Tried to search for an answer - no luck, so posting a question.
I have
#ConfigurationProperties
class XYZConfig {
int f1....
}
I'm trying later to get this bean by name in my application, but the only one name available is a fully qualified one. I tried to use #Component(value="xyzconfig") no luck either
I wonder if there is a way to set a short name for the bean without going into xml and specifying it explicitly?
I don't fully understand what are you trying but if you class XYZConfig should be configuration class and there will be created beans than you need to annotate this class with #Configuration. Also in your context .xml file you need to add <annotation-driven/> and set <context:component-scan base-package="your.package.wit.classes.for.scanning"></context:component-scan>.
But, if this class really has to be Bean then create simple java class (i.e.: BeanClass) and later in your configuration create method like this:
#Bean
public BeanClass beanClassName(){
BeanClass bc = new BeanClass()
...
return bc;
Later this bean will be visible with id/name beanClassName
Related
Even when we create the Beans in a Spring configuration class, I feel it is still useful to use #Component annotation on the class just to document/indicate that it's a Bean. Is it a good idea? Can there be any other issue that Spring will find the same bean defined in two different ways?
It is bad practice to create two beans from one class...
#Component
class SimpleComponent {
}
#Bean
public SimpleComponent simpleComponentBean(){
new SimpleComponent();
}
By default if we use #Component spring creates bean with name of class, but starts with small letter simpleComponent, if we use #Bean it takes method name and create bean with name simpleComponentBean and we have duplicated beans...
If we have method name the same, as component class name, spring replace one of them and we can Inject unexpected bean.
PS: intellij idea enterprise - correct indicate about all beans.
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 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).
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.
Is it possible to #Autowire a bean by name (ie. use a #Qualifier) but get the name of the bean from a property set by the BeanFactoryPostProcessor. So in short something like this:
#Autowired
#Qualifier(#Value("${name.of.my.object}"))
private MyObject obj;
Assuming that there are more than one MyObject beans that have been created and there is a property called name.of.my.object=foo in my properties files read by the PropertyPlaceholderConfigurer
That would be nice, but I don't think you can do such a thing.
The closest I can think of is to define a bean alias in XML:
<alias bean="${name.of.my.object}" alias="myAlias"/>
and then refer to the alias in the qualifier:
#Autowired
#Qualifier("myAlias")
private MyObject obj;
Not very elegant, and I haven't actually tried it before, but I think it should work.