Java(TM) Boutique - Trader Pattern for Invoking Services

Reviews : Trader Pattern for Invoking Services :

Parsing the configuration information

Now once we have the configuration of Trader object pretty much done, we can write the parser that will parse these configuration files and create the appropriate object and return it to the calling client. Here we shall see a pretty much native and trivial implementation of the XML parsing. After all, the purpose of this article is not to show the best way of parsing XML but to show how it is used to get a Trader pattern up and running.

� We now write a class that is the Trader object. (Download the source code to see a complete source for this).

�
public class TraderConfigParser
{

�

� The parser is mainly responsible for the following activities:

Parse the component-definition.xml file and find the name of the component, its instance and interface definition and the service type.

�
  /**
     * Loads the trader configuration data.
     * @throws JDOMException
     */
    private void loadTraderConfigData() throws JDOMException

�

Parse the service-config.xml file.
Load the service configuration defined in this file with the component name as the key from the component-definition.xml file. For example, the component definition.xml file defines only two components Account and Person. So the attempt should only be to load the service information for these two components albeit there may be other component service configurations defined which are not in use.
Check for the specified service type in the component- definition.xml file and load the service configuration information for that service type only. For example, the Account component has definition for both "ejb" and "Java" service types. However, in the component-definition.xml file we have specified the service-type as "Java" . So the Trader should load the configuration information for the service type "Java" only.
Create an appropriate instance of the defined component instance and put it in a hashtable with the name of the component as the key.

All of this is done within a method called

�
/**
     * load the service configuration data  and creates 
	the instance of the requested
     * object and puts it into the hashtable with the 
	name of the component as the key.
     * @param componentName
     * @param interfaceName
     * @param instanceName
     * @param serviceType
     * @throws JDOMException
     * @throws ClassNotFoundException
     * @throws NamingException
     */
    private void loadServiceConfigData(String componentName, String
    interfaceName, String instanceName, String serviceType)
    throws JDOMException, ClassNotFoundException, NamingException

There is a public method to allow clients to get hold of the required instance of a service component by specifying the name of the component.

/**
     * Returns the requested component instance. Note that the client 
        needs to 
     * cast it back to the appropriate interface or implementation 
        class.
     * @param componentName
     * @return
     */ 
    public Object getComponent(String componentName)

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