java - 如何从 spring-boot 应用程序中的 application.yml 文件读取属性

Question

我的应用程序已将嵌套属性存储在 application.yml 文件中。
我想在应用程序启动时将这些属性映射到 POJO。

Application.yml:

    demo:
     - A:
       - type: A
         prop1: 1
         prop2: 2
         proop3: 3
       - type: B
         prop1: 1
         prop2: 2
         proop3: 3
     - B:
       - type: A
         prop1: 1
         prop2: 2
         proop3: 3
       - type: B
         prop1: 1
         prop2: 2
         proop3: 3

为了实现这一点，我使用以下注释:

@配置
@EnableConfigurationProperties
@ConfigurationProperties("演示")

类演示:

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties("demo")
public class Demo {
    @JsonProperty("A")
    private List<A> a = null;
    @JsonProperty("B")
    private List<B> b = null;

    @JsonProperty("A")
    public List<A> getA() {
        return a;
    }

    @JsonProperty("A")
    public void setA(List<A> a) {
        this.a = a;
    }

    @JsonProperty("B")
    public List<B> getB() {
        return b;
    }

    @JsonProperty("B")
    public void setB(List<B> b) {
        this.b = b;
    }

    @Override
    public String toString() {
        return "Demo [a=" + a + ", b=" + b + "]";
    }   
}

A类:

public class A {

    @JsonProperty("type")
    private String type;
    @JsonProperty("prop1")
    private Integer prop1;
    @JsonProperty("prop2")
    private Integer prop2;
    @JsonProperty("proop3")
    private Integer proop3;

    @JsonProperty("type")
    public String getType() {
        return type;
    }

    @JsonProperty("type")
    public void setType(String type) {
        this.type = type;
    }

    @JsonProperty("prop1")
    public Integer getProp1() {
        return prop1;
    }

    @JsonProperty("prop1")
    public void setProp1(Integer prop1) {
        this.prop1 = prop1;
    }

    @JsonProperty("prop2")
    public Integer getProp2() {
        return prop2;
    }

    @JsonProperty("prop2")
    public void setProp2(Integer prop2) {
        this.prop2 = prop2;
    }

    @JsonProperty("proop3")
    public Integer getProop3() {
        return proop3;
    }

    @JsonProperty("proop3")
    public void setProop3(Integer proop3) {
        this.proop3 = proop3;
    }

    @Override
    public String toString() {
        return "A [type=" + type + ", prop1=" + prop1 + ", prop2=" + prop2 + ", proop3=" + proop3 + "]";
    }
}

B类

public class B {

    @JsonProperty("type")
    private String type;
    @JsonProperty("prop1")
    private Integer prop1;
    @JsonProperty("prop2")
    private Integer prop2;
    @JsonProperty("proop3")
    private Integer proop3;

    @JsonProperty("type")
    public String getType() {
        return type;
    }

    @JsonProperty("type")
    public void setType(String type) {
        this.type = type;
    }

    @JsonProperty("prop1")
    public Integer getProp1() {
        return prop1;
    }

    @JsonProperty("prop1")
    public void setProp1(Integer prop1) {
        this.prop1 = prop1;
    }

    @JsonProperty("prop2")
    public Integer getProp2() {
        return prop2;
    }

    @JsonProperty("prop2")
    public void setProp2(Integer prop2) {
        this.prop2 = prop2;
    }

    @JsonProperty("proop3")
    public Integer getProop3() {
        return proop3;
    }

    @JsonProperty("proop3")
    public void setProop3(Integer proop3) {
        this.proop3 = proop3;
    }

    @Override
    public String toString() {
        return "B [type=" + type + ", prop1=" + prop1 + ", prop2=" + prop2 + ", proop3=" + proop3 + "]";
    }
}

主类

@SpringBootApplication
@ComponentScan(basePackages = {"com.microservice.*"})
@EnableJpaRepositories("com.microservice.*")
@EntityScan("com.microservice.*")
public class MainApplication {  
    public static void main(String[] args) {
         SpringApplication app = new SpringApplication(MainApplication.class);
            app.run();
            System.out.println("step 1");
            Demo config = new Demo();
            System.out.println("name: " + config);
        }

        public void run(String... args) throws Exception {
            System.out.println("step 2");

        }
}

但我低于o/p:
第 1 步
名称:演示 [a=null, b=null]

Answer 1

当您手动创建属性 POJO 的实例时，Spring 不知道它，并且属性绑定(bind)不会发生。

 SpringApplication app = new SpringApplication(MainApplication.class);
    app.run();
    System.out.println("step 1");
    Demo config = new Demo(); // Not a Spring managed bean!
    System.out.println("name: " + config);
}

您可以将 Demo 作为一个 bean，而不是使用 @EnableConfigurationProperties 注释配置，如 Type-safe Configuration Properties 所示。 .

@Component
@ConfigurationProperties("demo")
public class Demo {
    ...
}

然后你可以从上下文中获取Demo bean:

@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);
        Demo demo = (Demo) context.getBean("demo");
        System.out.println(demo.getName());
    }
}

UPD:“a”和“b”之前不能有连字符:

demo:
  a:
    - type: A
      prop1: 1
      prop2: 2
      proop3: 3
    - type: B
      prop1: 1
      prop2: 2
      proop3: 3
  b:
    - type: B
      prop1: 1
      prop2: 2
      proop3: 3

UPD2:回复评论。您可以使用 ObjectMapper 从 Demo bean 构建 JSON:

@SpringBootApplication
public class MainApplication {

    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper();
    }

    public static void main(String[] args) throws JsonProcessingException {
        ...
        ObjectMapper objectMapper = (ObjectMapper) context.getBean("objectMapper");
        System.out.println(objectMapper.writeValueAsString(demo));
    }
}

使用 spring-boot-starter-web 不需要额外的依赖项。否则，您可以添加 jackson :

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.0.1</version>
</dependency>