Add core-di: constructor vs setter vs field injection and @Autowired candidate resolution on Boot 4.1
Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01JoVmf2fWvcpoXndcDSwRf7
This commit is contained in:
Claude
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# The same OrderService built with plain 'new', no Spring anywhere
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--- constructor injection ---
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new ConstructorOrderService(gateway, notifier).place("A-1", 500)
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OK -> charged 500 cents for A-1
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charges=1, notifications=1
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--- setter injection, one setter forgotten ---
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new SetterOrderService(); setter.setGateway(gateway); // setNotifier never called
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NullPointerException: Cannot invoke "com.ankurm.coredi.injection.Notifier.send(String)" because "this.notifier" is null
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charges=1 <-- the customer was charged before the failure
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--- field injection ---
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new FieldOrderService().place("A-3", 500)
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NullPointerException: Cannot invoke "com.ankurm.coredi.injection.PaymentGateway.charge(String, int)" because "this.gateway" is null
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after ReflectionTestUtils.setField(...) twice:
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OK -> charged 500 cents for A-3
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# Which injected fields can be final? (reflection over the three variants)
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ConstructorOrderService gateway final=true
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ConstructorOrderService notifier final=true
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SetterOrderService gateway final=false
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SetterOrderService notifier final=false
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FieldOrderService gateway final=false
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FieldOrderService notifier final=false
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# The order Spring touches one bean that uses all three styles
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constructor : constructor arg=set, field=null, setter=null
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setter : setter arg=set, field=set
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@PostConstruct: constructor=set, field=set, setter=set
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# A field-injected collaborator used in the constructor
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context started: false
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top exception : org.springframework.beans.factory.BeanCreationException
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top message : Error creating bean with name 'fieldTrapService': Failed to instantiate [com.ankurm.coredi.injection.FieldTrapService]: Constructor threw exception
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root cause : java.lang.NullPointerException: Cannot invoke "com.ankurm.coredi.injection.PaymentGateway.charge(String, int)" because "this.gateway" is null
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# Two constructors: which one does Spring pick?
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--- TwoConstructorsService: no-arg + one-arg, neither annotated ---
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[no-arg constructor used]
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gateway injected: false
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--- TwoConstructorsNoDefault: one-arg + two-arg, neither annotated ---
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org.springframework.beans.factory.BeanCreationException
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Error creating bean with name 'twoConstructorsNoDefault': Failed to instantiate [com.ankurm.coredi.injection.TwoConstructorsNoDefault]: No default constructor found
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root cause: java.lang.NoSuchMethodException: com.ankurm.coredi.injection.TwoConstructorsNoDefault.<init>()
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--- TwoConstructorsAnnotated: @Autowired on one constructor ---
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[annotated constructor used]
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# @Autowired(required = false) on a setter
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with a Notifier bean : notifier present
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without a Notifier bean : no notifier configured, auditing silently
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# Inside a Spring context all three styles work
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ConstructorOrderService -> charged 700 cents for B-1
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SetterOrderService -> charged 700 cents for B-1
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FieldOrderService -> charged 700 cents for B-1
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# Constructor cycle vs field cycle: plain Spring and Spring Boot
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--- plain Spring, constructor cycle (CtorA <-> CtorB) ---
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started: false
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root cause: org.springframework.beans.factory.BeanCurrentlyInCreationException
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Error creating bean with name 'ctorA': Requested bean is currently in creation: Is there an unresolvable circular reference or an asynchronous initialization dependency?
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--- plain Spring, field cycle (FieldA <-> FieldB) ---
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started: true
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FieldA.b is FieldB: true
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--- Spring Boot, field cycle, default settings ---
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FAILED: BeanCurrentlyInCreationException: Error creating bean with name 'fieldA': Requested bean is currently in creation: Is there an unresolvable circular reference or an asynchronous initialization dependency?
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--- Spring Boot, field cycle, spring.main.allow-circular-references=true ---
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started
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--- Spring Boot, constructor cycle, spring.main.allow-circular-references=true ---
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FAILED: BeanCurrentlyInCreationException: Error creating bean with name 'ctorA': Requested bean is currently in creation: Is there an unresolvable circular reference or an asynchronous initialization dependency?
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# @Lazy on one constructor parameter breaks a constructor cycle
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context started: true
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LazyA.b runtime class : com.ankurm.coredi.injection.LazyB$$SpringCGLIB$$0
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LazyA.b.hello() : LazyB reached through LazyA's proxy
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LazyA.b is the real LazyB bean: false
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# Two PaymentGateway beans and a consumer that asks for one
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started: false
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top exception : org.springframework.beans.factory.UnsatisfiedDependencyException
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top message : Error creating bean with name 'checkoutPlain': Unsatisfied dependency expressed through constructor parameter 0: No qualifying bean of type 'com.ankurm.coredi.injection.PaymentGateway' available: expected single matching bean but found 2: stripeGateway,paypalGateway
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root cause : org.springframework.beans.factory.NoUniqueBeanDefinitionException
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root message : No qualifying bean of type 'com.ankurm.coredi.injection.PaymentGateway' available: expected single matching bean but found 2: stripeGateway,paypalGateway
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# Who wins when several rules apply at once? (one mini-context per row)
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beans registered / injection point winner
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---------------------------------------------------------- --------------------
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@Primary Stripe + Paypal; CheckoutPlain PrimaryStripeGateway
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@Primary Stripe + Paypal; @Qualifier("paypalGateway") PaypalGateway
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@Priority(1) Stripe + @Priority(2) Paypal; CheckoutPlain PriorityOneGateway
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@Priority(1) + Paypal(no priority); param named paypalGateway PaypalGateway
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Stripe + Paypal (plain); param named paypalGateway PaypalGateway
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Stripe (plain) + @Fallback Paypal; CheckoutPlain StripeGateway
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@Fast custom qualifier, FastGateway + Paypal; @Fast param FastGateway
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# No PaymentGateway bean at all
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top exception : org.springframework.beans.factory.UnsatisfiedDependencyException
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top message : Error creating bean with name 'checkoutPlain': Unsatisfied dependency expressed through constructor parameter 0: No qualifying bean of type 'com.ankurm.coredi.injection.PaymentGateway' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
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root cause : org.springframework.beans.factory.NoSuchBeanDefinitionException
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root message : No qualifying bean of type 'com.ankurm.coredi.injection.PaymentGateway' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
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# Five ways to say 'this may not exist', with zero and with two Notifier beans (Email registered before Sms)
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--- zero Notifier beans ---
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plain constructor param : FAILED NoSuchBeanDefinitionException
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Optional<Notifier> : isPresent=false
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@Nullable Notifier : value=null
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ObjectProvider.getIfAvailable() : null
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ObjectProvider.getIfUnique() : null
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ObjectProvider.getObject() : NoSuchBeanDefinitionException: No qualifying bean of type 'com.ankurm.coredi.injection.Notifier' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
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@Autowired(required=false) setter: value=null
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--- two Notifier beans (Sms, Email), no @Primary ---
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ObjectProvider.getIfAvailable() : NoUniqueBeanDefinitionException: No qualifying bean of type 'com.ankurm.coredi.injection.Notifier' available: expected single matching bean but found 2: emailNotifier,smsNotifier
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ObjectProvider.getIfUnique() : null
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ObjectProvider.stream() classes : [EmailNotifier, SmsNotifier]
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ObjectProvider.orderedStream() : [SmsNotifier, EmailNotifier]
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Optional<Notifier> with two beans: FAILED NoUniqueBeanDefinitionException
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No qualifying bean of type 'com.ankurm.coredi.injection.Notifier' available: expected single matching bean but found 2: emailNotifier,smsNotifier
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# List, Map and Set injection; registered Push, Email, Sms in that order
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List<Notifier> order : [SmsNotifier, EmailNotifier, PushNotifier]
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Map<String,Notifier> : [pushNotifier, emailNotifier, smsNotifier]
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Set<Notifier> size : 3
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# A List<Plugin> injection point when zero Plugin beans exist
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--- required List<Plugin>, zero Plugin beans ---
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single constructor param : started (empty list injected)
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@Autowired ctor + no-arg ctor : started (empty list injected)
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FieldInjected : FAILED NoSuchBeanDefinitionException
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No qualifying bean of type 'java.util.List<com.ankurm.coredi.resolution.Plugin>' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
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SetterInjected : FAILED NoSuchBeanDefinitionException
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No qualifying bean of type 'java.util.List<com.ankurm.coredi.resolution.Plugin>' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
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--- ways to make an absent collection legal ---
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Optional<List<Plugin>> : isPresent=false
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@Nullable List<Plugin> : value=null
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ObjectProvider<Plugin> -> list : []
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@Autowired(required=false) list: []
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# Generic type arguments and @Resource
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List<Handler<String>> : [StringHandler]
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Handler<Integer> : IntegerHandler
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@Resource : paypalGateway field -> PaypalGateway, whateverIWantToCallIt field -> StripeGateway
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# getDependenciesForBean: who did Spring wire into whom?
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constructorOrderService depends on [paymentGateway, notifier]
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setterOrderService depends on [paymentGateway, notifier]
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fieldOrderService depends on [paymentGateway, notifier]
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paymentGateway is used by [constructorOrderService, setterOrderService, fieldOrderService]
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# The parameter-name fallback needs javac -parameters (compiled twice from the same source)
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javac -parameters : started, picked PaypalGateway
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javac (no flag) : FAILED NoUniqueBeanDefinitionException
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No qualifying bean of type 'com.ankurm.coredi.injection.PaymentGateway' available: expected single matching bean but found 2: stripeGateway,paypalGateway
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# Boot start-up failure for a constructor cycle: --spring.profiles.active=ctor-cycle
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ERROR --- o.s.b.d.LoggingFailureAnalysisReporter :
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***************************
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APPLICATION FAILED TO START
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***************************
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Description:
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The dependencies of some of the beans in the application context form a cycle:
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┌─────┐
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| bootCycles.CtorOne defined in URL [jar:nested:target/core-di-1.0.0.jar/!BOOT-INF/classes/!/com/ankurm/coredi/boot/BootCycles$CtorOne.class]
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↑ ↓
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| bootCycles.CtorTwo defined in URL [jar:nested:target/core-di-1.0.0.jar/!BOOT-INF/classes/!/com/ankurm/coredi/boot/BootCycles$CtorTwo.class]
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└─────┘
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Action:
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Relying upon circular references is discouraged and they are prohibited by default. Update your application to remove the dependency cycle between beans. As a last resort, it may be possible to break the cycle automatically by setting spring.main.allow-circular-references to true.
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# Boot start-up failure for a field-injection cycle: --spring.profiles.active=field-cycle
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ERROR --- o.s.b.d.LoggingFailureAnalysisReporter :
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***************************
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APPLICATION FAILED TO START
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***************************
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Description:
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The dependencies of some of the beans in the application context form a cycle:
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┌─────┐
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| bootCycles.FieldOne (field com.ankurm.coredi.boot.BootCycles$FieldTwo com.ankurm.coredi.boot.BootCycles$FieldOne.two)
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↑ ↓
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| bootCycles.FieldTwo (field com.ankurm.coredi.boot.BootCycles$FieldOne com.ankurm.coredi.boot.BootCycles$FieldTwo.one)
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└─────┘
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Action:
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Relying upon circular references is discouraged and they are prohibited by default. Update your application to remove the dependency cycle between beans. As a last resort, it may be possible to break the cycle automatically by setting spring.main.allow-circular-references to true.
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# Same field cycle with --spring.main.allow-circular-references=true
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STARTED. Beans from the cycle: [bootCycles.FieldOne, bootCycles.FieldTwo]
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# @Lazy on one constructor parameter: --spring.profiles.active=lazy-cycle
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STARTED. Beans from the cycle: [bootCycles.LazyOne, bootCycles.LazyTwo]
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# DefaultListableBeanFactory.determineAutowireCandidate, read with javap
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# jar: spring-beans-7.0.9.jar
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protected java.lang.String determineAutowireCandidate(java.util.Map<java.lang.String, java.lang.Object>, org.springframework.beans.factory.config.DependencyDescriptor);
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invokevirtual #1076 // Method org/springframework/beans/factory/config/DependencyDescriptor.getDependencyType:()Ljava/lang/Class;
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invokevirtual #1039 // Method determinePrimaryCandidate:(Ljava/util/Map;Ljava/lang/Class;)Ljava/lang/String;
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invokevirtual #1169 // Method org/springframework/beans/factory/config/DependencyDescriptor.getDependencyName:()Ljava/lang/String;
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invokeinterface #970, 1 // InterfaceMethod java/util/Map.keySet:()Ljava/util/Set;
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invokeinterface #397, 1 // InterfaceMethod java/util/Set.iterator:()Ljava/util/Iterator;
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invokeinterface #304, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z
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invokeinterface #309, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
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invokevirtual #1393 // Method matchesBeanName:(Ljava/lang/String;Ljava/lang/String;)Z
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invokevirtual #150 // Method getAutowireCandidateResolver:()Lorg/springframework/beans/factory/support/AutowireCandidateResolver;
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invokeinterface #1172, 2 // InterfaceMethod org/springframework/beans/factory/support/AutowireCandidateResolver.getSuggestedName:(Lorg/springframework/beans/factory/config/DependencyDescriptor;)Ljava/lang/String;
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invokeinterface #970, 1 // InterfaceMethod java/util/Map.keySet:()Ljava/util/Set;
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invokeinterface #397, 1 // InterfaceMethod java/util/Set.iterator:()Ljava/util/Iterator;
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invokeinterface #304, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z
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invokeinterface #309, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
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invokevirtual #1393 // Method matchesBeanName:(Ljava/lang/String;Ljava/lang/String;)Z
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invokevirtual #1043 // Method determineHighestPriorityCandidate:(Ljava/util/Map;Ljava/lang/Class;)Ljava/lang/String;
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invokevirtual #1046 // Method determineDefaultCandidate:(Ljava/util/Map;)Ljava/lang/String;
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invokeinterface #1230, 1 // InterfaceMethod java/util/Map.entrySet:()Ljava/util/Set;
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invokeinterface #397, 1 // InterfaceMethod java/util/Set.iterator:()Ljava/util/Iterator;
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invokeinterface #304, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z
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invokeinterface #309, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
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invokeinterface #1235, 1 // InterfaceMethod java/util/Map$Entry.getKey:()Ljava/lang/Object;
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invokeinterface #1238, 1 // InterfaceMethod java/util/Map$Entry.getValue:()Ljava/lang/Object;
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invokeinterface #1399, 2 // InterfaceMethod java/util/Map.containsValue:(Ljava/lang/Object;)Z
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# DefaultSingletonBeanRegistry: the fields that hold early references, read with javap
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# jar: spring-beans-7.0.9.jar
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private final java.util.Map<java.lang.String, java.lang.Object> singletonObjects;
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private final java.util.Map<java.lang.String, org.springframework.beans.factory.ObjectFactory<?>> singletonFactories;
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private final java.util.Map<java.lang.String, java.lang.Object> earlySingletonObjects;
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private final java.util.Set<java.lang.String> singletonsCurrentlyInCreation;
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# DefaultListableBeanFactory / AbstractAutowireCapableBeanFactory: the allow-circular-references switch
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private boolean allowCircularReferences;
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public void setAllowCircularReferences(boolean);
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public boolean isAllowCircularReferences();
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# org.springframework.lang.Nullable in spring-core-7.0.9.jar, read with javap -v
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#9 = Utf8 Deprecated
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#10 = Utf8 RuntimeVisibleAnnotations
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#22 = Utf8 Ljava/lang/Deprecated;
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#23 = Utf8 since
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Deprecated: true
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RuntimeVisibleAnnotations:
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java.lang.Deprecated(
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since="7.0"
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# spring-boot-starter-parent-4.1.1.pom: the compiler flag that parameter-name matching depends on
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111- <artifactId>maven-compiler-plugin</artifactId>
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112- <configuration>
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113: <parameters>true</parameters>
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114- </configuration>
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115- </plugin>
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