112 lines
4.3 KiB
Plaintext
112 lines
4.3 KiB
Plaintext
Spring proxies are based on the *Proxy design pattern* and serve as intermediaries to other resources, offering extra features at a slight performance penalty.
|
|
For example, they facilitate lazy resource initialization and data caching.
|
|
|
|
The `@Configuration` annotation enables this mechanism by default through the `proxyBeanMethods` attribute set to `true`.
|
|
This ensures that the `@Bean` methods are proxied in order to enforce bean lifecycle behavior, e.g. to return shared singleton bean instances even in case of direct `@Bean` method calls in user code.
|
|
This functionality is achieved via method interception, implemented through a runtime-generated *https://github.com/cglib/cglib/wiki[CGLIB]* subclass.
|
|
|
|
== Why is this an issue?
|
|
|
|
When setting the `proxyBeanMethods` attribute to `false` the `@Bean` methods are not proxied and this is similar to removing the `@Configuration` stereotype.
|
|
In this scenario, `@Bean` methods within the `@Configuration` annotated class operate in https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/Bean.html[_lite mode_], resulting in a new bean creation each time the method is invoked.
|
|
|
|
For `Singleton` beans, this could cause unexpected outcomes as the bean is created multiple times instead of being created once and cached.
|
|
|
|
The rule raises an issue when the `proxyBeanMethods` attribute is set to `false` and the `@Bean` method of a `Singleton` bean is directly invoked in the `@Configuration` annotated class code.
|
|
|
|
== How to fix it
|
|
|
|
The issue can be fixed in the following ways:
|
|
|
|
* Not invoking the `@Bean` method directly, but rather injecting the bean in the context and using it, by means of `@Bean` https://docs.spring.io/spring-framework/reference/core/beans/java/bean-annotation.html#beans-java-dependencies[method parameters].
|
|
|
|
* If the performance penalty is negligible, consider not disabling the `proxyBeanMethods` attribute, so that the `@Bean` methods are proxied and the bean lifecycle is enforced.
|
|
|
|
=== Code examples
|
|
|
|
==== Noncompliant code example
|
|
|
|
In the example below, every instance of `PrototypeBean` will have a different instance of `SingletonBean`, as `singletonBean()` is called directly from `prototypeBean()`.
|
|
|
|
[source,java,diff-id=1,diff-type=noncompliant]
|
|
----
|
|
@Configuration(proxyBeanMethods = false)
|
|
class ConfigurationExample {
|
|
@Bean
|
|
public SingletonBean singletonBean() {
|
|
return new SingletonBean();
|
|
}
|
|
|
|
@Bean
|
|
@Scope("prototype")
|
|
public PrototypeBean prototypeBean() {
|
|
return new PrototypeBean(singletonBean()); // Noncompliant, the singletonBean is created every time a prototypeBean is created
|
|
}
|
|
|
|
class SingletonBean {
|
|
// ...
|
|
}
|
|
|
|
class PrototypeBean {
|
|
// ...
|
|
|
|
public PrototypeBean(SingletonBean singletonBean) {
|
|
// ...
|
|
}
|
|
|
|
// ...
|
|
}
|
|
}
|
|
----
|
|
|
|
==== Compliant solution
|
|
|
|
The compliant solution relies on the `@Bean` method parameter to automatically inject the `SingletonBean` from the `ApplicationContext`.
|
|
This way every instance of `PrototypeBean` will have the same instance of `SingletonBean`.
|
|
|
|
[source,java,diff-id=1,diff-type=compliant]
|
|
----
|
|
@Configuration(proxyBeanMethods = false)
|
|
class ConfigurationExample {
|
|
@Bean
|
|
public SingletonBean singletonBean() {
|
|
return new SingletonBean();
|
|
}
|
|
|
|
@Bean
|
|
@Scope("prototype")
|
|
public PrototypeBean prototypeBean(SingletonBean singletonBean) { // Compliant, the singletonBean is injected in the context and used by every prototypeBean
|
|
return new PrototypeBean(singletonBean);
|
|
}
|
|
|
|
class SingletonBean {
|
|
// ...
|
|
}
|
|
|
|
class PrototypeBean {
|
|
// ...
|
|
|
|
public PrototypeBean(SingletonBean singletonBean) {
|
|
// ...
|
|
}
|
|
|
|
// ...
|
|
}
|
|
}
|
|
----
|
|
|
|
== Resources
|
|
=== Documentation
|
|
|
|
* Spring - https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/Configuration.html#proxyBeanMethods()[Configuration - proxyBeanMethods]
|
|
|
|
* Spring - https://docs.spring.io/spring-framework/reference/core/aop/proxying.html[Proxying Mechanisms]
|
|
|
|
* Spring - https://docs.spring.io/spring-framework/reference/core/beans/java/bean-annotation.html#beans-java-dependencies[Bean Annotation - Dependencies]
|
|
|
|
* GitHub - https://github.com/cglib/cglib/wiki[CGLIB]
|
|
|
|
=== Articles & blog posts
|
|
|
|
* Medium - https://blog.devgenius.io/demystifying-proxy-in-spring-3ab536046b11[Demystifying Proxy in Spring]
|