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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.svl;

/**
 * Interface for the resolution of vars with a default value if the resolve() method returns null.
 *
 * 
 * For example, to resolve the system property "myProperty" but resolve to "not found" if the
 * property doesn't exist: "$S{myProperty,not found}"
 *
 * 

 * Subclasses must implement the following method:
 * 

 * 	{@link #resolve(VarResolverSession, String)}
 * 
 *
 * See Also:

 * 	Simple Variable Language

 * 
 */
public abstract class DefaultingVar extends SimpleVar {

	/**
	 * Constructor.
	 *
	 * @param name The name of this variable.
	 */
	public DefaultingVar(String name) {
		super(name);
	}

	@Override /* Var*/
	public String doResolve(VarResolverSession session, String s) throws Exception {
		int i = s.indexOf(',');
		if (i == -1)
			return resolve(session, s.trim());
		String s1 = s.substring(0, i);
		String s2 = s.length() == i ? null : s.substring(i+1);
		String v = resolve(session, s1);
		if (v == null)
			v = s2;
		return v;
	}
}