How does autowired work

Remember that autowiring only works with Spring managed beans. Notice how we annotate our example classes with Component. This registers our class as a Spring bean. Spring can automatically figure this out at runtime and save you some boilerplate code. You can use the Autowired annotation on setters , properties , and constructors. When annotated with Autowired , the setter method will be called automatically when A is initialized.

It will pass the Spring managed B as an argument. Annotating setter methods with Autowired removes the need to explicitly set B when initializing A. Notice how no setter method is defined when we annotate a property with Autowired.

This is because Spring automatically sets property B with the Spring managed B dependency. Annotating properties with Autowired makes sense when you want to automatically set managed dependencies AFTER the class is initialized. Annotating constructors with Autowired will automatically inject Spring managed B when B is initialized.

This is preferable because managed dependencies are explicitly required for creating A. When the HelloWorld bean is initialized:. In the runtime, this annotation is available in metadata via reflection. In metadata structure below, the targetClass points to HelloWorld bean, and injectedElements points to the User class to be injected. In doResolveDependency, the definition for User bean is searched based on this. Once found, the found result is added to array candidateNames:.

Then the constructor of User bean class is called still triggered by getBean call , the user instance is created by calling constructor:. Finally the user reference is set to user attribute of HelloWorld instance via reflection. Here the variable bean in line points to HelloWorld instance, and value points to user instance.

Once field. The following example will work even if you do not pass any value for age property but still it will demand for name property. You can try this example yourself because this is similar to Required annotation example except that only Student. Spring Autowired Annotation Advertisements.

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