How can I use JPA to create a Settings class for my Java Servlet application? I'm thinking of something like a static class with a map of key/value pairs for storing the application settings like e-mail server address etc. Something like this:
public class ApplicationSettings {
private static Map<String, String> settings;
You can use Caching for storing the properties from database. You can use @Cacheable("properties") for calling the database service and load it in the cache. If you want to update, delete or add new property you can use @CacheEvict(value = "properties", allEntries = true) where you can call the database service to use do the actual operation. @CacheEvict will clear all the existing cache mapped for properties key and loads the new properties by calling @Cacheable("properties") implicitly
@Repository
public class ApplicationSettings {
private DatabaseService databaseService;
public ApplicationSettings(DatabaseService databaseService) {
this.databaseService = databaseService;
}
@Cacheable("properties")
public Map<String, String> getAppProperties() {
return databaseService.getAppProperties();
}
@CacheEvict(value = "properties", allEntries = true)
public void updateAppProperties(String key, String value) throws IOException {
databaseService.updateAppProperties(key, value);
}
}
You can now use ApplicationSettings wherever want can the properties like
@Autowired
private ApplicationSettings applicationSettings;
:
:
Map<String, String> appProperties = applicationSettings.getAppProperties();
You can use EhCache or simply use Sevlet Listener for achieving the above scenario
in web.xml
<web-app ....>
<listener>
<listener-class>
com.listernerpackage.ApplicationInitializationListener
</listener-class>
</listener>
:
Create a ServletContextListener
public class ApplicationInitializationListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent event) {
ServletContext context = event.getServletContext();
Map<String, String> properties = someDbManager.getAppProperties();
context.setAttribute("properties", properties );
}
}
You can retrieve the properties in servlet by calling
Map<String, String> properties = (Map<String, String>) this.getContext().getAttribute("properties");