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package cn.tom.mvc.ext;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import javassist.ClassClassPath;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.NotFoundException;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.LocalVariableAttribute;
import javassist.bytecode.MethodInfo;

public class JavassistUtil {
	
	/**
	 * 得到方法参数名称数组 由于java没有提供获得参数名称的api，利用了javassist来实现
	 * 
	 * @return 参数名称数组
	 */
	public static String[] getMethodParamNames(Class clazz, Method method) {
		Class[] paramTypes = method.getParameterTypes();

		try {
			ClassPool pool = ClassPool.getDefault();
			
			pool.insertClassPath(new ClassClassPath(clazz));
			 
			CtClass cc = pool.get(clazz.getName());

			String[] paramTypeNames = new String[method.getParameterTypes().length];
 
			for (int i = 0; i < paramTypes.length; i++) {
				paramTypeNames[i] = paramTypes[i].getName();
			}

			CtMethod cm = cc.getDeclaredMethod(method.getName(), pool.get(paramTypeNames));

			/* 使用javaassist的反射方法获取方法的参数名 */
			MethodInfo methodInfo = cm.getMethodInfo();

			CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
			LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute.getAttribute(LocalVariableAttribute.tag);
			if (attr == null) {
				throw new RuntimeException("class:" + clazz.getName() + ", have no LocalVariableTable, please use javac -g:{vars} to compile the source file");
			}

			int startIndex = getStartIndex(attr);
			String[] paramNames = new String[cm.getParameterTypes().length];
			int pos = Modifier.isStatic(cm.getModifiers()) ? 0 : 1;

			for (int i = 0; i < paramNames.length; i++)
				paramNames[i] = attr.variableName(startIndex + i + pos);

			return paramNames;

		} catch (NotFoundException e) {
			e.printStackTrace();
			return new String[0];
		}
	}
	
	private static int getStartIndex(LocalVariableAttribute attr) {

		int startIndex = 0;
		for (int i = 0; i < attr.length(); i++) {
			if ("this".equals(attr.variableName(i))) {
				startIndex = i;
				break;
			}
		}
		return startIndex;
	}

}