I'm rephrasing my existing question to a more generic one. I want to know if Velocity has got implicit object references like JSP does.
I'm particularly interested in knowing about the request object.
In JSP we can get the attribute in the request scope like <%= request.getAttribute("req1") %>
I know that JSP is a servlet and <%= request.getAttribute("req1") %> ends up as a part of _jspService() method which has the request object available to it before the scope of the request ends.
I'm not sure how Velocity works behind the scenes (it may be leaving the request object behind by the time it plays it role)
To test that I did the following thing which was a the part of my previous question.
I have a Spring MVC TestController in which I'm setting a request attribute. I'm using Velocity templates for rendering the views.
#RequestMapping(value="/test", method=RequestMethod.GET)
public ModelAndView display(HttpServletRequest req, HttpServletResponse resp){
...
req.setAttribute("req1", "This should be present for first request");
...
}
In the Velocity template I'm doing something like
Request: $request.getAttribute('req1')
but I'm not getting the value of req1. I know I should have put req1 in model map instead of request but I want to know about implicit request object ref.
I tried $req1 as well but its not working.
When I'm doing the same thing with the model and returning it back, everything is working correctly.
Where am I going wrong?
Update: The same thing is happening with req.getSession().setAttribute("req1", testObject) also.
Salaam,
req.getSession().getAttribute("req1", testObject) == $req1
AFAIK, you cannot access the request object at VelocityViewServlet's templates, unless you explicity set the request object in context or use a v-tool .
Take a look at this question: Velocity + Spring. The Spring folks haven't kept the integration with Velocity very up to date.
Once you've created that extension and set it up to be used properly in your servlet configuration, you'd be able to simply put the object on the ModelAndView and from there do whatever you need with it.
Related
I have a quick question on scope of ModelAttributes.
Dev. Env: Spring MVC 3.1/Java 6/JSP w/JSTL for Views
In my controller, I add an attribute to the model via
model.addAttribute(“appForResubmission”, appForResubmission);
In the JSP(served out in response to a GET request) I read it’s contents as:
${appForResubmission.appId}
— works fine and the data is shown on JSP as expected.
Upon submission of the JSP, in the same controller in a different method(in response to a PUT request), I try to read the attributes from the Model for any changes and I am doing this as
#ModelAttribute(“appForResubmission”) Application app
in the method signature.
However, all I get is a new Application object when I try to interrogate the object for data. Spring’s documentation says this kind of instantiation of a new object happens when the requested attribute does not exist in the Model.
What would cause the attribute to be lost? Any ideas? I am suspecting it is a scope issue someplace but I am not sure where the problem could be.
Any pointers you could provide is greatly appreciated?
Thank you,
M. Reddy
The scope of a modelattribute is the request, internally it is just equivalent to HttpSerletRequest.setAttribute("model", model).
If you want the model to be available in a different controller you probably have two options, one is to reconstruct it, based on what you submit to the controller or using your persistent source. The second option is for specific model attributes to be added to the session using #SessionAttribute({'modelname'}), but just be careful that you have to call SessionStatus.complete to remove the model added to the session later.
I have read the Spring documentation and I was not able to find relevant information regarding the expected behavior of a Spring MVC controller method returning null (with a return type of String).
Can someone please provide a reply or direct me to relevant documentation? Or to put it another way, what would be the benefit of returning null from a Spring MVC controller method?
In Spring 2, when you returned null from a controller you were saying to the Spring dispatcher that you don't want it to search for a view.
You did this if you were handling the response yourself by writing the response content directly and then flushing the output stream (you were managing a file download for example).
If you didn't return null, Spring would have forwarded to a view who would try to write to the response also, messing up your already written data or resulting in an exception if the response was already commited.
Returning null was a way of saying back off to Spring's view resolver.
A lot of things changed in Spring 3 and now the same can be obtained by having an #RequestMapping annotated method that returns void.
If you have a return type of String but you return null I think that it uses the default RequestToViewNameTranslator for translating an incoming HttpServletRequest into a logical view name when the view name wasn't explicitly supplied.
Return type String in spring mvc generally returns your view resolver, it can be your JSP, html or any other view page.
http://www.mkyong.com/spring3/spring-3-mvc-hello-world-example/
Suppose you want to return a normal String like "hi", you can use #ResponseBody annotation to do this.
I'm currently using the #ModelAttribute annotation in my controllers to add reference data to my pages and forms, ie:
#ModelAttribute("someValue")
public String getSomeValue() {
return someValue;
}
This works great until I start using redirects from the controllers. All of the values from methods marked with #ModelAttribute appear in the URL, ie:
http://somedomain.com/page?someValue=value
Is there a setting to turn this off? Or is there a simple fix for this?
I read something about creating an interceptor for adding reference data into a model, but that just seems wrong:
http://developingdeveloper.wordpress.com/2008/02/28/common-reference-data-in-spring-mvc/
I found out that there is a setter on the RedirectView object called setExposeModelAttributes. If you set it to false, the attributes don't get thrown into the URL.
I got some help from PUK_999 in the spring source forums:
http://forum.springsource.org/showpost.php?p=274948&postcount=6
This is intentional and specific behaviour of #ModelAttribute, even if it does feel wrong and broken.
An interceptor is really one of the easiest ways of doing this.
I have hijacked the normal processing of velocity templates by calling response.getOutputStream in my controller, and I do get an image, but there is an exception "java.lang.IllegalStateException: getOutputStream() has already been called for this response" whenever an image is generated. Is there a way to tell velocity not to parse the file for a certain controller?
Return null from your Controller's handleRequest() (or handleRequestInternal()) method to indicate that you have already handled the response and view should not be rendered.
API documentation
I am using methods with the Attribute [WebMethod] in my aspx pages. I don't use any asp.net ajax but jQuery to call these methods and return objects in JSON. This all works fine.
Next I added an authorization check inside the webMethod, if the current user doesn't have access to the feature I need to let the calling JavaScript know.
So I am throwing an AccessViolationException exception which can then be parsed by the OnError callback function in JavaScript. This works too but the exception includes the full StackTrace and I don't want to make this available to the calling client.
What other ways I could use to return an "Access Denied" to the client when the WebMethod returns a business object?
I'm using ASP.Net 3.5SP1 and jQuery 1.32
You can also add a:
customErrors mode="On"/
in your web.config, this will cut away the stack trace and leave you only the exception message
Why propagate errors through the wire? why not use an error response ?
Just wrap your object in a response object wich can contain an error code for status and an error message to present to users.
As suggested by NunFur I changed my approach and rather than throwing an error, I return a 'richer' object.
There are at least two options, the first one would be to encapsulate my business object into a response object with some status properties. I tried this but it makes the JSON more complicated.
So rather than adding a new object I added two properties to my business object, something like ServiceStatus and ServiceMessage. By default these are 200 and '', but can be set by the WebMethod code if anything goes wrong (no access, proper error). In this case they business object will be 'empty' (no data). The JavaScript code then first checks for the ServiceStatus and reacts appropriately.
I add the two fields to all my objects that are returned by WebMethods, even a simple string. They have to implement an Interface with those two properties.
Now I have complete control over that goes over the wire in case something unexpected is happening.
Thanks for the input
I save exceptions for when things go really wrong. (e.g. can't connect to the database)
Either return nothing (null/nill/whatever), or return a false bool value.
Sorry that I don't have a better answer than that...I'll have to keep looking myself.
You could look at SoapException: http://msdn.microsoft.com/en-us/library/system.web.services.protocols.soapexception(VS.71).aspx
I'm just not sure, if it will work when it is called from JavaScript. Espeially if it's called with a get-request.
BTW AccessViolationException is to my best knowlegde ment to be thrown when the application is accessing memory it has no access to.
/Asger