[英]Why do I not need @Autowired on @Bean methods in a Spring configuration class?
[英]How do I make Autowired work inside a Configuration class?
我試圖在@Configuration類中自動裝配標記為@Service
的屬性(myService),但得到了NullPointer。
相反,如果我將myService
自動連接到非配置類中,則沒有問題。
這是我在自動裝配時遇到的問題@Service:
package com.myapp.resources;
@Service
class MyService {
public List<String> getRoutingKeys() {
List<String> routingKeys;
//Do stuff
return routingKeys;
}
public String aMethod() {
return "hello";
}
}
這是@Configuration類,在這里我無法自動連接服務
package com.myapp.messaging;
import com.myapp.resources;
import org.springframework.amqp.core.Binding;
import org.springframework.amqp.core.BindingBuilder;
import org.springframework.amqp.core.Queue;
import org.springframework.amqp.core.TopicExchange;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import java.util.List;
@Configuration
public class RabbitConfiguration {
private List<String> routingKeys = writeRoutingKeys();
@Autowired
private MyService myService;
private List<String> writeRoutingKeys() {
boolean test = myService == null;
System.out.println("is the service null? " + test); //output: true!!!
return myService.getRoutingKeys(); //here I get a NullPointer
}
//Methods with bean declarations for RabbitMQ
}
如果有幫助,這是我的主類:
package com.myapp;
import com.myapp.resources;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import java.util.List;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
ConfigurableApplicationContext appContext = SpringApplication.run(Application.class, args);
MyService myService = (MyService) appContext.getBean(MyService.class);
boolean test = myService == null;
System.out.println("is the service null? " + test); //output: false
//Do stuff
}
}
如果有幫助,這里是另一個類(@RestController),我可以在其中自動裝配服務
package com.myapp.resources;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class MyController {
@Autowired
private MyService myService;
@GetMapping("/endpoint")
public String myRestMethod() {
boolean test = myService == null;
System.out.println("is the service null? " + test); //output: false
return myService.aMethod();
}
}
我也嘗試過在Configuration類中添加@ComponentScan,但是我仍然得到一個NullPointer
package com.myapp.messaging;
//list of imports...
@Configuration
@ComponentScan("com.myapp.demo")
public class RabbitConfiguration {
@Autowired
private MyService myService;
//...
}
我建議通過任何需要它的@Bean
創建方法來注入服務:
@Bean
public MyBean create(MyService myService)
然后將該服務傳遞到writeRoutingKeys(MyService myService)
方法中以進行相應處理。
每個文檔:
@Configuration類在上下文的初始化過程中很早就被處理,強制以這種方式注入依賴項可能導致意外的早期初始化。 只要有可能,請像上面的示例中那樣使用基於參數的注入。
Spring僅在實例化bean之后或實例時注入依賴項(取決於是否使用構造函數注入)。 但是,您現在正在字段初始化期間訪問依賴項MyService
,這在初始化bean之前發生。因此,由於尚未注入,它無法在字段初始化期間訪問MyService
。
您可以通過更改為使用構造函數注入並routingKeys
在構造函數內部初始化routingKeys
來簡單地修復它:
@Configuration
public class RabbitConfiguration {
private List<String> routingKeys ;
private MyService myService;
@Autowired
public RabbitConfiguration(MyService myService){
this.myService = myService
this.routingKeys = writeRoutingKeys();
}
private List<String> writeRoutingKeys() {
return myService.getRoutingKeys();
}
}
或者簡單地:
@Autowired
public RabbitConfiguration(MyService myService){
this.myService = myService
this.routingKeys = myService.getRoutingKeys();
}
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