spring Spring在没有@Autowired注解的构造函数中注入依赖
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Spring injects dependencies in constructor without @Autowired annotation
提问by winter
I'm experimenting with examples from this official Spring tutorialsand there is a dependency on this code:
https://github.com/spring-guides/gs-async-method/tree/master/complete
我正在尝试使用这个官方 Spring教程中的示例，并且依赖于此代码：https:
//github.com/spring-guides/gs-async-method/tree/master/complete
If you look at the code on AppRunner.javaclass, I have 2 questions:
如果您查看AppRunner.java课堂上的代码，我有两个问题：
- When server is starting, if I put a breakpoint in this class's constructor, seems like in the constructor, the
GitHubLookupServiceis provided by spring, using the@Servicebean that was configured. BUT, there was no@Autowiredannotation on the constructor, so how in the world this constructor get called with the right dependency? It was supposed to benull.
- 当服务器启动时，如果我在这个类的构造函数中放置一个断点，看起来就像在构造函数中一样，
GitHubLookupService由 spring 提供，使用@Service配置的bean。但是，@Autowired构造函数上没有注释，那么这个构造函数到底是如何被调用的？它应该是null。
Is it an automatic assumption of Spring Boot?
Does Spring see "private field + constructor argument, and it assumes it should look for an appropriate bean?
Is it Spring Frameworkor Spring boot?
Am I missing something?
它是Spring Boot的自动假设吗？
Spring 是否看到“私有字段 + 构造函数参数，并假设它应该寻找合适的 bean？
它是Spring Framework还是Spring boot？
我错过了什么吗？
- As I remember, it was mendatory to provide default constructorto beans / service etc. How come this class (
AppRunner) doesn't have a default constructor? How does Spring knows that it should run the constructor with the argument? Is it because it is the only constructor?
- 我记得，必须为beans/service 等提供默认构造函数。为什么这个类 (
AppRunner) 没有默认构造函数？Spring 如何知道它应该使用参数运行构造函数？是因为它是唯一的构造函数吗？
回答by dunni
Starting with Spring 4.3, if a class, which is configured as a Spring bean, has only one constructor, the @Autowiredannotation can be omitted and Spring will use that constructor and inject all necessary dependencies.
从 Spring 4.3开始，如果配置为 Spring bean 的类只有一个构造函数，则@Autowired可以省略注释，Spring 将使用该构造函数并注入所有必要的依赖项。
Regarding the default constructor: You either need the default constructor, a constructor with the @Autowiredannotation when you have multiple constructors, or only one constructor in your class with or without the @Autowiredannotation.
关于默认构造函数：@Autowired当您有多个构造函数时，您要么需要默认构造函数，一个带有注释的构造函数，要么在您的类中只需要一个带有或不带有@Autowired注释的构造函数。
Read the @Autowiredchapter from the official Spring documentation for more information.
阅读@Autowired官方 Spring 文档中的章节以获取更多信息。
