How to get nested Spel expression based objects through @ConfigurationProperties in Spring Boot?

huangapple
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英文:

How to get nested Spel expression based objects through @ConfigurationProperties in Spring Boot?

问题

这是我的 application.yml 文件内容：

  1. translations:
  2.   en:
  3.     title: 'english'
  4.     description: 'english text'
  5.   fr:
  6.     title: 'french'
  7.     description: 'french text'
  8.   de:
  9.     title: 'german'
  10.     description: 'french text'
  12. codes:
  13.   GB:
  14.     en: ${translations.en}
  15.   CA:
  16.     en: ${translations.en}
  17.     fr: ${translations.fr}
  18.   DE:
  19.     en: ${translations.en}
  20.     fr: ${translations.fr}
  21.     de: ${translations.de}

现在考虑这段代码（为简洁起见，删除了不必要的 getter 方法，并且使用了 Project Lombok）：

  1. @SpringBootApplication
  2. public class DemoApplication implements CommandLineRunner {
  3.     // 内部类，但这些也可以放在外面
  4.     @ConfigurationProperties
  5.     @Getter
  6.     @Component
  7.     class Config {
  8.         Map<String, Map<String, LanguageDTO>> codes;
  9.     }
  11.     @Data
  12.     @AllArgsConstructor
  13.     class LanguageDTO {
  14.         String title;
  15.         String description;
  16.     }
  18.     @Autowired
  19.     Config config;
  21.     public static void main(String[] args) {
  22.         SpringApplication.run(DemoApplication.class, args);
  23.     }
  25.     @Override
  26.     public void run(String... args) throws Exception {
  27.         // 在下面的这行代码上出现了错误
  28.         Map<String, Map<String, LanguageDTO>> codes = config.getCodes();
  29.     }
  30. }

现在当我启动应用程序时，我会收到如下错误：

  1. APPLICATION FAILED TO START
  2. ***************************
  4. Description:
  6. Failed to bind properties under 'codes.gb.en' to com.example.demo.DemoApplication$LanguageDTO:
  8.     Property: codes.gb.en
  9.     Value: ${translations.en}
  10.     Origin: class path resource [application.yml]:24:9
  11.     Reason: No converter found capable of converting from type [java.lang.String] to type [com.example.demo.DemoApplication$LanguageDTO]
  13. Action:
  15. Update your application's configuration

我的需求是什么？

我希能够将 codes 读取为一个 Map<String, Map<String, LanguageDTO>>。也就是说，我应该能够执行 config.getCodes().get("GB").get("en") --> 这应该返回一个类型为 LanguageDTO 的数据。

英文:

This is in my application.yml

  1. translations:
  2.   en:
  3.     title: &#39;english&#39;
  4.     description: &#39;english text&#39;
  5.   fr:
  6.     title: &#39;french&#39;
  7.     description: &#39;french text&#39;
  8.   de:
  9.     title: &#39;german&#39;
  10.     description: &#39;french text&#39;
  12. codes:
  13.   GB:
  14.     # I am assuming that en here will have an object with both title and description properties
  15.     en: ${translations.en}
  16.   CA:
  17.     en: ${translations.en}
  18.     fr: ${translations.fr}
  19.   DE:
  20.     en: ${translations.en}
  21.     fr: ${translations.fr}
  22.     de: ${translations.de}

Now consider this piece of code(removed unnecessary getters etc and also using project lombok for brevity)

  1. @SpringBootApplication
  2. public class DemoApplication implements CommandLineRunner {
  3.     // Inner classes, but these can be outside as well
  4.     @ConfigurationProperties
  5.     @Getter
  6.     @Component
  7.     class Config {
  8.         Map&lt;String, Map&lt;String, LanguageDTO&gt;&gt; codes;
  9.     }
  11.     @Data
  12.     @AllArgsConstructor
  13.     class LanguageDTO {
  14.         String title;
  15.         String description;
  16.     }
  18.     @Autowired
  19.     Config config;
  21.     public static void main(String[] args) {
  22.         SpringApplication.run(DemoApplication.class, args);
  23.     }
  25.     @Override
  26.     public void run(String... args) throws Exception {
  27.         // Getting error on this line below
  28.         Map&lt;String, Map&lt;String, LanguageDTO&gt;&gt; codes = config.getCodes();
  29.     }
  30. }

Now when I start the app, I am getting an error like this:

  1. APPLICATION FAILED TO START
  2. ***************************
  4. Description:
  6. Failed to bind properties under &#39;codes.gb.en&#39; to com.example.demo.DemoApplication$LanguageDTO:
  8.     Property: codes.gb.en
  9.     Value: ${translations.en}
  10.     Origin: class path resource [application.yml]:24:9
  11.     Reason: No converter found capable of converting from type [java.lang.String] to type [com.example.demo.DemoApplication$LanguageDTO]
  13. Action:
  15. Update your application&#39;s configuration

What I want?

I want to be able to read codes as a Map&lt;String, Map&lt;String, LanguageDTO&gt;. That is, I should be able to do config.getCodes().get(&quot;GB&quot;).get(&quot;en&quot;) --> which should in turn have a data type of LanguageDTO.

答案1

得分: 1

我认为这是不可行的：Spring仅在application.yaml文件中支持简单的属性占位符（就我所知）。不过，你可以利用YAML格式的内置功能，使用锚点和别名：

  1. translations:
  2.   en: &en
  3.     title: '英文'
  4.     description: '英文文本'
  5.   fr: &fr
  6.     title: '法文'
  7.     description: '法文文本'
  8.   de: &de
  9.     title: '德文'
  10.     description: '法文文本'
  12. codes:
  13.   GB:
  14.     en: *en
  15.   CA:
  16.     en: *en
  17.     fr: *fr
  18.   DE:
  19.     en: *en
  20.     fr: *fr
  21.     de: *de

为使其工作，LanguageDTO类需要具有setter方法和默认构造函数。@AllArgsConstructor不起作用。或者你可以尝试与constructor binding一起使用，尽管我不确定是否可行。

英文:

I don't think it's doable: Spring supports only simple property placeholders inside the application.yaml file (as far as I know). What you could do though, is leveraging YAML format built-in functionality, anchors and aliases:

  1. translations:
  2.   en: &amp;en
  3.     title: &#39;english&#39;
  4.     description: &#39;english text&#39;
  5.   fr: &amp;fr
  6.     title: &#39;french&#39;
  7.     description: &#39;french text&#39;
  8.   de: &amp;de
  9.     title: &#39;german&#39;
  10.     description: &#39;french text&#39;
  12. codes:
  13.   GB:
  14.     en: *en
  15.   CA:
  16.     en: *en
  17.     fr: *fr
  18.   DE:
  19.     en: *en
  20.     fr: *fr
  21.     de: *de

> For it to work, the LanguageDTO class needs to have setters and a default constructor. @AllArgsConstructor won't work. Alternatively you might try to get it work in conjunction with constructor binding, although I'm not sure if it's possible.

huangapple
  • 本文由 发表于 2020年10月15日 02:34:46
  • 转载请务必保留本文链接：https://go.coder-hub.com/64359514.html
  • java
  • spring
  • spring-boot
  • spring-el
  • yaml
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