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reading and writing configuration in Spring Boot

I'm building a fairly simple Spring Boot application which needs some configuration to be set (and regularly updated as part of it's use). I'd like to create a simple admin interface and first-run wizard to set/update this configuration.
I'd like a way to easily read and write these configuration values within the application and have them persist. I would like to avoid the overhead of a database for 5-10 configuration strings. There is some good documentation on externalising configuration in Spring Boot but it doesn't talk about how this config could be updated and persisted by the app.
Options I have come up with:
There is a write option with Spring configuration that I'm not aware of (this would be awesome)
Don't use the Spring Boot configuration functionality, instead use apache commons configuration (or similar??) to read and write to a file which lives in a location specified by an environment variable
as per option 2 but use HSQL, H2 or Derby as a file-based database
Thanks for any suggestions as to how best to achieve this.

Where to save a configuration file uploaded by admin?

I am working on a web application, developed using spring mvc and server is tomcat. Now one of the requirement is that admin can upload a spring related service configuration file(which is different from the spring service configuration file residing in src code) with some changes because we want to make it configurable. Now server will be restarted to get the modified changes.
Now I am confused about one thing, where I should upload this file(file system?) so that when server is started then configured listener will pick up new configuration file.
Pls suggest solution considering it as enterprose aplication.

Find out the reasonable place to keep your system files, other than in webapps/.
(I had kept next to log folder.)
Use Spring's PropertyPlaceholderConfigurer to read file locations from properties file.
Use same locations and Create ApplicationContext object, in a factory method (You can pass any number of files).
Use getBean on applicationContext object to use beans.

Spring MVC Web App with Default user

I am developing a web app using Spring MVC and Hibernate that I hope to package up as a WAR file and distribute for users to deploy where needed.
The application will require the database connection details before deploying, can anyone advise on the best practice of how to do this? currently my database.properties file is packaged as part of the WAR file, is there an easier way than asking the user to manually edit this file inside the WAR file or in the source and then expect them to build the war file themselves?
I would also like an easy way for users to create a single admin user on first deploy easily - is it best to just provide a sql script to create that or is there a way to include the functionality in the web app so on first deploy it creates the user?
Thanks

Since web applications are not focused to "mass production", I can't tell if something like that is possible.
You can make an SQL script containing all your CREATE statements limited by "IF NOT EXISTS" to avoid deleting existing data. Hibernate can execute a sql script at the moment of creating the SessionFactory, if Hibernate finds a file named "import.sql" located in the classpath root, Hibernate will execute it. Also you can always edit the database.properties of an application already deployed without re-packaging the WAR.

Try Liquibase, http://www.liquibase.org/ . It does not allow your users to setup database connection details but it allows you to manage the database schema (create and update the schema) and default data.

Streaming Dynamic Files from Spring MVC

I've got a Spring Web MVC application (and also a BlazeDS application, though not as relevant) where files are dynamically generated based on certain client actions.
I'd like to just map a certain directory on the file system to Spring MVC (or the app server) url and let it serve the files in that directory (with streaming and standard last-modified header support). Ideally, the mapped directory would be configured via the spring config, since I already have support per-machine for setting that up.
So, how can I do this? The best I can find so far is to write a controller that reads the file manually and streams it byte-by-byte. However, that seems far less than ideal. Is support for something like this already baked into Spring MVC or the standard application server spec?
Thanks!

If your processing model supports it, why not cut the middleman of the filesystem out of the picture completely and just stream the files back through the response stream as they are generated? Take a look at the AbstractExcelView and AbstractPDFView classes of Spring MVC to see some examples of how this is done.

or the standard application server spec?
Yes, there is. As you didn't mention which one you're using, I'll give a Tomcat-targeted answer. All you basically need to do is to add a Context element for /path/to/your/resources in /conf/server.xml:
<Context docBase="/path/to/your/resources" path="/resources" />
This way they'll be accessible through http://example.com/resources/...

Ideal for this is using an lightweight proxying server in front of your appserver, like a nginx or lighthttpd. You can configure it for serving static content, without calling your app.
If directory and files so dynamic, you can prepare real path to file at your controller and give this filepath to the frontend server, using headers. For example for nginx it's a X-Accel-Redirect header. Read more about this (and follow links for other http servers) there

What is the best way to allow both a servlet and client-side scripts read the same file?

We want to share user validation configuration between a Java validation class (for sanity checking) and a Javascript-enabled form web interface (for usability). What's the best way to deploy this static file in our web application so that it is both available to the server-side code, and available via a URL accessed by the client?
So far I've thought of putting the file in the application root and pointing the validation class at it when it is used, and putting the file in the WEB-INF/classes directory and somehow configuring the container to serve it.
Has anyone else configured a web application like this? What did you end up doing?

Yeah. Put it in the WEB-INF/classes and have a servlet serve out the relevant portion of the validation configurations based on something like a form-id. Better yet, have the servlet transform the configuration into a JSON object and then you can simply include a script tag and start using it :)