Tag Archives: Java

Articles that discuss the Java programming language, the Java virtual machine or related topics.

Managed configuration in Spring

The Spring Framework offers many options to configure your applications. Most of these options, however depend on a fixed location for your properties file. Though having a fixed location offers a lot of convenience, sometimes this is not what you want.
For a reason project I investigated a method to allow early checking for the configuration. I found that Spring Framework offers a ApplicationContextInitializer that allows you to inject custom initialisation code early in the wiring of the context. This simple example shows how to set it based on a system property and check that the file is readable.

public class PropertiesInitializer implements ApplicationContextInitializer<ConfigurableWebApplicationContext> {
     * A logger instance used for logging messages.
    private static final Logger logger = LoggerFactory.getLogger(PropertiesInitializer.class);
    private static final String CONFIG_PATH = "WEBCONFIG_LOCATION";
    public void initialize(ConfigurableWebApplicationContext ctx) {
        final String userLocation = System.getProperty(CONFIG_PATH);
        if (userLocation != null) {
            Path propertiesFile = Paths.get(userLocation);
            if (propertiesFile.toFile().canRead()) {

                final Properties userProperties = new Properties();
                try (Reader propertiesReader = Files.newBufferedReader(propertiesFile, StandardCharsets.UTF_8)) {
                    final PropertiesPropertySource ps = new PropertiesPropertySource("USER_PROPERTIES", userProperties);
                } catch (final IOException ex) {
                    logger.warn("Exception while reading the properties", ex);
            } else {
                logger.warn("The file {} does not exist.", userLocation);
        } else {
            logger.info("The Java system property {} was not set."
                    + " You can set it to the location of a properties file to override the default configuration.",

This technique however allows to do a lot more than that. For instance you could do extensive validation on your properties: are all properties set; are file locations valid; is the database readable; etc. The advantage of checking this yourself is that you can fail early with a clear error message instead of making the administrator go throw a long list of exceptions to find out what’s wrong.

The complete code for this example project can be found in my github repository: https://github.com/djvanenckevort/allthingsdigital/