java - 使用 SnakeYaml 将 java 对象写入文件 - 使用 Yaml.dump() 时不会写出内部对象列表

Question

我在使用 SnakeYaml 将 java 对象写入 yml 文件时遇到问题。我已经使用一个简单的 application.yml 设置了一个 spring boot 项目，我将其转换为一组 java 对象。在实际应用程序中添加了一些对象，当应用程序完成后我想写出新的 application.yml。

输入的 application.yml 如下所示:

sample:
  name: toyota
  cars:
     - model: prius
       colour: silver
     - model: avensis
       colour: red

映射这个application.yml的java对象:

@Configuration
@ConfigurationProperties(prefix="sample")
public class Config {

    private String name;
    private final List<Car> cars = new ArrayList<>();

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public List<Car> getCars() {
        return cars;
    }
}

以及写出 yaml 的示例类:

@Component
public class Example {

    @Autowired
    private Config config;

    @PostConstruct
    private void init(){
        Yaml yaml = new Yaml();
        StringWriter writer = new StringWriter();
        yaml.dump(config, writer);      
        System.out.println(writer.toString());          
    }
}

输出只是:name: toyota(省略了一些也被写出的 yaml 设置)。但是我希望输出与输入完全相同:

sample:
  name: toyota
  cars:
     - model: prius
       colour: silver
     - model: avensis
       colour: red

有办法吗？

编辑:

用户 flyx 正确指出了以下 documentation .

我调整后的代码:

Constructor constructor = new Constructor(Config.class);
TypeDescription configDescription = new TypeDescription(Config.class);
configDescription.putListPropertyType("cars", Car.class);
constructor.addTypeDescription(configDescription);
Yaml yaml = new Yaml(constructor);
StringWriter writer = new StringWriter();
yaml.dump(config, writer);      
System.out.println(writer.toString()); 

给出以下输出:

$$beanFactory: !!org.springframework.beans.factory.support.DefaultListableBeanFactory
  allowBeanDefinitionOverriding: true
  allowEagerClassLoading: true
  autowireCandidateResolver: !!org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver {}
  beanClassLoader: !!sun.misc.Launcher$AppClassLoader {}
  beanExpressionResolver: !!org.springframework.context.expression.StandardBeanExpressionResolver {}
  cacheBeanMetadata: true
  conversionService: null
  dependencyComparator: !!org.springframework.core.annotation.AnnotationAwareOrderComparator {}
  parentBeanFactory: null
  serializationId: application
  tempClassLoader: null
  typeConverter: !!org.springframework.beans.SimpleTypeConverter {conversionService: null}
name: toyota

Answer 1

由于类型删除，SnakeYAML 在运行时无法获取 List 的元素类型。该文档有一个 example你需要做什么。

像这样的东西应该可以工作:

@PostConstruct
private void init(){
    Constructor c = new Constructor(Config.class);
    TypeDescription configD = new TypeDescription(Config.class);
    configD.putListPropertyType("cars", Car.class);
    c.addTypeDescription(configD);
    Yaml yaml = new Yaml(c);
    StringWriter writer = new StringWriter();
    yaml.dump(config, writer);      
    System.out.println(writer.toString());          
}