运行问题 求解

package priv.jwh.aop.demo3;

public interface StudentDao {
   void save();
   void update();
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns:context="http://www.springframework.org/schema/context"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
   <!--  <bean id="userService" class="priv.jwh.ioc.demo1.UserServiceImpl">
         <property name="name" value="贾伟航"/>
     </bean>

     <bean id="food" class="priv.jwh.ioc.demo1.Food">
         <property name="name" value="苹果"/>
         <property name="taste" value="很脆"/>
         <property name="kind" value="富士"/>
     </bean>
     &lt;!&ndash;Bean实例化的三种方式&ndash;&gt;
     <bean id="bean1" class="priv.jwh.ioc.demo2.Bean1"/>
     <bean id="bean2" class="priv.jwh.ioc.demo2.Bean2Factory" factory-method="createBean2"/>
     <bean id="bean3Factory" class="priv.jwh.ioc.demo2.Bean3Factory"/>
     <bean id="bean3" factory-bean="bean3Factory" factory-method="createBean3"/>

     <bean id="person" class="priv.jwh.ioc.demo3.Person" scope="prototype"/>-->
   <context:component-scan base-package="priv.jwh.ioc.demo4"/>

   <bean id="studentDao" class="priv.jwh.aop.demo3.StudentDaoImpl"/>
   <bean id="myBeforeAdvice" class="priv.jwh.aop.demo3.MyBeforAdvice"/>

   <bean id="studentDaoProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
       <property name="target" ref="studentDao"/>
       <property name="proxyInterfaces" value="priv.jwh.aop.demo3.StudentDao"/>
       <property name="interceptorNames" value="myBeforeAdvice"/>
   </bean>

</beans>

package priv.jwh.aop.demo3;

import org.springframework.aop.MethodBeforeAdvice;

import java.lang.reflect.Method;

public class MyBeforAdvice implements MethodBeforeAdvice {
   @Override
   public void before(Method method, Object[] objects, Object o) throws Throwable {
       System.out.println("前置增强");
   }
}

package priv.jwh.aop.demo3;

public class StudentDaoImpl implements StudentDao {
   @Override
   public void save() {
       System.out.println("存储学生信息");
   }

   @Override
   public void update() {
       System.out.println("删除学生信息");
   }
}

package priv.jwh.aop.demo3;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import javax.annotation.Resource;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class SpringDemo {
   private StudentDao studentDao;

   @Resource(name = "studentDao")
   public void setStudentDao(StudentDao studentDao) {
       this.studentDao = studentDao;
   }

   @Test
   public void demo1() {
      /* ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
       StudentDao studentDao = (StudentDao) applicationContext.getBean("studentDaoProxy");*/
       studentDao.save();
       studentDao.update();
   }
}

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>

 <groupId>priv.jwh</groupId>
 <artifactId>spring_ioc</artifactId>
 <version>1.0-SNAPSHOT</version>
 <packaging>war</packaging>

 <name>spring_ioc Maven Webapp</name>
 <!-- FIXME change it to the project's website -->
 <url>http://www.example.com</url>

 <properties>
   <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   <maven.compiler.source>1.7</maven.compiler.source>
   <maven.compiler.target>1.7</maven.compiler.target>
 </properties>

 <dependencies>
   <dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-beans</artifactId>
     <version>4.3.14.RELEASE</version>
   </dependency>
   <dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-context</artifactId>
     <version>4.3.14.RELEASE</version>
   </dependency>
   <dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-core</artifactId>
     <version>4.3.14.RELEASE</version>
   </dependency>
   <dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-expression</artifactId>
     <version>4.3.14.RELEASE</version>
   </dependency>
   <!-- https://mvnrepository.com/artifact/org.springframework/spring-aop -->
   <dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-aop</artifactId>
     <version>4.3.14.RELEASE</version>
   </dependency>
   <!-- https://mvnrepository.com/artifact/org.springframework/spring-test -->
   <dependency>
     <groupId>org.springframework</groupId>
     <artifactId>spring-test</artifactId>
     <version>4.3.14.RELEASE</version>
   </dependency>

   <!-- https://mvnrepository.com/artifact/aopalliance/aopalliance -->
   <dependency>
     <groupId>aopalliance</groupId>
     <artifactId>aopalliance</artifactId>
     <version>1.0</version>
   </dependency>

   <dependency>
     <groupId>commons-logging</groupId>
     <artifactId>commons-logging</artifactId>
     <version>1.2</version>
   </dependency>
   <!-- https://mvnrepository.com/artifact/log4j/log4j -->
   <dependency>
     <groupId>log4j</groupId>
     <artifactId>log4j</artifactId>
     <version>1.2.17</version>
   </dependency>
   <!-- https://mvnrepository.com/artifact/junit/junit -->
   <dependency>
     <groupId>junit</groupId>
     <artifactId>junit</artifactId>
     <version>4.12</version>
   </dependency>
 </dependencies>

 <build>
   <finalName>spring_ioc</finalName>
   <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
     <plugins>
       <plugin>
         <artifactId>maven-clean-plugin</artifactId>
         <version>3.0.0</version>
       </plugin>
       <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
       <plugin>
         <artifactId>maven-resources-plugin</artifactId>
         <version>3.0.2</version>
       </plugin>
       <plugin>
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.7.0</version>
       </plugin>
       <plugin>
         <artifactId>maven-surefire-plugin</artifactId>
         <version>2.20.1</version>
       </plugin>
       <plugin>
         <artifactId>maven-war-plugin</artifactId>
         <version>3.2.0</version>
       </plugin>
       <plugin>
         <artifactId>maven-install-plugin</artifactId>
         <version>2.5.2</version>
       </plugin>
       <plugin>
         <artifactId>maven-deploy-plugin</artifactId>
         <version>2.8.2</version>
       </plugin>
     </plugins>
   </pluginManagement>
 </build>
</project>

在测试类中 使用注解就会产生 空指针异常,,,使用以前的加载 配置文件的方法 就可以正常输出,请问是怎么回事?