I am using
<context:component-scan base-package="com.package.dao"/> (Spring 3)
and in my controllers with #Autowired will retrieve automatically the DAO I need. That's perfect and works.
The problem is when I need more than one DAO manager.
How can I do?
I tried with #Qualifier but I am not sure about the name of the dao-manager. className doesn't work
someone can help me?
Thank you!
See in the spring documentation:
#Autowired is fundamentally about type-driven injection with optional semantic qualifiers. This means that qualifier values, even when using the bean name fallback, always have narrowing semantics within the set of type matches; they do not semantically express a reference to a unique bean id
...
If you intend to express annotation-driven injection by name, do not primarily use #Autowired - even if is technically capable of referring to a bean name through #Qualifier values. Instead, prefer the JSR-250 #Resource annotation which is semantically defined to identify a specific target component by its unique name, with the declared type being irrelevant for the matching process.
Use #Resource instead, see here.
Related
I need to create a means to add a custom annotation like
#Value("${my.property}")
However, in my case I need to get the value from a database rather then a properties file.
Basically I would like to create a bean on container startup that reads in property name value pairs from a database and can then inject these into fields belonging to other beans.
Approach #1:
One way is to create an Aspect, with a point-cut expression that matches any method having this annotation.
Your aspect will then:
Read the property value in the annotation
Look up the required value an inject it into the class.
AOP Kickstart
Here's a guide to getting started with AOP in Spring
http://www.tutorialspoint.com/spring/aop_with_spring.htm
Joinpoint matching
Here's a reference that describes how to create a join-point that matches on annotations: http://eclipse.org/aspectj/doc/next/adk15notebook/annotations-pointcuts-and-advice.html
Approach #2:
Another way is to use a BeanFactoryPostProcessor - this is essentially how a PropertyPlaceholderConfigurer works.
It will look at your bean definitions, and fetch the underlying class.
It will then check for the annotation in the class, using reflection.
It will update the bean definition to include injecting the property as per the value in the annotation.
. . actually I think approach #2 sounds more like what you want - all of the processing happens on "start-up". . . (In actual fact your modifying the bean recipes even before startup). . whereas if you used AOP, you'd be intercepting method invocations, which might be too late for you?
Namespace Handler
If you wanted you could even create your own Spring namespace handler to turn on your post processor in a terse way. Eg:
<myApp:injectFromDb />
as an alternative to:
<bean class="MyDatabaseLookupProcessorImpl etc, etc. />
Update: Approach #3
As of Spring 3.1 there's also the PropertySourcesPlaceholderConfigurer, that will provide most of the plumbing for you, so you can achieve this with less code.
Alternatively you should be able to configure kind of properties repository bean and then use it in SpEL directly in #Value annotation.
Let's say you'd have bean called propertiesRepository in your context that implements following interface:
interface PropertiesRepository {
String getProperty(String propertyName);
}
then on bean where you want to inject values you can use following expression
#Value("#{propertiesRepository.getProperty('my.property')}")
String myProperty;
You can use #Value annotation by injecting database configuration in application environment itself.
I know this is an old question but I didn't find an exact solution. So documenting it here.
I have already answered the same on different forum.
Please refer to this answer for exact solution to your problem.
I'm wondering if I add a #Value annotation on a property, the class who contains this property cannot be used by another one with a different value, Example :
MyClassUtil.java had
#Value("${some.value}")
private int _myProperty;
And of course there is one module.properties who contain :
some.value=10
Another class ClassA.java wants to use this class with value 10. Ok, no problem.
But another class ClassB.java wants to use this class but with another value : 20. I cannot do this if I'm not mistaken.
Because before #Value era, I could declare two beans in the moduleContext.xml without any problem.
So, is #Value pushes you to do some strong coupling ?
You are right that the annotation configuration can not be instance specific. It is important to understand the concept of bean definitions in bean factory.
Manual bean definition:
Single <bean> element in your XML config leads to a single bean definition. Multiple <bean> mean multiple definitions (regardless of a bean type).
Single #Bean method within #Configuration class leads to a single bean definition. Multiple #Bean methods mean multiple definitions (regardless of a bean type).
However when using component scan, classes annotated with #Component-like annotations are auto-registered as a single bean definition. There is no way you can register bean multiple times via component scan.
Similarly, annotation configurations (#Value, #Autowired, etc.) are type-wide. Your bean instances are always augmented and processed with the same effect (e.g. injecting the same value). There is no way you can alter annotation processing behaviour from instance to instance.
Is this tight coupling? It is not in its general understanding - bean factory (Spring) is still free to inject whatever it thinks is suitable. However it is more of a service lookup pattern. This simplifies your life when working with domain specific singletons. And most beans in an application context tend to be singletons, many of them domain specific (controllers, services, DAOs). Framework singletons (non-project specific reusable classes) should never use annotation based configuration - in this scope, it is an unwanted tight coupling.
If you need different bean instances, you should not use annotation configuration and define your beans manually.
I want to use the #Cachable annotation on one of my methods, but I have the problem, that the result depends on an attribute of a spring bean that is not part of the method signature.
So I want something like this:
#Cachable(value="mycache", key="#id, #myspringbean.referenceId")
MyResult myMethod(int id);
I guess these are actually two problems: How to get use a composite key and how to use another spring bean in the expression.
The problem of how to use a composite key can probably be solved like in this SO question: #Cacheable key on multiple method arguments
However, I could not find anythig about how to reference to another spring bean in this expression. Is it possible and if yes, how?
You can have a lot a details on SpEL in the Spring documentation (http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/expressions.html). As you can see, you can use bean references using the #myBean syntax. You have to include a bean resolver in your context to do that.
It's not possible to use the current Spring bean name.
I think I would use the following pattern so that each bean object will have it's own "key-space" see also What can be the default key generator.
As for the problem above one can use:
#Cachable(value="mycache", key = "{#id, #root.targetClass.getDeclaredField('attribute').get(#root.target)}")
MyResult myMethod(int id);
just make sure your attribute is public
I have an application that has 2 beans with the same name, but which are in different packages. My Spring application fails because it cannot decide on which bean to take. Is there any solution for this? The beans do not currently implement specific interfaces.
See below an edited example of the exception:
Caused by:
org.springframework.context.annotation.ConflictingBeanDefinitionException:
Annotation-specified bean name 'dataTransferHandler' for bean class
[aaaaa.ws.handler.DataTransferHandler] conflicts with existing,
non-compatible bean definition of same name and class
[bbbbb.ws.handler.DataTransferHandler]
You will have to give your beans different names - if multiple beans are defined with the same name, then the one defined later will override the one defined earlier - so in your case only one bean will exist with the name of dataTransferHandler.
You can give these two beans different names, so that both can exist and you can inject in the correct one either using:
#AutoWired #Qualifier("dataTransferHandler")
OR
#Resource(name="dataTransferHandler")
You can give attribute primary="true" to the bean defination you want to have the preference when autowired. But the bean names must be different. There is no solution for same bean name.
At run-time when you will get the autowired class then the primary true bean will get the preference for autowiring. Hope this helps you. Cheers.
I asked another question regarding the same problem, and there is a solution that doesn't require using the #Qualifier annotation: if both of your DataTransferHandler classes have a #Component annotation, you can simply add a String argument to one of their constructions (i.e. #Component("Foo")), and that should solve the problem without needing additional changes.
See User9123's answer on my question for more details.
We use Spring in a project and #Autowired for automatically injecting dependencies. I would like to prohibit autowiring of certain beans from specific modules, so for example, it would be possible to autowire beans from module A in module B, but not in module C. Is it possible with Spring?
Unfortunately beans in single application context are flat i.e. they are all equivalent. However if you define two application contexts, parent and child, then beans from child have access to beans from parent but not the other way around. Beans defined in child context are simply invisible to parent.
In your case you place module A and B in parent context and C in child context.
The best way to approach the problem is through javax.inject qualifiers. Annotate your beans with the appropriate qualifier and then use it at the injection point:
#Autowired
#FooQualifier
private YourService service;
Otherwise it will soon become a mess which implementation is injected where.
Another option is to designate one bean as #Primary - it will be preferred to other beans for a given injection point.
Yes, it's possible but not "pretty". You could use a BeanPostProcessor and when you get a bean, check if it's one of your "parent" types and if all its child beans are of the allowable types. Otherwise you can either throw an exception or set those fields to null.