如果在命令行中提供了新值，如何覆盖从属性文件加载的值

Question

Funny enough there are 2 almost identical questions with a similar title that I found:

Q1

Q2

however my case seems to be slightly different.

So I have a config.properties file that is being loaded by ConfigurationGetter class like this:

public class ConfigurationGetter {

    Properties prop = new Properties();
    InputStream inputStream = null;

    public Properties getPropValues() throws IOException {

        try {
            String fileName = "config.properties";

            inputStream = getClass().getClassLoader().getResourceAsStream(fileName);

            if (inputStream != null) {
                prop.load(inputStream);
            } else {
                throw new FileNotFoundException("property file '" + fileName + "' not found in the classpath");
            }

        } catch (Exception e) {
            System.out.println("Exception: " + e);
        } finally {
            inputStream.close();
        }

        return prop;

    }

Then I instantiate this class in another class like this:

ConfigurationGetter config = new ConfigurationGetter();
props = config.getPropValues();

And then I can extract the properties by key like this:

props.getProperty("keyName")

Whet I want to do is to overwrite this value I get from properties file if I provide it via command line. For example, if I have a line like this in my config.properties that I loaded as explained above:

keyName=true

and I also run the code like this:

mvn test -DkeyName=false

then false will be the one resolved.

Answer 1

After loading the properties file, I do the following:

for (String propertyName : properties.stringPropertyNames()) {
    String systemPropertyValue = System.getProperty(propertyName);

    if (systemPropertyValue != null) {
        properties.setProperty(propertyName, systemPropertyValue);
    }
}

This gives you the behavior you want by overriding the value from the property file with the corresponding system property value if it is present.