Is it bad practice to inject a value into a Spring controller? - spring

I have a Spring controller and there is a String parameter I want to inject into this controller. So I'm considering adding a new constructor to the controller which accepts the String as a parameter. Is this a bad practice since Spring controllers are singletons ?

You can inject your String parameter instead:
#Value("${dropbox.access-token")
private String accessToken;

Related

Feign Client with Spring Boot: RequestParam.value() was empty on parameter 0

I created a simple Feign Client with Spring Boot like this:
#FeignClient("spring-cloud-eureka-client")
public interface GreetingClient {
#RequestMapping("/greeting")
String greeting(#RequestParam String name);
}
But when I try just to start an application I get an error:
java.lang.IllegalStateException: RequestParam.value() was empty on parameter 0
First I didn't understand what is the reason and googled a lot but didn't find an answer. Almost excidentely I figured out that it works if to write request param name explicitly:
#RequestParam("name") String name
So my question: is it a bug or could it be configured to not write request params names explicitly?
Both Spring MVC and Spring cloud feign are using the same ParameterNameDiscoverer - named DefaultParameterNameDiscoverer to find parameter name. It tries to find the parameter names with the following step.
First, it uses StandardReflectionParameterNameDiscoverer. It tries to find the variable name with reflection. It is only possible when your classes are compiled with -parameters.
Second, if it fails, it uses LocalVariableTableParameterNameDiscoverer. It tries to find the variable name from the debugging info in the class file with ASM libraries.
The difference between Spring MVC and Feign occurs here. Feign uses above annotations (like #RequestParam) on methods of Java interfaces. But, we use these on methods of Java classes when using Spring MVC. Unfortunately, javac compiler omits the debug information of parameter name from class file for java interfaces. That's why feign fails to find parameter name without -parameter.
Namely, if you compile your code with -parameters, both Spring MVC and Feign will succeed to acquire parameter names. But if you compile without -parameters, only Spring MVC will succeed.
As a result, it's not a bug. it's a limitation of Feign at this moment as I think.
Just use String greeting(#RequestParam("name") String name);
#FeignClient("spring-cloud-eureka-client")
public interface GreetingClient {
#RequestMapping("/greeting")
String greeting(#RequestParam("name") String name);
}
I use upgrade maven-compiler-plugin to solve this plobrem. you can access: https://blog.51cto.com/thinklili/2566864
This worked for me.
#FeignClient(name="session-service", url="${session.host}")
public interface SrocessingProxy {
#RequestMapping(value = "/process/{key}", method = RequestMethod.POST)
public Response processSession(#RequestParam String key, #RequestBody PayloadHolder payload);
}
//Service
#RequestMapping(value = "/process/{key}", method = RequestMethod.POST)
public Response processSession(#RequestParam String key, #RequestBody PayloadHolder payload) {
System.out.print("Key : " + key);
}

Spring Boot MVC request mapping overrides static resources

I want to have rest controller in Spring Boot to handle all requests like this: "/{arg}", EXCEPT "/sitemap.xml". How can I achieve that?
You could specify your request mapping on the controller level via regex and exclude some resources (e.g. 'excludeResourceA' and 'excludeResourceB') with:
#RestController
#RequestMapping(value = "/{arg:(?!sitemap.xml|excludeResourceA|excludeResourceB).*$}")
public class YourRestController {
// your implementation
}
Of course you can also specify the request mapping on the method level with the same regex relative to your controller path matching and you can pass the argument with #PathVariable("arg") String arg in your method signature to your method body if you need it.

Spring Controller fetch query parameter for a wrapper request class

I am trying to build RESTful web service by using spring 4.0
I have a controller:
#Controller
#RequestMapping("test")
public class Controller{
#RequestMapping("fetch",method=RequestMethod.GET)
#ResponseStatus(value=HttpStatus.OK)
#ResponseBody
public ResultResponse fetchController(ResultRequest req){
if((req.getName).equals("John"))
return new ResultResponse(100);
else
return new ResultResponse(0);
}
}
and my ResultRequest.class
public class ResultRequest{
private String name;
//getter,setter
}
If I hit the url to //host//contextPath/test/fetch?name=John
the controller will return the object ResultResponse(100)
my question is, there no #RequestParam or other annotation in the request parameter,
how does the spring controller know to set the query parameter "name" as the property of wrapper class
ResultRequest ?
Thanks
Spring uses implementations of an interface called HandlerMethodArgumentResolver for resolving arguments to pass to handler methods, ie. methods annotated with #RequestMapping.
One of these is a ModelAttributeMethodProcessor. Its javadoc states
Resolves method arguments annotated with #ModelAttribute and handles
return values from methods annotated with #ModelAttribute.
Model attributes are obtained from the model or if not found possibly
created with a default constructor if it is available. Once created,
the attributed is populated with request data via data binding and
also validation may be applied if the argument is annotated with
#javax.validation.Valid.
When this handler is created with annotationNotRequired=true, any
non-simple type argument and return value is regarded as a model
attribute with or without the presence of an #ModelAttribute.
Spring registers two objects of this type. One to handle parameters annotated with #ModelAttribute and one to handle ones without.
Further reading:
Form submit in Spring MVC 3 - explanation
An Errors/BindingResult argument is expected to be declared immediately after the model attribute, the #RequestBody or the #RequestPart arguments

How to get Spring MVC #PathVariable without using an annotation?

Given the spring mvc method like the one below.
#RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(#PathVariable("ownerId", int ownerId,
#PathVariable("petId") int petid) {
}
Is there some way to write the method so that all the URI templates variables are passed in as a
map to the handler? something along the lines of ?
#RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(Map<String,Object> allPathVariables) {
Integer ownerId = allPathVariables.get("ownerId");
Integer petId = allPathVariables.get("petId");
}
Is there a way to put all the URI templates in a Map that is passed to a handler method?
Looks like this can't be done with Spring MVC 3.1 there is an issue for it on the spring JIRA which is marked fixed for Spring MVC 3.2 https://jira.springsource.org/browse/SPR-9289

Mapping same URL to different controllers in spring based on query parameter

I'm using spring annotation based controller. I want my URL /user/messages to map to some controller a if query parameter tag is present otherwise to some different controller b. This is required because when parameter tag is present then some more parameters can be present along with that which i want to handle in different controller to keep the implementation clean.Is there any way to do this in spring. Also is there any other elegant solution to this problem ?
You can use the params attribute of the #RequestMapping annotation to select an controller method depending on Http parameters.
See this example:
#RequestMapping(params = "form", method = RequestMethod.GET)
public ModelAndView createForm() {
...
}
#RequestMapping(method = RequestMethod.GET)
public ModelAndView list() {
...
}
It is a REST style like Spring ROO uses: if the request contains the parameter forms then the createForm handler is used, if not the list method is used.
If you want to go the Spring route, you can checkout the HandlerInterceptor mentioned here. The Interceptor can take a look at your query param and redirect the link to something else that can be caught by another SimpleUrlMapper.
The other way is to send it to a single controller and let the controller forward to another action if the query parameter is "b".

Resources