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Basic configuration tactics

Arguments, variables, options and properties

The traditional approach to make an application is to extract relevant properties and put them in external property files. Setting environmental variables or command-line arguments are two other approaches. The following table gives an overview.

Type Get Set
[Command-Line Arguments http://java.sun.com/docs/books/tutorial/essential/environment/cmdLineArgs.html] just fetch from args in the main method: public static void main (String[] args) java Sort friends.txt, where Sort is the application and friends.txt is a command-line argument.
[java options - standard options http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/java.html] ManagementFactory.getRuntimeMXBean().getInputArguments() java -Xms1024m -Xmx1024m Sort
[java options - system property value http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/java.html] System.getProperty(key) java -Dproperty=value Sort
[System Properties http://java.sun.com/docs/books/tutorial/essential/environment/sysprop.html] System.getProperty("path.separator"); System.setProperties(new Properties(System.getProperties()));
[Environment Variables http://java.sun.com/docs/books/tutorial/essential/environment/env.html] System.getEnv export $ENV=environmentA (linux), set ENV=environmentA (windows)

File-based approaches

Load properties from a .properties file

  • Get from classpath Smartly load your properties - Classpath resources

  • Get from a jar file: 

    Properties properties = new Properties();
InputStream in = FileLoader.class.getClassLoader().getResourceAsStream("filename.properties");
if (in != null) {
    properties.load(in);
}

  • Get from filesystem: 

    Properties properties = new Properties().load(new FileInputStream("filename.properties"));

\ - Set: properties.store(new FileOutputStream("filename.properties"), null);

Read and write files

Use Apache Commons-IO

Configuration in Spring

Advanced Spring configuration Chapter 4: Resources PropertyConfigurers

TODO Many use Spring to load property-files during application context initialization. Can this be achieved by extending PropertyOverrideConfigurer and PropertyPlaceholderConfigurer?

If beans that need properties from external property-files are set to lazy-init, it is possible to load properties manually after application context initialization, but before the properties are actually used in the relevant beans.

Apache Commons Configuration

Apache Commons Configuration SpringModules Commons support Using Spring and Commons Configuration - an example

Load configuration from multiple sources with a priority

Properties can come from multiple sources, and it is necessary to prioritize the different sources.

Initial suggestion:

1a. Properties loaded from a path given as part of the command-line 1b. Properties loaded from default path 2. From ConfigService 3. From deployed jar file

Choosing the correct property files is easy when properties are loaded during the applications life-cycle.

Load properties directly from a database

Don't?