Question

State whether each of the following is true or false. If \(f\) alse, explain why. a) All methods of a web service class can be invoked by clients of that web service. b) When consuming a web service in a client application created in Netbeans, you must create the proxy class that enables the client to communicate with the web service. c) A proxy class communicating with a web service normally uses SOAP to send and receive messages. d) Session tracking is automatically enabled in a client of a web service. c) Web methods cannot be declared static. f) A user-defined type used in a web service must define both get and set methods for any property that will be serialized.

Short answer

a) False; b) False; c) True; d) False; e) True; f) True.

Step-by-step solution

Analyzing part (a)

For part (a), we need to determine if all methods of a web service class are accessible to clients. Not all methods may be accessible because a method must be marked as a web method or have specific access annotations or configurations to be exposed to clients. Therefore, the statement is false.

Evaluating part (b)

For part (b), it asks if a proxy class must be created manually in NetBeans for client-server communication. Modern IDEs like NetBeans can generate proxy classes automatically when consuming a web service, so manual creation isn't always necessary. Hence, the statement is false.

Assessment of part (c)

For part (c), the statement claims that a proxy class uses SOAP. This is typically true for many SOAP-based web services. However, there's also REST, which does not use SOAP. The statement lacks this context but in SOAP-specific scenarios, it's true.

Explanation of part (d)

For part (d), it states that session tracking is automatically enabled for web service clients. This is typically false as web services themselves, especially RESTful services, are stateless by design. Therefore, explicit session handling must be implemented if needed.

Clarification for part (e)

The statement in part (e) claims that web methods cannot be static. This is true because web methods are intended to operate on instances of a class and static methods do not have access to instance members.

Understanding part (f)

Part (f) claims user-defined types must have get and set methods for serialization. This is generally true as properties of user-defined types are typically serialized using their getter and setter methods to be correctly marshaled or unmarshaled.

Key concepts

Web Service Methods

Web services allow clients and servers to communicate over a network by invoking methods that perform specific operations. However, not all methods in a web service class are accessible to clients directly. Only methods that are explicitly exposed as web methods, through annotations like `@WebMethod` in Java, can be called by external clients. This restriction helps maintain security and encapsulation, ensuring that only the necessary functionality is available outside the service. Not exposing all methods helps in controlling what the clients can do, keeping internal logic safe from unwanted interactions.
It's crucial to understand that web methods should be designed with care, focusing on the needs of the client while protecting the backend logic. This is why understanding the method's access control and configuration is essential for designing robust web services.

Proxy Class

In the context of web services, a proxy class acts as an intermediary between the client and the web service itself. It essentially serves as a local representation of the service, presenting the service methods to the client application in a way that's easy to interact with. When using IDEs like NetBeans, this proxy class can often be generated automatically. This auto-generation simplifies the task for developers, saving time and reducing the chance of errors that can occur with manual coding.
The proxy class abstracts the complexities involved in communication protocols, allowing developers to focus on integrating the web service into their applications without delving into the underlying communication details. By using a proxy class, developers can call web service methods as if they were local methods, making the coding experience seamless and efficient.

SOAP vs REST

SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) are two popular approaches for web services. SOAP is known for its robust standardization and supports complex operations by leveraging XML-based messaging. This protocol is often used in enterprise environments for its strong security and transaction management capabilities.
REST, on the other hand, is more lightweight and uses standard HTTP methods, making it easier to implement and utilize. It typically works well with a wide range of data formats, including JSON, making it a preferred choice for web services that require high scalability and flexibility. While SOAP services use a WSDL to describe its interface, REST is more about resources and is designed to work over the HTTP protocol.

• SOAP is protocol-driven; REST is resource-driven.
• SOAP offers built-in security (WS-Security); REST can use HTTPS.
• SOAP is more secure and has features for operations like transactions.
• REST is simpler and operates over standard web protocols.

This comparison highlights why developers might choose one over the other depending on their specific needs.

Session Tracking

Session tracking is an important feature, especially in web applications that require stateful interactions. However, many web services, particularly RESTful services, are designed to be stateless. This means they do not maintain session state between requests, providing a simple and scalable interaction model.
To implement session tracking in such stateless frameworks, developers often resort to using tokens or custom mechanisms to track sessions, if required. This can include passing session identifiers or using frameworks that support session persistence. The lack of built-in session tracking enables better scalability but requires developers to design session management carefully when state needs to be preserved across multiple interactions.

Static Methods

In object-oriented programming, static methods belong to the class rather than any particular instance. They are designed to be called on the class itself rather than on a specific object instance. This is why web methods, which operate on instances, cannot be static. By definition, web methods often need to interact with the instance-specific data and state maintained by the web service.
Static methods lack access to instance fields and properties, making them unsuitable for tasks that require instance-specific actions or state alterations. Therefore, web services are typically designed with instance methods to properly respond to client requests using the current state of an object, ensuring correct and meaningful interactions.

Serialization

Serialization is the process of converting an object into a format that can be easily transported over a network or stored. This is crucial in web services where data needs to be sent between different systems. Serialization typically involves converting objects into XML or JSON, which can be easily parsed by various programming environments.
In the context of web services, user-defined types need to have properties that can be serialized and deserialized, typically through getter and setter methods. This ensures that all necessary data is correctly marshaled before being sent and accurately reconstructed when received. Serialization allows complex data types to be transmitted across different platforms, enabling interoperability between various technologies and systems.