java - 通过带有参数表的注释选择 CDI bean

Question

如何根据注解选择CDI java bean，然后注解构成参数表？

使用示例展示问题比描述问题更容易。

假设对于类型为问题的每个对象，我们必须选择合适的解决方案。

public class Problem {

    private Object data;
    private ProblemType type;

    public Object getData() { return data; }
    public void setData(Object data) { this.data = data; }
    public ProblemType getType() { return type; }
    public void setType(ProblemType type) { this.type = type;}
}

有几种类型的问题:

public enum ProblemType {
    A, B, C;
}

解决方案很少:

public interface Solution {
    public void resolve(Problem problem);
}

比如FirstSolution:

@RequestScoped
@SolutionQualifier(problemTypes = { ProblemType.A, ProblemType.C })
public class FirstSolution implements Solution {

    @Override
    public void resolve(Problem problem) {
        // ...
    }
}

和SecondSolution:

@RequestScoped
@SolutionQualifier(problemTypes = { ProblemType.B })
public class SecondSolution implements Solution {

    @Override
    public void resolve(Problem problem) {
        // ...
    }
}

应根据注解@SolutionQualifier选择解决方案:

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface SolutionQualifier {

    ProblemType[] problemTypes();

    public static class SolutionQualifierLiteral extends AnnotationLiteral<SolutionQualifier> implements SolutionQualifier {

        private ProblemType[] problemTypes;

        public SolutionQualifierLiteral(ProblemType[] problems) {
            this.problemTypes = problems;
        }

        @Override
        public ProblemType[] problemTypes() {
            return problemTypes;
        }
    }
}

通过 SolutionProvider:

@RequestScoped
public class DefaultSolutionProvider implements SolutionProvider {

    @Inject
    @Any
    private Instance<Solution> solutions;

    @Override
    public Instance<Solution> getSolution(Problem problem) {

        /**
         * Here is the problem of choosing proper solution.
         * I do not know how method {@link javax.enterprise.inject.Instance#select(Annotation...)}
         * works, and how it compares annotations, so I do no know what argument I should put there
         * to obtain proper solution.
         */

        ProblemType[] problemTypes = { problem.getType() };
        return solutions.select(new SolutionQualifier.SolutionQualifierLiteral(problemTypes));
    }
}

最后一个有问题: 我不知道 javax.enterprise.inject.Instance#select(Annotation...) 方法在内部如何工作，以及它如何比较注释，所以我不知道我应该在那里获取什么参数适当的解决方案。如果出现A 类型的问题，表ProblemType[] 将包含一个参数，而FirstSolution.class 用@ 注释SolutionQualifier 有两个参数，因此我不会得到正确的实例。

Answer 1

我没有找到使用 CDI API 解决它的方法，而是:

我创建了另一个枚举:

public enum SoultionType {
    A(ProblemType.A, ProblemType.C), 
    B(ProblemType.A);

    //...

    SoultionType(ProblemType problems...) {
        // ...
    }

    public static SoultionType getByProblemType(ProblemType problem) {
        // ...
    }
}

改成SolutionQualifier里面只有SoultionType字段，所以比较没有问题。