spring - 自定义 Spring 范围中的 resolveContextualObject 和 getConversationId

Question

我想知道 org.springframework.beans.factory.config.Scope.resolveContextualObject(String key) 的目的是什么和 org.springframework.beans.factory.config.Scope.getConversationId() ?

来自 javadoc :

Object resolveContextualObject(String key)

Resolve the contextual object for the given key, if any. E.g. the HttpServletRequest object for key "request".

String getConversationId()

Return the conversation ID for the current underlying scope, if any. The exact meaning of the conversation ID depends on the underlying storage mechanism. In the case of session-scoped objects, the conversation ID would typically be equal to (or derived from) the session ID; in the case of a custom conversation that sits within the overall session, the specific ID for the current conversation would be appropriate.

这个描述并没有告诉我太多。
你能给我一些例子来演示如何使用这些方法吗？

我的观察是 resolveContextualObject(String key)看起来像代码异味，其中 Scope 可以暴露一些内部对象。

Answer 1

拥有:

public class MyCustomScope implements Scope {

    private Pair<String, String> myPair;

    @Override
    public Object resolveContextualObject(String key) {
        if ("myKey".equals(key)) return myPair;
        return null;
    }

    // ...
}

@Configuration
public class RegisterMyScopeConfig {

    @Bean
    public BeanFactoryPostProcessor beanFactoryPostProcessor() {
        return beanFactory -> beanFactory.registerScope(
            "mycustomscope", new MyCustomScope()); 
    }
}

然后你可以:

@Scope("mycustomscope")
@Component 
class MyComponent {

    @Value("#{myKey.first}")
    private String firstOfMyPair;

    // or 

    @Value("#{myKey}")
    private Pair<String,String> myPair;
}

当然，您如何解析与键匹配的对象的方式可能更有趣；)。
例如，在 GenericScope它看起来像这样:

@Override
public Object resolveContextualObject(String key) {
    Expression expression = parseExpression(key);
    return expression.getValue(this.evaluationContext, this.beanFactory);
}