When you want to externalize some of your configuration in a .properties file. A lot of the times it can be for things like the database.url and database username, because that will be different for each environment you deploy and
test on you don't want that information to be put in your Spring xml file. So you can bump it out to a .properties file.
The PropertyPlaceholderConfigurer is a BeanFactoryPostProcess that looks at the configuration that was read in and replace any "${variableName}" with the value for the variableName that is in the .properties file set in the location property of the PropertyPlaceholderConfigurer
so
and your myprops.properties file could look like
I don't remember URLs for datasources but that still shows you how it works.
Now, I hope you didn't have me write all that out just so you could have a question in this forum for the Book giveaway?
Mark