I am a Spring neophyte who is working on a large Spring-based project that has extensive coupling between Spring beans. I am trying to write some integration tests that exercise subsets of the total application functionality. To do so, I'd like to override some of the autowiring.
For example, suppose I have a class
public class MyDataServiceImpl implements MyDataService {
#Qualifier("notNeededForMyDataServiceTest")
#Autowired
private NotNeededForMyDataServiceTest notNeededForMyDataServiceTest;
//...
}
and a context file with:
<bean id="myDataService"
class="MyDataServiceImpl">
</bean>
In my test, I have no need to use the notNeededForMyDataServiceTest field. Is there some way I can override the #Autowired annotation and set notNeededForMyDataServiceTest to null, perhaps in the XML file? I don't want to modify any of the Java classes, but I do want to avoid the (problematic) configuration of notNeededForMyDataServiceTest.
I tried doing:
<bean id="myDataService"
class="MyDataServiceImpl">
<property name="notNeededForMyDataServiceTest"><null/></property>
</bean>
That doesn't work. IntelliJ informs me "Cannot resolve property 'notNeededForMyDataServiceTest'", apparently because there are no getters and setters for that field.
I'm using Spring Framework 3.1.3.
The following configuration should work, I took the liberty of mixing in Java configuration
#Configuration
//This will load your beans from whichever xml file you are using
#ImportResource("classpath:/path/beans.xml")
public class TestConfigLoader{
// This will declare the unused bean and inject MyDataServiceImpl with null.
public #Bean(name="notNeededForMyDataServiceTest") NotNeededForMyDataServiceTest getNotNeededForMyDataServiceTest(){
return null;
}
... any other configuration beans if required.
}
And annotate your test class like so:
// In your test class applicationContext will be loaded from TestConfigLoader
#ContextConfiguration(classes = {TestConfigLoader.class})
public class MyTest {
// class body...
}
These could help:
Context configuration with annotated classes
Testing with #Configuration Classes and Profiles
Spring TestContext Framework
and profiles:
beans profile="..."
Introducing #Profile
You could create different beans definition in the XML configuration and then activate them using the -Dspring.profiles.active="profile1,profile2" env.
You're using the #Autowired mechanism wrong. The qualifier is not a property that you need to set. That's actually the name of a bean, so that the container will be able to choose one particular instance in case multiple beans of the same type are defined in the same context.
So the container will look for a bean of type NotNeededForMyDataServiceTest and the name (which would actually be the bean id in XML): notNeededForMyDataServiceTest.
What I think you want is to instruct the container to not inject anything in that field if no bean of type NotNeededForMyDataServiceTest is defined in the application context. That could be achieved simply by setting the required attribute of the annotation to false:
#Autowired(required = false)
NotNeededForMyDataServiceTest someOptionalDependency;
The only drawback of this approach would be that the container will never complain at runtime if there's nothing to inject in that field (and perhaps you would want this sanity check when your code runs in production).
If you don't want to make that dependency optional (or you can't edit that code for some reason), you'll need to provide a mock / null value for that field by setting that explicitly in your context. One option to do that would be to use Java configuration instead of XML (like in #Abe's answer) and another approach would be to make use of a factory bean which returns null (like in this question).
Related
Java configuration allows us to manage bean creation within a configuration file. Annotated #Component, #Service classes used with component scanning does the same. However, I'm concerned about using these two mechanisms at the same time.
Should Java configuration and annotated component scans be avoided in the same project? I ask because the result is unclear in the following scenario:
#Configuration
public class MyConfig {
#Bean
public Foo foo() {
return new Foo(500);
}
}
...
#Component
public class Foo {
private int value;
public Foo() {
}
public Foo(int value) {
this.value = value;
}
}
...
public class Consumer {
#Autowired
Foo foo;
...
}
So, in the above situation, will the Consumer get a Foo instance with a 500 value or 0 value? I've tested locally and it appears that the Java configured Foo (with value 500) is created consistently. However, I'm concerned that my testing isn't thorough enough to be conclusive.
What is the real answer? Using both Java config and component scanning on #Component beans of the same type seems like a bad thing.
I think your concern is more like raised by the following use case:
You have a custom spring-starter-library that have its own #Configuration classes and #Bean definitions, BUT if you have #Component/#Service in this library, you will need to explicitly #ComponentScan these packages from your service, since the default #ComponentScan (see #SpringBootApplication) will perform component scanning from the main class, to all sub-packages of your app, BUT not the packages inside the external library. For that purpose, you only need to have #Bean definitions in your external library, and to inject these external configurations via #EnableSomething annotation used on your app's main class (using #Import(YourConfigurationAnnotatedClass.class) OR via using spring.factories in case you always need the external configuration to be used/injected.
Of course, you CAN have #Components in this library, but the explicit usage of #ComponentScan annotation may lead to unintended behaviour in some cases, so I would recommend to avoid that.
So, to answer your question -> You can have both approaches of defining beans, only if they're inside your app, but bean definitions outside your app (e.g. library) should be explicitly defined with #Bean inside a #Configuration class.
It is perfectly valid to have Java configuration and annotated component scans in the same project because they server different purposes.
#Component (#Service,#Repository etc) are used to auto-detect and auto-configure beans.
#Bean annotation is used to explicitly declare a single bean, instead of letting Spring do it automatically.
You can do the following with #Bean. But, this is not possible with #Component
#Bean
public MyService myService(boolean someCondition) {
if(someCondition) {
return new MyServiceImpl1();
}else{
return new MyServiceImpl2();
}
}
Haven't really faced a situation where both Java config and component scanning on the bean of the same type were required.
As per the spring documentation,
To declare a bean, simply annotate a method with the #Bean annotation.
When JavaConfig encounters such a method, it will execute that method
and register the return value as a bean within a BeanFactory. By
default, the bean name will be the same as the method name
So, As per this, it is returning the correct Foo (with value 500).
In general, there is nothing wrong with component scanning and explicit bean definitions in the same application context. I tend to use component scanning where possible, and create the few beans that need more setup with #Bean methods.
There is no upside to include classes in the component scan when you create beans of their type explicitly. Component scanning can easily be targeted at certain classes and packages. If you design your packages accordingly, you can component scan only the packages without "special" bean classes (or else use more advanced filters on scanning).
In a quick look I didn't find any clear information about bean definition precedence in such a case. Typically there is a deterministic and fairly stable order in which these are processed, but if it is not documented it maybe could change in some future Spring version.
I know and understand constructor based injection. But, the autowiring modes confuse me.
1) I have read that default mode for autowiring is 'no autowiring' i.e. We have to manually set the properties in xml file. But, isn't xml based configuration a type of autowiring? How can it be considered 'No autowiring'?
2) Other modes for autowiring are i) byName ii) byType iii)constructor iv) auto-detect. Am i correct to assume the following:
a) When using xml configuration based autowiring, the default mode is 'byName'(i.e. I have to keep the name of property reference the same as the name of the bean which is being used as a property.)
b) When using Annotations, default mode is 'byType'( Regardless of the place the #Autowired keyword is placed i.e on the setter, on the constructor or on the property, it will search the type of the property being autowried)
3) What is the difference between constructor based injection and 'constructor' mode of autowiring?(I have read that constructor mode means it applies byType mode on all the constructor arguments, but how is it different from placing #Autowired keyword on the constructor)
4) I know that to enable autowired mode byName in annotations, in the bean definition in the xml file, I have to use " autowire = 'byName' ". But, suppose I am using Annotations only config( using #Component, and no bean definitions in the xml ), and I want to use byName autowire mode, then what is the way of doing that?
I think you are a bit confused. First, you need to understand dependency injection (see here). There is ton of info about DI but in short, it means some third party (e.g spring IOC) passes the dependencies to the objects rather than the objects to create/obtain the references themselves. This could happen either through constructor or setter. For instance, consider constructor DI
class B{
}
class A{
private B b;
public A(B b){
this.b = b;
}
}
Some third party will inject an instance of class B into A rather class A create a reference to B itself. Very often you would use an interface so class A wouldn't even know what object will be injected into it.
Now in Spring there are different ways to configure these associations between the objects (the example above). You can either use XML, Java Config or Autowiring. They are independent but do the same stuff.
In both XML and JAVA config you need to configure the dependencies explicitly - either in xml file or having a #Configuration class for the JAVA Config and annotating the beans with #Bean. The autowiring is different. There you create simple POJOs which you annotate with #Component, #Controller, #Service or #Repository. They will be automatically registered as beans via component scanning. With autowiring you don't need to explicitly configure the dependencies in XML file or JAVA Config class. You can do it in code directly. For instance, if we have to compare java config vs autowiring using the previous example
Java Config (explicit config in a config class)
#Bean
public A getA(){
return new A(new B());
}
Autowiring (implicit - done in code)
#Component
class B{
}
#Component
class A{
private B b;
#Autowired
public A(B b){
this.b = b;
}
}
In the latter we autowire class B into class A (they both will be registered as beans due to #Component annotation) without having explicitly defined this association in an xml file or java config class. I hope it makes sense.
If you have to specify the bean names in the xml, its not happening automatically, hence its not autowiring.
With autowiring spring will figure out what bean to inject even though it may not be explicitly written.
When using xml configuration based autowiring, the default mode is 'byName'
When using Annotations, the ordering that happens depends on the annotation used as there are a few that can be used. #Autowire #Resource #Inject.
When using #Component, the default wiring is of type. The method below will resolve on any autowiring needs for a Service object.
#Bean
public Service getMyService(){
return new Service();
}
If there are multiple #Bean methods that return a Service you will get an error.
If you wanted to do wire via name while using #Component you would add the #Qualifier("nameToUse") annotation to the variable. It would find an #Bean annotated method called getNameToUse().
#Autowired
#Qualifier("nameToUse")
private Service myService;
I'm pretty new to the Spring Framework and I got problems to understand the #Required annotation in combination with a Java configured application.
Here is an example.
Config-File
#Configuration
public class AppConfig {
#Bean
public Movie movieA() {
return new Movie();
}
#Bean
public MovieHolder holder() {
return new MovieHolder();
}
}
MovieHolder.java
public class MovieHolder {
private Movie movie;
public Movie getMovie() {
return movie;
}
#Required
public void setMovie(Movie movie) {
this.movie = movie;
}
}
Context initialization
ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
MovieHolder holder = (MovieHolder) context.getBean("holder");
System.out.println("movie: " + holder.getMovie());
As far as I understood the documentation of the #Required annotation, there should rise an exception, because movie isn't set directly or by autowiring. Instead is the output movie: null.
What am I doing wrong? Or isn't this the correct use of the #Required annotation?
Setting the required properties in the beans that you are instantiating is your own responsibility. The BeanPostProcessor that processes the bean-definitions in the classes annotated with #Configuration is called ConfigurationClassPostProcessor. The BeanPostProcessor that processes your #Required annotation defaults to RequiredAnnotationBeanPostProcessor, which is registered by default when you use context:annotation-config and context:component-scan in your configuration. If you are not using these two tags, you can even register your own RequiredAnnotationBeanPostProcessor as a bean.
Now, the default implementation of the RequiredAnnotationBeanPostProcessor has a method called boolean shouldSkip(..) that checks for a boolean attribute named SKIP_REQUIRED_CHECK_ATTRIBUTE. The value of this attribute is checked for each bean during the post-processing by the RequiredAnnotationBeanPostProcessor. If it returns false, the #Required constraint is enforced, otherwise it is not.
Now, the ConfigurationClassPostProcessor set the value of this attribute to true while creating the bean definitions from the #Configuration classes (I guess for the reason that if you are defining a bean, you should ensure that it has the required properties). Hence, the #Required is not enforced for such beans.
As an aside, You might think that where did this SKIP_REQUIRED_CHECK_ATTRIBUTE attribute come from and where is it set: it is set on the instances of BeanDefinition that are used by Spring internally for bean creation and post-processing.
If you really want to enforce the #Required constraints, you would have to override the RequiredAnnotationBeanPostProcessor, override the boolean shouldSkip(..) method and register this class instead of the default RequiredAnnotationBeanPostProcessor. And as the documentation for RequiredAnnotationBeanPostProcessor says:
A default RequiredAnnotationBeanPostProcessor will be registered by the "context:annotation-config" and "context:component-scan" XML tags. Remove or turn off the default annotation configuration there if you intend to specify a custom RequiredAnnotationBeanPostProcessor bean definition.
Another way would be to use the initMethod attribute on your #Bean annotation. Which could perform checks to see that the required properties are indeed set. However, since this is code based configuration, you could just as well call that init method yourself.
Also, in my opinion, there is not much point in going through a lot of trouble to use your own RequiredAnnotationBeanPostProcessor, as the following documentation says:
Please note that an 'init' method may still need to implemented (and may still be desirable), because all that this class does is enforce that a 'required' property has actually been configured with a value. It does not check anything else... In particular, it does not check that a configured value is not null.
So, to summarize: #Required doesn't work with #Configuration classes by default. If you need to make sure that all your properties are set, you can just as well do it yourself when you create the bean in the #Bean methods (By calling some init method that performs such validations, or just supplying the required properties yourself). And if you really need to make the #Required annotation work, you'd need to use your own implementation of the RequiredAnnotationBeanPostProcessor, register it as a bean in the spring context and give up the benefits of context:annotation-config.
Just tried to declare a #Bean RequiredAnnotationBeanPostProcessor with overridden shouldSkip() method.
Yes, it checks my beans, but it fails even if I set all the required properties, i.e. it always fails.
I think Spring has a real problem with supporting #Required annotation for Java Config, since Spring has no way to tell whether or not you have set the property when you do it directly in Java code. (It can't inspect for 'null' fields later, since this would mean changing the semantics of the #Required annotation which should allow explicitly set null values).
When you use an XML config, Spring creates a wrapper object to set the properties, so it can track all the configured 'setXxx()' operations.
Conclusion: there is no reasonable way to enable #Required annotation for beans created in Java #Configuration classes.
(Very unfortunate feature, in my opinion, since the bean class writer and the class user might be different persons).
Is there a way to specify the default type for Spring #autowired annotation? For example, I have bean ValidatorA and bean ValidatorB that extends ValidatorA.
The ValidatorA is used in some other places and is injected using #autowired.
Is there a way to force Spring to inject ValidatorB instead of ValidatorA without changing the existing code?
The only solution I found at How to override the behavior of Spring #Autowired suggests to exclude ValidatorA from the context.
Is there any other way?
For example, with Guice I would just bind the ValidatorA.class to ValidatorB.class and that will do exactly what I need.
I have no problem to add #Qualifier to ValidatorB but ValidatorA should stay unchanged.
Guice provides ability to define "Providers", is there something similar in Spring? Maybe with #Configuration annotation?
I think you could use primary indicator there. If your bean is defined through annotation, add #Primary to ValidatorB definition. If you are using xml config add primary="true" to <bean> definition.
Is there a way to force Spring to inject ValidatorB instead of ValidatorA without changing the existing code?
Without changing the code, I doubt it very much. You could change the app context or alter the code something like this :
#Component
#Qualifier("B")
public class ValidatorB extends ValidatorA {
}
and then inject like so (there are other syntactic options as well)
#Resource
#Qualifier("B")
private ValidatorA validatorB;
This might be an obvious but I'm having a hard time understanding why we need to define the class of a bean in two places....
From the spring reference manual...
...
<bean id="petStore"
class="org.springframework.samples.jpetstore.services.PetStoreServiceImpl">
<property name="accountDao" ref="accountDao"/>
<property name="itemDao" ref="itemDao"/>
<!-- additional collaborators and configuration for this bean go here -->
</bean>
// retrieve configured instance
PetStoreServiceImpl service = context.getBean("petStore", PetStoreServiceImpl.class);
Shouldn't the xml fine be enough for the container to know the class of petStore?
You can use the following method:
context.getBean("petStore")
However, as this returns a java.lang.Object, you'd still need to have a cast:
PetStoreServiceImpl petstore = (PetStoreServiceImpl)context.getBean("petStore");
However, this could lead to problems if your "petStore" bean is not actually a PetStoreServiceImpl, and to avoid casts (which since the advent of Generics are being seen as a bit dirty), you can use the above method to infer the type (and let's spring check whether the bean you're expecting is really of the right class, so hence you've got:
PetStoreServiceImpl service = context.getBean("petStore", PetStoreServiceImpl.class);
Hope that helps.
EDIT:
Personally, I would avoid calling context.getBean() to lookup methods as it goes against the idea of dependency injection. Really, the component that uses the petstore bean should have a property, which can then be injected with the correct component.
private PetStoreService petStoreService;
// setter omitted for brevity
public void someotherMethod() {
// no need for calling getBean()
petStoreService.somePetstoreMethod();
}
Then you can hook up the beans in the application context:
You could also do away with the configuration via XML and use annotation to wire up your beans:
#Autowired
private PetStoreService petStoreService;
As long as you've got
in your spring context, the "petStore" bean defined in your application context will automatically be injected. If you've got more than one bean with the type "PetStoreService", then you'd need to add a qualifier:
#Autowired
#Qualifier("petStore")
private PetStoreService petStoreService;
There's no requirement to specify the class in the getBean() method. It's just a question of safety. Note there's also a getBean() that takes only a class so that you can just look up beans by type instead of needing to know the name.