SystemPropertyUtils.java

package org.theonefx.wcframework.utils;

import org.theonefx.wcframework.utils.PropertyPlaceholderHelper.PlaceholderResolver;

public abstract class SystemPropertyUtils {

	/** Prefix for system property placeholders: "${" */
	public static final String PLACEHOLDER_PREFIX = "${";

	/** Suffix for system property placeholders: "}" */
	public static final String PLACEHOLDER_SUFFIX = "}";

	/** Value separator for system property placeholders: ":" */
	public static final String VALUE_SEPARATOR = ":";


	private static final PropertyPlaceholderHelper strictHelper =
			new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, false);

	private static final PropertyPlaceholderHelper nonStrictHelper =
			new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, true);


	/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding system property values.
	 * @param text the String to resolve
	 * @return the resolved String
	 * @see #PLACEHOLDER_PREFIX
	 * @see #PLACEHOLDER_SUFFIX
	 * @throws IllegalArgumentException if there is an unresolvable placeholder
	 */
	public static String resolvePlaceholders(String text) {
		return resolvePlaceholders(text, false);
	}

	/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding system property values.
	 * Unresolvable placeholders with no default value are ignored and passed through unchanged if the
	 * flag is set to true.
	 * @param text the String to resolve
	 * @param ignoreUnresolvablePlaceholders flag to determine is unresolved placeholders are ignored
	 * @return the resolved String
	 * @see #PLACEHOLDER_PREFIX
	 * @see #PLACEHOLDER_SUFFIX
	 * @throws IllegalArgumentException if there is an unresolvable placeholder and the flag is false
	 */
	public static String resolvePlaceholders(String text, boolean ignoreUnresolvablePlaceholders) {
		PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper);
		return helper.replacePlaceholders(text, new SystemPropertyPlaceholderResolver(text));
	}


	private static class SystemPropertyPlaceholderResolver implements PlaceholderResolver {

		private final String text;

		public SystemPropertyPlaceholderResolver(String text) {
			this.text = text;
		}

		public String resolvePlaceholder(String placeholderName) {
			try {
				String propVal = System.getProperty(placeholderName);
				if (propVal == null) {
					// Fall back to searching the system environment.
					propVal = System.getenv(placeholderName);
				}
				return propVal;
			}
			catch (Throwable ex) {
				System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" +
						this.text + "] as system property: " + ex);
				return null;
			}
		}
	}

}