Evan Summers's Blog

System Properties

Let's use reflection to set a bunch of configurable values via the command-line using "system properties."

Code Snippet

We put our configurable properties into a separate object, specifying the default values, as follows.

public class CommandoDemoProperties {    
    public String host = "aptframework.net";
    public int port = 80;
    public int sslPort = 443;
    public boolean useSSL = true;    
    public String clientKeyStoreFileName = "keystores/client.private";    
    public String serverKeyStoreFileName = "keystores/server.public";    
    ...
}    

We create the following helper to inject any command-line parameters via reflection, according to the field names, eg. -Dport=8080.

public class QSystemPropertyHelper {
    ...
    protected void injectSystemProperties(Object properties) 
    throws IllegalAccessException {
        for (Field field : properties.getClass().getFields()) {
            Class type = field.getType();
            String key = field.getName();
            Object defaultValue = field.get(properties);
            Object value = defaultValue;
            String string = System.getProperty(key);
            if (string == null) continue;
            if (type == String.class) {
                value = string;
            } else if (type == Integer.class || type == int.class) {
                value = Integer.getInteger(key);
            } else if (type == Boolean.class || type == boolean.class) {
                value = Boolean.getBoolean(key);
            } else {
                logger.warning(key, type);
            }
            if (value != defaultValue) {
                field.set(properties, value);
            }
        }
    }    
}

where we support properties which are strings, integers or boolean values.

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