I am getting an error while trying to up my application
Description:
Field conversionService in com.profectus.dashboard.service.impl.DashBoardSettingsServiceimpl required a single bean, but 2 were found:
- mvcConversionService: defined by method 'mvcConversionService' in class path resource [org/springframework/web/servlet/config/annotation/DelegatingWebMvcConfiguration.class]
- defaultConversionService: defined by method 'defaultConversionService' in class path resource [org/springframework/data/rest/webmvc/config/RepositoryRestMvcConfiguration.class]
Action:
Consider marking one of the beans as #Primary, updating the consumer to accept multiple beans, or using #Qualifier to identify the bean that should be consumed
Why 2 beans are created and how to keep only one converter, I just want only spring core converter who can convert entity to pojo or pojo to entity.
I am stuck because of this issue, any lead would be helpful.
Service class code:-
import org.springframework.core.convert.ConversionService;
//other imports
#Service
public class DashBoardSettingsServiceimpl implements DashBoardSettingsService {
#Autowired
private DashBoardSettingJpaRepository dashBoardSettingRepo;
#Autowired
private ConversionService conversionService;
#Override
public DashBoardSettingResponse save(UserInfo userInfo, DashBoardSettingRequest request) {
//other coded
DashBoardSettigEntity entity = conversionService.convert(request.getDashBoardSetting(),
DashBoardSettigEntity.class);
DashBoardSettigEntity entityRetrieve = dashBoardSettingRepo.save(entity);
DashBoardSetting setting = conversionService.convert(entityRetrieve, DashBoardSetting.class);
DashBoardSettingResponse response = new DashBoardSettingResponse();
response.addDashBoardSetting(setting);
return response;
}
}
Autowire type DefaultConversionService instead of ConversionService
Seems like it has something to do with spring data rest having its own ConversionService instance.
Can you try this:
#Autowired #Qualifier("mvcConversionService") ConversionService conversionService;
It worked for me.
Don't forget to add your converters to a WebMvcConfigurer implementation.
I have the following problem.
It is necessary for me that the classes implementing the certain interface automatically became beans(like with #Component).
For example, I have package com.test with context:component-scan base-package="com.test" that has two classes. One of them has annotation #Component, but other only implements specific interface.
I need a class with this interface to become a bean as well as a class with an annotation.
How can i do this?
You can add annotation #Component or #Service to your class and it wil be bean or you could add you class as #Bean to your spring configuration
You can use reflection to access all classes implementing a given interface and then add them manually to your context but please don't.
Just add #Component (and #Qualifier("beanName") if you have more than one bean implementing this interface)
There are multiple ways to achieve this
Add Spring Stereotype #Componenet, #Serivce, #Repository etc. based on your type of class
Explicitly define the Bean in your configurations
#Bean
public InterfaceType methodname(){
return new Implementation();
}
Programmatically using org.springframework.beans.factory.config.ConfigurableBeanFactory
#Configuration
#DependsOn("ContextProvider") //Not sure whether we need this
public class BeanConfig implements BeanFactoryAware {
private BeanFactory beanFactory;
#SuppressWarnings({ "rawtypes" })
private void createBean() throws Exception{
if(null == beanFactory){
throw new Exception("Couldnot load Bean Factory");
}
ConfigurableBeanFactory configurableBeanFactory = (ConfigurableBeanFactory) beanFactory;
configurableBeanFactory.registerSingleton("name", implementation);;
}
}
If you have multiple implementations of an interface then please provide a name with Bean or Stereotype Annotations and use that name while Autowiring.
I am using #ComponentScan and #Component to define my spring beans. What I would like is to declare one of these beans to be autowire-candidate=false.
This could be done with this attribute in xml. Isn't there the equivalent in annotations?
The reason I want this is because I have 2 implementations of the same interface and I don't want to use #Qualifier.
EDIT: Using #Primary is a valid work-around, but autowire-candidate seems to me like a useful feature with its own semantics.
Thanks
Looks like Spring refused autowire-candidate=false concept and it no longer supported. There is no analogue with annotations, so #Primary is the best work-around as you noticed.
Another way is to use custom org.springframework.beans.factory.support.AutowireCandidateResolver, which is used in DefaultListableBeanFactory, with logic that exclude undesirable beans from autowire candidates. In such case, the technology will be similar to that used for autowire-candidate=false in SimpleAutowireCandidateResolver.
Since Spring 5.1 , you can configure autowire-candidate in #Bean through autowireCandidate attribute:
#Bean(autowireCandidate = false)
public FooBean foo() {
return newFooBean();
}
You can also use the bean accessor to tune it's visibiltiy.
see Bean visibility
#Configuration
public abstract class VisibilityConfiguration {
#Bean
public Bean publicBean() {
Bean bean = new Bean();
bean.setDependency(hiddenBean());
return bean;
}
#Bean
protected Bean hiddenBean() {
return new Bean("protected bean");
}
}
You can then #Autowire the Bean class and it will autowire the public bean (without complaining about multiple matching beans)
As a class' definition (unless embedded) does not allow private / protected accessor the work around would be to use an #Configuration class that would instantiate all the beans an publish the public beans while hiding the private/protected (instead of directly annotating the classes #Component \ #Service)
Also package-protected accessor may worth a try to hide #Component annotated classes. I don't know if that may work.
We can do this by using the #Qualifier annotations with name mentioned in the #Component annotations
Bean classes -
#Component("fooFormatter")
public class FooFormatter implements Formatter {
public String format() {
return "foo";
}
}
#Component("barFormatter")
public class BarFormatter implements Formatter {
public String format() {
return "bar";
}
}
Injecting bean in service class -
public class FooService {
#Autowired
#Qualifier("fooFormatter")
private Formatter formatter;
}
For more details please refer - https://www.baeldung.com/spring-autowire#disambiguation. Above example taken from this link.
I've followed the instructions in the Spring 4.0.5 documentation for configuring Bean Validation in the container, with Hibernate Validator 5.1 and this (Groovy) configuration class:
#Configuration("validationConfig")
#Import(CreatorConfig)
#ImportResource("/META-INF/spring/mockito-mocks.xml")
static class Config {
#Bean
validator() {
new LocalValidatorFactoryBean()
}
#Bean
mvpp() {
new MethodValidationPostProcessor()
}
}
My class being tested is instantiated in the referenced CreatorConfig class:
#Configuration
#DependsOn("validationConfig")
static class CreatorConfig {
#Bean
ticketCreator(TicketRepository tickets) {
new UploadTicketCreator(tickets)
}
}
I separated this out into a separate configuration class under the belief that I needed the postprocessor registered before creating the UploadTicketCreator bean, which is annotated according to the documentation:
#Validated
public class UploadTicketCreator {
public UploadTicket createTicket(#Valid CreateTicketRequest request) {
// do stuff
}
}
I'm then injecting the UploadTicketCreator into the test case. I've verified that the autowiring is operating properly (the field is populated, and its own tickets field is a Mockito mock). However, the validation logic is not being applied to my creator bean, and the injected bean is the raw POJO without any proxying.
Am I missing a piece of the validation setup? Is there an additional required step not mentioned in the documentation?
The Spring configuration processor appears to be inspecting the declared return type of the bean declarations. I was using Groovy's implicit return type, which presumably was compiled to Object, and adding an explicit return type of MethodValidationPostProcessor or even BeanPostProcessor caused the validation advice to be applied.
I understand that #Component annotation was introduced in spring 2.5 in order to get rid of xml bean definition by using classpath scanning.
#Bean was introduced in spring 3.0 and can be used with #Configuration in order to fully get rid of xml file and use java config instead.
Would it have been possible to re-use the #Component annotation instead of introducing #Bean annotation? My understanding is that the final goal is to create beans in both cases.
#Component
Preferable for component scanning and automatic wiring.
When should you use #Bean?
Sometimes automatic configuration is not an option. When? Let's imagine that you want to wire components from 3rd-party libraries (you don't have the source code so you can't annotate its classes with #Component), so automatic configuration is not possible.
The #Bean annotation returns an object that spring should register as bean in application context. The body of the method bears the logic responsible for creating the instance.
#Component and #Bean do two quite different things, and shouldn't be confused.
#Component (and #Service and #Repository) are used to auto-detect and auto-configure beans using classpath scanning. There's an implicit one-to-one mapping between the annotated class and the bean (i.e. one bean per class). Control of wiring is quite limited with this approach, since it's purely declarative.
#Bean is used to explicitly declare a single bean, rather than letting Spring do it automatically as above. It decouples the declaration of the bean from the class definition, and lets you create and configure beans exactly how you choose.
To answer your question...
would it have been possible to re-use the #Component annotation instead of introducing #Bean annotation?
Sure, probably; but they chose not to, since the two are quite different. Spring's already confusing enough without muddying the waters further.
#Component auto detects and configures the beans using classpath scanning whereas #Bean explicitly declares a single bean, rather than letting Spring do it automatically.
#Component does not decouple the declaration of the bean from the class definition where as #Bean decouples the declaration of the bean from the class definition.
#Component is a class level annotation whereas #Bean is a method level annotation and name of the method serves as the bean name.
#Component need not to be used with the #Configuration annotation where as #Bean annotation has to be used within the class which is annotated with #Configuration.
We cannot create a bean of a class using #Component, if the class is outside spring container whereas we can create a bean of a class using #Bean even if the class is present outside the spring container.
#Component has different specializations like #Controller, #Repository and #Service whereas #Bean has no specializations.
Let's consider I want specific implementation depending on some dynamic state.
#Bean is perfect for that case.
#Bean
#Scope("prototype")
public SomeService someService() {
switch (state) {
case 1:
return new Impl1();
case 2:
return new Impl2();
case 3:
return new Impl3();
default:
return new Impl();
}
}
However there is no way to do that with #Component.
Both approaches aim to register target type in Spring container.
The difference is that #Bean is applicable to methods, whereas #Component is applicable to types.
Therefore when you use #Bean annotation you control instance creation logic in method's body (see example above). With #Component annotation you cannot.
I see a lot of answers and almost everywhere it's mentioned #Component is for autowiring where component is scanned, and #Bean is exactly declaring that bean to be used differently. Let me show how it's different.
#Bean
First it's a method level annotation.
Second you generally use it to configure beans in Java code (if you are not using xml configuration) and then call it from a class using the
ApplicationContext.getBean method. Example:
#Configuration
class MyConfiguration{
#Bean
public User getUser() {
return new User();
}
}
class User{
}
// Getting Bean
User user = applicationContext.getBean("getUser");
#Component
It is the general way to annotate a bean and not a specialized bean.
It is a class level annotation and is used to avoid all that configuration stuff through java or xml configuration.
We get something like this.
#Component
class User {
}
// to get Bean
#Autowired
User user;
That's it. It was just introduced to avoid all the configuration steps to instantiate and use that bean.
You can use #Bean to make an existing third-party class available to your Spring framework application context.
#Bean
public ViewResolver viewResolver() {
InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
viewResolver.setPrefix("/WEB-INF/view/");
viewResolver.setSuffix(".jsp");
return viewResolver;
}
By using the #Bean annotation, you can wrap a third-party class (it may not have #Component and it may not use Spring), as a Spring bean. And then once it is wrapped using #Bean, it is as a singleton object and available in your Spring framework application context. You can now easily share/reuse this bean in your app using dependency injection and #Autowired.
So think of the #Bean annotation is a wrapper/adapter for third-party classes. You want to make the third-party classes available to your Spring framework application context.
By using #Bean in the code above, I'm explicitly declare a single bean because inside of the method, I'm explicitly creating the object using the new keyword. I'm also manually calling setter methods of the given class. So I can change the value of the prefix field. So this manual work is referred to as explicit creation. If I use the #Component for the same class, the bean registered in the Spring container will have default value for the prefix field.
On the other hand, when we annotate a class with #Component, no need for us to manually use the new keyword. It is handled automatically by Spring.
When you use the #Component tag, it's the same as having a POJO (Plain Old Java Object) with a vanilla bean declaration method (annotated with #Bean). For example, the following method 1 and 2 will give the same result.
Method 1
#Component
public class SomeClass {
private int number;
public SomeClass(Integer theNumber){
this.number = theNumber.intValue();
}
public int getNumber(){
return this.number;
}
}
with a bean for 'theNumber':
#Bean
Integer theNumber(){
return new Integer(3456);
}
Method 2
//Note: no #Component tag
public class SomeClass {
private int number;
public SomeClass(Integer theNumber){
this.number = theNumber.intValue();
}
public int getNumber(){
return this.number;
}
}
with the beans for both:
#Bean
Integer theNumber(){
return new Integer(3456);
}
#Bean
SomeClass someClass(Integer theNumber){
return new SomeClass(theNumber);
}
Method 2 allows you to keep bean declarations together, it's a bit more flexible etc. You may even want to add another non-vanilla SomeClass bean like the following:
#Bean
SomeClass strawberryClass(){
return new SomeClass(new Integer(1));
}
You have two ways to generate beans.
One is to create a class with an annotation #Component.
The other is to create a method and annotate it with #Bean. For those classes containing method with #Bean should be annotated with #Configuration
Once you run your spring project, the class with a #ComponentScan annotation would scan every class with #Component on it, and restore the instance of this class to the Ioc Container. Another thing the #ComponentScan would do is running the methods with #Bean on it and restore the return object to the Ioc Container as a bean.
So when you need to decide which kind of beans you want to create depending upon current states, you need to use #Bean. You can write the logic and return the object you want.
Another thing worth to mention is the name of the method with #Bean is the default name of bean.
Difference between Bean and Component:
#component and its specializations(#Controller, #service, #repository) allow for auto-detection
using classpath scanning. If we see component class like #Controller, #service, #repository will be scan automatically by the spring framework using the component scan.
#Bean on the other hand can only be used to explicitly declare a single bean in a configuration class.
#Bean used to explicitly declare a single bean, rather than letting spring do it automatically. Its make septate declaration of bean from the class definition.
In short #Controller, #service, #repository are for auto-detection and #Bean to create seprate bean from class
- #Controller
public class LoginController
{ --code-- }
- #Configuration
public class AppConfig {
#Bean
public SessionFactory sessionFactory()
{--code-- }
Spring supports multiple types annotations such as #Component, #Service, #Repository. All theses can be found under the org.springframework.stereotype package.
#Bean can be found under the org.springframework.context.annotation package.
When classes in our application are annotated with any of the above mentioned annotation then during project startup spring scan(using #ComponentScan) each class and inject the instance of the classes to the IOC container. Another thing the #ComponentScan would do is running the methods with #Bean on it and restore the return object to the Ioc Container as a bean.
#Component
If we mark a class with #Component or one of the other Stereotype annotations these classes will be auto-detected using classpath scanning. As long as these classes are in under our base package or Spring is aware of another package to scan, a new bean will be created for each of these classes.
package com.beanvscomponent.controller;
import org.springframework.stereotype.Controller;
#Controller
public class HomeController {
public String home(){
return "Hello, World!";
}
}
There's an implicit one-to-one mapping between the annotated class and the bean (i.e. one bean per class). Control of wiring is quite limited with this approach since it's purely declarative. It is also important to note that the stereotype annotations are class level annotations.
#Bean
#Bean is used to explicitly declare a single bean, rather than letting Spring do it automatically like we did with #Controller. It decouples the declaration of the bean from the class definition and lets you create and configure beans exactly how you choose. With #Bean you aren't placing this annotation at the class level. If you tried to do that you would get an invalid type error. The #Bean documentation defines it as:
Indicates that a method produces a bean to be managed by the Spring container.
Typically, #Bean methods are declared within #Configuration classes.We have a user class that we needed to instantiate and then create a bean using that instance. This is where I said earlier that we have a little more control over how the bean is defined.
package com.beanvscomponent;
public class User {
private String first;
private String last;
public User(String first, String last) {
this.first = first;
this.last = last;
}
}
As i mentioned earlier #Bean methods should be declared within #Configuration classes.
package com.beanvscomponent;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
#Configuration
public class ApplicationConfig {
#Bean
public User superUser() {
return new User("Partho","Bappy");
}
}
The name of the method is actually going to be the name of our bean. If we pull up the /beans endpoint in the actuator we can see the bean defined.
{
"beans": "superUser",
"aliases": [],
"scope": "singleton",
"type": "com.beanvscomponent.User",
"resource": "class path resource
[com/beanvscomponent/ApplicationConfig.class]",
"dependencies": []
}
#Component vs #Bean
I hope that cleared up some things on when to use #Component and when to use #Bean. It can be a little confusing but as you start to write more applications it will become pretty natural.
#Bean was created to avoid coupling Spring and your business rules in compile time. It means you can reuse your business rules in other frameworks like PlayFramework or JEE.
Moreover, you have total control on how create beans, where it is not enough the default Spring instantation.
I wrote a post talking about it.
https://coderstower.com/2019/04/23/factory-methods-decoupling-ioc-container-abstraction/
1. About #Component
#Component functs similarily to #Configuration.
They both indicate that the annotated class has one or more beans need to be registered to Spring-IOC-Container.
The class annotated by #Component, we call it Component of Spring. It is a concept that contains several beans.
Component class needs to be auto-scanned by Spring for registering those beans of the component class.
2. About #Bean
#Bean is used to annotate the method of component-class(as mentioned above). It indicate the instance retured by the annotated method needs to be registered to Spring-IOC-Container.
3. Conclusion
The difference between them two is relatively obivious, they are used in different circumstances.
The general usage is:
// #Configuration is implemented by #Component
#Configuration
public ComponentClass {
#Bean
public FirstBean FirstBeanMethod() {
return new FirstBean();
}
#Bean
public SecondBean SecondBeanMethod() {
return new SecondBean();
}
}
Additional Points from above answers
Let’s say we got a module which is shared in multiple apps and it contains a few services. Not all are needed for each app.
If use #Component on those service classes and the component scan in the application,
we might end up detecting more beans than necessary
In this case, you either had to adjust the filtering of the component scan or provide the configuration that even the unused beans can run. Otherwise, the application context won’t start.
In this case, it is better to work with #Bean annotation and only instantiate those beans,
which are required individually in each app
So, essentially, use #Bean for adding third-party classes to the context. And #Component if it is just inside your single application.
#Bean can be scoped and #component cannot
such as
#Scope(value = WebApplicationContext.SCOPE_REQUEST, proxyMode = ScopedProxyMode.TARGET_CLASS)