I'm having some issues with injection in the application I'm working on (using Spring Version 3.1.2). To start with, I'm seeing a lot of code like this:
#Value("#{searchRequestBean}")
private SearchRequest searchRequest;
#Value("#{searchResponseBean}")
private SearchResponse searchResponse;
#Autowired
private SavedSearchService service;
Each of these three appears to have the effect of autowiring the specified bean/service into the class. What I don't understand is, what's the difference between #Value and #Autowired in these cases? Every example I find online seems to use #Value to inject values from a properties file. In this case, SearchResponse and SearchRequest are abstract classes.
I'm hoping that a better understanding of this will help me solve some issues I'm having with my Session bean.
#Value can be used for injecting default values. A good example is to inject the default of a String to be the value of a property file. In your example, #Value is used to set the default value of a class to be a Spring managed bean.
#Autowired can't be used for the first example: It's not property file aware. #Autowired is only for DI of a bean. It is more specific than #Value, but you can use #Value to do the same thing.
Here is a good tutorial for #Value: http://www.mkyong.com/spring3/spring-value-default-value/
Related
I need to assure data migration using mongock.
The #ChangeUnit class holds the logic for migration. It has a field annotated with #Value which is always null, even though I properly initialized in application.properties:
mongock.migration-scan-package=my.package
login-secret=test
Then the MigrationConfiguration looks as follows:
#ChangeUnit(id = "test", order = "001", author = "test")
#RequiredArgsConstructor
#Configuration
public class InitUsersChangeLog {
private final MyService service;
private final MongoTemplate template;
#Value("${login-secret}")
private String LOGIN;
#Execution
public void initUser() {
service.create(User.builder().login(LOGIN).build());
}
}
Main class:
#EnableMongock
#SpringBootApplication
public class MailServiceApplication {...}
My assumption is that this value is not injected properly into the MongockConfiguration bean. I tried to configure the bean manually (without using mongock.migration-scan-package=my.package) in the properties, but with no success.
As Mongock currently doesn't support #Value annotation you can try to use getProperty method from Environment bean. Environment bean can be injected same as other beans using constructor or Lombok annotations.
You want to change this:
#Value("your.key.property")
to that:
private final Environment env;
public void method(){
env.getProperty("your.key.property")
}
Mongock currently no supports #value injection via field o method parameter. We will provide that in a future minor release within version 5, but we can't give you dates, yet.
Extending MichalJ's answer, which is absolutely valid. I would like to add that the changeUnits are not retrieved by Mongock via Springboot, they are processed by Mongock independently. So the annotation #Configuration, #Component, etc. won't be taken into account and they could even be damaging.
Related to that, this code won't work, at least not in a near future:
#Value("${login-secret}")
private String LOGIN;
First, as said, Mongock doesn't support value currently, but the first approach will require the constructor parameter to have that #Value("${login-secret}"), not at the field level.
It seems not the case. I used to have the notion that XML configurations are meant to override annotations. But when I set autowire="no" in the XML configuration, the bean's #Autowired annotated property still takes effect. I'm no longer sure if XML autowire has anything to do with #Autowired anymore. It's quite counter-intuitive in my opinion.
Can someone point me to a documentation that says something about this?
Here's my example:
<bean class="com.example.Tester"></bean>
<bean class="com.example.ClassToTest" autowire="no"></bean>
public class Tester
{
#Autowired
ClassToTest testSubject;
}
public class ClassToTest
{
#Autowired // I want this not to get autowired without removing this annotation
private OtherDependency;
}
autowire="no" means we have to explicit wire our dependencies using either XML-based configuration or #Autowire and it is default setting.
Auto-wiring by xml configutaion or by annotation means implicitly mapping dependencies using given strategy.
For more details refer here
I don’t see any difference between two ways, #Qualifier is always used with #Autowired.
#Autowired
#Qualifier("alpha")
VS
#Resource(name="alpha")
Anyone could let me know the difference? Thanks!
#Autowired can be used alone . If it is used alone , it will be wired by type . So problems arises if more than one bean of the same type are declared in the container as #Autowired does not know which beans to use to inject. As a result , use #Qualifier together with #Autowired to clarify which beans to be actually wired by specifying the bean name (wired by name)
#Resource is wired by name too . So if #Autowired is used together with #Qualifier , it is the same as the #Resource.
The difference are that #Autowired and #Qualifier are the spring annotation while #Resource is the standard java annotation (from JSR-250) . Besides , #Resource only supports for fields and setter injection while #Autowired supports fields , setter ,constructors and multi-argument methods injection.
It is suggested to use #Resource for fields and setter injection. Stick with #Qualifier and #Autowired for constructor or a multi-argument method injection.
See this:
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.
I was facing some issues with #Autowired and then started using #Qualifier and I was finally able to find out the when to use #Autowired with #Qualifier when multiple beans of same type are defined.
Suppose you define 2 beans of same type but different values :
<bean id="appContext1" class="com.context.AppContext">
<constructor-arg value="abc" />
<bean/>
<bean id="appContext2" class="com.context.AppContext">
<constructor-arg value="ABC" />
<bean/>
Then if you just are trying to use #Autowire, then you have to use the same variable name as of the bean name else it will give error as multiple types found.
#Autowired
AppContext appContext;
For the above use case you have to use Qualifier.
#Autowired
#Qualifier("appContext1")
AppContext appContext;
Instead, if you use the variable name same as bean name, you can eliminate the use of #Qualifier.
#Autowired
AppContext appContext1;
I was always using the variable name same as bean name, but accidentally had some other variable name and faced this issue.
Let me know if there are any doubts.
#Autowired is old school Spring. #Resource is the Java EE CDI standard. Spring handles both (as well as #Inject, which is very similar) and does pretty much the same thing in both situations. I would recommend #Resource, #Autowired was made prior to the standard and seems to be supported mostly for backward compatibility.
I am going through some blogs on SpringSource and in one of the blogs, author is using #Inject and I suppose he can also use #Autowired.
Here is the piece of code:
#Inject private CustomerOrderService customerOrderService;
I am not sure about the difference between #Inject and #Autowired and would appreciate it if someone explained their difference and which one to use under what situation?
Assuming here you're referring to the javax.inject.Inject annotation. #Inject is part of the Java CDI (Contexts and Dependency Injection) standard introduced in Java EE 6 (JSR-299), read more. Spring has chosen to support using the #Inject annotation synonymously with their own #Autowired annotation.
So, to answer your question, #Autowired is Spring's own annotation. #Inject is part of a Java technology called CDI that defines a standard for dependency injection similar to Spring. In a Spring application, the two annotations works the same way as Spring has decided to support some JSR-299 annotations in addition to their own.
Here is a blog post that compares #Resource, #Inject, and #Autowired, and appears to do a pretty comprehensive job.
From the link:
With the exception of test 2 & 7 the configuration and outcomes were
identical. When I looked under the hood I determined that the
‘#Autowired’ and ‘#Inject’ annotation behave identically. Both of
these annotations use the ‘AutowiredAnnotationBeanPostProcessor’ to
inject dependencies. ‘#Autowired’ and ‘#Inject’ can be used
interchangeable to inject Spring beans. However the ‘#Resource’
annotation uses the ‘CommonAnnotationBeanPostProcessor’ to inject
dependencies. Even though they use different post processor classes
they all behave nearly identically. Below is a summary of their
execution paths.
Tests 2 and 7 that the author references are 'injection by field name' and 'an attempt at resolving a bean using a bad qualifier', respectively.
The Conclusion should give you all the information you need.
To handle the situation in which there is no wiring, beans are available with #Autowired required attribute set to false.
But when using #Inject, the Provider interface works with the bean which means that the bean is not injected directly but with the Provider.
The key difference(noticed when reading the Spring Docs) between #Autowired and #Inject is that, #Autowired has the 'required' attribute while the #Inject has no 'required' attribute.
As of Spring 3.0, Spring offers support for JSR-330 dependency injection annotations (#Inject, #Named, #Singleton).
There is a separate section in the Spring documentation about them, including comparisons to their Spring equivalents.
Better use #Inject all the time. Because it is java configuration approach(provided by sun) which makes our application agnostic to the framework. So if you spring also your classes will work.
If you use #Autowired it will works only with spring because #Autowired is spring provided annotation.
#Autowired annotation is defined in the Spring framework.
#Inject annotation is a standard annotation, which is defined in the standard "Dependency Injection for Java" (JSR-330). Spring (since the version 3.0) supports the generalized model of dependency injection which is defined in the standard JSR-330. (Google Guice frameworks and Picocontainer framework also support this model).
With #Inject can be injected the reference to the implementation of the Provider interface, which allows injecting the deferred references.
Annotations #Inject and #Autowired- is almost complete analogies. As well as #Autowired annotation, #Inject annotation can be used for automatic binding properties, methods, and constructors.
In contrast to #Autowired annotation, #Inject annotation has no required attribute. Therefore, if the dependencies will not be found - will be thrown an exception.
There are also differences in the clarifications of the binding properties. If there is ambiguity in the choice of components for the injection the #Named qualifier should be added. In a similar situation for #Autowired annotation will be added #Qualifier qualifier (JSR-330 defines it's own #Qualifier annotation and via this qualifier annotation #Named is defined).
In addition to the above:
The default scope for #Autowired beans is Singleton whereas using JSR 330 #Inject annotation it is like Spring's prototype.
There is no equivalent of #Lazy in JSR 330 using #Inject.
There is no equivalent of #Value in JSR 330 using #Inject.
#Inject has no 'required' attribute
#Autowired(required=false)
By default the dependency injection for #Autowired must be fulfilled because the value of required attribute is true by default. We can change this behavior by using #Autowired(required=false). In this case if bean is not found for dependency injection, it will not through error.
Please have look at
https://www.concretepage.com/spring/spring-autowired-annotation#required-false
But #Inject doesn’t need (required=false) it will not through error if dependency is not found
The #Inject annotation is one of the JSR-330 annotations collection. This has Match by Type,Match by Qualifier, Match by Name execution paths.
These execution paths are valid for both setter and field injection.The behavior of #Autowired annotation is same as the #Inject annotation. The only difference is the #Autowired annotation is a part of the Spring framework. #Autowired annotation also has the above execution paths. So I recommend the #Autowired for your answer.
I've started using Spring 3 Java Config with the JSR-330 #Inject annotations. Unlike the Spring #Autowire, Spring does not fail at startup if the #Inject parameters are null. Is there a way to do this within Java Config?
Edit: Just a clarification, I would like this as the default behaviour so I don't have to put #Required on every field.
I think you can use #Required on a setter for the dependency, in addition to #Inject.