does not pass through the model binder, so it is conceivable in this instance for you to create a new model in a POST controller action, and redirect to a GET controller action, passing along a sanitised model. That model cannot be populated by the client, but we are free to populate it ourselves on the server side.
The only time I bind to a model is when I have a view model and an associated editor for that model. This makes it really easy to inject a common editor into a page and to encapsulate those properties. If you have to exclude certain properties from being bound to I would argue that you are doing it wrong.
Update
Following your comments I think I can see why you might be confused. The model bind excluder prevents the client from ever setting a model property. If you need this property to do your updating then you simply can't exclude it. What this does mean then is that the user could potentially post back any ID. In this case you should check that the user has permission to be modifying any objects or database records associated with this ID before serving the requested update. Validating the arguments is a manual process. You can use data annotations for validating inputs, but this isn't likely to help very much with access permissions. It's something you should be checking for manually at some stage.
You know the ID because it's passed to you through the page address. So:
http://yoursite.com/admin/users/edit/20
Will populate your ID parameter with 20. If it's used in a POST (ie, the information is filled in), just manually fill in the ID field and pass it to the database controller in whatever manner you have devised.
This is also immune to (trivial) hijacks because if they were to write some other ID besides 20, they wouldn't be updating the user with ID 20 now would they? :)
After writing a few lesser programs when learning Java the way I've designed the programs is with Model-View-Control. With using MVC I have a plethora of getter methods in the model for the view to use.
It feels that while I gain on using MVC, for every new value added I have to add two new methods in the model which quickly get all cluttered with getter & setters.
So I was thinking, maybe I should use the notifyObserver method that takes an argument. But wouldn't feel very smart to send every value by itself either so I figured, maybe if I send a kind of container with all the values, preferably only those that actually changed.
What this would accomplish would be that instead of having a whole lot of getter methods I could just have one method in the model which put all relevant values in the container.
Then in the view I would have a method called from the update which extracted the values from the container and assigning them to the correct fields.
I have two questions concerning this.
First: is this actually a viable way to do this. Would you recommend me doing something along these lines?
Secondly: if I do use this plan and I don't want to keep sending fields that didn't actually change. How would I handle that without having to have if statements to check if the value is not null for every single value?
I've more familiar with the MVP paradigm, but hopefully they're similar enough to comment. While getters (and setters) in and of themselves are not necessarily evil, they are sometimes a sign that your subsystems are too strongly coupled. One really great way to decouple this is to use an event bus: see Best practices for architecting GWT apps. This allows the view to just shoot off events for the controller to listen for whenever something important happens, and the view can listen for events whenever something changes in the model that corresponds to updating the view. Ideally you wouldn't even need to ever pass the model to the view, if you can break up any changes into incremental pieces and just tell the view to change this part and then this other part.
If you feel you have too many getters (and setters) in your model class, maybe you have too many fields altogether. Is it possible that there are several distinct classes hiding within your model? If you extract these into separate classes, it may make your model more manageable.
OTOH the associated container you are thinking about could also be viable - but then why duplicate all data? You could instead use the associated container directly in the model to store all properties you can think of. And you can also pass this around for observers to get updates (preferably wrapped into an unmodifiable container, of course) - although in this setup you wouldn't need to.
In general, Java is a verbose language which expects you to put all those getters and setters (and a lot more) in place. However, any decent IDE can generate those for you with a few keypresses. Note also that you need to write them only once, and you will read and call them many many more times. Verbose also means easily readable.
If you have too many getter it's ok. But you shouldn't need the setter. The view is supposed to only read/query the model.
The MVC pattern should promote something that is asymmetric: the control update the model by calling methods in the model that embed the logic and update the sate accordingly; this respects encapsulation. The view reads/queries the model via the getters. This goes a bit against information hiding, but that's how MVC works.
I wouldn't personally pass all information in the events. It sounds complicated to me: either you end up with something that is not statically typed (e.g. you pass hashmaps), or with a plethora of typed events. I would stick with something simple, and have (possibly many) getter in the model.
I am building an application using Spring MVC. I want to make certain changes to my Model for every Controller in the application. In particular, I want to insert certain extra data into the model which will be present for all pages of the application.
I could do this several ways: just add the data at the end of every Controller, use a subclass of Model that adds my extra data, use a subclass of ModelAndView that wraps my Model, use a subclass of VelocityView that wraps the Model before using it... I'm sure there are other options.
But I have an "elegance" constraint: I don't want to write code in each and every Controller, I want this behavior defined in one-and-only-one place. Ideally, it would be controlled by my IOC bean config file.
Does anyone have a recommendation of how to achieve this elegantly?
Aspects are a good approach, but Spring MVC makes it even easier -- you can define a HandlerInterceptor that will be called before or after every time a request is handled. In the HandlerInterceptor postHandle method (in your class that implements the HandlerInterceptor interface) you can add your data to the ModelAndView. You define which handlers should be intercepted in your config file.
You could take a look at using Aspects. Spring even has an AOP extension that you could use.
In brief an aspect would allow you to define code once that would then get "woven" into your classes either when you compile the classes or when they are loaded by the classloader. It's relatively advanced stuff and isn't the most intuitive thing for new programmers to pick up, but it's intended to solve exactly the problem you're referring to.
I might be wrong, but I suspect that you may have described your requirements incorrectly.
You seem to be saying 'I want certain data to be added to my model, for all controllers'.
I suspect that you mean 'I want certain data to be available for all views'.
If my suspicions are correct, then adding the data to you model is polluting your model and violating the single responsibility principle. This is especially true if the same data is to be added to several models. Be careful that you are not just using your model as a convenient 'carrier' of the data - where the data doesn't really have anything to do with the model.
Admittedly, I'm not completely familiar with the Spring MVC way of doing things, but a more detailed example of what you're trying to achieve may allow for a more informed discussion.