@Autowired还可以注入List和Map(@LoadBalanced)

@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();

这个restTemplates能够将所有标注了@LoadBalanced的RestTemplate自动注入进来呢？这就要说说@Autowired注解和@Qualifier这两个注解了。
大家日常使用很多都是用@Autowired来注入一个bean,其实@Autowired还可以注入List和Map,比如我定义两Bean:

@Bean("user1")
User user1() {
return new User("1", "a");
}
@Bean("user2"))
User user2() {
return new User("2", "b");
}

然后我写一个Controller:

import com.example.demo.domain.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
@RestController
public class MyController {
    @Autowired(required = false)
    private List<User> users = Collections.emptyList();
    @Autowired(required = false)
    private Map<String,User> userMap = new HashMap<>();
    @RequestMapping("/list")
    public Object listUsers() {
        return users;
    }
    @RequestMapping("/map")
    public Object mapUsers() {
        return userMap;
    }
}

在controller中通过:

@Autowired(required = false)
private List<User> users = Collections.emptyList();
@Autowired(required = false)
private Map<String,User> userMap = new HashMap<>();

就可以自动将两个bean注入进来，当注入map的时候，map的key必须是String类型，然后bean name将作为map的key,本例，map中将有两个key分别为user1和user2,value分别为对应的User Bean实例。
访问http://localhost:8080/map:

{
"user1": {
"id": "1",
"name": "a"
},
"user2": {
"id": "2",
"name": "b"
}
}

访问http://localhost:8080/list:

[
{
"id": "1",
"name": "a"
},
{
"id": "2",
"name": "b"
}
]

然后我们给user1和user2分别打上@Qualifier修饰符:

@Bean("user1")
@Qualifier("valid")
User user1() {
return new User("1", "a");
}
@Bean("user2")
@Qualifier("invalid")
User user2() {
return new User("2", "b");
}

然后将controller中的user list 和user map分别也打上@Qualifier修饰符:

import com.example.demo.domain.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
@RestController
public class MyController {
    @Autowired(required = false)
    @Qualifier("valid")
    private List<User> users = Collections.emptyList();
    @Autowired(required = false)
    @Qualifier("invalid")
    private Map<String,User> userMap = new HashMap<>();
    @RequestMapping("/list")
    public Object listUsers() {
        return users;
    }
    @RequestMapping("/map")
    public Object mapUsers() {
        return userMap;
    }
}

那么所有标注了@Qualifier(“valid”)的user bean都会自动注入到List users中去(本例是user1)，所有标注了@Qualifier(“invalid”)的user bean都会自动注入到Map userMap中去（本例是user2），我们再次访问上面两个url:

访问http://localhost:8080/list:

[
{
"id": "1",
"name": "a"
}
]

访问http://localhost:8080/map:

{
"user2": {
"id": "2",
"name": "b"
}
}

看到这里我们可以理解@LoadBalanced的用处了，其实就是一个修饰符，和@Qualifier一样，比如我们给user1打上@LoadBalanced:

@Bean("user1")
@LoadBalanced
User user1() {
return new User("1", "a");
}
@Bean("user2")
User user2() {
return new User("2", "b");
}

然后controller中给List users打上@LoadBalanced注解:

@Autowired(required = false)
@LoadBalanced
private List<User> users = Collections.emptyList();

访问http://localhost:8080/list：

[
{
"id": "1",
"name": "a"
}
]

和@Qualifier注解效果一样，只有user1被注入进了List，user2没有修饰符，没有被注入进去。
另外当spring容器中有多个相同类型的bean的时候，可以通过@Qualifier来进行区分，以便在注入的时候明确表明你要注入具体的哪个bean,消除歧义