plugins/org.eclipse.epp.installer.core/src/org/eclipse/epp/installer/core/Variables.java

package org.eclipse.epp.installer.core;

/**
 * Variables is used to resolve variables in strings.
 */
public class Variables {
	private static final String VARIABLE_TOKEN_BEGIN = "${"; 
	private static final String VARIABLE_TOKEN_END = "}"; 
	
	/**
	 * If there is a platform-dependent variable with the same name. Otherwise return value of variable in options.
	 * 
	 * @param varName
	 * 			variable name.
	 * @param options
	 * 			InstallOptions from where variable value will be taken.
	 * @return variable value.
	 */
	private static String getString(String varName, InstallOptions options) {
		String varValue = options.getString(varName);
		if (varValue == null) {
			varValue = Platform.getVarString(varName);
		}
		return varValue;
	}
	
	/**
	 * Returns a string where all variables are replaced with their values.
	 * 
	 * @param string
	 *			string to resolve.
	 * @param options
	 * 			InstallOptions from where variable values will be taken.
	 * @return resolved string.
	 */
	public static String resolve(String string, InstallOptions options) {

		if (string == null) {
			return null;
		}

		StringBuffer resultString = new StringBuffer("");
		String curString = string;
		while (curString.length() > 0) {
			if (curString.indexOf(VARIABLE_TOKEN_BEGIN) > -1) {
				int indexBegin = curString.indexOf(VARIABLE_TOKEN_BEGIN);
				// append part of string before variable to result
				resultString.append(curString.substring(0, indexBegin));
				
				curString = curString.substring(indexBegin + VARIABLE_TOKEN_BEGIN.length());
				if (curString.indexOf(VARIABLE_TOKEN_END) <= -1) {
					break;
				}
				int indexEnd = curString.indexOf(VARIABLE_TOKEN_END);
				String varName = curString.substring(0, indexEnd);
				
				String varValue = getString(varName, options);
				if (varValue != null) {
					// append variable value to result, do recursive variable replacement
					resultString.append(resolve(varValue, options)); 
				} else {
					// if not found, leave as it was
					resultString.append(VARIABLE_TOKEN_BEGIN);
					resultString.append(varName);
					resultString.append(VARIABLE_TOKEN_END);
				}
				curString = curString.substring(indexEnd + VARIABLE_TOKEN_END.length());
			} else {
				// append rest part of string to result				
				resultString.append(curString);
				break;
			}
		}
				
		return resultString.toString();
	}
}