Web services can be created using two ways: top-down development and bottom-up development.

Top-down web services development

• Top-down Web services development involves creating a WSDL and then creating the Web service using the WSDL file. 

  • In top-down approach, first you design the implementation of the Web service by creating a WSDL file. You can then create the Web service skeleton Java classes from the wsdl, and add the required code. 

• JAX-WS tool wsimport can be used for creating a top down web service.

  • The wsimport can create stubs from a wsdl. 

  • See notes on JAX-WS tools wsimport and wsgen.

• Top down approach is also called as contract first or WSDL first approach.

• Most common in production scenarios.

• Example scenarios:

  • Users will be responsible for developing their own clients using different frameworks, based on a published WSDL.

Development tips

• Even in WSDL first approach, you can write a simple throwaway java class, generate a WSDL and then start customizing it based on our need.

Bottom-up web services development

• When creating a Web service using a bottom-up approach, first you write the java classes for the web service and then create the WSDL file and publish the web service.

  • Although bottom-up Web service development may be faster and easier, the top-down approach is the recommended way of creating a Web service.

• JAX-WS tool wsgen can be used for creating a bottoms up web service. 

  • The wsgen tool reads an existing web service implementation class (SIB) and generates the required JAX–WS portable artifacts for web service development and deployment.​

  • See notes on JAX-WS tools wsimport and wsgen.

• Bottum up approach is also called as Service first or code first approach.

• Ideal for learning web services.

  • Example scenarios:

    • Situations which need quick and faster completion may prefer Java approach

      • Java first approach is often the fastest and easiest approach.

    • Code reuse is required.

      • It may be better to write code first if you want to reuse code.