Which statement is true about Java methods that are exposed as Web Service operations by using JAX-WS API?
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A. B. C. D.D.
Java methods that are exposed as Web Service operations using JAX-WS API should meet certain requirements to ensure that they can be consumed by clients in a standard and interoperable way. Let's analyze each option to identify the true statement:
A. The @WebResult annotation must exist. This statement is not entirely true. The @WebResult annotation is used to customize the name, target namespace, and other properties of the output message of a Web Service operation. However, if the method returns a single value or object, the @WebResult annotation is optional. If the method returns multiple values or objects, @WebResult must be used to annotate each return value or object.
B. Method parameters and return types must be JAXB compatible. This statement is true. JAXB (Java Architecture for XML Binding) is a framework that allows Java objects to be mapped to XML representations and vice versa. JAX-WS uses JAXB to serialize and deserialize parameters and return values of Web Service operations. Therefore, method parameters and return types must be annotated with JAXB annotations or be JAXB compatible, such as primitive types, String, and some standard Java classes.
C. Method parameters must be declared by using @WebParam. This statement is partially true. The @WebParam annotation is used to customize the name, target namespace, and other properties of the input message of a Web Service operation. However, if the method has only one parameter, the @WebParam annotation is optional. If the method has multiple parameters, @WebParam must be used to annotate each parameter.
D. The @WebMethod annotation must exist. This statement is not entirely true. The @WebMethod annotation is used to customize the name, operation style, and other properties of a Web Service operation. However, if the method meets the default requirements of JAX-WS, the @WebMethod annotation is optional. The default requirements are: the method name is used as the Web Service operation name, the method is public, the method is not static or final, and the method has a JAXB compatible return type or void.
In summary, option B is the true statement. Method parameters and return types must be JAXB compatible to be exposed as Web Service operations using JAX-WS API. The other options contain some inaccuracies or exceptions to the rules.