在使用@value注释的Spring Boot中无法从属性文件中读取值

Question

helloWorldUrl = null
Exception in thread "main" java.lang.IllegalArgumentException: URI must not be null
    at org.springframework.util.Assert.notNull(Assert.java:115)
    at org.springframework.web.util.UriComponentsBuilder.fromUriString(UriComponentsBuilder.java:189)
    at org.springframework.web.util.DefaultUriTemplateHandler.initUriComponentsBuilder(DefaultUriTemplateHandler.java:114)
    at org.springframework.web.util.DefaultUriTemplateHandler.expandInternal(DefaultUriTemplateHandler.java:103)
    at org.springframework.web.util.AbstractUriTemplateHandler.expand(AbstractUriTemplateHandler.java:106)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:612)
    at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:287)
    at com.example.HelloWorldClient.main(HelloWorldClient.java:19)

public class HelloWorldClient {

    @Value("${rest.uri}")
    private static String helloWorldUrl;

    public static void main(String[] args) {
        System.out.println("helloWorldUrl = " + helloWorldUrl);
        String message = new RestTemplate().getForObject(helloWorldUrl, String.class);
        System.out.println("message = " + message);
    }

}

Application.Properties

rest.uri=http://localhost:8080/hello

Answer 1

您的代码中有几个问题。

>

从你发布的样本来看，Spring似乎还没有开始。main类应该运行main方法中的上下文。

@SpringBootApplication
public class HelloWorldApp {

     public static void main(String[] args) {
          SpringApplication.run(HelloWorldApp.class, args);
     }

}

不可能将值注入到静态字段中。您应该从将其更改为常规类字段开始。

@Component
public class HelloWorldClient {
    // ...
}

@SpringBootApplication
public class HelloWorldApp {

  // ...    

  @Bean
  public HelloWorldClient helloWorldClient() {
     return new HelloWorldClient();
  }

}