I need to customize the default KafkaProducerFactory (or any other default factory, say KafkaConsumerFactory) that ships with micronaut-kafka dependency. For that I tried to replace the existing factory using,
#Factory
#Replaces(factory = KafkaProducerFactory.class)
class CustomFactory extends KafkaProducerFactory {
#Bean
#Any
public <K, V> Producer<K, V> getProducer(
#Nullable InjectionPoint<KafkaProducer<K, V>> injectionPoint,
#Nullable #Parameter AbstractKafkaProducerConfiguration<K, V> producerConfiguration) {
validate(producerConfiguration); //this is my primary intension
super.getProducer(injectionPoint, producerConfiguration);
}
}
But it seems that Micronaut is not able to replace KafkaProducerFactory hence both the factory exists and I am getting error saying
"multiple candidate bean exists [CustomFactory, KafkaProducerFactory]"
I also thought to exclude the KafkaProducerFactory while the application loads, but could not find anything similar to Spring's ComponentScan.excludeFilter in Micronaut.
Is there anything wrong in my configuration or is there any other way to achieve the same?
Finally I got the answer. Let me elaborate little more for the actual context,
Problem
We have custom way of creating producer/consumer instances i.e. a custom class that creates those given the config properties. Now I had to modify the default factories so that instead of creating the instances on its own, the factory should invoke our custom class to instantiate producer/consumers.
Solution
I had to add #Primary along with other annotations and its working,
#Factory
#Replaces(factory = KafkaProducerFactory.class)
#Primary
class CustomFactory extends KafkaProducerFactory {
//code here
}
But the way I acheived this is kind of a work around because,
my primary intension was to override the producer/consumer creation part of default factory in a sub class and then replacing the default factory by the sub class. But as per the code structure in default factory class, it was not a single place where we can plug our custom code (no specific public method present consolidating the code for creating producer/consumer, it was being created from 3 separate places with "new") to create the producer. Hence we had to copy the entire default factory class and replaced the 3 places with custom code which does not seem to be a correct way.
Related
Here're my use case:
When my app launched, N beans of type A will be created.
I'd like to have my own biz logic to check these N beans 1 by 1 and:
if none of them satisfy my criteria, I'll create another bean of type A to spring container.
if any of them satisfy my criteria, just do nothing.
I'm not sure whether I can simply use Optional like this:
#Autowired
List<A> beans;
#Bean
public Optional<A> maybeA(){
//check beans and optionally create a A
}
Defining bean that returns type Optional is very unusual and not a good solution.I suggest you check if you could implement your logic as described https://iamninad.com/conditional-bean-creation-in-spring-boot/ or if you insist to follow your solution, you can create a new class as :
public class UnMatchedACriteriaImpl implements A {
public void testMethod() throws UnSatisfiedXCriteria {
throw new UnSatisfiedXCriteria();
}
}
and change your bean definition to :
#Bean
public A maybeA(){
//check beans and optionally create a A
}
When you criteria does not match you return UnMatchedACriteriaImpl version of A. which is clear and manageable when you want to use it in your application.
I am having two implementations of my component.
public interface MyComponent {
}
imple1
#Component("impCompf")
#Lazy
#RequestScope
public class ImpComp1 implements MyComponent {
}
imple2
#Component("impComps")
#Lazy
#RequestScope
public class ImpComp2 implements MyComponent {
}
What I did so far is to create two conditions like so:
imple1
public class FirstCondition implements Condition {
#Override
public boolean matches(ConditionContext arg0, AnnotatedTypeMetadata arg1) {
return staticVariable.contains("impCompf");
}
}
Same goes for imple2
and define a configuration class
#Configuration
public class MyConfiguration {
#Bean
#Conditional(FirstCondition .class)
#Primary
public MyComponent getComp1() {
return new ImpComp1();
}
public static String staticVariable= "impCompf";
and in My main controller:
#RequestMapping(value="api/{co}", method=RequestMethod.POST)
public ResponseEntity<Modelx> postSe(#PathVariable("co") String co) {
if(co.contains("impCompf"))
staticVariable = "impCompf";
else (co.contains("impComps"))
staticVariable = "impComps";
What I want: for every http request I want to load proper implementation
But however what I am getting is the implementation defined first in the static variable.
If is there another elegant and better way, i'd like to know about it.
I think there is some confusion here about the purpose of the conditions. These aren't being used at the time your requests arrive to autowire the candidate bean into your controller. These are being used when the application is started to configure the application context based on the environment and classpath etc...
There is no need for the conditional classes that you have created. This is defining the configuration of the beans when the context starts and not on a per request basis at runtime.
The use of the static variable is also problematic is a scenario with one or more concurrent requests or in a case where multiple threads may observe different values unless some other mechanism in the java memory model is being used (such as volatile or establishing a happens before relationship, e.g. with sychnronized)
There are a number of ways to do what you appear to be trying to achieve. Since ultimately, you appear to be using a path parameter supplied by a client to determine which service you want to invoke you could use a classic factory pattern to return the correct interface implementation based on the string input programmatically.
Alternatively you could create two distinct controller methods which are distinguished by a query parameter or endpoint name or path match etc. You could then have the appropriate service injected by a qualified bean name
Although perhaps generally recommended, you could also inject an application context instance and search the it looking for the relevant bean by name or class: https://brunozambiazi.wordpress.com/2016/01/16/getting-spring-beans-programmatically/ - although This is more cumbersome and you'd need to handle things like org.springframework.beans.factory.NoSuchBeanDefinitionException or casting in some cases - best avoided in favour of one of the other methods.
I would like to build a Spring application, where new components can be added easily and without much configuration. For example: You have different kinds of documents. These documents should be able to get exported into different fileformats.
To make this functionality easy to maintain, it should (basically) work the following way:
Someone programs the file format exporter
He/ She writes a component, which checks if the file format exporter is licensed (based on Spring Conditions). If the exporter is licensed a specialized Bean is injected in the application context.
The "whole rest" works dynamically based on the injected beans. Nothing needs to be touched in order to display it on the GUI, etc.
I pictured it the following way:
#Component
public class ExcelExporter implements Condition {
#PostConstruct
public void init() {
excelExporter();
}
#Bean
public Exporter excelExporter(){
Exporter exporter= new ExcelExporter();
return exporter;
}
#Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return true;
}
}
In order to work with those exporters (display them, etc.) I need to get all of them. I tried this:
Map<String, Exporter> exporter =BeanFactoryUtils.beansOfTypeIncludingAncestors(appContext, Exporter.class, true, true);
Unfortunate this does not work (0 beans returned). I am fairly new to this, would anyone mind to tell me how this is properly done in Spring? Maybe there is a better solution for my problem than my approach?
You can get all instances of a given type of bean in a Map effortlessly, since it's a built in Spring feature.
Simply autowire your map, and all those beans will be injected, using as a key the ID of the bean.
#Autowired
Map<String,Exporter> exportersMap;
If you need something more sophisticated, such as a specific Map implementation or a custom key. Consider defining your custom ExporterMap, as follows
#Component
class ExporterMap implements Map{
#Autowired
private Set<Exporter> availableExporters;
//your stuff here, including init if required with #PostConstruct
}
I would like my other classes to interact with my domain's interfaces rather than implementation, and i would like to avoid hardcoding the implementation in the code, such as this example :
public void addToMyList(String s, int i) {
DomainModel model = new DefaultDomainModelImpl(); // it's hardcoding the implementation here
model.setName(s).setAge(i);
myList.add(model);
}
If i use spring container, with the prototype scope, i can use something like :
// <bean id="myDomainBean" scope="prototype" class="my.package.domain.MyDomainImpl" />
DomainModel myDomainModel = springContext.getBean("myDomainBean");
But i would like to avoid accessing springContext explicitly in my code.
I wonder what's the clean way to do this ?
Im currently thinking of creating a factory implementation for each domain implementation, and autowire the factory to create the beans, but that means different implementations of my domain will have different implementations of the factory also.
Please share your opinions, thank you !
Im currently thinking of creating a factory implementation for each domain implementation, and autowire the factory to create the beans, but that means different implementations of my domain will have different implementations of the factory also.
That is not 100% correct. You can have a factory that take the Interface (class) of the Domain objects that needs to be create. You can inject that factory in you class.
So you will get all the requriements you asked for:
no hard coded new
the domain object code has no dependence to spring
you only have one factory class and one factory method.
example
#Inject
MyStrangeSpringHiddingFactory myStrangeSpringHiddingFactory;
DomainModel myDomainModel = this.myStrangeSpringHiddingFactory.
createInstanceOf(DomainModel.class);
class MyStrangeSpringHiddingFactory implements MyStrangeSpringHiddingFactory {
#Inject
ApplicationContext springContext:
public <T> createInstanceOf(Class<T> clazz) {
return springContext.getBean(clazz);
}
}
This are only my thoughts, because I do not know your use case: Do you really need such in abstraction? Do you really have a domain model where a domain class have several subclasses that need a factory.
Is it possible to write a custom JSP tag to take an i18n message key and output the translation phrase for the given request?
Normally in JSP/JSTL, I do:
<fmt:message key="${messageKey}"><fmt:param>arg1</fmt:param></fmt:message>
And I get the translation phrase. Now I need to do the following (there's a good reason for this):
<custom:translate key="${messageKey}" arg="arg1"/>
But I don't know how to look up the translation in the custom tag code. The TagSupport base class provides a pageContext from which I can get a ServletRequest which has the Locale... but how do I then look up the translation for a key?
I use Spring 3.0 and in my application-context.xml, I've defined a ReloadableBundleMessageSource so I can call:
messageSource.getMessage(
key, new Object[] {arg}, pageContext.getRequest().getLocale()
);
but I don't think I can inject messageSource into a custom tag, can I? Otherwise I can instantiate a new one, but would it load my tens of thousands of translations for every call? I don't want to resort to making messageSource a static member of a static class.
I don't do Spring, but in "plain" JSP you can just put the ResourceBundle instance in the session scope with help of a Filter or Servlet
ResourceBundle bundle = ResourceBundle.getBundle(basename, request.getLocale());
request.getSession().setAttribute("bundle", bundle);
And treat it in JSP like any other bean in EL.
${bundle[messageKey]}
It must be possible to have Spring to put that as a bean in the session scope.
There is a utility in spring to access the web application context. Then you can look up a bean by its name or type.
To get hold of your resource bundle, you could do something like:
WebApplicationContext springContext = WebApplicationContextUtils.getWebApplicationContext(pageContext.getServletContext());
messageResource = springContext.getBean("messageResource");
This question is very old but I think it is worth to share another way to solve this.
To access the Spring message source in a custom tag you only need to extend the class org.springframework.web.servlet.tags.RequestContextAwareTag instead of TagSupport.
In this case you have to implement the method doStartTagInternal() instead of doStartTag(), but inside this method you will have access to the MessageSource through getRequestContext().getMessageSource() method.
Therefore, your class would look like:
public class CreateCustomFieldTag extends RequestContextAwareTag{
//variables (key, arg...), getters and setters
#Override
protected int doStartTagInternal() throws Exception {
getRequestContext().getMessageSource().getMessage(
key, new Object[] {arg}, getRequestContext().getLocale());
}
}