spring AOP @AfterThrowing没有返回值的原因

import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.apache.log4j.Logger;
import org.apache.shiro.web.servlet.ShiroHttpServletRequest;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;

/**
* 类说明:系统服务组件Aspect切面Bean
*
* @author 作者 LzwGlory
* @version 创建时间：2015年12月14日 下午5:36:13
*/
@Component
@Aspect
public class ServiceAspect {

private static final Logger log = Logger.getLogger(ServiceAspect.class);

// 配置切入点,该方法无方法体,主要为方便同类中其他方法使用此处配置的切入点
@Pointcut("execution(* com.ultrapower.rw.web.ows.controller.app..*(..))")
public void aspect() {
}

/*
* 配置前置通知,使用在方法aspect()上注册的切入点 同时接受JoinPoint切入点对象,可以没有该参数
*/
@Before("aspect()")
public void before(JoinPoint joinPoint) {
Object[] args = joinPoint.getArgs();// 获得目标方法的参数
String name = joinPoint.getSignature().getName();// 获得目标方法名
log.info("<=============" + name + "方法--AOP 前置通知=============>");
if (args != null && args.length > 0
&& args[0].getClass() == ShiroHttpServletRequest.class) {
HttpServletRequest request = (HttpServletRequest) joinPoint
.getArgs()[0];
String requestURI = request.getRequestURI();
@SuppressWarnings("unchecked")
Map<String, String> parameterMap = request.getParameterMap();
StringBuilder paramStr = new StringBuilder();
for (Map.Entry<String, String> param : parameterMap.entrySet()) {
paramStr.append(param.getKey()).append("=")
.append(param.getValue());
}
if (paramStr.length() > 0) {
requestURI = requestURI + "?" + paramStr.toString();
}
log.info(name + " 方法请求路径与参数：" + requestURI);
}

}

// 配置后置通知,使用在方法aspect()上注册的切入点
@After("aspect()")
public void after(JoinPoint joinPoint) {
if (log.isInfoEnabled()) {
String name = joinPoint.getSignature().getName();// 获得目标方法名
log.info("<=============" + name + "方法--AOP 后置通知=============>");
}
}

// 配置环绕通知,使用在方法aspect()上注册的切入点
@Around("aspect()")
public Object around(ProceedingJoinPoint joinPoint) {
String name = joinPoint.getSignature().getName();// 获得目标方法名
log.info("<=============" + name + "方法--AOP 环绕通知=============>");
long start = System.currentTimeMillis();
Object result = null;
try {
result = joinPoint.proceed();
long end = System.currentTimeMillis();
if (log.isInfoEnabled()) {
log.info("around " + joinPoint + "\tUse time : "
+ (end - start) + " ms!");
}
} catch (Throwable e) {
long end = System.currentTimeMillis();
if (log.isInfoEnabled()) {
log.info("around " + joinPoint + "\tUse time : "
+ (end - start) + " ms with exception : "
+ e.getMessage());
}
}
return result;
}

// 配置后置返回通知,使用在方法aspect()上注册的切入点
@AfterReturning(pointcut = "aspect()", returning = "result")
public void afterReturn(JoinPoint joinPoint, Object result) {
String name = joinPoint.getSignature().getName();// 获得目标方法名
log.info("<=============" + name + "方法--AOP 后置返回通知=============>");
log.info(name + "方法返回参数：" + result);
}

// 配置抛出异常后通知,使用在方法aspect()上注册的切入点
@AfterThrowing(pointcut = "aspect()", throwing = "ex")
public void afterThrow(JoinPoint joinPoint, Exception ex) {
String name = joinPoint.getSignature().getName();// 获得目标方法名
log.info("<=============" + name + "方法--AOP 异常后通知=============>");
log.info(name + "方法抛出异常为：" + "\t" + ex.getMessage());
}

}