java 为什么我必须在@Constructor 注解的 Spring 配置类中有一个默认构造函数？
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Why I must have a default constructor in a Spring configuration class annoted by the @Constructor annotation?
提问by Java Surfer
I am studying for Spring Core certification and, on the provided study stuff, I have this question but I can't give an answer to it.
我正在学习 Spring Core 认证，在提供的学习资料上，我有这个问题，但我无法给出答案。
Why must you have to have a default constructor in your @Configuration annotated class?
为什么必须在 @Configuration 注释类中有一个默认构造函数？
I don't declare any constructor into my configuration classes annoted by the @Configurationannotation. The default constructor is the one inherited by the super class? or what? Why I must have a default constructor and I can't override it?
我没有在@Configuration注释所注释的配置类中声明任何构造函数。默认构造函数是超类继承的构造函数吗？要不然是啥？为什么我必须有一个默认构造函数而我不能覆盖它？
Tnx
田纳西州
回答by Vojtech Ruzicka
According to official spring javadoc, spring @Configuration annotated classes are required to have default no-arg constructor
根据官方 spring javadoc，spring @Configuration 注释类需要具有默认的无参数构造函数
@Configuration classes must have a default/no-arg constructor and may not use @Autowired constructor parameters. Any nested configuration classes must be static
@Configuration 类必须具有默认/无参数构造函数，并且不能使用 @Autowired 构造函数参数。任何嵌套的配置类都必须是静态的
The reason is that spring uses CGLIB to proxy @Configurationclasses and there is limitation in Spring, that classes proxied with CGLIB prior to version 4 are required to have default no-args constructor.
原因是 spring 使用CGLIB 来代理 @Configuration类，并且在 Spring 中存在限制，版本 4 之前用 CGLIB 代理的类需要具有默认的无参数构造函数。
Prior to Spring 4, CGLIB-based proxy classes require a default constructor. And this is not the limitation of CGLIB library, but Spring itself. Fortunately, as of Spring 4 this is no longer an issue. CGLIB-based proxy classes no longer require a default constructor.
在 Spring 4 之前，基于 CGLIB 的代理类需要一个默认构造函数。而这不是CGLIB库的限制，而是Spring本身的限制。幸运的是，从 Spring 4 开始，这不再是问题。基于 CGLIB 的代理类不再需要默认构造函数。
