variablemapperfactory.java

java属性邦定的（JSR-295）的一个实现

/*
 * Copyright (C) 2007 Sun Microsystems, Inc. All rights reserved. Use is
 * subject to license terms.
 */

package org.jdesktop.el.impl.lang;

import org.jdesktop.el.ValueExpression;
import org.jdesktop.el.VariableMapper;

public class VariableMapperFactory extends VariableMapper {

    private final VariableMapper target;
    private VariableMapper momento;
    
    public VariableMapperFactory(VariableMapper target) {
        if (target == null) {
            throw new NullPointerException("Target VariableMapper cannot be null");
        }
        this.target = target;
    }
    
    public VariableMapper create() {
        return this.momento;
    }

    public ValueExpression resolveVariable(String variable) {
        ValueExpression expr = this.target.resolveVariable(variable);
        if (expr != null) {
            if (this.momento == null) {
                this.momento = new VariableMapperImpl();
            }
            this.momento.setVariable(variable, expr);
        }
        return expr;
    }

    public ValueExpression setVariable(String variable, ValueExpression expression) {
        throw new UnsupportedOperationException("Cannot Set Variables on Factory");
    }
}