ioc实例

简单的实现了一下控制反转，将各个visitor访问代码分不到不同的visitor类中

 

visitor-->node 

 

	private static Map<Class<?>, AbstractNodeVisitor<IPigBuilder>> visitMap;
	static {
		visitMap = new ConcurrentHashMap<Class<?>,AbstractNodeVisitor<IPigBuilder>>();
		visitMap.put(FilterNode.class, new FilterNodeVisitor());
		visitMap.put(GroupNode.class, new GroupNodeVisitor());
		visitMap.put(JoinNode.class, new JoinNodeVisitor());
		visitMap.put(StoreNode.class,new  StoreNodeVisitor());
		visitMap.put(LoadNode.class, new LoadNodeVisitor());
		visitMap.put(DBStoreNode.class, new DBStoreNodeVisitor());
		visitMap.put(DBLoadNode.class, new DBLoadNodeVisitor());
		visitMap.put(OrderByCnd.class, new OrderByNodeVisitor());
	}

	@Override
	public IPigBuilder visit(AbstractNode node) throws NodeErrorException {
		if (!visitMap.containsKey(node.getClass())) {
			return null;
		}
		AbstractNodeVisitor<IPigBuilder> visitor = visitMap.get(node.getClass());
		return visitor.visit(node);
	}