I'm started a position where the backend is in Spring and I'm having trouble. In Django, Flask, Rails, Express.js, etc, there are route files where you can find the declarations of the different URLs the server has responses configured for, and find your way around from there. Spring doesn't seem to have that....there's just files everywhere with annotations that transform the various classes into endpoints.
How do you find your way around or form some sort of mental conceptualization of the codebase's structure?
Here are some general-purpose tips:
Java IDEs are great, use them extensively. They can help in many cases.
All of them support spring boot applications. So you can open, say, pom.xml file and it will load the project.
All Rest Controllers are usually annotated with #RestController annotation
If you think the #RestController is too generic and you need something much more fine-grained in your project, consider using Spring Feature called "Stereo Type annotations". In short, you can define your own annotation (like #MyOwnVeryCustomProjectController) that will be itself marked as #RestController so that Spring boot will treat the classes annotated with that custom annotation just like Rest Controllers (you can also set up any parameter with reasonable defaults with this method).
If you use Java Configurations as opposed to a purely declarative approach with annotations and component scanning, then you might check whether there are #Configuration classes that aggregate bean definitions for all controllers.
Use Spring Actuator in Spring Boot services. In short, it exposes some HTTP endpoints, to any spring-boot process. Among other (fairly useful) endpoints, there is a mappings endpoint, it displays a list of all #RequestMapping paths in Runtime.
Try to find a class marked with the annotation #RestController. This class will serve as a controller to the path in #RequestMapping("/student") with multiple URL/ endpoints marked by any of the one annotations:
#RequestMapping("delete")
#PostMapping("/create")
#GetMapping("/list")
#DeleteMapping("{id}")
#PutMapping("{id}")
Likewise, there can be multiple controllers each, in turn, having multiple endpoints.
Hope this helps.
Related
I am writing a Spring Boot service and wanted to include some form of RequestContext available to the controllers that might store things like the authenticated user and a request id. However, I see multiple approaches:
Use an #RequestScope bean
Use ServletRequest.setAttribute
Use Spring RequestContextHolder
What are the tradeoffs between these approaches?
Broadly speaking, RequestScope is the Spring magic way. It internally uses a RequestContextHolder which in turn depends on ServletRequest.setAttribute.
Said differently, the Spring way, is IMHO RequestScope. RequestContextHolder makes sense if you prefer limit the magic of Spring annotations.
Finaly, ServletRequest.setAttribute is still lower level, and should mainly be used if you want the code to be compatible with a non Spring application.
Moreover, for the first two ways, Spring uses a thread scoped object to store a reference to the request context, which allows the programmer to access the beans even in methods that do not explicitely receive the Request object.
I'm providing a Spring RestController as a part of a library. Currently I have reusable jaxrs services, but I need to make Spring Boot alternatives. One RestController for example has 2 dependencies: one is a service that I could see being a bean and the other a String property.
I'm wondering what is the idiomatic way to expect to get those dependencies from users consuming the library. I had a few ideas about how it might happen, but wasn't sure what was the right or at least best practice way to do it.
Should users construct the RestController manually using the constructor (not using dependency injection)? I actually couldn't even figure out how to do this such that the Spring Boot Application knew about it and didn't see it in guides, so I was assuming this isn't the normal way to provide RestControllers. I only wondered if this was the right way to go as dependency injection being used for a third party library class's dependencies seems like it could be hard to manage.
Should both be beans, with the String property being a named bean? I have this one working, but I'm wondering if consumers of the library having to provide beans that the library's RestController expects is tricky or a bad practice.
Should the simple service be a bean and the String injected via #Value?
Is there some alternative or better way?
I have just started learning Java Spring and the concept of Dependency Injection (DI) and Inversion of Control (IoC).
I learned that all objects whether it is singleton, prototype or request and sessions, are all retrieved from the container.
The container manages the dependencies between classes and the lifecycle/scope of the object.
The fundamental idea behind this is there are no "new" operators for application using Spring Framework as the backbone of the system. (Please correct me if I am wrong).
I wanted to modernize legacy applications coded without the Spring framework and manages the 3rd party libraries classes and injects them using Spring.
How should I approach this?
I learned that all objects whether it is singleton, prototype or request and sessions, are all retrieved from the container.
That is not quite right. Not all objects, but those you have the cotainer told to resolve, are retrieved from the container. In general you use the #Component annotation to mark which of your objects should the container know of. Besides #Component there are other annotations which do in principle the same, but allow a more finegrained semantics, e.g. #Repository annotation, which is at its base #Component and put #Target, #Retention, #Documented on top.
The container manages the dependencies between classes and the lifecycle/scope of the object.
Yes. The container does the wiring up for you, i.e. resolving dependencies annotated with #Ressource, #Autowired or #Inject depending on which annotation you prefer.
During the lifecycle there are possible events, which allow usage of lifecycle callbacks.
Also: You could determine the bean scope.
The fundamental idea behind this is there are no "new" operators for application using Spring Framework as the backbone of the system. (Please correct me if I am wrong).
The fundamental principle is, that you delegate the creation of objects of a certain kind to the container. Separation of creation and consumption of objects allows greater flexibility and in consequence better testability of your application.
Besides the "components" of your application, there are e.g. the typical containers like ArrayList or HashMap, upon which you use the new-operator as before.
I wanted to modernize legacy applications coded without the Spring framework and manages the 3rd party libraries classes and injects them using Spring.
How should I approach this?
From what was said above, it should be "simple":
1) Go through each class file and look for its dependencies
2) Refactor those out and put #Component on top of the class
Special case: 3rd party objects, where you do not have access to the source. Then you have to wrap its construction yourself into a factory e.g. with #Bean.
3) Add the missing dependencies via #Autowired (the spring specific annotation for marking dependencies)
4) Refactor components of the service layer with #Service annotationinstead of #Component.
5) Refactor the data access layer, instead of using #Component, you can use #Repository.
This should give you a base to work with.
Extending spring based interfaces is discouraged as it unnecessarily couples the code with Spring. Does the same reasoning applies to annotations as well? We need to have them imported in the source code before using them.
I'll take the opposite viewpoint--of course using a Spring-specific annotation ties the class to Spring. I claim it's self-evident that importing and using Spring annotations ties the code to Spring (although you could trivially redefine those annotations for a non-Spring environment). The key for me is how deeply it's tied to Spring.
It's easier to check for, and process, annotations, than it is to restructure a class hierarchy or duplicate the functionality of a non-marker interface. Assuming you wanted to leave the annotations in, and could duplicate the logic behind the annotations, it'll be easier to do that (IMO) than to recreate whatever class/interface hierarchy implemented similar functionality.
The other key is the word "unnecessarily". I have yet to create a Spring application and need those classes outside of a Spring environment. When I have (generally for exposed APIs) it's been at the interface level. Note, however, that I knew from the onset that this exposure would exist and I planned accordingly.
Most would argue that this does not. While you've imported those annotations needed to ensure that Spring handles the request or wraps the transactions, you are not extending or implementing a specific class or interface.
Think about it this way, when you've annotated that class you're telling Spring to do various things based upon your configuration. Take out those annotations, and what you have is a POJO which just has some methods. It's a completely valid object without those annotations, it might not do what you wish it do (i.e. handle requests), but the code is still performing the same logic as it was with the annotations -- you are just now responsible for calling it appropriately.
I have been able to define multiple aspects (one is #Before and another is #Around) using Spring AOP (combined with AspectJ annotations) over a business service class.
Currently they are getting called one by one (in sequence). However I would like to know how the priority of calling the aspects can be defined and where.
Please guide me with respect to Spring AOP. Please note that I am using Spring 2.5.3 framework.
I found the answer to this problem.
One can use #Order annotation to specify the order / sequence for particular Aspect class (the class annotated with #Aspect).
Or the aspect class can implement org.springframework.core.Ordered interface to provide order value to Spring framework.