Spring如何在Java应用程序中自动实现依赖注入

Question

最近开发一个Java应用程序，希望能使用Spring来实现依赖注入。

在Web应用程序中，可以在web.xml文件中配置listener来自动实现注入。

在Java Application中，可以通过如下的方式来加载Spring：

ClassPathXmlApplicationContext ctx = new FileSystemXMLApplicationContext("beans.xml");
Hello hello = ctx.getBeans("hello");

但这样的一个问题是，在每次使用一个bean时，都需要显示调用一次getBeans。

不知有什么好的方法，能够让Spring自动加载对象，而不需要显式调用getBeans?
更多 0

Answer 1

Write two more lines following your example.

public class Main{

  public static void main(String[] args){
    ClassPathXmlApplicationContext ctx = new FileSystemXMLApplicationContext("beans.xml");
    Hello hello = ctx.getBeans("hello");
    hello.say();
  }
}

class Hello {
  @Autowired
  private DbUtil db;

  public void say(){
    System.out.println(db.getWelcomeInfo());
  }
}

The layer that initially handles requests in the web project still needs to be generated through getBeans(). It's just that this step is done by tomcat/strtus/springMVC.
Spring will automatically inject classes managed by it. However, the main class started by your program is not generated by Spring management.

Answer 2

You need Autowired

Answer 3

To use Spring's dependency injection, you must first obtain the bean from Spring, so as to ensure that the bean's dependencies have been injected. If you create a new object yourself, how can Spring inject it for you?

You can encapsulate the getBeans method yourself

Answer 4

You have to treat your HELLO as a member variable, and then go to @autowired or @Resourse

Answer 5

Dependency injection is nothing more than two steps:

1. declare bean

2. Inject beans

How to declare a bean:

1. In xml

2. Add @Component, @Service, etc. to the class

3. Write the method with @Bean in the class with @Configuration

How to inject beans:

1. In xml

2. Annotations like @Autowire

It may not be all mentioned, but these should be the commonly used ones. For details, please refer to the spring documentation and ioc part

Let’s ask a question

1. There is no need to configure listener in web.xml in web applications (the prerequisite is servlet3.0+, such as tomcat7+)

2. For Java Application, why not try Spring boot?

Answer 6

Recommended topic owner can take a look @Chachage Servlet 3 + Spring MVC zero configuration: remove all xml