对Spring ConfigurationProperties子类使用构造函数注入

问题描述

我正在查看此状态：

您实际上尝试混合其行为。

值不是Spring环境的属性，而是 my-config.values 是。

甚至在<$ c $内部声明c> MyConfig ，例如 @Value（ $ {values}） ，它不会更改 @ConfigurationProperties 将属性绑定到结构化对象。当然，它不会在Spring环境中创建新属性，这就是 @Value（）寻找解析值表达式的地方。

而解决 $ {values} 的异常。

作为 MyConfig 是组件 @Value 应该是您所需要的：

  @Component 
公共类MyConfig {
 
 private final List< String>价值观
 
 public MyConfig（@Value（ $ {my-config.values}）List< String>值）{
 this.values = ImmutableList.copyOf（values）; 
} 
} 
  

您也可以通过保护设置器来防止可变性进行检查，但这只会在运行时检测到问题：

  @ConfigurationProperties（ my-config）
 public class MyConfig {
 
 private final List< String>价值观
 
公共列表< String> getValue（）{
返回值； 
} 
 public void setValue（List< String> values）{
 if（this.values！= null）{
 throw new IllegalArgumentException（ ...）; 
} 
 this.values = ImmutableList.copyOf（values）; 
} 
} 
  

I was looking at this https://www.baeldung.com/configuration-properties-in-spring-boot and was wondering if it was possible to use constructor injection for these in order to enforce some immutability properties.

For example would it be possible to do this:

@Component
@ConfigurationProperties("my-config")
public class MyConfig {

    private final List<String> values;

    public MyConfig(@Value("${values}") List<String> values) {
        this.values = ImmutableList.copyOf(values);
    }
}

And then in my yml config have

my-config.values:
  - foo
  - bar

But I get this error:

java.lang.IllegalArgumentException: Could not resolve placeholder 'values' in string value "${values}"

解决方案

The documentation states :

You actually try to mix their behavior.
values is not a property of the Spring environment but my-config.values is.
Even declared inside MyConfig such as @Value("${values})" it doesn't change anything as @ConfigurationProperties bounds the properties to a structured object. And of course it doesn't create new properties in the Spring environment, that is where @Value() looks for to resolve the value expression.
Whereas the exception to resolve ${values}.

As MyConfig is a component @Value should be what you need :

@Component
public class MyConfig {

    private final List<String> values;

    public MyConfig(@Value("${my-config.values}") List<String> values) {
        this.values = ImmutableList.copyOf(values);
    }
}

You could also prevent the mutability by protecting the setter with a check but this will detect the issue only at runtime :

@ConfigurationProperties("my-config")
public class MyConfig {

    private final List<String> values;

    public List<String> getValue(){
         return values;
    }
    public void setValue(List<String> values){
         if (this.values != null){
             throw new IllegalArgumentException("...");
         }
         this.values = ImmutableList.copyOf(values);
    }
}

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