I am creating a String based on some input parameters when a rest call is executed. I have created my own Annotation to intercept certain methods which will be called later on (within the same request). The Interceptor needs to know the String created at the beginning. My initial thought was to add the String into the Spring context like this:
ConfigurableListableBeanFactory beanFactory = ((ConfigurableApplicationContext) context).getBeanFactory();
beanFactory.registerSingleton("myValue", "generatedString");
And just inject it to the interceptor. However i can only add it once this way and i really dont want it to be a singleton. Each request has its own "generatedString". I could not find a suitable way of solving this. What i actually want is to register an object on runtime for the current thread so i can inject it later on. When the Thread is done it should disappear.
Related
I have a controller that exposes the following endpoint:
#RequestMapping("/all-users")
List<User> getAllUsers() {
...
}
I have also an annotation that helps me out with versioning of those endpoints, which ends up on something like this:
#RequestMapping("/all-users")
#Version(version=1, latests=LATEST_ALL_USERS)
List<User> getAllUsers() {
...
}
Now I want to introduce an additional standard behavior to all handlers mapped wish method contains #Version annotation which will simply wrap the response object into another object which contains the current version and latest version of the invoked method. Some information to build this object are provided by #PathVariable parameters. I'm trying to find a hook that allows me that but no luck so far.
I tried first to have a custom RequestResponseBodyMethodProcessor but if I add it will not take any effect because the original RequestResponseBodyMethodProcessor comes before and I don't want to remove the ResponseBody from my endpoints.
Afterward I tried to go for the mapping instead, once I cannot handle it on the processor, maybe I could handle that on mapping time introducing my code pre and post method invocation, but got stuck on the point where mapping is registered where a method object is needed, not allowing me to introduce my advice code.
Is there any way to get this done?
Edit:
Some of the information needed to build the new returned object are provided as #PathVariables, and are available on end-point method call.
I have a Spring Batch job that reads in a very large fixed length file and maps it just fine to an object. Validated all of the data in the associated processing task.
Being rather new to Spring and Spring Batch I am wondering if it is possible to get out of the job, a fully populated object to be used in a particular case when I am running the job as part of another process ( that I would like to have access to the data).
I realize that I could do the above without Batch, and it seems to be designed with scope limitations for its purpose.
I could serialize the objects in the processor and go that route but for my immediate satisfaction I am hoping there is a way to get around this.
Thanks
In my #configuration class for the batch processing, I created a class variable (it is a list of the object I want to get back) and instantiated with the no arg constructor.
My Step, ItemReader, LineMapper are setup to use a list for input. The custom FieldSetMapper takes that list instantiated from the constructor as a parameter and adds to the list as the file is read and mapped. Similarly my custom ItemProcessor takes the list as input and returns it.
Finally I created a ReturnObjectList bean that returns the populated list.
In my main I cast the AnnotationConfigApplicationContext getbean to the list of that object type. I am now able to use the list of objects generated from the fixed file in the scope of my main application.
Not sure if this is a healthy work around in terms of how Spring Java config is supposed to work, but it does give me what I need.
If I use Spring, which of these two methods is more correct.
Can I use the new() operator even if I use dipendency injection?.Can I mix both?
I would like to have some clarification on these concepts.
Thanks
First method:
#RequestMapping(method=RequestMethod.GET)
public String create(Model model){
model.addAttribute(new User());
return "index";
}
Second Method:
#Autowired
User user;
#RequestMapping(method=RequestMethod.GET)
public String create(Model model){
model.addAttribute(user);
return "index";
}
By using dependency injection does not mean that the use of new operator is automatically prohibited throughout your code. It's just different approaches applied to different requirements.
A web application in spring is composed of a number of collaborating beans that are instantiated by the framework and (unless overriding the default scope) are singletons. This means that they must not preserve any state since they are shared across all requests (threads). In other words if you autowire the User object (or any other model attribute), it is created on application context initialization and the same instance is given to any user request. This also means that if a request modifies the object, other requests will see the modification as well. Needless to say this is erroneous behavior in multithreaded applications because your User object (or other model attribute) belongs to the request, so it must have the very narrow scope of a method invocation, or session at most.
You can also have spring create beans with different scopes for you, but for a simple scenario of a model attribute initialization, the new operator is sufficient. See the following documentation if interested in bean scopes : Bean scopes
So in your use case, the second method is totally wrong.
But you can also delegate the creation of your model attributes to spring if they are used as command objects (i.e. if you want to bind request parameters to them). Just add it in the method signature (with or without the modelattribute annotation).
So you may also write the above code as
#RequestMapping(method=RequestMethod.GET)
public String create(#ModelAttribute User user){
return "index";
}
see also : Supported method argument types
If you want your beans to be "managed" by Spring (for e.g. to use with Dependency Injection or PropertySources or any other Spring-related functionality), then you do NOT create new objects on your own. You declare them (via XML or JavaConfig) and let Spring create and manage them.
If the beans don't need to be "managed" by Spring, you can create a new instance using new operator.
In your case, is this particular object - User - used anywhere else in code? Is it being injected into any other Spring bean? Or is any other Spring bean being injected in User? How about any other Spring-based functionality?
If the answer to all these questions is "No", then you can use the first method (create a new object and return it). As soon as the create() method execution is complete, the User object created there would go out of scope and will be marked for GC. The User object created in this method will eventually be GC-ed.
Things can be injected in two ways in a Spring MVC applications. And yes, you can you can mix injection and creation if doing right.
Components like the controller in your example are singletons managed by the application context. If you inject anything to them it is global, not per request or session! So a user is not the right thing to inject, a user directory can be. Be aware of this as you are writing a multithreaded application!
Request related things can be injected to the method like the used locale, the request, the user principal may be injected as parameters, see a full list at Spring MVC Documentation.
But if you create a model attribute you may use new() to create it from scratch. I will not be filled by spring but to be used by your view to display data created by the controller. When created in the request mapped method that is ok.
I have had chance of working on only one project using spring , and the way it worked was
Make a singleton class (lets say MySpringHelper), that has method like getBean(String beanName)
What getBean(String) does is, it first checks existence of applicationContext, if it exists uses same to get the bean , else creates new applicationContext and returns the bean
Wherever in you project you need a bean simply call MySpringHelper.getBean("abc")
Keeping this in mind , when i was studying spring , i noticed interface "ApplicationContextAware" ... I am not sure when will this be needed, uses above pattern such interface seems not of any use. Or the above Singleton MySpringHelper pattern/approach is incorrect ??
Looking forward to learn from your experience
To give more details on application , its like a pdf file generator, 1 pdf file having 12-15 different charts, so the main method runs 1 thread for each chart , and inside these chart logic we are using singleton MySpringHelper
Why are you checking the existance of applicationContext? It should be there if your helper bean is configured in xml and has setter method in it. There is no need to create application context in that case.
For your case, I would suggest you get applicationContext injected by Spring rather than by using ApplicationContextAware.
Suppose I have a certain operation that should be available to every process running in Spring MVC.
Say string normalization--
i need to run a method that normalizes the string fields before doing anything else on that form/data.
One thing specific to do is, to normalize the String fields on every input form before
they are dispatched to the back-end services. Likewise, that operation (normalization)
should be run on data from the back-end before it is dispatched to the view component.
One way of doing this that I can think of is:
Code a bean doing it-- the normalization. Then, define this bean somewhere at the top in
the context hierarchy of Spring-- ApplicationContext.xml or WebApplicationContext.xml(?),
so that it will be visible and can be used
accross all the processes/servlets in the application.
Then, Whenever and from wherever needed, invoke that method on the bean defined up there.
Or, inject it to the relevant fields in the bean definitions(?)
In this case, is there a way to call it before or during a HandlerMapping is running? if so, how?
Another i can come up with is:
Code a validator (implement Validator) to run that process and "validate" the String fields for you.
But i dont see how this would be of good help.
From what i know, a validator runs on specific object types. I can define that type generically(?)
but then I'm operating on the fields-- not objects as a whole each.
Coding validator(s) seems too costly to me for this use-- even if it is an option here.
I'm new to Spring. pls bear with me on this.