is it possible to forward value of annotation from declaration?
Example:
#Component
public class A {
#Autowired
#Value(value = "sessionFactory1") //forward value "sessionFactory1" into Dao
private Dao dao;
}
#Repository
public class Dao {
#Autowired
#Qualifier(<value>) //get value for #Qualifier ("sessionFactory1") from declaration in class A
private SessionFactory sessionFactory;
}
Something like that.
Is it possible?
No, you can't define one bean from another bean as you are trying to do and you shouldn't. If it worked, you would be adding a dependency from class A to the SessionFactory, while the dependency should really only be between Dao and SessionFactory.
Related
Why do we use qualifiers with #Bean when we can have different names for different beans of the same type (class)?
#Bean
#Qualifier("fooConfig")
public Baz method1() {
}
Isn't the following code more clean?
#Bean("fooConfig")
public Baz method1() {
}
If I create two beans of the same type with different names (using #Bean annotation), then can we inject them specifically using the #Qualifier annotation(can be added on field/constructor parameter/setter) in another bean?
#Bean("fooConfig")
public Baz method1(){
}
#Bean("barConfig")
public Baz method2(){
}
// constructor parameter of a different bean
final #Qualifier("fooConfig") Baz myConfig
If the above is true, then where do we use #Qualifier (with #Bean or #Component) instead of giving the bean a name as shown below?
#Bean
#Qualifier("fooConfig")
public Baz method1(){
}
#Bean
#Qualifier("barConfig")
public Baz method2(){
}
// constructor parameter of a different bean
final #Qualifier("fooConfig") Baz myConfig
Beans have names. They don't have qualifiers. #Qualifier is annotation, with which you tell Spring the name of Bean to be injected.
No.
Default Qualifier is the only implementation of the interface(example is below, 4th question) or the only method with a particular return type. You don't need to specify the #Qualifier in that case. Spring is smart enough to find itself.
For example:
#Configuration
public class MyConfiguration {
#Bean
public MyCustomComponent myComponent() {
return new MyCustomComponent();
}
}
If you will try to inject myComponent somewhere, Spring is smart enough to find the bean above. Becaude there is only one Bean with return type MyCustomComponent. But if there was a couple of methods, that would return MyCustomComponent, then you would have to tell Spring which one to inject with #Qualifier annotation.
SIDENOTE: #Bean annotation by default Spring uses the method name as a bean name. You can also assign other name like #Bean("otherComponent").
You have one Interface, and a couple of Classes implementing it. You inject bean of your interface. How can Spring know which Class should be used?
This is you interface:
public interface TestRepository{}
This is your implementation 1:
#Repository
public class Test1Repository implements TestRepository{}
Your implementation 2:
#Repository
public class Test2Repository implements TestRepository{}
Now you are injecting it like:
private final TestRepository testRepository;
public TestServiceImpl(TestRepository testRepository) {
this.testRepository= testRepository;
}
QUESTION! How is Spring supposed to know which class to inject? Test1 or Test2? That's why you tell it with #Qualifier which class.
private final TestRepository testRepository;
public TestServiceImpl(#Qualifier("test1Repository") TestRepository testRepository) {
this.testRepository= testRepository;
}
I Prefer different method to not using #Qualifier
Create common Interface
public interface CommonFooBar{
public String commonFoo();
public String commonBar();
}
Extends to each service
public interface FooService extends CommonFooBar {
}
public interface BarService extends CommonFooBar {
}
Then using it to your class
#Autowired
FooService fooService;
or
#Autowired
BarService barService;
so, we can defined the single responsibility to each interface and This kind of segregation is more readable to every junior.
I quite like a different way of working. Surely if you provide a unique name for your bean, then that is all you need?
Given the example below, its easy to see that Spring will name the beans based on the method name used to create the beans. In other words, if you give your beans sensible names, then the code should become self-explanatory. This also works when injecting beans into other classes.
The end result of this is:
Spring will name your beans based on the method used to create them.
If you import a bean, Spring will try to match on the bean name.
If you try to import a bean that does not match the name, Spring will attempt to match the class.
If your injected field name does not match the bean name and there are more than one instance of your bean, Spring will throw an exception on startup as it won't know which one to inject.
Lets not over-complicate Spring.
#Bean
mqConnectionFactory() {
ConnectionFactory connectionFactory = new MQXAConnectionFactory();
return connectionFactory;
}
#Bean
public ConnectionFactory pooledConnectionFactory(ConnectionFactory mqconnectionFactory) {
JmsPoolConnectionFactory connectionFactory = new JmsPoolConnectionFactory();
connectionFactory.setConnectionFactory(mqConnectionFactory);
return connectionFactory;
}
#Bean
public ConnectionFactory cachingConnectionFactory(ConnectionFactory mqConnectionFactory) {
CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
connectionFactory.setTargetConnectionFactory(mqConnectionFactory);
return connectionFactory;
}
#Bean
public JmsTemplate jmsTemplate(ConnectionFactory cachingConnectionFactory) {
JmsTemplate jmsTemplate = new JmsTemplate();
jmsTemplate.setConnectionFactory(cachingConnectionFactory);
return jmsTemplate;
}
#Bean
public DefaultMessageListenerContainer messageListenerContainer(ConnectionFactory pooledConnectionFactory) {
DefaultMessageListenerContainer container = new DefaultMessageListenerContainer();
container.setConnectionFactory(pooledConnectionFactory);
...
return container;
}
I'm looking for a way to list the beans that are injected into a particular Spring bean at runtime. For example, given these two classes:
#Controller
public class TestController {
#Autowired
private TestComponent testComponent;
private final TestService testService;
public TestController(TestService testService) {
this.testService = testService;
}
}
and
#Service
public class TestService {
}
and
#Component
public class TestComponent {
}
The list of beans for the TestController class should return:
TestService (injected via constructor)
TestComponent (injected via #Autowired annotation)
Is there an existing Spring helper/utility that can return this information for me?
You can query names of dependent beans from the ConfigurableBeanFactory for a given bean name with the method getDependenciesForBean(). So in your example the code could look like
try (ConfigurableApplicationContext app = SpringApplication.run(MySpringApplication.class)) {
ConfigurableListableBeanFactory beanFactory = app.getBeanFactory();
String[] dependencies = beanFactory.getDependenciesForBean("testController");
System.out.println(Arrays.toString(dependencies)); // [testService, testComponent]
}
The problem hereby is that you only work on names of beans. So to make the code generic for a given bean instance you would have to find out the name of the bean (which can be non-unique) and also when getting the actual injected beans for these names it can be possible that you don't get the same instances (because of #Scope(SCOPE_PROTOTYPE) on the bean definition).
As the question suggests, how do you Autowire a class with non SpringBoot managed class as constructor args.
The following is a code block illustrating this:
#Component
class Prototype
{
#Autowired
private Repository repository;
private NonSpringBootManagedBean bean;
Prototype(NonSpringBootManagedBean bean)
{
this.bean = bean;
}
}
#Component
class PrototypeClient
{
#Autowired
private ApplicationContext context;
private void createNewPrototype(NonSpringBootManagedBean bean)
{
// This throws an error saying no bean of type NonSpringBootManangedBean found
Prototype prototype = context.getBean(Prototype.class, bean);
}
}
The reason I am using ApplicationContext to obtain an instance of Prototype instead of using #Autowired is because I need a new instance of Prototype within the method createNewPrototype() every time it's invoked and not a singleton instance (Also, please advise if this way obtaining a new instance is incorrect).
Update:
As others have stated to move my creation of bean to a Java configuration class and adding method annotated by #Bean and instantiating the NonSpringBootManagedBean in the #Bean method. But I think this is not possible as this NonSpringBootManagedBean is passed by caller of PrototypeClient.createNewPrototype().
Update
I have updated my above code example with a more clarity. Please refer this now.
#Component
class Prototype
{
#Autowired
private Repository repository;
// Here Session is part of javx.websocket package and cannot be added as part of
// Java configuration class with a #Bean annotation
// In this case how can I use constructor injection?
private Session session;
Prototype(Session session)
{
this.session = session;
}
}
#Component
class PrototypeClient
{
#Autowired
private ApplicationContext context;
private void createNewPrototype(Session session)
{
Prototype prototype = context.getBean(Prototype.class, session);
}
}
#ServerEndpoint(value = "/resources")
class WebSocketController
{
private PrototypeClient client = ApplicationContext.getBean(PrototypeClient.class);
#OnMessage
void handleMessage(Session session, String message)
{
client.createNewPrototype(session);
}
}
Did you know that you can change your bean scope to be a prototype reference instead of a singleton. That way you can scope a single bean definition to any number of object instances.
https://docs.spring.io/spring/docs/3.0.0.M3/reference/html/ch04s04.html
private NonSpringBootManagedBean bean = new NonSpringBootManagedBean();
#Bean
public Prototype getPrototype(){
return new Prototype(bean);
}
Spring can not Autowire an Object if it is not aware of it. Some where there need to be #Component or #Bean or some other annotation like #Service etc to tell spring to manage the instance .
Also it is suggested that if you are using a private variable in Autowire it should be part of constructor(for constructor injection ) or a setter method must be provided(setter injection)
To solve your error : you can create a java config class and place it in you base pkg (same as #SpringBootApplication or add #ComponentScan("pkg in which config is present") on class with #SpringBootApplication)
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Configuration;
#Configuration
public class myconfig {
#Bean
public NonSpringBootManagedBean nonSpringBootManagedBean()
{
return new NonSpringBootManagedBean();
}
}
Define a bean with scope prototype
That is each time injected as new instance.
In SpringBoot you can use the annotation #Scope("prototype") to your bean class Prototype.
#Component
#Scope("prototype")
class Prototype {
#Autowired
private Repository repository;
private NonSpringBootManagedBean bean;
Prototype() {
// you can only modify this 'NonSpringBootManagedBean' later
// because Spring calls constructor without knowing NonSpringBootManagedBean
this.bean = new NonSpringBootManagedBean();
// do something with 'repository' because its defined
}
public void setNonSpringBootManagedBean(NonSpringBootManagedBean bean) {
this.bean = bean;
}
}
Use instances of this bean
Via injection (e.g. #Autowired to constructor) you can use different instances of this prototypical bean within other beans.
#Component
class PrototypeClient {
// ApplicationContext still used?
#Autowired
private ApplicationContext context;
private Prototype prototypeInstance;
#Autowired // injects the new instance of Prototype
public PrototypeClient(Prototype p)
this.prototypeInstance = p;
// here you can change the NSBMB
modifyPrototype();
}
private void modifyPrototype(NonSpringBootManagedBean bean) {
this.prototypeInstance.setNonSpringBootManagedBean( new NonSpringBootManagedBean() );
}
}
Why is your exception thrown?
no bean of type NonSpringBootManangedBean found
Spring complains when trying to instantiate the bean of type Prototype
Prototype prototype = context.getBean(Prototype.class, bean);
because for calling its constructor it needs to pass an argument of type NonSpringBootManagedBean. Since all this bean-instantiating is done internally by Spring(Boot), you can not intercept and tell Spring: "Hey, use this bean of class NonSpringBootManagedBean" like you tried in method createNewPrototype(NonSpringBootManagedBean bean).
Why could'nt the NonSpringBootManagedBean be managed as bean by Spring(Boot)?
Autowiring in SpringBoot is a way of dependency-injection. This means a bean has been previously instantiated by SpringBoot, automatically at startup (when Spring boots). And this bean is now injected as dependency into another bean, etc. because this other bean depends on it.
If you tell us some more background, we could possibly bring light into your situation. This can be some answers to:
What is NonSpringBootManagedBean and why is it no managed bean?
What is Prototype and for which purpose does it use NonSpringBootManagedBean?
What is PrototypeClient and why does it create its own Prototype ?
I am not sure if I have understood the relationship and purpose between your objects/classes.
I'm not sure if I understand it correctly, but from what I got, is that I can use #Value annotations to read values from my application.properties.
As I figured out this works only for Beans.
I defined such a bean like this
#Service
public class DBConfigBean {
#Value("${spring.datasource.username}")
private String userName;
#Bean
public String getName() {
return this.userName;
}
}
When the application starts I'm able to retrieve the username, however - how can I access this value at runtime?
Whenever I do
DBConfigBean conf = new DBConfigBean()
conf.getName();
* EDIT *
Due to the comments I'm able to use this config DBConfigBean - but my initial problem still remains, when I want to use it in another class
#Configurable
public SomeOtherClass {
#Autowired
private DBConfigBean dbConfig; // IS NULL
public void DoStuff() {
// read the config value from dbConfig
}
}
How can I read the DBConfig in a some helper class which I can define as a bean
Thanks
As Eirini already mentioned you must inject your beans.
The #Value annotation only works on Spring beans.
There is another way of accessing configuration with #ConfigurationProperties.
There you define a class that holds the configuration.
The main advantage is, that this is typesafe and the configuration is in one place.
Read more about this:
https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html#boot-features-external-config-vs-value
You shouldn't instantiate your service with the new operator. You should inject it, for example
#Autowired
private DBConfigBean dbConfig;
and then dbConfig.getName();
Also you don't need any #Bean decorator in your getName() method
You just need to tell spring where to search for your annotated beans. So in your configuration you could add the following:
#ComponentScan(basePackages = {"a.package.containing.the.service",
"another.package.containing.the.service"})
EDIT
The #Value, #Autowired etc annotations can only work with beans, that spring is aware of.
Declare your SomeOtherClass as a bean and add the package config in your #Configuration class
#Bean
private SomeOtherClass someOtherClass;
and then
#Configuration
#ComponentScan(basePackages = {"a.package.containing.the.service"
"some.other.class.package"})
public class AppConfiguration {
//By the way you can also define beans like:
#Bean
public AwesomeService service() {
return new AwesomeService();
}
}
Wrap your DBConfig with #Component annotation and inject it using #Autowired :
#Autowired
private DBConfig dbConfig;
Just add below annotation to your DBConfigBean class:
#PropertySource(value = {"classpath:application.properties"})
I came across this code
#Singleton
#Controller
#Autowire(mode = AutowireMode.BY_NAME)
#Path("/")
public class RootResource {
}
I have seen #Autowire on fields,
It means autowiring by type, and class with this field will get bean with particular type.
But in above code I am not sure who is using this RootResource bean?
This is Spring-jersey Rest project.
What I understand is spring will create bean of RootResource and Some class will use this bean to set its property. (I cant see any explicit configuration for this bean)
My question is,
1) Who is this class?
2) Here Autowiring by name is done, Can I replace #Autowired with #Resource ?
The use of #Autowire in this case is to instruct the Spring container to inject dependencies into RootResource by using beans with names matching property names in RootResource.
This is similar to that autowire attribute of the bean element using XML configuration. Assuming RootResource has
#Singleton
#Controller
#Autowire(mode = AutowireMode.BY_NAME)
#Path("/")
public class RootResource{
private SomeService someService;
private AnotherService anotherService;
public void setSomeService(SomeService someService){
this.someService = someService;
}
public void setAnotherService(AnotherService anotherService){
this.anotherService = anotherService;
}
}
The container will attempt to find beans named someService and anotherService and will try to set the corresponding properties. Take note you don`t require any dependency inject annotations the property or field level.
You can use #Resource / #Autowired to achieve the same thing. However you have to annotate the fields or setters in this case. And also injection will fail if the dependency is not found in the container
#Singleton
#Controller
#Autowire(mode = AutowireMode.BY_NAME)
#Path("/")
public class RootResource{
private SomeService someService;
private AnotherService anotherService;
#Resource
public void setSomeService(SomeService someService){
this.someService = someService;
}
#Resource
public void setAnotherService(AnotherService anotherService){
this.anotherService = anotherService;
}
}
#Resource will use bean name and fall back to type matching whilst #Autowired always uses type matching
Also note that #Autowire and #Autowired have different behaviour. The RootResource bean does not need to be explictly configured in the application context. It will be auto detected by the component scanner as it has a stereotype annotation i.e #Controoler