Web service Interview Question

  • What Are Web Services?
  • Web services are client and server applications that communicate over the WWW's HTTP. As described by the World Wide Web Consortium (W3C), web services provide a standard means of interoperating between software applications running on a variety of platforms and frameworks. Web services are characterized by their great interoperability and extensibility as well as their machine-processable descriptions. Web services can be combined in a loosely coupled way to achieve complex operations. Programs providing simple services can interact with each other to deliver sophisticated added-value services.
  • Why web services?
  • 1) Interoperability : work outside of private networks, can easily programming with other languages (virtually platform-independent)
    2) Loosely Coupled: independently work
    3) Usability
    4) Deployability : Easily deploy, can use SSL
    5) Reuse
  • Explain web service architecture?
  • 3 different layers and roles are as below
    Service Provider: Service provider role is to create the web service and makes it accessible to the client applications over the internet for their usage.
    Service Requestor: Any consumer of web service like any client application. Client applications are written in any language contact web service for any type of functionality by sending XML request over network.
    Service Registry: Service registry is the centralized directory which helps locate web services for client applications.

    The Service Provider uses the ‘Publish’ interface of Service Registry to make the existing web services available to client applications. With all the information provided by the service registry, service requestor is able to bind or invoke services.
  • What are different types of Web Services?
  • There are two types of web services : 'big' and RESTful. Big(SOAP) Web Services: Runs on SOAP protocol and uses XML technology for sending data. RESTful Web Services: Runs on HTTP/HTTPS protocol almost all the time. RESTful is a stateless client-server architecture where web services are resources and can be identified by their URIs. Client applications can use HTTP GET/POST methods to invoke RESTful web services.
  • What are the components of web service?
  • SOAP- Simple Object Access Protocol
    XML- Extensible Markup Language
    WSDL- Web Service Description language
    UDDI- Universal Description, Discovery, and Integration
    RDF- Resource Description Framework
  • Explain the term Interoperability with respect of Web services?
  • The term widely used in product marketing description which defines the ability of different products or systems working together without any special effort from the customer part. Communication between various applications, sharing of data as well as services among themselves. There is no restriction on the which type of application to be in communication. If any code is written, it will be treated as generic code that will be understood by all application. Thus, the cost of writing specific codes for each application is reduced.
  • Define web service protocol stack and its layers?
  • 1) Service transport: Helps in transporting XML messages between various client applications.
    Commonly uses the below-mentioned protocols:
    HTTP(Hypertext Transport Protocol)
    SMTP(Simple Mail Transport Protocol)
    FTP(File Transfer Protocol)
    BEEP(Block Extensible Exchange Protocol)

    2) XML messaging: Messages are encoded in common XML format which is easily understood by others.
    This layer includes : XML-RPC and SOAP(Simple Object Access Protocol)

    3) Service description: Location, available functions, and data types for XML messaging which describes the public interface to a specific web service.
    This layer includes : WSDL(Web Service Description Language)

    4) Service discovery: Responsible for providing a way to publish and find web services over the web.
    This layer includes: UDDI(Universal Description, Discovery, and Integration)
  • What is XML-RPC?
  • RPC(Remote Procedure Call) is the method of calling a procedure or function available on any remote computer and XML (Extensible Markup Language).
    XML-RPC represents a simple protocol that performs RPCs by using XML messaging. Excellent tool for connecting different environments and establishing connections between wide varieties of computers.
  • What are the features of XML-RPC?
  • What are advantages of web services?
  • Differentiate SOAP and REST?

    SOAP web service

    RESTful web service

    Java API for SOAP web service is JAX-WS. Java API for RESTful web service is JAX-RS.
    Simple Object Access Protocol (SOAP) serves as a standard protocol for web service creation. Representational State Transfer (REST) is an architectural style for web service creation.
    Web services and clients are tightly coupled and define some standards that need to be strictly followed. It does not follow many standards and is loosely coupled.
    It requires more bandwidth and resource as well as uses service interfaces for exposing business logic. It requires less bandwidth and resource as well as uses URI (Uniform Resource Identifiers) for exposing business logic.
    Permits XML data format only. Permits data formats like Plain text, HTML, JSON, etc.
    It is usually less preferred It is usually more preferred
    SOAPUI can be used for testing SOAP web services. Browsers and extensions such as Chrome postman are used for testing RESTful web services.
    Its own security and uses WSDL contract for binding web services and client programs. It does not have any defined contract as well as does not have its own security methods.
    Standard communication protocol on top of transport protocols such as HTTP, SMTP, Messaging, TCP, UDP, etc. transmitted over transport protocol such as HTTP(S).
    SOAP Layers REST Layers
    cannot be cached can be cached
    Supports both SSL security and WS-security Supports only point-to-point SSL security
    Has comprehensive support for both ACID based transaction management for short-lived transactions and compensation based transaction management for long-running transactions. It also supports two-phase commit across distributed resources. REST supports transactions, but it is neither ACID compliant nor can provide two phase commit across distributed transactional resources as it is limited by its HTTP protocol.
    SOAP has success or retry logic built in and provides end-to-end reliability even through SOAP intermediaries. REST does not have a standard messaging system, and expects clients invoking the service to deal with communication failures by retrying.
  • WS-Security maintains its encryption right up to the point where the request is being processed.
  • WS-Security allows you to secure parts (e.g. only credit card details) of the message that needs to be secured. Given that encryption/decryption is not a cheap operation, this can be a performance boost for larger messages.
  • It is also possible with WS-Security to secure different parts of the message using different keys or encryption algorithms. This allows separate parts of the message to be read by different people without exposing other, unneeded information.
  • SSL security can only be used with HTTP. WS-Security can be used with other protocols like UDP, SMTP, etc.
  • Client encrypts all of the requests based on a key retrieved from a third party. When the request is received at the destination, it is decrypted and presented to the service. This means the request is only encrypted while it is traveling between the client and the server. Once it hits the server (or a proxy which has a valid certificate), it is decrypted from that moment on.
  • The SSL encrypts the whole message, whether all of it is sensitive or not.
  • Can we maintain user session in web services?
  • Web services are stateless so we can’t maintain user sessions in web services.
  • What is difference between SOA and Web Services?
  • Service Oriented Architecture (SOA) is an architectural pattern where applications are designed in terms of services that can be accessed through communication protocol over network. SOA is a design pattern and doesn’t go into implementation.
    Web Services can be thought of as Services in SOAP architecture and providing means to implement SOA pattern.
  • Define SOA?
  • SOA (Service Oriented Architecture ) is an architectural pattern consisting of services. Application components provide services to the other components using communication protocol over the network. This communication involves data exchanging or some coordination activity between services. Key principles of SOA
  • What is the role of SOAPUI?