package learn;
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;
import org.junit.Test;
public class LearnJssist {
/**
* 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
*/
public String[] getMethodParamNames(Class<?> clazz, String methodName) {
Method method =null;
try {
ClassPool pool = ClassPool.getDefault();
pool.insertClassPath(new ClassClassPath(clazz));
CtClass cc = pool.get(clazz.getName());
//DEBUG, 函数名相同的方法重载的信息读不到 2011-03-21
CtMethod cm = cc.getDeclaredMethod(method.getName());
//2011-03-21
// 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(new String[] {}));
// 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");
}
// for(int i = 0 ; i< attr.length() ; i++){
// System.out.println(i);
// try {
// System.out.println("===="+attr.nameIndex(i));
// System.out.println("===="+attr.index(i));
//// System.out.println("===="+attr.nameIndex(i));
// System.out.println(clazz.getName()+"================"+i+attr.variableName(i));
//
//
// } catch (Exception e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
// }
//addContextVariable by lzw 用于兼容jdk 编译时 LocalVariableTable顺序问题
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);
// paramNames即参数名
for (int i = 0; i < paramNames.length; i++) {
System.out.println(paramNames[i]);
}
return paramNames;
} catch (NotFoundException e) {
e.printStackTrace();
return new String[0];
}
}
private int getStartIndex(LocalVariableAttribute attr){
// attr.st
int startIndex = 0;
for(int i = 0 ; i< attr.length() ; i++){
if("this".equals(attr.variableName(i))){
startIndex = i;
break;
}
}
return startIndex;
}
}