[FIXED] Spring Boot Upgrade to 2.2.6 - Unable to bind yaml properties to list of objects

Issue

I am in the process to upgrade a project to Spring Boot 2.2.6. Following compilation errors are there wrt to binding yaml properties data to list of objects -

** Please note the project is compiling in previous version of spring-boot (2.2.1) I have been using**

java.lang.IllegalStateException: Failed to load ApplicationContext Caused by: org.springframework.boot.context.properties.ConfigurationPropertiesBindException: Error creating bean with name 'webUiApplication.States': Could not bind properties to 'WebUiApplication.States' : prefix=states, ignoreInvalidFields=false, ignoreUnknownFields=true; nested exception is org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'states.defaults' to java.util.List

application.yml

   states:
  defaults:
    -
      postal-code: AL
      name: Alabama
    -
      postal-code: AK
      name: Alaska
    -
      postal-code: AZ
      name: Arizona

Configuration

    @Data 
   @Configuration
   @ConfigurationProperties("states")
   public static class States {

      private List<State> defaults;

      private List<State> docVerify;

      private List<State> registration;

  }

POJO

@Data
@EqualsAndHashCode(onlyExplicitlyIncluded = true)
@ToString(onlyExplicitlyIncluded = true)
public class State implements ListOption {
   public static final Comparator<State> DISPLAY_COMPARATOR = new ListOption.DisplayComparator<>();

   @NonNull private final String postalCode;

   @NonNull private final String name;

@Override
   @EqualsAndHashCode.Include
   public String getValue() {
      return this.postalCode;
   }

   @Override
   @ToString.Include
   public String getLabel() {
      return String.format("%s - %s", postalCode, name);
   }
}

Have come across posts where members have received the similar issue but have not been been able to come to a solution. Looking forward to your inputs.

Solution

Refactor your code:

States:

@Data

    @Configuration
    @ConfigurationProperties("states")
    @ToString
    @NoArgsConstructor
    public class States {
        private List<State> defaults;
        private List<State> docVerify;
        private List<State> registration;

    }

State:

@Data
@EqualsAndHashCode(onlyExplicitlyIncluded = true)
@ToString(onlyExplicitlyIncluded = true)
@NoArgsConstructor
public class State {
    @NonNull
    private String postalCode;

    @NonNull
    private String name;

    @EqualsAndHashCode.Include
    public String getValue() {
        return this.postalCode;
    }

    @ToString.Include
    public String getLabel() {
        return String.format("%s - %s", postalCode, name);
    }
}

application.yaml

states:
  defaults:
    -
      postal-code: AL
      name: Alabama
    -
      postal-code: AK
      name: Alaska
    -
      postal-code: AZ
      name: Arizona

We need to have an empty object and then fill it with data. This is why we need no args constructor.

Answered By - Bhushan Uniyal
Answer Checked By - Mary Flores (JavaFixing Volunteer)