How Spring able to read or implement the Annotations called #Autowired, #Component and where the logic available in spring source code?
Spring context understand annotation by set of classes which implements bean post processor interface. so to handle different type of annotation we need to add different annotation bean post processors.
if you add in you configuration xml then you need not to add any annotation bean post processors.
Post processor provide methods to do pre and post processing for each bean initialization. you can write your own bean post processors to do custom processing by created a bean which implements BeanPostProcessor interface.
Annotations are metadata that can be read from the java source code. Spring Container understands what has to be done when it encounters these annotations in a source file.
Read through on each of these annotations.
Component
Autowire
More on Autowiring
1.4.5. Autowiring Collaborators
The following class does the autowiring magic.
AutowiredAnnotationBeanPostProcessor
Related
I have a CDI bean that is annotated with #ApplicationScoped. Is there a way to tell Spring to pick it up during component scan, as if it were annotated with #Component? Spring does understand the #Inject annotation so why not #ApplicationScoped?
The idea is that it would be handy to use CDI beans in Spring (at least if they only use plain dependency injection without the fancy CDI stuff like interceptors, decorators...)
It is not entirely clear how is your code structured, if possible just annotate it with #Component as well. A component bean in Spring has similar properties as an application scoped bean. The default scope of a bean in Spring is singleton and it can be proxied, similar to what #ApplicationScoped would offer.
Spring does understand the #Inject annotation so why not #ApplicationScoped?
Spring offers support for JSR 330 annotation, #ApplicationScoped is nor part of those.
I seems have problem understanding these 2 annotation. I have try to read the javadocs but still cannot figure out. Can anyone help to explain with simple code about these 2 ?
Thank so much in advance.
You use #Configuration as a replacement to the XML based configuration for configuring spring beans. So instead of an xml file we write a class and annotate that with #Configuration and define the beans in it using #Bean annotation on the methods.
And finally you use AnnotationConfigApplicationContext to register this #Configuration class and thus spring manages the beans defined. Small example you can find at Spring Configuration Documentaion.
Quoting from the above link
It is just another way of configuration Indicates that a class declares
one or more #Bean methods and may be processed by the Spring container
to generate bean definitions and service requests for those beans at
runtime.
And #Configurable is an annotation that injects dependencies into objects that are not managed by Spring using aspectj libraries. i.e., you still use old way of instantiation with plain new operator to create objects but the spring will take care of injecting the dependencies into that object automatically for you.
#Configuration is the heart of the Java-based configuration mechanism and provides an alternative to XML-based configuration.
#Configuration classes are just like regular #Components classes, except that methods annotated with #Bean are used to factory beans.
In this example on spring dependency injection here
Whne the final test class is run, after this line:
MySpringBeanWithDependency test = (MySpringBeanWithDependency) factory
.getBean("mySpringBeanWithDependency");
Which implementation of writer class will get injected? The test class still is responsbile for creating an actual implementation and injecting it before calling business methods on the Writer. Is it true?
In both the annotation-based example and the XML-based example, Spring will inject the NiceWriter bean into the MySpringBeanWithDependency bean.
For the annotation example, this is because the NiceWriter class is annotated with #Service (while the Writer class is not) and Spring will discover this via classpath scanning and autowire it into MySpringBeanWithDependency.
For the XML example, this is because the NiceWriter class is used to define the bean with id writer, which is referenced as the "writer" property of the bean with id mySpringBeanWithDependency.
In both cases, the MySpringBeanWithDependency bean is instantiated with dependencies injected via Spring, and is thus ready to use. It is not responsible for managing its IWriter dependency. This is why dependency injection (DI for short) usually goes hand-in-hand with inversion-of-control (IoC for short). Spring provides an IoC container that uses DI.
In XML file in spring we have two bean with different id but same class. They have the same properties offcourse. Now I have InitializingBean interface and in afterPropertySet() I am just printing the value of properties.
Its printing the values two times for me?
According Spring Documentation:
afterPropertySet()
Invoked by a BeanFactory after it has set all bean properties supplied (and satisfied BeanFactoryAware and ApplicationContextAware).
So the short answer on your question is: yes
Spring doesn't manipulate classes or object. Spring manipulates Bean Entity. It is the simplest object manipulated by Spring IOC. Bean has additional behaivior rules introduced by Spring.
If you create two beans for example with Singleton scope and not Lazy initializated Spring creates two instances of your class.
Probably you are calling this Class also invoking a Test or by launching a Integration test like this . check the breakpoints , if you are using SpringRunner, try to mock the component
I have a question about spring and struts.
Currently I have spring injecting my struts action classes for me.
I was experimenting and trying to get Spring to inject my Struts action classes
for me using autowiring.
I have my spring applicationContext config file scanning the base package that the
action class is in using context:component-scan base-package="my.package",
and im using #Component annotation at the action classes class level.
Im also using #Qualifier("myActionClass") at the same action classes class level.
Im not configuring the action class as a Spring bean in applicationContext.
Then in my struts.xml config file, while configuring my action class, instead of giving the fully qualified package and class name, I use the #Qualifier annotation name "myActionClass".
This doesnt work though.
If in my applicationContext config file, configure my action class as a spring bean, get rid of the #Component and #Qualifier annotation on the action class, and in struts.xml, put the action classes Spring bean id for the class, then Spring injects my action class for me and everything is dandy. Only, this isnt using Autowiring the action class, and thats what I was testing.
Anyone know if autowiring using context:component-scan base-package
to scan your packages for your action classes so you dont have to configure them in applicationContext is possible?
Everything is explained in Spring documentation: Apache Struts 1.x and 2.x.
I am not sure whether you are using Struts 1 or 2. For Struts 1 you had to add Spring plugin to Struts configuration (I know it works). In Struts 2 all actions are created by Spring hence they are fully capable of Spring injection like all other beans.
Struts 2 seems to rely on there being a spring bean with the same spring bean-name matching the action class name (full name with package). You can specify the bean name in the #Component annotation, and it's also possible to make a global user-defined bean naming strategy so you can avoid adding this information to all your beans