Background: I am working in a project named com.x.myproject. I have the dependency of two other packages com.x.document and com.x.library. both packages have the same class with name QueueHelper.
Now, In my project, I have to scan one other package com.x.security which internally scans com.x, something like that:
#SpringBootApplication
#ComponentScan(basePackages = {"com.x"})
#EnableCaching
public class Security {
.......
}
in com.x.myproject
#SpringBootApplication
#ComponentScan(basePackages = {"com.x.myproject","com.x.security"}, excludeFilters={
#ComponentScan.Filter(type=FilterType.REGEX, pattern="com.x.document.*"),
#ComponentScan.Filter(type=FilterType.REGEX, pattern="com.x.library.*")})
public class MyProject{
.......
}
It all works fine when I use excludefilters in com.x.security but I want to use it in com.x.myproject
The exception which I got is
Annotation-specified bean name 'queueHelper' for bean class [com.x.library.utils.QueueHelper] conflicts with existing, non-compatible bean definition of same name and class [com.x.document.utils.QueueHelper]
Three answers come to my mind:
Give a different names to com.x.library.utils.QueueHelper and com.x.document.utils.QueueHelper via the #Component annotation. Spring will use the simple class name by default for naming the beans. You can annotate one with #Component('libraryQueueHelper') and the other with #Component('documentQueueHelper'). However, now you'll have to give a #Qualifier(<name>) in each place you're autowiring these beans.
Exclude them in your module, like you do in your question and then change their names using #Bean annotated methods within a #Configuration. When using in the third module, you'll need to use a #Qualifier to autowire the correct bean.
Rename the classes. This is the best solution in this case, but since you asked this question, I guess it's not viable.
I'm trying to understand the transition from using xml annotation to java based annotation in Spring. I have these definitions
<context:annotation-config>: Scanning and activating annotations for already registered beans in spring config xml.
<context:component-scan>: Bean registration + <context:annotation-config>
is #Configuration and is #ComponentScan.
If lets say I declare all my beans with #Component (disregard first the more specific ones like #Repository, #Service etc) annotation and make sure that the packages are getting scanned by the #ComponentScan annotation, what is a particular use case where I will still annotate my class with both #Configuration together with #ComponentScan?
I ask this question because sometimes I see classes annotated with both #Configuration and #ComponentScan at the same time.
First read the following carefully:
Difference between <context:annotation-config> vs <context:component-scan>
Thus <context:component-scan> does the scan job and the same job than <context:annotation-config> does, it means work around with the DI annotations
Then now consider:
<context:component-scan> equivalent to #ComponentScan
<context:annotation-config> no equivalent for annotation.
what is a particular use case where I will still annotate my class
with both #Configuration together with #ComponentScan?
#Configuration is used to define beans about Infastructure such as Database, JMS etc...
Yes, a class can use both, It could be used for example for MVC Infrastructure #Configuration such as:
#EnableWebMvc
#Configuration
#ComponentScan("com.manuel.jordan.controller", "com.manuel.jordan.rest")
public class WebMvcConfig extends WebMvcConfigurerAdapter {
Thus from that class your are configuring MVC and indicating only to scan the MVC classes created by you for the "web side", such as: #Controller, #RestController.
This really depends on your likings and coding style. Documentation states:
Either basePackageClasses() or basePackages() (or its alias value()) may be specified to define specific packages to scan. If specific packages are not defined, scanning will occur from the package of the class that declares this annotation.
So every time you see just #ComponentScan annotation this means that all sub-packages should be scanned. This is a reasonable approach to take with package per feature layout: when you have a #Configuration class for your feature and all #Components related to the feature in sub-packages.
I am trying to understand how beans that we make using #Configuration tends to override the beans that are generated by SpringBoot by default. I have been working on a project where in many cases we create beans for things like ZuulConfigs and the assumption is, whatever we are making shall take precedence over the default generated bean. I have been trying to figure this out but can't. Basically,
Is Spring achieving this via some custom class loader
If not how is this precedence working. Can I give some precedence in similar manner to my beans
Can I generate similar hierarchy in my project,if so how
The help is highly appreciated
Spring AutoConfiguration is used to provide a basic configuration if certain classes are in the classpath or not.
If you want to configure the order in which beans are instantiated by spring you can use
#DependsOn("A")
public class B {
...
}
This would create bean "A", then "B". Hence you can order the configuration depending upon the beans need first to be done. Anyways Spring automatically detects the dependencies by analyzing the bean classes.
for more help check this question
Spring Boot AutoConfiguration Order
Alternative :
There is also "#AutoConfigureOrder" annotation(where you can prioritise the configuration), you can have a look in the code for deeper understanding.
Documentation of AutoConfiguration is here
First of all, class loading and bean creation are two different things. We don't need to create a bean to load a class, however, a class has to be loaded in order to create a bean.
Now, coming back to Spring's example, Spring looks into all the packages configured by #componentScan and creates beans of all the classes annotated with #Bean, #Configuration and/or #Component. Spring's container keeps track of all the beans created and hence, when it encounters user defined bean with same name and class type as default bean, it replaces the original definition with user defined one (e.g. we can create our custom #ObjectMapper to override Spring boot's own instance). You can also use #Primary annotation to make you bean take precedence if another definition with same class exists (documentation here).
Below are the answers for your questions:
Spring uses reflection to load the classes and create instances. Although you can load the classes with your custom class loader (more on that here), you don't need to worry about it for #Configuration.
Yes, you can use #Primary annotation to give your bean a precedence. You can also use #Order(here) to define the creation order for your beans.
With #Primary, #Order and #Qualifier annotation you can define your own hierarchy for bean creation.
Can I give some precedence in similar manner to my beans
Yes.
A) To define a specific order your Configuration classes will be handled (by the way, a Configuration class does not have to be annotated with #Configuration (so-called full definition), but it's enough to be annotated with #Component, #ComponentScan, #Import, #ImportResource or just have a method annotated with #Bean - so-called lite definition), you should
1) add your Configuration Candidates to your SpringApplication's primarySource, for example, in your main method like that
SpringApplication.run(
new Class[]{YourSpringBootApplication.class, Config1.class, Config2.class, ...},
args);
2) and annotate each of your Configuration Candidates with #Order annotation, any other ordering means like Ordered interface, #DependsOn etc will be ignored by ConfigurationClassPostProcessor, the order in the primarySource array will also be ignored.
Then ConfigurationClassPostProcessor will sort your Configuration Candidates and handle them according the #Order annotation value you specified.
B) The precedence can also be achieved by defining your own AutoConfiguration classes. Although both Configuration and AutoConfiguration are handled by the same ConfigurationClassPostProcessor, they are essentially distinctive machineries. To do so
1) define in your classpath /META-INF/spring.factories file and put in the EnableAutoConfiguration section of it your AutoConfiguration classes like that
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
your.package.AutoConfig1,your.package.AutoConfig2
2) and annotate your AutoConfiguration classes with #AutoConfigureOrder, #AutoConfigureAfter, or #AutoConfigureAfter annotations, any other ordering means again will be ignored.
Like #Strelok pointed out, AutoConfiguration classes, your own and provided e.g. by spring-boot-autoconfigure library alike, will be added to the end of the list of Configuration Candidates.
Remember, however, that the order the Configuration Candidates will be handled by ConfigurationClassPostProcessor does not necessarily coincide with the order the beans defined by the Configuration classes will be created. For example, you might define your Configuration class that overrides TomcatServletWebServerFactory to make your own customization of Tomcat web server like
#Configuration
public class EmbeddedTomcatConfig {
#Bean
public TomcatServletWebServerFactory containerFactory() {
...
return customizedTomcatWebServerFactory;
}
but this method will be called right at the moment when your Spring Boot application decides to create a Web server, regardless of how you defined the precedence for your EmbeddedTomcatConfig Configuration class.
Is Spring achieving this via some custom class loader
There is no need to. Although you could, as always with Spring, define your own ClassLoader for BeanFactory, standard ClassLoader is good enough if everything you need for Configuration in your application is available in the classpath. Please notice, that at first phase ConfigurationClassPostProcessor does not load (i.e. does not resolve) the Configuration candidates classes (otherwise, most of the classes in spring-boot-autoconfigure library will fail to load). Instead it analyzes their annotations with bytecode analyzer, ASM by default. For that purpose, it is just enough to get a binary form, a byte array, of a class to feed it to bytecode analyzer.
Just know this: Spring Boot (specifically) auto configuration classes are always configured last. After all user beans have been created. Spring Boot auto configuration classes almost always use the #ConditionalXXXX annotations to make sure that any beans of the same type/name and other conditions that are configured in your application will take precedence over the Spring Boot auto-configured beans.
If you want your #Component to take precedence over other #Component while scanning all the components by spring, use #Order(Ordered.LOWEST_PRECEDENCE) i.e. the max value to load your component over other.
#Primary is used to give your bean a default preference, we can override the default preference using #Qualifier
I have a problem integrating external library with Spring. It contains a class annotated with #Configuration and it has a method annotated with #Bean. I don't want it to be instantiated (it's not needed and introduces dependency on a Spring Boot, which I don't use.
Unfortunately this #Configuration-annotated class is used elsewhere in the library (required by the class type, not interface type, so I need to instantiate exactly this class).
I exluded it's package from auto-scanning, I'm not importing it directly. Just constructing it by hand and registering in own configuration as a bean.
So, to make story short - I need to register a bean, but exclude it from annotation scnanning (to not process it's #Bean-annotated methods). Any way for doing this?
If you mean you have library in your maven, gradle, then you can exclude spring beans from being initialized. I found exclude #Component from #ComponentScan
#Configuration
#EnableSpringConfigured
#ComponentScan(
basePackages = {"com.example"},
excludeFilters = {
#ComponentScan.Filter(
type = FilterType.ASSIGNABLE_TYPE,
value = Foo.class)})
public class MySpringConfiguration {
}
And if you do not want to include transitive dependencies, thus you do not want your dependency to add other dependencies it uses, you have to exclude them from your dependncy (in maven, gradle).
Right now i have a inherited project that is using annotation based spring dependency injection. So all classes are simply marked with #Component (or specific stereoTypes like #service, #Repository,#RestController, etc). This makes it a little hard to find where the dependency is located and i was thinking to change it so that each package has its own dependency configuration and then add each package to the #ComponentScan afterwards.
So for example if i had a package called com.mycoolpackage.login and mycoolpackage.networking
then i'd have a Spring configuration like this in first package:
#Configuration
public class LoginDIConfig {
#Bean
public LoginServiceImpl loginServiceImpl() {
return new LoginServiceImpl();
}
}
and in the second package i'd have the following:
#Configuration
public class NetworkDIConfig {
#Bean
public NetworkServiceImpl networkServiceImpl() {
return new NetworkServiceImpl();
}
}
and my#ComponentScan would look like this:
#ComponentScan(basePackages = {"com.mycoolpackage.login","com.mycoolpackage.network"})
So i have two questions about this approach.
How can i use a #Service annotation instead of bean here
Do you think this design is more easier as it tells you what your package dependencies are very easily instead of hunting them
down.
If you want to configure some been properties manually then you should go for above configuration else you should stick with exiting one.
This makes it a little hard to find where the dependency is located
#Autowire Or #Inject annotation will always lead you to dependency class.