Develop Reference

Unable to call function of autowired class

I have the following classes :
Class 1:
package com.assets;
#Component
#Scope("request)
public class AssetDetailsImpl implements AssetApi
{
public void function1(){
....
}
public void function2(){
AssetUtil.test1();
}
}
Class 2:
package com.assets;
#Component
public class AssetUtil
{
#Autowired
AssetDetailsImpl impl;
//some functions
public static void test1{
impl.function1();// NPE I am getting
}
Here my auto wiring not working, its coming null. Both the classes are in the same package. Is it because of the request scope which is there in AssetDetailsImpl? I even tried with #Inject that also was not working. Can anyone please help me to resolve this? Thanks in advance!
I have tried removing the scope, but then also the same problem.
I have also tried:
AssetUtil(AssetDetailsImpl impl) {
this.impl = impl;
}
But I am not sure how to deal with the static thing then also how to invoke this constructor?

The method test1 is static.
But Spring doesn't work with static members because it creates instances of the beans.
Remove static:
public void test1{
impl.function1();
}
And now you have to make sure that the client of this method is also using autowiring to get an instance of AssetUtil

It looks to me like the issue is that the AssetDetailsImpl Component is Request-scoped, which means it comes and goes with each HTTP request, while the AssetUtil Component which is trying to use it is default-scoped, which is Application/singleton scope.
Personally, I try to use singletons as much as possible. I wouldn't use request scope for the first Component.

Spring Boot can't access REST Controller

I have a simple problem - SpringBootApplication doesn't see my controller - what's more weird - only one of three.
I have UserController, WalletController and DashboardController - this one is not visible for my application.
What I have already done is:
Every package with controller is under the main package, where my SpringBootApplication.class is,
I tried annotate main SpringBootApplication.class with #ComponentScan both with basePackages and basePackageClasses,
There is no other beans - which should be annotated #Component, I removed them and moved methods to my DashboardService.class
This is my controller, which is not visible:
DashboardController
And this is my package structure(seems to be right): Package Structure
Thank You for help!
EDIT:
It might be important, that I use the third-party api to get the data I need
In that methods I use url:
private String getNbpJson(String url) {
return new RestTemplate().getForObject(url, String.class);
}
private CurrentRateDTO getCurrentExchangeRate(String json) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(json);
String code = node.get("code").toString();
String date = node.get("rates").get(0).get("effectiveDate").toString();
double bid = node.get("rates").get(0).get("bid").asDouble();
double ask = node.get("rates").get(0).get("ask").asDouble();
return new CurrentRateDTO(code, date, bid, ask);
}
And then in ExchangeService this is my url
#Service
public class ExchangeRateService implements IExchangeRateService {
private static final Logger logger = LoggerFactory.getLogger(ExchangeRateService.class);
private String NBP_CURRENT_RATE_URL = "http://api.nbp.pl/api/exchangerates/rates/c/eur/2020-12-11/?format=json";
What's more... when I move methods from DashboardController to WalletController (which works)
Another thing that I have found out is that only methods, which make use of the third-party api don't work.
Basically, I retrieve data from the url above - I get the specific fields, create an objects with filled fields.
May it be a problem with retrieving data from the third-party and then implementing it in my app?
I have no more ideas for now...

Maybe your controller is registered but you type a slightly different url. Try this property logging.level.org.springframework.web.servlet.mvc.method.annotation: TRACE
and check on application startup if the controller is registered under some other url.
Try to add this to your controller
#RestController()
#RequestMapping("exchangerates")

Okay, I probably found out the problem... Before I have 3 controllers:
#RestController("/api")
public class UserController {}
#RestController("/wallets")
public class WalletController {}
#RestController("/exchangerates")
public class DashboardController {}
I changed the above to
#RestController("/api")
public class UserController {}
#RestController
public class WalletController {}
#RestController
public class DashboardController {}
So, basically I removed base ?endpoint? for each controller and now it works... It seems like basic endpoints in three RestControllers is too much and the third one is not available, but I don't know is it truth (I bet that it's not).
Why that happened then, can anybody explain that behaviour of controllers?
Thank You for explanantion.

Spring boot custom resolver for class variable

I'm trying to achieve something like this:
#Controller
public SomeController {
#CustomConfig("var.a")
private String varA;
#CustomConfig("var.b")
private String varB;
#RequestMapping(value = "/", method = RequestMethod.GET)
public String get() {
return varA;
}
}
CustomConfig would be an #Interface class that accepts one value parameter. The reason why we are not using #Value is because this will not come from config file but from API (such as https://getconfig.com/get?key=var.a). So we are going to make HTTP request to inject it.
So far I've only manage to make something work if the varA and varB is inside get() method as parameter, by using below in a class that extends WebMvcConfigurerAdapter:
#Override
public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
CustomConfigResolver resolver = new CustomConfigResolver();
argumentResolvers.add(resolver);
}
And inside CustomComfigResolver.resolveArgument() we would do the HTTP query, but that's not really what we wanted, we need it to be injected as class variable.
Does anyone have experience in resolving it at class variable level?
Thank you

This could work if you use #Value instead of your own custom annotation. This uses the built in environment:
#Order(Ordered.HIGHEST_PRECEDENCE)
#Configuration
public class TcpIpPropertySourceConfig implements InitializingBean {
#Autowired
private ConfigurableEnvironment env;
#Autowired
private RestTemplate rest;
public void afterPropertiesSet() {
// Call your api using Resttemplate
RemoteProperties props = //Rest Call here;
// Add your source to the environment.
MutablePropertySources sources = env.getPropertySources();
sources.addFirst(new PropertiesPropertySource("customSourceName", props)
}
}
What you are trying to achieve is difficult when you start to consider "unhappy" scenarios. Server down / not reachable. You need to account for all of that in the method above.
I would highly recommend to instead use Spring Cloud Config. Great guide on that is here: https://www.baeldung.com/spring-cloud-configuration
This provides:
- Reloading of your #Value() properties, so no custom annotation needed.
- A more stable server and great Spring integration out of the box.
Best of all, it is easy to apply Retries and Backoffs if the configuration server goes down (see https://stackoverflow.com/a/44203216/2082699). This will make sure your app doesn't just crash when the server is not available.

#Service, #Repository class dependency-injection to static field is good for static method usage?

Using static-method makes code more clean.
So I wanna use static-method even used with #Service, #Repository class in it.
You can more easily understand by code. Very short one and It works!!
But I want to know it is okay to use in any situation.
I didn't see like that code before, so I am afraid it is the effective code to use. If you have any idea about that, could you advise me, please?
#Repository
public class TruckRepository {
public Integer selectWheelCount() {
//which is searching truck database to get some data about trucks.
//Such as how many wheels does the truck have, something like that.
}
}
#Component
public class CarFactory {
private static TruckRepository truckRepository;
//#Autowired << can be omitted after spring 4.3 as I know
NewsSourceFactory(TruckRepository truckRepository) {
this.truckRepository = truckRepository;
}
public static Integer getWheelCount(String carType) {
swtich(carType) {
case TRUCK:
return truckRepository.selectWheelCount();
}
}
}
#Component
public class SomeCode {
public void something() {
Integer count = CarFactory.getWheelCount("TRUCK");
}
}
Add Comments
I very empressive the code of "Duration.class", "Stream.class" in java.
They are also using static-method, Of course they have no dynamic injection in there.
Just in case of thinking about the concise of code or clearness, isn't it the merit of static-method, dont you think? is it really harmless?

You are using static method which uses static field which is initialized in constructor. In this code it's not even clear when Spring will create a new instance of CarFactory (maybe it won't at all, if none is referencing it). And if no instance of CarFactory created, your static method is broken too, because static field is not initialized.
I don't see any benefits of using static methods in your case, after all you can always inject instance of CarFactory into SomeCode.
Simple as:
#Autowired
private CarFactory cartFactory;
Or better:
private CarFactory cartFactory;
public SomeCode(#Autowired CarFactory pCartFactory) {
cartFactory = pCartFactory;
}

Do Spring beans that depend on other beans get singleton versions of those beans by default?

I am new to using the Spring-Framework, and I am actually using the spring-boot library. I have the following question:
I understand that beans registered in the #Configuration class with #Bean are singleton by default, however I am finding that beans that rely on other beans are getting their own instances of those beans, not the singleton instance I would like them to have.
For example:
#Bean
public static void myFirstService() {
return new MyFirstService(foo(), bar());
}
#Bean
public static void mySecondService() {
return new MySecondService(foo(), bar());
}
#Bean
public static void foo() {
return new Foo();
}
#Bean
public static void bar() {
return new Bar();
}
I would like the instances of MyFirstService and MySecondService to have the same instances of foo and bar. That is what should be happening by default, right? Or am I misunderstanding something completely with how beans are handled?
I have played around with the #Scope annotation (to no avail), but it is my understanding I shouldn't have to.
Thanks in advance for any input! :)

No sooner had I posted this, I realised the problem... (always the way...)
I figured out the answer. Just in case anyone else made the same mistake. My IDE corrected the methods to be "static", which of course they should not be.
I have changed these methods to instance methods, and everything worked as expected.

You should have used #Autowired here as follows:
#Autowired
private MyFirstService myFirstService;
#Autowired
private MySecondService mySecondService;
And in java class code for MyFirstService and MySecondService, auto wire the foo and bar also.