Suppose I have an EntityManagerFactory reference instantiated within an init-method of a servlet:
StartServlet.java:
#WebServlet("/start")
public class StartServlet extends HttpServlet {
private EntityManagerFactory factory;
#Override
public void init() {
factory = Persistence.createEntityManagerFactory("jpa");
getServletContext().setAttribute("factory", factory);
}
}
Which I also do visible for all other servlets within the "container". Now, lets say I want to access this reference in another servlet, like:
AnotherServlet.java:
#WebServlet("/another")
public class AnotherServlet extends HttpServlet {
private EntityManagerFactory factory;
#Override
public void init() {
factory = (EntityManagerFactory) getServletContext().getAttribute("factory");
if(factory == null) {
//factory not instantiated from StartServlet, what to do?
}
}
}
What do I do if its not instantiated from StartServlet.java (init has not been invoked)? Hope my question is precise enough!
-Superdids
Don't depend on the servlet container's order of Servlet initialization.
Instead, do the initialization in a ServletContextListener.
Related
I'm using spring-kafka-2.2.7-RELEASE. I'm trying to capture the event when a consumer is ready to consume message and trying to use ConsumerAwareRebalanceListener but it's not working. Please suggest.
#Component
public class ConsumerAwareRebalanceListenerImpl implements ConsumerAwareRebalanceListener {
public void ConsumerAwareRebalanceListenerImpl(){
System.out.println(" In ConsumerAwareRebalanceListenerImpl constructor");
}
#Override
public void onPartitionsRevoked(Collection<TopicPartition> partitions) {
}
#Override
public void onPartitionsAssigned(Collection<TopicPartition> partitions) {
partitions.forEach( item -> {
TestConsumerConstants.consumerEventsMap.put("key-"+item.partition(), item.partition());
});
}
#Override
public void onPartitionsAssigned(Consumer<?, ?> consumer, Collection<TopicPartition> partitions){
TestConsumerConstants.consumerEventsMap.put(consumer.toString(), partitions);
}
}
I fixed the problem and it's working now. All I had to do is, set the containerProperty 'setConsumerRebalanceListener' of the ConcurrentKafkaListenerContainerFactory to my custom class instance as shown below
ConcurrentKafkaListenerContainerFactory factory = new
ConcurrentKafkaListenerContainerFactory<>();
factory.getContainerProperties().setConsumerRebalanceListener(kafkaConsumerRebalanceListener);
I'm using custom crudrespository to persist data in redis. However, I'm unable to autowire custom repository.
All the configuration seems correct and redis is running on my local.
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
#Repository
public interface CustomRepository extends CrudRepository<String,
Long> {
String get(String key);
void put(String key, String value);
}
//////////
public class StorageServiceImpl implements IStorageService {
#Autowired
private CustomRepository respository;
#Override
public void saveParameter() {
this.respository.put("key1","value1");
}
#Override
public String getParameter() {
return this.respository.get("key1");
}
/////
#Service
public interface IStorageService {
void saveParameter();
String getParameter();
}
///////
#SpringBootApplication(scanBasePackages = {"com.example.cache"})
#EnableRedisRepositories(basePackages = {"com.example.cache.repository"})
public class ApplicationConfiguration {
public static void main(String[] args){
SpringApplication.run(ApplicationConfiguration.class, args);
new StorageServiceImpl().saveParameter();
System.out.println(new StorageServiceImpl().getParameter());
}
}
When I try running this application using gradle bootRun, I get
Exception in thread "main" java.lang.NullPointerException
at com.example.cache.impl.StorageServiceImpl.saveParameter(StorageServiceImpl.java:16)
at com.example.cache.ApplicationConfiguration.main(ApplicationConfiguration.java:17)
Not sure what's wrong?
You can't use new on any bean, you need to #Autowire it. The annotations only work with spring managed beans at every level.
Add a new bean with a a storage service and a method that makes your call after it is created.
Also, I can't remember if the spring-boot creates the bean if there is only one implementation but I believe your StorageServiceImpl needs the #Service annotation, not the interface.
Delete this from your ApplicationConfiguration class.
new StorageServiceImpl().saveParameter();
System.out.println(new StorageServiceImpl().getParameter());
Then add this new class.
#Service
public class Startup {
#Autowired
IStorageService storageService;
#PostConstruct
public void init(){
storageService.saveParameter();
System.out.println(storageService().getParameter());
}
}
And you need a config
#Configuration
#EnableRedisRepositories
public class ApplicationConfig {
#Bean
public RedisConnectionFactory connectionFactory() {
return new JedisConnectionFactory();
}
#Bean
public RedisTemplate<?, ?> redisTemplate() {
RedisTemplate<byte[], byte[]> template = new RedisTemplate<byte[], byte[]>();
return template;
}
}
My use case is running custom code before a controller method by annotating methods.
HandlerInterceptor seems the way to go but it seems impossible to inject dependencies into it because it needs to be registered before the context is being created.
All examples I've found so far use empty constructors (see spring boot adding http request interceptors) or autowire properties in the configuration which fails because I declare dependent beans in the same configuration (Requested bean is currently in creation: Is there an unresolvable circular reference?).
Is there a better way that does not involve AOP?
Assume that your interceptor has constructor dependencies like that:
public class CustomInterceptor extends HandlerInterceptor {
private final DependentBean bean;
public CustomInterceptor(DependentBean bean) {
this.bean = bean;
}
}
Then you can register your handler like that:
#Configuration
public WebConfig extends WebMvcConfigurerAdapater {
#Bean
public DependentBean dependentBean() {
return new DependentBean();
}
#Bean
public CustomInterceptor customInterceptor() {
return new CustomInterceptor(dependentBean());
}
#Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(customInterceptor());
}
}
#Configuration will ensure each Bean method call return the same bean instance
Building on the answer above from Mạnh, if using component scan for dependency injection of the dependency, then that can be Autowired in the WebConfig
#Configuration
public WebConfig extends WebMvcConfigurerAdapater {
#Autowired
DependentBean dependentBean;
#Bean
public CustomInterceptor customInterceptor() {
return new CustomInterceptor(dependentBean);
}
#Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(customInterceptor());
}
}
Also building on previous answers, and if you use Lombok, you can further simplify.
Have your interceptor implementation been a #Component
Add a private final DependentBean field to it.
Also add a #RequiredArgsConstructor annotation to it, to have Lombok generating a constructor with a single DependentBean parameter.
In your WebConfig, use the same technic to have a private final CustomInterceptor field been injected by Spring IOC.
This way the CustomInterceptor instance will be available & initialized the right way when addInterceptors will be called
Here are the corresponding code samples :
The CustomInterceptor :
#Component
#RequiredArgsConstructor
public class CustomInterceptor implements HandlerInterceptor {
private final DependentBean dependentBean;
#Override
public boolean preHandle( final HttpServletRequest request,
final HttpServletResponse response,
final Object handler ) throws Exception {
// your Interceptor Implementation goes here ...
}
}
The WebConfig :
#Configuration
#RequiredArgsConstructor
public class WebConfig implements WebMvcConfigurer {
private final CustomInterceptor customInterceptor;
#Override
public void addInterceptors( final InterceptorRegistry registry ) {
registry.addInterceptor( customInterceptor );
}
}
All classes that inherit from controller have already inserted the dependencies, but I do not know how to inject those who do not inherit from contoller.
in the example below the SendEmailAndLog() method waits for the ILoggerService interface to be injected. but I do not know how to do this.
public async Task Execute(IJobExecutionContext context)
{
SendEmailHelper sendEmailHelper = new SendEmailHelper();
await sendEmailHelper.SendEmailAndLog(user, "Task", user.UserName, UserManager, loggerService);
}
this task is called the method Application_Start() on Global.asax.cs
I created a constructor to receive this service as a parameter, this is working for the methods within the controllers that call the Class Emailservice. However there are classes that do not inherit from controller so I do not know how to inject.
My Service is:
public interface ILoggerService
{
void Error(ExceptionLogger exception);
void SaveLog();
}
public class LoggerService : ILoggerService
{
private readonly ILoggerRepository loggerRepository;
private readonly IUnitOfWork unitOfWork;
public LoggerService(ILoggerRepository loggerRepository, IUnitOfWork unitOfWork)
{
this.loggerRepository = loggerRepository;
this.unitOfWork = unitOfWork;
}
public void Error(ExceptionLogger exception)
{
loggerRepository.Error(exception);
}
public void SaveLog()
{
unitOfWork.Commit();
}
}
I'm using SpringBoot and I am trying to create a service layer for my web application but i cant make it work.
My classes look like this
ServiceFactory
#Service
public class ServiceFactory {
#Autowired
public static EncuestaService getEncuestaService()
{
return new EncuestaServiceImpl();
}
}
EncuestaService
public interface EncuestaService {
void crearEncuesta(Encuesta encuesta, Map<String,String> parametros);
}
EncuestaServiceImpl
#Service
public class EncuestaServiceImpl implements EncuestaService {
#Override
public void crearEncuesta(Encuesta encuesta, Map<String, String> parametros) {
CrearEncuesta nueva = new CrearEncuesta(encuesta,parametros);
nueva.execute();
}
}
CrearEncuesta
#Service
public class CrearEncuesta {
private Encuesta encuesta;
private Map<String,String> parametros;
#Autowired
private RespuestasRepository respuestasRepository;
#Autowired
private EncuestasRepository encuestasRepository;
public CrearEncuesta(Encuesta encuesta, Map<String,String> parametros) {
super();
this.encuesta = encuesta;
this.parametros = parametros;
}
public void execute()
{
encuestasRepository.save(encuesta);
}
}
Everytime I call ServiceFactory.getEncuestasService().crearEncuesta() from any Controller it returns me a NullPointerException.
From what I have been reading I should not be creating a new EncuestsaServiceImpl() in my ServiceFactory but I don't really know the correct way to do so. I would appreciate if anyone could help me out :P.
Edit:
#SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
Controller
#Controller
public class EncuestaController {
#RequestMapping(value ="registrarEncuesta", method = RequestMethod.POST)
private String formularioEncuesta(#Valid #ModelAttribute("formEncuesta") EncuestaForm formEncuesta, BindingResult bindingResult,#RequestParam Map<String,String> allRequestParams)
{
if (bindingResult.hasErrors()) {
return "nuevaEncuesta";
}
try {
Encuesta nueva = formEncuesta.toEncuesta();
ServiceFactory.getEncuestaService().crearEncuesta(nueva,allRequestParams);
} catch (DataIntegrityViolationException e) {
return "nuevaEncuesta";
}
return "redirect:/encuestas";
}
}
You will have to read a little bit more about dependency injection. The central principle in Spring Framework is dependency injection which should be used to avoid referencing beans (service implementations, repository implementations etc...) statically. Spring container also servers as a bean factory that will instantiate and inject (autowire) implementations to beans that need them.
Because Spring will instantiate service interface implementations for you, you don't need ServiceFactory. In your controller you need to add a reference (a field) to EncuestaService and annotate it as Autowired and Spring will wire in the implementation. And then you can just use it in your controller.
#Controller
public class EncuestaController {
#Autowired
EncuestaService encuestaService;
#RequestMapping(value ="registrarEncuesta", method = RequestMethod.POST)
private String formularioEncuesta(#Valid #ModelAttribute("formEncuesta") EncuestaForm formEncuesta, BindingResult bindingResult,#RequestParam Map<String,String> allRequestParams)
{
if (bindingResult.hasErrors()) {
return "nuevaEncuesta";
}
try {
Encuesta nueva = formEncuesta.toEncuesta();
encuestaService.crearEncuesta(nueva,allRequestParams);
} catch (DataIntegrityViolationException e) {
return "nuevaEncuesta";
}
return "redirect:/encuestas";
}
}