javawebparts.listener
Class AppConfigContextListener

java.lang.Object
  |
  +--javawebparts.listener.AppConfigContextListener

All Implemented Interfaces:

java.util.EventListener, javax.servlet.ServletContextListener

public class AppConfigContextListener

extends java.lang.Object

implements javax.servlet.ServletContextListener

Most applications of even modest complexity require configuration information. A common method of providing this information is via XML file. Often times a developer will want to expose this information via a simple Javabean throughout the rest of the application. This ServletContextListener provides a simple way to read in an XML configuration file and populate a bean, either one the developer creates or a simple "default" bean.

Init parameters are:

• configFile - The context-relative path to the XML configuration file for the context. This is the only required parameter, but there are some limitations if it is all you supply. See the comments after this parameter list for those details. Required: yes. Default: none.



• rootElement - Defines what the root element of the config file is. If none is specified, <config> is used by default. Required: no. Default: config.



• configClass - This parameter names the class that will act as the configuration information holder. Typically, this class will expose getters and setters for each element in the configuration file and store all the data in static members. In other words, something like this is typical:
  
  For an XML config file like this:
  <config>
  <firstName>Frank</firstName>
  </config>
  
  The following bean could be used:
  public class MyConfigBean {
  private static String firstName;
  public void setFirstName(String inFirstName) {
  firstName = inFirstName;
  }
  public String getFirstName() {
  return firstName;
  }
  }
  
  If this parameter is not present, the AppConfig class will be used. The AppConfig class defines a single String get(String key) method for your use, whereas a custom class can expose real setters and getters for each element, or even more complex constructs if required (i.e., maybe one of your parameters is a comma-separated list, and you want your setter to parse it into a List). Required: no. Default: AppConfig class.



• rulesetClass - When a custom configClass is used, the developer can also create a class that sets Commons Digester rules. This allows for parsing of more complex XML files. This is only applicable when configClass is used, and even then is optional. If a rulesetClass is NOT defined, then the config file must follow the same rules as when a custom appConfig class is not used, namely that the root element must be <config> and it must be "flat" (i.e., all elements must be direct children of <config>). Required: no. Default: none.

Three "modes" of operation are suppported and you can think of them as Basic, Intermediate and Advanced. The Basic configuration requires that you specify the configFile parameter only. In this mode, the AppConfig object will be used and the root element of the config file MUST be "config". The config file must be "flat", that is, elements can only be nested under the root, not under any other child nodes of root. In Intermediate mode, you will specify the configFile, as well as the root element and the configClass. Your class must expose setters for each element of the config file. In Advanced mode, you will also specify a class that sets Commons Digester rules to use to parse the XML. This is good if you have a more complex structure that you want to support (i.e., repeating elements for a collection or multi-level nesting).

Example configuration in web.xml:

<context-param>
<param-name>configFile</param-name>
<param-value>/WEB-INF/app_config.xml< /param-value></context-param>
<context-param>
<param-name>rootElement</param-name>
<param-value>config</param-value> </context-param>
<context-param>
<param-name>configClass</param-name>
<param-value>javawebparts.sampleapp. SampleAppConfigBean</param-value>
</context-param>
<context-param>
<param-name>AjaxPartsTaglibConfig</param-name>
<param-value>/WEB-INF/ajax_config.xml</param-value>
</context-param>

<listener>
<listener-class>javawebparts.listener. AppConfigContextListener</listener-class>
</listener>

Author:

Frank W. Zammetti.

Field Summary

private java.lang.String	configClass The class that holds our config information.
private java.lang.String	configFile Path to the config file.
private static org.apache.commons.logging.Log	log Log instance.
private java.lang.String	rootElement The root element of the config file.
private java.lang.String	rulesetClass The class that is called to configure the Digester ruleset.

Constructor Summary

AppConfigContextListener()

Method Summary

void	contextDestroyed(javax.servlet.ServletContextEvent sce) Doesn't do anything, but needed to be here.
void	contextInitialized(javax.servlet.ServletContextEvent sce) The container calls this when the context is initialzed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

log

private static org.apache.commons.logging.Log log

Log instance.

configFile

private java.lang.String configFile

Path to the config file.

rootElement

private java.lang.String rootElement

The root element of the config file.

configClass

private java.lang.String configClass

The class that holds our config information.

rulesetClass

private java.lang.String rulesetClass

The class that is called to configure the Digester ruleset.

Constructor Detail

AppConfigContextListener

public AppConfigContextListener()

Method Detail

contextInitialized

public void contextInitialized(javax.servlet.ServletContextEvent sce)

The container calls this when the context is initialzed.

Specified by:

contextInitialized in interface javax.servlet.ServletContextListener

Parameters:

sce - ServletContextEvent instance reference

contextDestroyed

public void contextDestroyed(javax.servlet.ServletContextEvent sce)

Doesn't do anything, but needed to be here.

Specified by:

contextDestroyed in interface javax.servlet.ServletContextListener

Parameters:

sce - ServletContextEvent instance reference