Reason: The elements were left unbound

Question

How can I load List of objects from configuration yml file in java springboot application?

I already tried several sources:

configuration-properties-in-spring-boot

spring-boot-configurationproperties-example

SpringBoot 2 the elements were left unbound

Stack: Java 11, SpringBoot 2.1.4, Lombok, configuration file in .yml format.

I tried to implement simple @Component, which will load data from configuration file.

Configuration values are:

allowed:
  - first-crossroad: ONE
    second-crossroad: TWO
    third-crossroad: TWO
    fourth-crossroad: THREE
  - first-crossroad: ONE
    second-crossroad: THREE
    third-crossroad: TWO
    fourth-crossroad: ONE

Java class for data loading is:

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties(prefix = "")
@Data
public class AllowedCrossroads {

  private List<CrossroadCombination> allowed;
}

Java CrossroadCombination object definition:

@Data
@Builder
@AllArgsConstructor
public class CrossroadCombination {

  private String firstCrossroad;
  private String secondCrossroad;
  private String thirdCrossroad;
  private String fourthCrossroad;
}

I expected values to be loaded during application run. But I am getting error:

Property: allowed[0].first-crossroad
    Value: ONE
    Origin: class path resource [application.yml]:644:17
    Reason: The elements [allowed[0].first-crossroad,allowed[0].fourth-crossroad,allowed[0].second-crossroad,allowed[0].third-crossroad,allowed[1].first-crossroad,allowed[1].fourth-crossroad,allowed[1].second-crossroad,allowed[1].third-crossroad,allowed[2].first-crossroad,allowed[2].fourth-crossroad,allowed[2].second-crossroad,allowed[2].third-crossroad] were left unbound.

Answer 1

(One of many) Solution:

• add: @NoArgsConstructor

to java class:

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class CrossroadCombination {

  private String firstCrossroad;
  private String secondCrossroad;
  private String thirdCrossroad;
  private String fourthCrossroad;
}

Explanation:

It is because when we create an object, we need to have an empty object and then fill it with data. This is why we need no args constructor.

Anyway solution from "@Daniel V" is also correct and thanks for that one!

Answer 2

Making The Inner class as static will work

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties(prefix = "")
@Data
public class AllowedCrossroads {

    private List<CrossroadCombination> allowed;

    @Data
    public static class CrossroadCombination {
        private String firstCrossroad;
        private String secondCrossroad;
        private String thirdCrossroad;
        private String fourthCrossroad;
    }
}

Answer 3

including Getters and Setters for all fields solved the issue

Answer 4

Did you try with java ResourceBundle library?

for example:

ResourceBundle configApp = ResourceBundle.getBundle("path to your configuration file");

after that you can use configApp like so:

configApp.getString("first-crossroad");

can you try that and tell me how it goes.

EDIT:

The data in your configuration file if your planning to use ResourceBundle should look like this:

allowed=[first-crossroad= ONE, second-crossroad= TWO, third-crossroad= TWO,fourth-crossroad= THREE,first-crossroad= ONE, second-crossroad= THREE,third-crossroad= TWO, fourth-crossroad= ONE]

the "[]" isn't neccesary but it makes it look more readable

then you call it like this:

configApp.getObject("allowed");

that will store it like this:

[first-crossroad= ONE, second-crossroad= TWO, third-crossroad= TWO,fourth-crossroad= THREE,first-crossroad= ONE, second-crossroad= THREE,third-crossroad= TWO, fourth-crossroad= ONE]

then you can cast this to an array or play with it like this.

Answer 5

In my case the variable name is not matched. Please check all fields names and mapping configuration key names.