SOAP Web Services Interview Questions- Part 4

Answer:

In Web Services Description Language (WSDL), which is an XML-based language used to describe web services, there are several types of operations that can be defined. These operation types specify the kind of interaction that clients can have with the web service. The following are the operation types commonly used in WSDL:

• One-way: This operation type is used when the client sends a request message to the server but does not expect a response in return. It’s a simple fire-and-forget mechanism where the client sends a request and moves on without waiting for a reply.
• Request-Response: This is a typical synchronous operation where the client sends a request message to the server and waits for a corresponding response message. It’s a simple back-and-forth interaction pattern.
• Solicit-Response: This operation type is the reverse of Request-Response. In this case, the server initiates the communication by sending a request to the client, and the client responds with a message.
• Notification: Also known as “event” or “publish-subscribe”, this operation type is used when the server sends a message to multiple clients that have subscribed to a particular event or notification.
• Request-Optional-Response: This operation type is similar to Request-Response, but the response is optional. The server can choose to send a response or not based on certain conditions.
• Robust In-Only: In this operation type, the client sends a message to the server, and the server acknowledges the receipt of the message. If the message is not received successfully, the server retries until it receives the message.
• Robust Out-Only: This is similar to the Robust In-Only operation, but in this case, the server sends a message to the client, and the client acknowledges the receipt.
• Robust In-Out: This combines the concepts of Robust In-Only and Request-Response. The client sends a message to the server and waits for a response. If the response is not received successfully, the server retries until the response is received.

Answer:

In a WSDL document, the element is used to define a specific endpoint for a particular service in a portType. It’s part of the overall description of a web service, helping to define its interface and binding.

The < port > element has two important attributes:

• name: This attribute specifies the name of the port. It serves as a unique identifier for the port within the context of the WSDL document. The name attribute is used to reference this port when defining bindings that implement the operations defined in the associated portType.
• binding: The binding attribute is used to associate the port with a particular binding in the WSDL document. It specifies the name of the binding that should be used for this port. The binding defines the concrete protocol and message format details for the operations described in the portType. By specifying the binding, the element essentially links the abstract operations defined in the portType with the concrete implementation defined in the binding.

Answer:

WSDL permits the inclusion of extensibility elements utilized for defining binding details. The following key aspects should be taken into account when performing binding:

• A port should only indicate a single address and;
• Must refrain from indicating any binding details apart from address information.

Answer:

Web service deployment commonly relies on a layered stack of technologies. Another way to analyze the architecture of a web service is by examining its protocol stack. To put it simply, this stack consists of a set of protocols that enable the exploration and execution of online services. The web service protocol stack is currently organized into four tiers, as outlined below:

1. Service Transport: This tier manages the transportation of communications between various programs. Its role is to establish communication technology standards and enable the smooth flow of messages or information across a network. Protocols such as HTTP, SMTP, FTP, and DEEP are utilized to transfer data.
2. XML Messaging: This layer is responsible for encoding messages into XML format, ensuring mutual understanding on both ends. Typical examples of this layer include XML-RPC and SOAP.
3. Service Description: The Service Description tier is tasked with providing a description of the public web interface. WSDL is the standard format used to describe services in this context.
4. Service Discovery: This tier primarily centralizes services into a single registry, simplifying the process of publishing and discovering online services. UDDI is a commonly used standard for service discovery.

Answer:

Statelessness in the context of RESTful web services refers to a fundamental principle where each HTTP request from a client to a server must contain all the information necessary to understand and process that request. In other words, the server should not rely on any information stored on its side from previous requests.

Answer:

The SOAP (Simple Object Access Protocol) message or document is a protocol used for exchanging structured information in the implementation of web services. A SOAP message consists of the following key elements:

1. Envelope: This is the outermost element that encloses the entire SOAP message. It defines the start and end of the message and contains two mandatory child elements: the Header and the Body.
2. Header: The Header is an optional element that carries additional information about the SOAP message, such as authentication credentials, message routing instructions, or any other metadata. It’s often used for passing context information relevant to the processing of the message.
3. Body: The Body is a mandatory element that contains the main content of the SOAP message. It holds the data being exchanged between the sender and the receiver. The actual payload, which could be in various formats (e.g., XML), resides within the Body.

Answer:

.NET Web services and .NET Remoting are both technologies used in the Microsoft .NET framework for building distributed applications, but they have some key differences in terms of their focus and usage:

1. Communication Protocol:
   • .NET Web services: Web services primarily use the Simple Object Access Protocol (SOAP) over HTTP as the communication protocol. They are designed to be platform-independent and can be consumed by various clients, including those developed on different platforms.
   • .NET Remoting: .NET Remoting uses a binary communication protocol and is optimized for communication within the .NET framework. It offers more efficient communication between objects hosted on different application domains within the same process or across processes on the same machine.
2. Communication Format:
   • .NET Web services: Web services use XML for data serialization, making them human-readable and platform-independent. This can lead to increased message size and slower performance compared to binary formats.
   • .NET Remoting: .NET Remoting uses binary serialization, which results in more compact messages and faster communication between components within the same framework.
3. Use Cases:
   • .NET Web services: Web services are best suited for scenarios where interoperability with non-.NET applications or technologies is important. They are often used for exposing APIs that can be accessed over the internet or intranet.
   • .NET Remoting: .NET Remoting is better suited for scenarios where performance and tight integration within the .NET ecosystem are critical. It’s often used for communication between components within a single application, especially when high performance is required.
4. Security:
   • .NET Web services: Web services support various security mechanisms, including WS-Security, for securing communication and data integrity over the internet.
   • .NET Remoting: .NET Remoting typically relies on the underlying transport for security, such as using Secure Sockets Layer (SSL) for secure communication.
5. Cross-Platform Compatibility:
   • .NET Web services: Due to their use of standardized protocols like SOAP and HTTP, web services can be consumed by applications running on different platforms and using different programming languages.
   • .NET Remoting: .NET Remoting is more tightly coupled with the .NET framework and is generally not suitable for cross-platform communication.

Answer:

In the JAXB (Java Architecture for XML Binding) framework, there are three different packages that play key roles in the XML binding process. These packages are:

• xml.bind
• xml.bind.helper
• xml.bind.util

Answer:

• Technology Scope:
  • Web services are designed for communication over the internet using open standards and protocols.
  • CORBA is a middleware technology for distributed computing and supports multiple programming languages and platforms.
  • DCOM is a Microsoft-specific technology for distributed communication within Windows environments.
• Standards and Protocols:
  • Web services use HTTP, XML, and SOAP for communication, making them platform-independent and widely adopted.
  • CORBA uses its own protocol, IIOP (Internet Inter-ORB Protocol), for communication between objects.
  • DCOM relies on proprietary protocols developed by Microsoft.
• Platform Independence:
  • Web services and CORBA are designed to work across different platforms and operating systems.
  • DCOM is tightly integrated with Windows and is not as cross-platform as the other two technologies.
• Language Support:
  • Web services and CORBA are language-agnostic and support multiple programming languages.
  • DCOM is primarily designed for COM components written in languages like C++ and is closely associated with the Windows programming environment.

Answer:

Security in SOAP services can be achieved using various security standards such as WS-Security. This standard provides authentication, message integrity, and encryption through XML-based security tokens and signatures.

Answer:

JAX-RPC stands for Java API for XML-based Remote Procedure Call. It is a technology that was part of the Java EE (Enterprise Edition) platform, used for building and consuming web services in Java. JAX-RPC provided a set of APIs and tools that allowed developers to create remote procedure calls using XML-based protocols, such as SOAP. This enabled distributed communication between different software components running on different machines, making it possible to build applications that could interact over network.

Answer:

Below are the differences between RMI and Web Services:

1. Technology Stack:
   • RMI is specifically designed for Java applications, making it tightly coupled with the Java programming language.
   • Web Services are language-independent and can be implemented using a variety of programming languages, making them more versatile in heterogeneous environments.
2. Communication Protocol:
   • RMI often uses its own custom communication protocol, making it efficient for Java-to-Java communication.
   • Web Services typically use standard protocols like HTTP, SOAP, or REST, which enable interoperability between different platforms and languages.
3. Platform Independence:
   • RMI is more suitable for Java-centric environments and might face challenges when interacting with non-Java applications.
   • Web Services are designed to work seamlessly across diverse platforms and can facilitate communication between applications written in different languages.
4. Integration and Interoperability:
   • Web Services are better suited for integrating systems that use different technologies, as they follow standardized communication protocols.
   • RMI is better for scenarios where Java components need to communicate directly and efficiently within a Java ecosystem.
5. Flexibility:
   • Web Services offer various architectural styles like SOAP-based or RESTful services, providing flexibility in designing communication patterns.
   • RMI provides a more specific Java-oriented approach for remote method invocation.

Answer:

gRPC stands for “Remote Procedure Call” (RPC) over HTTP/2. It is a modern open-source framework developed by Google for creating efficient and high-performance APIs. gRPC allows you to define your service methods and data structures using Protocol Buffers (protobufs), a language-agnostic binary serialization format. These definitions are used to generate code for multiple programming languages, making it easy to create client and server implementations in various languages.

Answer:

While microservices focus on the architecture of breaking down an application into small, independent services, REST is an architectural style for designing networked applications. It’s worth noting that microservices can use REST as a communication mechanism between services, but they can also employ other communication methods like gRPC, messaging queues, etc.

Answer:

Here are the key differences between REST and GraphQL:

1. Data Fetching Flexibility:
   • REST: In a REST API, the server defines endpoints, and clients make requests to these endpoints to retrieve data. Each endpoint usually corresponds to a specific resource, and the server decides what data is returned.
   • GraphQL: With GraphQL, clients can request exactly the data they need using a single query. This eliminates over-fetching (receiving more data than needed) and under-fetching (receiving less data than needed) issues that might occur in REST APIs.
2. Number of Requests:
   • REST: Clients often need to make multiple requests to different endpoints to gather all the data they need. This can lead to over-fetching.
   • GraphQL: Clients can get all the required data in a single request, reducing the number of round trips between the client and the server.
3. Response Format:
   • REST: The server determines the structure of the response. Clients might receive more or less data than they actually require.
   • GraphQL: Clients specify the structure of the response in the query, and the server returns data in the exact format requested.
4. Versioning:
   • REST: Often requires versioning when changes are made to the API to maintain backward compatibility.
   • GraphQL: Since clients request only the data they need, adding or modifying fields usually doesn’t require versioning.
5. Complexity:
   • REST: Simpler for basic use cases, but can become complex when dealing with multiple resources and relationships.
   • GraphQL: Provides more control and flexibility, which can lead to simpler queries, but might also require more effort to set up and optimize.
6. Caching:
   • REST: Can use HTTP caching mechanisms effectively for individual resources.
   • GraphQL: Caching can be more challenging due to the dynamic nature of queries.
7. Security:
   • REST: Security mechanisms like API keys and OAuth can be applied at the endpoint level.
   • GraphQL: Requires careful validation of incoming queries to prevent potentially malicious or overly complex queries (GraphQL query depth and complexity limiting).
8. Tooling and Documentation:
   • REST: Usually has clear documentation for endpoints, but clients might need to consult multiple endpoints for related data.
   • GraphQL: Requires comprehensive schema documentation, but offers more self-documenting capabilities since clients can explore the schema and use introspection to understand available data and types.

Answer:

The wsimport tool is a command-line utility provided by the Java Platform, Enterprise Edition (Java EE) and Java Development Kit (JDK). It is used to generate Java classes or client-side artifacts from a given Web Services Description Language (WSDL) file. The wsimport tool helps simplify the process of creating Java classes that can interact with web services by automatically generating the necessary code to handle the communication and data mapping between the client and the service. It creates Java classes, interfaces, and other resources that allow developers to easily integrate and consume web services in their Java applications.

Answer:

Resources are at the core of the REST architectural style and play a crucial role in creating a structured and organized way of building web services. Each resource should have a unique URI that serves as its address, and clients can interact with these resources by making HTTP requests (GET, POST, PUT, DELETE, etc.) to their corresponding URIs.

Answer:

Both PUT and POST are HTTP methods used to send data to a server, but they have different purposes and use cases:

1. POST (Create):
   • Purpose: POST is primarily used to submit data to be processed to a specified resource. It’s often used to create a new resource on the server.
   • Idempotent: POST requests are not guaranteed to be idempotent, meaning that sending the same request multiple times may result in different outcomes.
   • Response: Typically, a successful POST request will return a status code indicating the creation of a new resource and a location header pointing to the newly created resource’s URL.
2. PUT (Update):
   • Purpose: PUT is used to update or replace a resource on the server. It sends the entire updated representation of the resource to the server.
   • Idempotent: PUT requests are designed to be idempotent, meaning that sending the same request multiple times will result in the same outcome as sending it once.
   • Response: A successful PUT request usually returns a status code indicating that the resource has been updated or replaced.

Answer:

WADL stands for Web Application Description Language. It refers to an XML description of a deployed RESTful web application.

Answer:

EasyRest, Jersey, and Restlet are used to implement REST Web Services.