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There is a newer version: 1.6.17
package com.anysoft.formula;

import java.util.Hashtable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 函数对象辅助器
 * 
 * 

 * 函数对象辅助器维护了一个函数的映射表，并根据框架的要求生成相应函数的实例

 * @author duanyy
 * @version 1.6.4.21 [20151229 duanyy] 

 * - 根据sonar建议优化代码 

 * 
 * @version 1.6.7.9 [20170201 duanyy] 

 * - 采用SLF4j日志框架输出日志 

 */

@SuppressWarnings("unchecked")
public class DefaultFunctionHelper implements FunctionHelper {
	/**
	 * a logger of log4j
	 */
	protected static final Logger LOG = LoggerFactory.getLogger(FunctionHelper.class);
	
	/**
	 * 父节点
	 */
	protected FunctionHelper parent = null;

	/**
	 * 函数映射表
	 */
	protected Hashtable> mappings = new Hashtable>(); // NOSONAR
	
	/**
	 * 内置静态的函数映射表
	 */
	protected static Hashtable> static_mappings = new Hashtable>(); // NOSONAR
	
	/**
	 * 内置的函数
	 */
	static {
		try {
			static_mappings.put("choice", (Class) Class
					.forName("com.anysoft.formula.Function$Choice"));
			static_mappings.put("nvl", (Class) Class
					.forName("com.anysoft.formula.Function$Nvl"));
			static_mappings.put("to_date", (Class) Class
					.forName("com.anysoft.formula.Function$Char2Date"));
			static_mappings.put("to_char", (Class) Class
					.forName("com.anysoft.formula.Function$Date2Char"));
			static_mappings.put("to_string", (Class) Class
					.forName("com.anysoft.formula.Function$ToString"));
			static_mappings.put("to_long", (Class) Class
					.forName("com.anysoft.formula.Function$ToLong"));
			static_mappings.put("to_double", (Class) Class
					.forName("com.anysoft.formula.Function$ToDouble"));
			static_mappings.put("substr", (Class) Class
					.forName("com.anysoft.formula.Function$SubStr"));
			static_mappings.put("instr", (Class) Class
					.forName("com.anysoft.formula.Function$InStr"));
			static_mappings.put("strlen", (Class) Class
					.forName("com.anysoft.formula.Function$StrLen"));
			static_mappings.put("match", (Class) Class
					.forName("com.anysoft.formula.Function$Match"));
		} catch (ClassNotFoundException e) {
			LOG.error(e.getMessage());
		}
	}	

	/**
	 * 构造函数 
	 * @param theParent 父节点
	 */
	public DefaultFunctionHelper(FunctionHelper theParent) {
		parent = theParent;
	}

	/**
	 * 构造函数
	 */
	public DefaultFunctionHelper() {
		this(null);
	}



	/**
	 * 注册函数映射
	 * @param funcName 函数名
	 * @param funClass 对应的函数实现的类名
	 */
	public void addFunction(String funcName, Class funClass) {
		mappings.put(funcName, funClass);
	}

	/**
	 * 注销函数映射
	 * @param funcName 函数名
	 */
	public void removeFunction(String funcName) {
		mappings.remove(funcName);
	}

	@Override
	public Expression customize(String funcName) {
		try {
			Class found = static_mappings.get(funcName);
			if (found != null) {
				return found.newInstance();
			}
			found = mappings.get(funcName);
			if (found != null) {
				return found.newInstance();
			}
			if (parent != null) {
				return parent.customize(funcName);
			}
			throw new FormulaException("Can not find function :" + funcName);
		} catch (Exception ex) {
			LOG.error(ex.getMessage());
			throw new FormulaException("Can not create function :" + funcName);
		}
	}


}