将ConfigurationProperties与内部类一起使用会导致“属性未绑定”异常

Question

我有一个名为LibraryConfig的带有注释的配置属性类。它使用内部类作为属性/配置结构的类型定义。当类是内部类而不是独立类时，我得到“元素[…]“未绑定”错误/异常。为什么会这样？我如何修复它？

application.yml

initdata:
  library:
    name: awesome library
    books:
      - title: Book1
        author: Author Abc
      - title: Book2
        author: Author Xyz

库配置。Java语言

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;

@Configuration
@ConfigurationProperties(prefix = "initdata.library")
public class LibraryConfiguration {
    private String name;
    private List<Book> books;

    // getters left out for simplicity of example
    public void setName(String name) {
        this.name = name;
    }
    public void setBooks(List<Book> books) {
        this.books = books;
    }

    public LibraryConfiguration() {
    }

    public static class Book {
        private String title;
        private String author;

        public Book() {
        }
        // getters left out for simplicity of example
        public void setTitle(String title) {
            this.title = title;
        }
        public void setAuthor(String author) {
            this.author = author;
        }
    }
}

Answer 1

您要么创建一个独立类，要么必须将内部类声明为静态类！否则，Spring不会将其视为一个“类型定义”，而是尝试创建它的一个实例——这当然不适用于给定的yml配置。将代码更改为以下内容

// ...
public LibraryConfiguration() {
}

// This class MUST be static, otherwise Spring will tell "Elements [...] were left unbound".
// If it's static, it's just a "type definition";
// otherwise spring tries to create an insance
public static class Book {
    private String title;
    private 
// ...