java - Java EE 中的 CDI - 哪些 Java 类不能注入(inject)？

Question

我正在浏览 Oracle Java EE 6 Tutorial在“Beans as Injectable Objects”部分下，它说

The following kinds of objects can be injected:

(Almost) any Java class

Session beans ......

无法注入(inject)的 Java 类的示例是什么？他们提到的只是一些理论上的技术限制，还是可以注入(inject)的类类型存在已知限制？

Answer 1

来自spec ， channel 。 2.2.1:

Almost any Java type may be a bean type of a bean:

• A bean type may be an interface, a concrete class or an abstract class, and may be declared final or have final methods.
• A bean type may be a parameterized type with actual type parameters and type variables.
• A bean type may be an array type. Two array types are considered identical only if the element type is identical.
• A bean type may be a primitive type. Primitive types are considered to be identical to their corresponding wrapper types in java.lang.
• A bean type may be a raw type.

A type variable is not a legal bean type. A parameterized type that contains a wildcard type parameter is not a legal bean type.

Note that certain additional restrictions are specified in Section 5.4.1, “Unproxyable bean types” for beans with a normal scope, as defined in Section 6.3, “Normal scopes and pseudo-scopes”.

然后是引用部分:

Certain legal bean types cannot be proxied by the container:

• classes which don't have a non-private constructor with no parameters,
• classes which are declared final or have final methods,
• primitive types,
• and array types.

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总结一下:任何 Java 类型(包括接口(interface)、抽象类)都可以是 CDI bean，除非它是“正常作用域”并且至少满足以下条件之一: p>

• 没有不带参数的非私有(private)构造函数
• 是最终的/有最终的方法
• 是原始类型(int、double 等)或数组

普通范围(例如@Application-、@Session-、@RequestScoped)意味着它需要由容器代理，因此上述限制可能会被“不可代理”所取代。 @Dependent 和 @javax.inject.Singleton 不是普通作用域，它们是伪作用域。