Spring-Boot AMQP根据数据库数据创建队列

Question

I want to use my Spring-Boot application to create queues in RabbitMQ, based on some data in my Database. As example: I have an entity with some queue names. I need to create a new queue for each of them. Later on I want to use them without creating them.

I have allready created some configurations to create queues and bind them to an exchange. But my data in my database will change and for each new entry in a specific entity I will lateron need a new Queue.

One idea was to @Autowired in one of my @Configuraion a service, that gets the needed data from the Database. Unfortunately this did not work because the service I autowired got a BeanCreationException.

What am I doing wrong or is there another way to create queues based on database entries?

This is the class i build:

@Configuration
public class RabbitMQQueueConfiguration {

private QueueNameService queueNameService;

@Autowired
public RabbitMQQueueConfiguration(QueueNameService queueNameService){
    this.queueNameService =queueNameService;
}

private String queueA = getQueueNameA(1L);
private String queueB="queueB";


@Bean
public Queue queueA() {
    return new Queue(queueA);
}

@Bean
public Queue queueB() {
    return new Queue(queueB);
}

private String getQueueNameA(Long queueID){
    return queueNameService.getQueueName(queueID);
}
}

And here is the stacktrace i got:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'rabbitMQQueueConfiguration' defined in file [...\classes\com\example\DemoRabbitMq\config\RabbitMQQueueConfiguration.class]: Bean instantiation via constructor failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.DemoRabbitMq.config.RabbitMQQueueConfiguration$$EnhancerBySpringCGLIB$$bc4b2845]: Constructor threw exception; nested exception is java.lang.NullPointerException: Cannot invoke "com.example.DemoRabbitMq.service.QueueNameService.getQueueName(java.lang.Long)" because "this.queueNameService" is null
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:313) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:294) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1356) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1203) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:897) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758) ~[spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750) ~[spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) ~[spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
at com.example.DemoRabbitMq.DemoRabbitMqApplication.main(DemoRabbitMqApplication.java:24) ~[classes/:na]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.DemoRabbitMq.config.RabbitMQQueueConfiguration$$EnhancerBySpringCGLIB$$bc4b2845]: Constructor threw exception; nested exception is java.lang.NullPointerException: Cannot invoke "com.example.DemoRabbitMq.service.QueueNameService.getQueueName(java.lang.Long)" because "this.queueNameService" is null
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:217) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:117) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:309) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
... 19 common frames omitted
Caused by: java.lang.NullPointerException: Cannot invoke "com.example.DemoRabbitMq.service.QueueNameService.getQueueName(java.lang.Long)" because "this.queueNameService" is null
at com.example.DemoRabbitMq.config.RabbitMQQueueConfiguration.getQueueNameA(RabbitMQQueueConfiguration.java:34) ~[classes/:na]
at com.example.DemoRabbitMq.config.RabbitMQQueueConfiguration.<init>(RabbitMQQueueConfiguration.java:19) ~[classes/:na]
at com.example.DemoRabbitMq.config.RabbitMQQueueConfiguration$$EnhancerBySpringCGLIB$$bc4b2845.<init>(<generated>) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:64) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481) ~[na:na]
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:204) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
... 21 common frames omitted

Edit: As requestet my service

@Service
public class QueueNameService {

private static final Logger LOGGER = LoggerFactory.getLogger(QueueNameService.class);

private final SomeOtherRepository someOtherRepository;
private final SomeRepository someRepository;


@Autowired
public QueueNameService(SomeOtherRepository someOtherRepository, SomeRepository someRepository) {
    this.someOtherRepository= someOtherRepository;
    this.someRepository= someRepository;
}

public String getQueueName(int tld_id) throws NoSuchElementException {
    Optional<Foo> foo= someOtherRepository.findById(foo_id);
    Optional<Bar> bar= someRepository.findById(foo.get().getBarId());
    return bar.map(Bar::getName).orElse(null);
}

}

Answer 1

You have a code like this:

private String queueA = getQueueNameA(1L);

which is called before constructor invocation. Since you try to get access to the property ( queueNameService ) which is initialized from the constructor therefore it ends up with that NullPointerException .

There is nothing Spring (or AMQP) specific in your problem: it is just general Java usage issue.