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Chapter 23. Bottom-Up Service Development

Abstract

There are many instances where you have Java code that already implements a set of functionality that you want to expose as part of a service oriented application. You may also simply want to avoid using WSDL to define your interface. Using JAX-WS annotations, you can add the information required to service enable a Java class. You can also create a Service Endpoint Interface (SEI) that can be used in place of a WSDL contract. If you want a WSDL contract, Apache CXF provides tools to generate a contract from annotated Java code.
To create a service starting from Java you must do the following:
  1. Create a Service Endpoint Interface (SEI) that defines the methods you want to expose as a service.
    Tip
    You can work directly from a Java class, but working from an interface is the recommended approach. Interfaces are better suited for sharing with the developers who are responsible for developing the applications consuming your service. The interface is smaller and does not provide any of the service's implementation details.
  2. Add the required annotations to your code.
  3. Generate the WSDL contract for your service.
    Tip
    If you intend to use the SEI as the service's contract, it is not necessary to generate a WSDL contract.
  4. Publish the service as a service provider.

23.1. Creating the SEI
링크 복사

Overview
링크 복사

The service endpoint interface (SEI) is the piece of Java code that is shared between a service implementation and the consumers that make requests on that service. The SEI defines the methods implemented by the service and provides details about how the service will be exposed as an endpoint. When starting with a WSDL contract, the SEI is generated by the code generators. However, when starting from Java, it is the developer's responsibility to create the SEI.
There are two basic patterns for creating an SEI:
  • Green field development — In this pattern, you are developing a new service without any existing Java code or WSDL. It is best to start by creating the SEI. You can then distribute the SEI to any developers that are responsible for implementing the service providers and consumers that use the SEI.
    Note
    The recommended way to do green field service development is to start by creating a WSDL contract that defines the service and its interfaces. See Chapter 25, A Starting Point WSDL Contract.
  • Service enablement — In this pattern, you typically have an existing set of functionality that is implemented as a Java class, and you want to service enable it. This means that you must do two things:
    1. Create an SEI that contains only the operations that are going to be exposed as part of the service.
    2. Modify the existing Java class so that it implements the SEI.
    Note
    Although you can add the JAX-WS annotations to a Java class, it is not recommended.

Writing the interface
링크 복사

The SEI is a standard Java interface. It defines a set of methods that a class implements. It can also define a number of member fields and constants to which the implementing class has access.
In the case of an SEI the methods defined are intended to be mapped to operations exposed by a service. The SEI corresponds to a wsdl:portType element. The methods defined by the SEI correspond to wsdl:operation elements in the wsdl:portType element.
Tip
JAX-WS defines an annotation that allows you to specify methods that are not exposed as part of a service. However, the best practice is to leave those methods out of the SEI.
Example 23.1, “Simple SEI” shows a simple SEI for a stock updating service.

Example 23.1. Simple SEI

package com.fusesource.demo;

public interface quoteReporter
{
  public Quote getQuote(String ticker);
}
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Implementing the interface
링크 복사

Because the SEI is a standard Java interface, the class that implements it is a standard Java class. If you start with a Java class you must modify it to implement the interface. If you start with the SEI, the implementation class implements the SEI.
Example 23.2, “Simple Implementation Class” shows a class for implementing the interface in Example 23.1, “Simple SEI”.

Example 23.2. Simple Implementation Class

package com.fusesource.demo;

import java.util.*;

public class stockQuoteReporter implements quoteReporter
{
  ...
public Quote getQuote(String ticker)
  {
    Quote retVal = new Quote();
    retVal.setID(ticker);
    retVal.setVal(Board.check(ticker));[2]
    Date retDate = new Date();
    retVal.setTime(retDate.toString());
    return(retVal);
  }
}
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[2] Board is an assumed class whose implementation is left to the reader.
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