I have a simple spring boot app with the following config:
#Configuration
public class MyConfig {
#Bean
#Scope(value = "prototype", proxyMode = ScopedProxyMode.TARGET_CLASS)
public HashMap<String, BidAskPrice> beanyBoi() {
System.out.println("creating a new one");
return dataFetcher().getPairPricesBidAsk();
}
}
and i have a service
#Service
public class ProfitCalculatorService {
#Autowired
private HashMap<String, BidAskPrice> prices;
public HashMap<String, BidAskPrice> getPrices() {
return prices;
}
}
and i have a controller
#RestController
public class TestController {
#Autowired
ProfitCalculatorService profitCalculatorService;
#GetMapping("/getprices")
public HashMap<String, BidAskPrice> someprices() {
return profitCalculatorService.getPrices();
}
}
}
now when i hit the /getprices endpoint, i was seeing some odd behaviour. The following message is logged twice: "creating a new one".
Your beans have a prototype scope, it means that every time that you asked for this bean a new instance will be created.
Official explanation:
The non-singleton prototype scope of bean deployment results in the
creation of a new bean instance every time a request for that specific
bean is made. That is, the bean is injected into another bean or you
request it through a getBean() method call on the container. As a
rule, you should use the prototype scope for all stateful beans and
the singleton scope for stateless beans.
https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-factory-scopes-prototype
Another thing is the proxyMode with TARGET_CLASS value. It means that the bean injected into the ProfitCalculatorService is not the BidAskPrice itself, but a proxy to the bean (created using CGLIB) and this proxy understands the scope and returns instances based on the requirements of the scope (in your case prototype).
So, my suggestion is: You don't need to create an explicitly bean of HashMap<String, BidAskPrice>. Since BidAskPrice is a bean, you can inject the HashMap<String, BidAskPrice> directly in your service, Spring will manage this list for you!
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;
}
Spring question.
I have two questions related to spring.
If I declare bean like this:
#Service
public class Downloader {
#Bean
public String bean1() {
return "bean1";
}
}
Then if other classes will be autowiring "bean1" then method bean1 will be called several times? Or one instance of bean1 will be created and reused?
Second question. How to Autowire some other bean e.g. "bean2" which is String "externalBean" that can be used to construct bean1.
#Service
public class Downloader {
#Autowire
private String bean2;
#Bean
public String bean1() {
return "bean1" + this.bean2;
}
}
Currently I'm trying to Autowire this bean2 but it is null during bean1 call. Is there any mechanism that I can specify order of this. I don't know in what context looking for this kind of info in Spring docs.
Just simple #Bean annotation used sets the scope to standard singleton, so there will be only one created. According to the docs if you want to change you need to explicitly add another annotation:
#Scope changes the bean's scope from singleton to the specified scope
Then if other classes will be autowiring "bean1" then method bean1
will be called several times? Or one instance of bean1 will be created
and reused?
There will be only a single instance of bean1, as the implicit scope is Singleton (no #Scope annotation present).
Second question. How to Autowire some other bean e.g. "bean2" which is
String "externalBean" that can be used to construct bean1.
Being that it is a String, a #Qualifier might be required
#Bean
#Qualifier("bean2")
public String bean2() {
return "bean2";
}
Then
#Bean
public String bean1(#Qualifier("bean2") final String bean2) {
return "bean1" + bean2;
}
However, this works too.
Spring will be able to look at the name of the Bean and compare it to the parameter's one.
#Bean
public String bean2() {
return "bean2";
}
and
#Bean
public String bean1(final String bean2) {
return "bean1" + bean2;
}
The order is calculated automatically by Spring, based on a Bean dependencies.
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 have two beans that implements the same interface. Both are created in Java configuration, like this:
#Bean
#Qualifier("kafkaEventSender")
public IKafkaEventSender<KafkaData> kafkaEventSender(#Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
return new KafkaEventSender<>(kafkaTemplate, false);
}
#Bean
#Qualifier("kafkaEventSenderAudited")
public IKafkaEventSender<KafkaData> kafkaEventSenderAudited(#Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
return new KafkaEventSenderAudited<>(kafkaTemplate, false);
}
The problem is that spring doesn't create first bean only the second. Any idea why?
Try using bean names instead:
#Bean(name = "kafkaEventSender")
public IKafkaEventSender<KafkaData> kafkaEventSender(#Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
return new KafkaEventSender<>(kafkaTemplate, false);
}
#Bean(name = "kafkaEventSenderAudited")
public IKafkaEventSender<KafkaData> kafkaEventSenderAudited(#Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
return new KafkaEventSenderAudited<>(kafkaTemplate, false);
}
Ok, the problem was with method name, after changing it, bean is properly created. In some other library configuration class was a method with same name. Guessing that was the problem.
#Qualifier annotation is used to select one bean over multiple available beans of same type in spring container.
when you annotate a method with #Bean annotation, default, it creates a bean whose name is the name of same method. So, for example:
#Bean
public BeanA itsBeanA() {
return new BeanA();
}
#Bean(name = "specialBeanA")
public BeanA itsAgainBeanA() {
return new BeanA("specialConstructorParam");
}
#Bean
public BeanB beanB(#Autowired #Qualifier("specialBeanA") BeanA beanA) {
return new BeanB(beanA);
}
first method will create an instance of BeanA with name 'itsBeanA'. Second, will create an instance with name 'specialBeanA' since we provided the name attribute here.
There maybe a scenario where you need to have multiple beans of same TYPE (like BeanA here). It will create ambiguity for container which bean to use of all same types, we specify the #Qualifier with the name of bean which we want.
I hope that helps.
I'm new to spring and spring mvc
I'm going over a course where they present the following #Configuration class:
#Configuration
public class MailConfig {
#Bean
#ConditionalOnProperty(name="spring.mail.host",
havingValue="foo",
matchIfMissing=true)
public MailSender mockMailSender() {
return new MockMailSender();
}
#Bean
#ConditionalOnProperty(name="spring.mail.host")
public MailSender smtpMailSender(**JavaMailSender javaMailSender**) {
SmtpMailSender mailSender = new SmtpMailSender();
mailSender.setJavaMailSender(javaMailSender);
return mailSender;
}
}
in the second bean (smtpMailSender) - there's a parameter :
JavaMailSender javaMailSender
but the parameter is not passed by the caller.
the instructors says : "inside bean methods if we pass parameter like this one , the parameters will be injected by spring"
My question is - how could I know that this is the expected behavior of Spring ? what is the instructor basing this on ?
is there a specific trait of JavaMailSender that is part of spring and therefor treated as a component or is something else in play here ?
That, simply said, is the way Spring works when using Java based configuration.
When a method annotated with #Bean is detected and it has parameters Spring will auto wire them by default. It does so by type.
#Bean
#ConditionalOnProperty(name="spring.mail.host")
public MailSender smtpMailSender(JavaMailSender javaMailSender) {
SmtpMailSender mailSender = new SmtpMailSender();
mailSender.setJavaMailSender(javaMailSender);
return mailSender;
}
In this case it will inject a bean of type JavaMailSender into this method. As you are using Spring Boot that is configured by default and will be injected. For a more information see the reference guide.