Both @Autowired (or @Inject) and @Resource work equally well. But there is a conceptual difference or a difference in the meaning @Resource means get me a known resource by name. The name is extracted from the name of the annotated setter or field, or it is taken from the name-Parameter. @Inject or @Autowired try to … Read more
Injection types There are three options for how dependencies can be injected into a bean: Through a constructor Through setters or other methods Through reflection, directly into fields You are using option 3. That is what is happening when you use @Autowired directly on your field. Injection guidelines A general guideline, which is recommended by … Read more
Yes, option B (which is called constructor injection) is actually recommended over field injection, and has several advantages: the dependencies are clearly identified. There is no way to forget one when testing, or instantiating the object in any other circumstance (like creating the bean instance explicitly in a config class) the dependencies can be final, … Read more
First, and most important – all Spring beans are managed – they “live” inside a container, called “application context”. Second, each application has an entry point to that context. Web applications have a Servlet, JSF uses a el-resolver, etc. Also, there is a place where the application context is bootstrapped and all beans – autowired. … Read more
@Component Preferable for component scanning and automatic wiring. When should you use @Bean? Sometimes automatic configuration is not an option. When? Let’s imagine that you want to wire components from 3rd-party libraries (you don’t have the source code so you can’t annotate its classes with @Component), so automatic configuration is not possible. The @Bean annotation … Read more
In short, no. You cannot autowire or manually wire static fields in Spring. You’ll have to write your own logic to do this.
TL;DR The @Autowired annotation spares you the need to do the wiring by yourself in the XML file (or any other way) and just finds for you what needs to be injected where and does that for you. Full explanation The @Autowired annotation allows you to skip configurations elsewhere of what to inject and just … Read more
The field annotated @Autowired is null because Spring doesn’t know about the copy of MileageFeeCalculator that you created with new and didn’t know to autowire it. The Spring Inversion of Control (IoC) container has three main logical components: a registry (called the ApplicationContext) of components (beans) that are available to be used by the application, … Read more