Spring and Springboot annotations for DI

摘要: Basic annotations for DI

Basic annotaions to describe a bean:

| Annotation | Meaning                                             |
+------------+-----------------------------------------------------+
| @Component | generic stereotype for any Spring-managed component |
| @Repository| stereotype for persistence layer                    |
| @Service   | stereotype for service layer                        |
| @Controller| stereotype for presentation layer (spring-mvc)      |

The above annotations can have a optional element: String value. The value may indicate a suggestion for a logical component name, to be turned into a Spring bean in case of an autodetected component.

@Autowired

Marks a constructor, field, setter method or config method as to be autowired by Spring's dependency injection facilities.
If autowire for an interface, it will search for the implementation and inject it.

If there'are multiple implementation, you can use a Map to store the injected implementations.

If you have an interface named

Example

public interface Example {
}

And two implementations:

@Component("foo")
public class FooExample implements Example {
}
@Component("bar")
public class BarExample implements Example {
}

You can have a map of

Example

beans injected:

@Component
public class ExampleConsumer {
private final Map<String, Example> examples;
@Autowired
public ExampleConsumer(Map<String, Example> examples) {
this.examples = examples;
}
}

In this case the map will contain two entries:

"foo"

->

FooExample

instance

"bar"

->

BarExample

instance

@Qualifier

Use with @AutowiredThis annotation may be used on a field or parameter as a qualifier for candidate beans when autowiring. It may also be used to annotate other custom annotations that can then in turn be used as qualifiers.

spring @Autowired @Qualifier @Resource
http://ljhzzyx.blog.163.com/blog/static/38380312201371385956237/

@Autowired: inject by type defaultly;
@Resource： inject by name defaultly.
Spring Injection with @Resource, @Autowired and @Inject
http://blogs.sourceallies.com/2011/08/spring-injection-with-resource-and-autowired/

Annotations

Annotation	Package	Source
@Resource	javax.annotation	Java
@Inject	javax.inject	Java
@Qualifier	javax.inject	Java
@Autowired	org.springframework.bean.factory	Spring

For example:

package com.sourceallies.person; ... ("personBean") @Component @Qualifier("personBean") public class Person implements Party { }

In this test I use a ‘@Qualifier’ annotation to point to the qualified name of the ‘Person’ component.

@Resource @Qualifier("personBean") private Party party;

@Autowired @Qualifier("personBean") private Party party;

@Inject @Qualifier("personBean") private Party party;

All of these annotations inject the ‘Person’ bean.

To add List of Beans

In this test I inject a list of beans.

@Resource private List<Party> parties;

@Autowired private List<Party> parties;

@Inject private List<Party> parties;