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This article mainly explains the "SpringBoot prohibition of circular dependency case analysis", the content of the article is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in depth, together to study and learn "SpringBoot prohibition circular dependency case analysis"!

Foreword:

The Bean management of Spring has always been a favorite thing in the whole system. In particular, the circular dependence of Bean is one of the most popular 2B knowledge points for many interviewers.

But in fact, there is a circular dependency on Bean in the project, which is a sign of poor code quality. Most people rely on the frame layer to wipe their buttocks, resulting in the design of the whole code getting worse and worse, and finally use some tricks to make up for the mistakes made.

Fortunately, SpringBoot finally couldn't stand this abuse and disabled circular dependency by default!

Starting with version 2.6, SpringBoot will refuse to start if there are still circular dependencies in your project!

Verify small snippets of code:

To verify this function, we only need two small pieces of code.

CircularDependencyA.java

@ Component@RequiredArgsConstructorpublic class CircularDependencyA {private final CircularDependencyB circB;}

CircularDependencyB.java

@ Component@RequiredArgsConstructorpublic class CircularDependencyB {private final CircularDependencyA circA;}

The RequiredArgsConstructor annotation, which is included in the lombok package, is used to implement simple constructor injection. As expected, when we started the code, we reported an error.

The error is as follows:

The dependencies of some of the beans in the application context form a cycle:

┌─┐

| | circularDependencyA defined in file [cir/CircularDependencyA.class] |

↑ ↓

| | circularDependencyB defined in file [cir/CircularDependencyB.class] |

└─┘

Action:

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.

Of course, some people have grown up, circular dependencies are everywhere, and changing the code is becoming more and more unrealistic. You can also enable circular dependency by configuring parameters in yaml.

Spring.main.allow-circular-references=true

It seems that SpringBoot's ability to tolerate evil forces is not firm enough.

There is more than one way to bypass the interception of SpringBoot, such as delayed initialization with the @ Lazy annotation. But all these are palliative rather than permanent, failing to live up to the painstaking efforts of SpringBoot.

Do the right thing:

In fact, we have been looking down the code, we will find that this switch is actually a function of Spring.

AbstractAutowireCapableBeanFactory#allowCircularReferences/** Whether to automatically try to resolve circular references between beans. * / private boolean allowCircularReferences = true

For a long time, the value of SpringBoot defaults to true. But this connivance has led to a flood of low-quality code, so much so that new employees have been wiping their buttocks.

Setting this value to false by default is the right thing to do. At the very least, when an engineer writes low-quality code, he can know what he is doing, rather than putting off the hidden dangers step by step and allowing the code to corrupt.

Thank you for your reading, the above is the content of "SpringBoot prohibition of circular dependence case analysis". After the study of this article, I believe you have a deeper understanding of the problem of SpringBoot prohibition of circular dependence case analysis, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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