How to stop a bean from instantiation after being registered in BeanDefinitionRegistry - spring

I need to de-register few beans from instantiation after being registered in BeanDefinitionRegistry. I need to do this on some condition.
If i write a code like this
#Component
public class DomainConfig implements BeanDefinitionRegistryPostProcessor {
#Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
beanDefinitionRegistry.removeBeanDefinition("createBlahExporter");
beanDefinitionRegistry.removeBeanDefinition("createBlahDataSource");
beanDefinitionRegistry.removeBeanDefinition("createBlahMonitorSettings");
beanDefinitionRegistry.removeBeanDefinition(("com.blah.BlahConfiguration));
}
}
I get the following error :
***************************
APPLICATION FAILED TO START
***************************
Description:
Field blahDataExporter in com.blah.BlahConfiguration required a bean of type
'com.blah.export.Exporter' that could not be found.
The injection point has the following annotations:
- #org.springframework.beans.factory.annotation.Autowired(required=true)
The following candidates were found but could not be injected:
- Bean method 'createProviderDumpExporter' in 'ProviderDumperConfig' not loaded because
#ConditionalOnProperty (providers.dump.local.enabled=true) found different value in property
'providers.dump.local.enabled'
Action:
Consider revisiting the entries above or defining a bean of type 'com.harman.inca.export.Exporter' in
your configuration.
Even after removing from here, someone, somewhere is holding the registered names. How do i remove the beans from registered set of beans.

You don’t specify what is ConfigFactory, but consider adding your own implementation of Conditional.
The custom conditional could read the definition from this configuration factory and the annotation bound to this custom conditional predicate could be put on the beans that you’ve planned to “de-register”. With this approach they won’t be registered in the application context so you won’t need to deregister them.
There are many tutorials on how to implement these custom conditions:
Schematically you should:
Implement the logic of the condition
class OnConfigFactoryCondition implements Condition {
#Override
public boolean matches(
ConditionContext context,
AnnotatedTypeMetadata metadata) {
// analyze the value from ConfigFactory whatever it is
Return true /false
}
}
Create a conditional annotation bound to your condition:
#Target({ElementType.TYPE, ElementType.METHOD})
#Retention(RetentionPolicy.RUNTIME)
#Conditional(OnConfigFactoryCondition.class)
public #interface ConditionalOnConfigFactory {
...
}
Then you can put this annotation next to #Component definition or #Bean if you’re using Java Config

Related

No qualifying bean of type [org.springframework.mail.javamail.JavaMailSender] while deploying service into PCF [duplicate]

Please explain the following about NoSuchBeanDefinitionException exception in Spring:
What does it mean?
Under what conditions will it be thrown?
How can I prevent it?
This post is designed to be a comprehensive Q&A about occurrences of NoSuchBeanDefinitionException in applications using Spring.
The javadoc of NoSuchBeanDefinitionException explains
Exception thrown when a BeanFactory is asked for a bean instance for
which it cannot find a definition. This may point to a non-existing
bean, a non-unique bean, or a manually registered singleton instance
without an associated bean definition.
A BeanFactory is basically the abstraction representing Spring's Inversion of Control container. It exposes beans internally and externally, to your application. When it cannot find or retrieve these beans, it throws a NoSuchBeanDefinitionException.
Below are simple reasons why a BeanFactory (or related classes) would not be able to find a bean and how you can make sure it does.
The bean doesn't exist, it wasn't registered
In the example below
#Configuration
public class Example {
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Example.class);
ctx.getBean(Foo.class);
}
}
class Foo {}
we haven't registered a bean definition for the type Foo either through a #Bean method, #Component scanning, an XML definition, or any other way. The BeanFactory managed by the AnnotationConfigApplicationContext therefore has no indication of where to get the bean requested by getBean(Foo.class). The snippet above throws
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [com.example.Foo] is defined
Similarly, the exception could have been thrown while trying to satisfy an #Autowired dependency. For example,
#Configuration
#ComponentScan
public class Example {
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Example.class);
}
}
#Component
class Foo { #Autowired Bar bar; }
class Bar { }
Here, a bean definition is registered for Foo through #ComponentScan. But Spring knows nothing of Bar. It therefore fails to find a corresponding bean while trying to autowire the bar field of the Foo bean instance. It throws (nested inside a UnsatisfiedDependencyException)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [com.example.Bar] found for dependency [com.example.Bar]:
expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true)}
There are multiple ways to register bean definitions.
#Bean method in a #Configuration class or <bean> in XML configuration
#Component (and its meta-annotations, eg. #Repository) through #ComponentScan or <context:component-scan ... /> in XML
Manually through GenericApplicationContext#registerBeanDefinition
Manually through BeanDefinitionRegistryPostProcessor
...and more.
Make sure the beans you expect are properly registered.
A common error is to register beans multiple times, ie. mixing the options above for the same type. For example, I might have
#Component
public class Foo {}
and an XML configuration with
<context:component-scan base-packages="com.example" />
<bean name="eg-different-name" class="com.example.Foo />
Such a configuration would register two beans of type Foo, one with name foo and another with name eg-different-name. Make sure you're not accidentally registering more beans than you wanted. Which leads us to...
If you're using both XML and annotation-based configurations, make sure you import one from the other. XML provides
<import resource=""/>
while Java provides the #ImportResource annotation.
Expected single matching bean, but found 2 (or more)
There are times when you need multiple beans for the same type (or interface). For example, your application may use two databases, a MySQL instance and an Oracle one. In such a case, you'd have two DataSource beans to manage connections to each one. For (simplified) example, the following
#Configuration
public class Example {
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Example.class);
System.out.println(ctx.getBean(DataSource.class));
}
#Bean(name = "mysql")
public DataSource mysql() { return new MySQL(); }
#Bean(name = "oracle")
public DataSource oracle() { return new Oracle(); }
}
interface DataSource{}
class MySQL implements DataSource {}
class Oracle implements DataSource {}
throws
Exception in thread "main" org.springframework.beans.factory.NoUniqueBeanDefinitionException:
No qualifying bean of type [com.example.DataSource] is defined:
expected single matching bean but found 2: oracle,mysql
because both beans registered through #Bean methods satisfied the requirement of BeanFactory#getBean(Class), ie. they both implement DataSource. In this example, Spring has no mechanism to differentiate or prioritize between the two. But such mechanisms exists.
You could use #Primary (and its equivalent in XML) as described in the documentation and in this post. With this change
#Bean(name = "mysql")
#Primary
public DataSource mysql() { return new MySQL(); }
the previous snippet would not throw the exception and would instead return the mysql bean.
You can also use #Qualifier (and its equivalent in XML) to have more control over the bean selection process, as described in the documentation. While #Autowired is primarily used to autowire by type, #Qualifier lets you autowire by name. For example,
#Bean(name = "mysql")
#Qualifier(value = "main")
public DataSource mysql() { return new MySQL(); }
could now be injected as
#Qualifier("main") // or #Qualifier("mysql"), to use the bean name
private DataSource dataSource;
without issue. #Resource is also an option.
Using wrong bean name
Just as there are multiple ways to register beans, there are also multiple ways to name them.
#Bean has name
The name of this bean, or if plural, aliases for this bean. If left
unspecified the name of the bean is the name of the annotated method.
If specified, the method name is ignored.
<bean> has the id attribute to represent the unique identifier for a bean and name can be used to create one or more aliases illegal in an (XML) id.
#Component and its meta annotations have value
The value may indicate a suggestion for a logical component name, to
be turned into a Spring bean in case of an autodetected component.
If that's left unspecified, a bean name is automatically generated for the annotated type, typically the lower camel case version of the type name. For example MyClassName becomes myClassName as its bean name. Bean names are case sensitive. Also note that wrong names/capitalization typically occur in beans referred to by string like #DependsOn("my BeanName") or XML config files.
#Qualifier, as mentioned earlier, lets you add more aliases to a bean.
Make sure you use the right name when referring to a bean.
More advanced cases
Profiles
Bean definition profiles allow you to register beans conditionally. #Profile, specifically,
Indicates that a component is eligible for registration when one or
more specified profiles are active.
A profile is a named logical grouping that may be activated
programmatically via
ConfigurableEnvironment.setActiveProfiles(java.lang.String...) or
declaratively by setting the spring.profiles.active property as a JVM
system property, as an environment variable, or as a Servlet context
parameter in web.xml for web applications. Profiles may also be
activated declaratively in integration tests via the #ActiveProfiles
annotation.
Consider this examples where the spring.profiles.active property is not set.
#Configuration
#ComponentScan
public class Example {
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Example.class);
System.out.println(Arrays.toString(ctx.getEnvironment().getActiveProfiles()));
System.out.println(ctx.getBean(Foo.class));
}
}
#Profile(value = "StackOverflow")
#Component
class Foo {
}
This will show no active profiles and throw a NoSuchBeanDefinitionException for a Foo bean. Since the StackOverflow profile wasn't active, the bean wasn't registered.
Instead, if I initialize the ApplicationContext while registering the appropriate profile
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.getEnvironment().setActiveProfiles("StackOverflow");
ctx.register(Example.class);
ctx.refresh();
the bean is registered and can be returned/injected.
AOP Proxies
Spring uses AOP proxies a lot to implement advanced behavior. Some examples include:
Transaction management with #Transactional
Caching with #Cacheable
Scheduling and asynchronous execution with #Async and #Scheduled
To achieve this, Spring has two options:
Use the JDK's Proxy class to create an instance of a dynamic class at runtime which only implements your bean's interfaces and delegates all method invocations to an actual bean instance.
Use CGLIB proxies to create an instance of a dynamic class at runtime which implements both interfaces and concrete types of your target bean and delegates all method invocations to an actual bean instance.
Take this example of JDK proxies (achieved through #EnableAsync's default proxyTargetClass of false)
#Configuration
#EnableAsync
public class Example {
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Example.class);
System.out.println(ctx.getBean(HttpClientImpl.class).getClass());
}
}
interface HttpClient {
void doGetAsync();
}
#Component
class HttpClientImpl implements HttpClient {
#Async
public void doGetAsync() {
System.out.println(Thread.currentThread());
}
}
Here, Spring attempts to find a bean of type HttpClientImpl which we expect to find because the type is clearly annotated with #Component. However, instead, we get an exception
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [com.example.HttpClientImpl] is defined
Spring wrapped the HttpClientImpl bean and exposed it through a Proxy object that only implements HttpClient. So you could retrieve it with
ctx.getBean(HttpClient.class) // returns a dynamic class: com.example.$Proxy33
// or
#Autowired private HttpClient httpClient;
It's always recommended to program to interfaces. When you can't, you can tell Spring to use CGLIB proxies. For example, with #EnableAsync, you can set proxyTargetClass to true. Similar annotations (EnableTransactionManagement, etc.) have similar attributes. XML will also have equivalent configuration options.
ApplicationContext Hierarchies - Spring MVC
Spring lets you build ApplicationContext instances with other ApplicationContext instances as parents, using ConfigurableApplicationContext#setParent(ApplicationContext). A child context will have access to beans in the parent context, but the opposite is not true. This post goes into detail about when this is useful, particularly in Spring MVC.
In a typical Spring MVC application, you define two contexts: one for the entire application (the root) and one specifically for the DispatcherServlet (routing, handler methods, controllers). You can get more details here:
Difference between applicationContext.xml and spring-servlet.xml in Spring Framework
It's also very well explained in the official documentation, here.
A common error in Spring MVC configurations is to declare the WebMVC configuration in the root context with #EnableWebMvc annotated #Configuration classes or <mvc:annotation-driven /> in XML, but the #Controller beans in the servlet context. Since the root context cannot reach into the servlet context to find any beans, no handlers are registered and all requests fail with 404s. You won't see a NoSuchBeanDefinitionException, but the effect is the same.
Make sure your beans are registered in the appropriate context, ie. where they can be found by the beans registered for WebMVC (HandlerMapping, HandlerAdapter, ViewResolver, ExceptionResolver, etc.). The best solution is to properly isolate beans. The DispatcherServlet is responsible for routing and handling requests so all related beans should go into its context. The ContextLoaderListener, which loads the root context, should initialize any beans the rest of your application needs: services, repositories, etc.
Arrays, collections, and maps
Beans of some known types are handled in special ways by Spring. For example, if you tried to inject an array of MovieCatalog into a field
#Autowired
private MovieCatalog[] movieCatalogs;
Spring will find all beans of type MovieCatalog, wrap them in an array, and inject that array. This is described in the Spring documentation discussing #Autowired. Similar behavior applies to Set, List, and Collection injection targets.
For a Map injection target, Spring will also behave this way if the key type is String. For example, if you have
#Autowired
private Map<String, MovieCatalog> movies;
Spring will find all beans of type MovieCatalog and add them as values to a Map, where the corresponding key will be their bean name.
As described previously, if no beans of the requested type are available, Spring will throw a NoSuchBeanDefinitionException. Sometimes, however, you just want to declare a bean of these collection types like
#Bean
public List<Foo> fooList() {
return Arrays.asList(new Foo());
}
and inject them
#Autowired
private List<Foo> foos;
In this example, Spring would fail with a NoSuchBeanDefinitionException because there are no Foo beans in your context. But you didn't want a Foo bean, you wanted a List<Foo> bean. Before Spring 4.3, you'd have to use #Resource
For beans that are themselves defined as a collection/map or array
type, #Resource is a fine solution, referring to the specific
collection or array bean by unique name. That said, as of 4.3,
collection/map and array types can be matched through Spring’s
#Autowired type matching algorithm as well, as long as the element
type information is preserved in #Bean return type signatures or
collection inheritance hierarchies. In this case, qualifier values can
be used to select among same-typed collections, as outlined in the
previous paragraph.
This works for constructor, setter, and field injection.
#Resource
private List<Foo> foos;
// or since 4.3
public Example(#Autowired List<Foo> foos) {}
However, it will fail for #Bean methods, ie.
#Bean
public Bar other(List<Foo> foos) {
new Bar(foos);
}
Here, Spring ignores any #Resource or #Autowired annotating the method, because it's a #Bean method, and therefore can't apply the behavior described in the documentation. However, you can use Spring Expression Language (SpEL) to refer to beans by their name. In the example above, you could use
#Bean
public Bar other(#Value("#{fooList}") List<Foo> foos) {
new Bar(foos);
}
to refer to the bean named fooList and inject that.

Spring annotation conditionalOnBean not working

I defined a class with annotation Configuration
#Configuration
#AutoConfigureAfter(EndpointAutoConfiguration.class)
public class EndpointConfiguration {
#Resource
private MetricsEndpoint metricsEndpoint;
#Bean
public MetricsFormatEndpoint metricsFormatEndpoint() {
return new MetricsFormatEndpoint(metricsEndpoint);
}
}
the MetricsFormatEndpoint works well.
but I use the annotation conditionalOnBean, it doesn't work at all.
#Bean
#ConditionalOnBean(MetricsEndpoint.class)
public MetricsFormatEndpoint metricsFormatEndpoint() {
return new MetricsFormatEndpoint(metricsEndpoint);
}
see the localhost:8080/beans,the spring applicationContext has the bean 'metricsEndpoint',
{"bean":"metricsEndpoint","scope":"singleton",
"type":"org.springframework.boot.actuate.endpoint.MetricsEndpoint",
"resource":"class path resource
[org/springframework/boot/actuate/autoconfigure/EndpointAutoConfiguration.class]",
"dependencies":[]}
I read the document of the annotation #ConditionalOnBean, it says The class type of bean that should be checked. The condition matches when any of the classes specified is contained in the {#link ApplicationContext}.
who can tell me why
The javadoc for #ConditionalOnBean describes it as:
Conditional that only matches when the specified bean classes and/or names are already contained in the BeanFactory.
In this case, the key part is "already contained in the BeanFactory". Your own configuration classes are considered before any auto-configuration classes. This means that the auto-configuration of the MetricsEndpoint bean hasn't happened by the time that your own configuration is checking for its existence and, as a result, your MetricsFormatEndpoint bean isn't created.
One approach to take would be to create your own auto-configuration class for your MetricsFormatEndpoint bean and annotate it with #AutoConfigureAfter(EndpointAutoConfiguration.class). That will ensure that its conditions are evaluated after the MetricsEndpoint bean has been defined.
ConditionalOnClass worked as well.
Javadoc said that AutoConfigureAfter should be applied after other specified auto-configuration classes.
And ConditionalOnClass matches when the specified classes are on the classpath. I think it's properer

How to activate lazy instantiation for all spring beans

in a project there is several applicationContext.xml file. there isn't any lazy definition for defined beans. then all singleton scoped beans instantiate in runtime.
Oops. it's very bad for development phase. near 2 minutes take time that server startup. Now i will know is there any solution for active lazy-instantiate in spring. For example a configuration in web.xml that set bean default-lazy-init="true".
Implement a custom BeanFactoryPostProcessor that sets lazy to true, e.g.:
public class BeanFactoryPostProcessorImpl implements BeanFactoryPostProcessor {
#Override
public void postProcessBeanFactory(final ConfigurableListableBeanFactory beanFactory) throws BeansException {
for (String beanName : beanFactory.getBeanDefinitionNames()) {
beanFactory.getBeanDefinition(beanName).setLazyInit(true);
}
}
}
To get it working, all you need to do then is to add it to your application context as a standard bean:
An ApplicationContext will detect any beans which are deployed into it
which implement the BeanFactoryPostProcessor interface, and
automatically use them as bean factory post-processors, at the
appropriate time. Nothing else needs to be done other than deploying
these post-processor in a similar fashion to any other bean.
In applicationContext.xml files you can add default-lazy-init attribute with value true on the <beans/> element. See reference.

How to do conditional auto-wiring in Spring?

Has anyone tried to auto-wire different beans into a Spring-managed bean based on a condition? For e.g. if some condition is met, inject class A, else B? I saw in one of the Google search results that it is possible with SpEL (Spring Expression Language), but could not locate a working example.
There are multiple ways to achieve this. Mostly this depends on the conditioning you want to perform.
Factory bean
You can implement simple factory bean to do the conditional wiring. Such factory bean can contain complex conditioning logic:
public MyBeanFactoryBean implements FactoryBean<MyBean> {
// Using app context instead of bean references so that the unused
// dependency can be left uninitialized if it is lazily initialized
#Autowired
private ApplicationContext applicationContext;
public MyBean getObject() {
MyBean myBean = new MyBean();
if (true /* some condition */) {
myBean.setDependency(applicationContext.getBean(DependencyX.class));
} else {
myBean.setDependency(applicationContext.getBean(DependencyY.class));
}
return myBean;
}
// Implementation of isSingleton => false and getObjectType
}
Maybe a bit better approach is if you use factory bean to create the dependency bean in case you want to have only one such bean in your application context:
public MyDependencyFactoryBean implements FactoryBean<MyDependency> {
public MyDependency getObject() {
if (true /* some condition */) {
return new MyDependencyX();
} else {
return new MyDependencyY();
}
}
// Implementation of isSingleton => false and getObjectType
}
SpEL
With SpEL there are many possibilities. Most common are system property based conditions:
<bean class="com.example.MyBean">
<property name="dependency" value="#{systemProperties['foo'] == 'bar' ? dependencyX : dependencyY}" />
</bean>
Property placeholder
You can have property placeholder resolve your bean reference. The dependency name can be part of the application configuration.
<bean class="com.example.MyBean">
<property name="dependency" ref="${dependencyName}" />
</bean>
Spring profiles
Usually the condition you want to evaluate means that a whole set of beans should or should not be registered. Spring profiles can be used for this:
<!-- Default dependency which is referred by myBean -->
<bean id="dependency" class="com.example.DependencyX" />
<beans profile="myProfile">
<!-- Override `dependency` definition if myProfile is active -->
<bean id="dependency" class="com.example.DependencyY" />
</beans>
Other methods can mark the bean definition as lazy-init="true", but the definition will be still registered inside application context (and making your life harder when using unqualified autowiring). You can also use profiles with #Component based beans via #Profile annotation.
Check ApplicationContextInitialier (or this example) to see how you can activate profiles programatically (i.e. based on your condition).
Java config
This is why Java based config is being so popular as you can do:
#Bean
public MyBean myBean() {
MyBean myBean = new MyBean();
if (true /* some condition */) {
myBean.setDependency(dependencyX());
} else {
myBean.setDependency(dependencyY());
}
return myBean;
}
Of course you can use more or less all configuration methods in the java based config as well (via #Profile, #Value or #Qualifier + #Autowired).
Post processor
Spring offers numerous hook points and SPIs, where you can participate in the application context life-cycle. This section requires a bit more knowledge of Spring's inner workings.
BeanFactoryPostProcessors can read and alter bean definitions (e.g. property placeholder ${} resolution is implemented this way).
BeanPostProcessors can process bean instances. It is possible to check freshly created bean and play with it (e.g. #Scheduled annotation processing is implemented this way).
MergedBeanDefinitionPostProcessor is extension of bean post processor and can alter the bean definition just before it is being instantiated (#Autowired annotation processing is implemented this way).
UPDATE Oct 2015
Spring 4 has added a new method how to do conditional bean registration via #Conditional annotation. That is worth checking as well.
Of course there are numerous other ways with Spring Boot alone via its #ConditionalOn*.
Also note that both #Import and #ComponentScan (and their XML counterparts) undergo property resolution (i.e. you can use ${}).
I had a case where I needed to inject different beans depending on property: "my.property". In my case this solution was successful:
<property name="name" ref="#{ ${my.property:false}==true ? 'bean1' : 'bean2' }"/>
I needed to add the apostrophes around bean names in order to make it work.
In your #Configuration class declare a bean to be conditionally created:
#Bean
#Conditional(CustomFeatureCondition.class)
public Stuff stuff() {
return new Stuff ();
}
In the place of using just #Autowire it with required = false option:
#Component
#Setter(onMethod_ = #Autowired(required = false))
public class AnotherStuff {
private Stuff stuff;
// do stuff here
}
This way you'll get Stuff bean if it exists in the context and stuff = null if it doesn't.
I suppose the simpest way:
#Autowired #Lazy
protected A a;
#Autowired #Lazy
protected B b;
void do(){
if(...) { // any condition
// use a
} else {
// use b
}
}
In case you do not declare nessassary bean, Spring throws at runtime NoSuchBeanDefinitionException

Autowiring doubts in spring?

After going thru autowiring concept
i have got some questions. These are:-
If i need to autowire below class byType or byName , is it mandatory to have setStudent() method in class College?
public class College {
private Student student1;
private String registration1;
}
<bean id="student1" class="Student"/> - in case of byname it will look into id attribute and in case of bytype it will look for class attribute in above
Stetement. Right? If incase it finds two bean dean tags for the same type it will throw fatal error in case of bytype. Correct?
autodetect Scenario chooses constructor or byType through introspection of the bean class. If a default constructor is found, the byType mode
will be applied.
My question here if default constructor is not found and constructor with argument is found then autowire by constructor
will be applied. Correct?
Do we need to specify #Autowired somewhere in College to apply the autowiring. As i can see this in this example
but nothing is specified here
1), 4) There are two separate ways of autowiring in Spring: XML-based and annotaion-based.
XML-based autowiring is activated from XML config, as described here. In the end, it will call setter method, so setStudent() method is required here.
Annonation-based autowiring, on the other hand, is performed via reflection magic. It attempts to fill everything you mark with #Autowired annotation. In fact, it can set private field with no accessors, as in
public class Foo {
#Autowired private Thingy thing; // No getThing or setThing methods
private void doStuff() {
// thing is usable here
}
}
For #Autowired annotaion to work, you will need to define corresponding bean post-processor; it is done by adding the following line to xml config:
<context:annotation-config/>
Note, that these two autowiring methods are independant, and it is possible(but not recommended) to use them simultaneously. In that case, xml autowiring will override annotations.
2) In general, autowiring will fail, if it cannot find one and only one candidate for injection. So, in your case, it will fail with exception upon container creation. There are some fallback quirks, but in general it works reliably.
3) Yes, documentaion says so.
About byName and byType autowiring. While byName autowiring simply tries to match bean name (can be specified with id attribute), byType is a bit more complex than class attribute lookup. It searches beans by type, and it will match interfaces. Example:
public interface SomeService {
void doStuff();
}
public class SomeServiceImpl implements SomeService {
#Override public void doStuff() {
// Implementation
};
}
public class ServiceUser {
#Autowired
private SomeService someService; // SomeServiceImpl instance goes here
}
P.S. You are referencing two different versions of Spring in your question, 2.5 and 3.0. Autowiring behavior is same in both.
In Addition if you are using #Autwired annotation you need to mark the classes as candidates for autowiring. It should be done by using one of these annotations:
#Repository
#Service
#Component
#Controller
and of cause you can configure it in different scopes:
#Scope("prototype")
#Repository
public class MovieFinderImpl implements MovieFinder {
// ...
}
Hope it makes it more clear.

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