在使用JPA的Spring MVC中使用@PersistenceContext时获取Null指针异常

Question

我正在尝试创建一个简单的基于库存的项目。我是Spring的新手，我已经按照http://www.objectdb.com/tutorial/jpa/eclipse/web链接来创建项目。但我无法运行该项目，因为@PersistenceContext没有在我的代码中注入实体管理器。 请在下面找到我的代码段

的pom.xml

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>InventoryMgmt</groupId>
  <artifactId>InventoryMgmt</artifactId>
  <packaging>war</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>InventoryMgmt Maven Webapp</name>


  <!-- Custom Code started -->
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties> 

    <repositories>
        <repository>
            <id>objectdb</id>
            <name>ObjectDB Repository</name>
            <url>http://m2.objectdb.com</url>
        </repository>
        <repository>
            <id>oss.sonatype.org</id>
            <name>OSS Sonatype Staging</name>
            <url>https://oss.sonatype.org/content/groups/staging</url>
        </repository>
    </repositories>

    <dependencies>
        <dependency>
            <groupId>com.objectdb</groupId>
            <artifactId>objectdb</artifactId>
            <version>2.0.4</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>3.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>3.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-orm</artifactId>
            <version>3.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>aopalliance</groupId>
            <artifactId>aopalliance</artifactId>
            <version>1.0</version>
        </dependency>
        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>2.2</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.6.10</version>
        </dependency>
        <dependency>
              <groupId>junit</groupId>
              <artifactId>junit</artifactId>
              <version>3.8.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.derby</groupId>
            <artifactId>derby</artifactId>
            <version>10.10.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.derby</groupId>
            <artifactId>derbyclient</artifactId>
            <version>10.10.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-instrument</artifactId>
            <version>3.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>eclipselink</artifactId>
            <version>2.5.0-RC1</version>
            <exclusions>
                <exclusion>
                    <groupId>org.eclipse.persistence</groupId>
                    <artifactId>commonj.sdo</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>1.5</source>
                    <target>1.5</target>
                </configuration>
            </plugin>
            <plugin>
                 <groupId>org.mortbay.jetty</groupId>
                 <artifactId>maven-jetty-plugin</artifactId>
                 <version>6.1.10</version>
                 <configuration>
                     <scanIntervalSeconds>10</scanIntervalSeconds>
                     <stopKey>foo</stopKey>
                     <stopPort>9999</stopPort>
                 </configuration>
                 <executions>
                     <execution>
                         <id>start-jetty</id>
                         <phase>pre-integration-test</phase>
                         <goals>
                             <goal>run</goal>
                         </goals>
                         <configuration>
                             <scanIntervalSeconds>0</scanIntervalSeconds>
                             <daemon>true</daemon>
                         </configuration>
                     </execution>
                     <execution>
                         <id>stop-jetty</id>
                             <phase>post-integration-test</phase>
                             <goals>
                                 <goal>stop</goal>
                             </goals>
                     </execution>
                 </executions>
             </plugin>
         </plugins>
        <finalName>InventoryMgmt</finalName>
    </build>


  <!-- Custom Code ended -->

</project>

web.inf

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <display-name>Inventory Management System</display-name>

  <servlet>
    <servlet-name>spring</servlet-name>
    <servlet-class>
      org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
    <load-on-startup>2</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>spring</servlet-name>
    <url-pattern>*.html</url-pattern>
  </servlet-mapping>
    <session-config>
    <session-timeout>
      30
    </session-timeout>
    </session-config>


   <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
</web-app>

弹簧servlet.xml中

<?xml version="1.0" encoding="windows-1252"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context-3.0.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">

    <!-- Use @Component annotations for bean definitions -->
    <context:component-scan base-package="com.stuffworks.Inventory" />

    <!-- Use @Controller annotations for MVC controller definitions -->
    <mvc:annotation-driven />

    <!-- Add JPA support -->
    <bean id="emf"
        class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">

        <property name="loadTimeWeaver">
            <bean
                class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver" />
        </property>

        <property name="persistenceUnitName" value="inventory" />
    </bean>

    <!-- Add Transaction support -->
    <bean id="myTxManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="emf" />
    </bean>

    <!-- Use @Transaction annotations for managing transactions -->
    <tx:annotation-driven transaction-manager="myTxManager" />

    <!-- View resolver -->
    <bean
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/" />
    </bean>

</beans>

的persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
 http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

  <persistence-unit name="inventory" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>com.stuffworks.inventory.entity.dto.Inventory</class>
    <class>com.stuffworks.inventory.entity.dto.PurchaseOrder</class>
    <class>com.stuffworks.inventory.entity.dto.Stock</class>
    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/testdbsw"/>
        <property name="javax.persistence.jdbc.user" value="usr"/>
        <property name="javax.persistence.jdbc.password" value="pwd"/>
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
    </properties>

    <!-- Properties for ObjectDB DB -->
    <!-- 
    <provider>com.objectdb.jpa.Provider</provider>
    <properties>
      <property name="javax.persistence.jdbc.url" value="$objectdb/db/guests.odb"/>
      <property name="javax.persistence.jdbc.user" value="usr"/>
      <property name="javax.persistence.jdbc.password" value="pwd"/>
    </properties>-->


    <!-- Properties for Derby DB -->
    <!-- 
    <class>com.stuffworks.inventory.entity.dto.Inventory</class>
    <class>com.stuffworks.inventory.entity.dto.PurchaseOrder</class>
    <class>com.stuffworks.inventory.entity.dto.Stock</class>
    <properties>
      <property name="eclipselink.target-database" value="DERBY"/>
      <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
      <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
      <property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost:1527/inventory;create=true"/>
      <property name="javax.persistence.jdbc.user" value="usr"/>
      <property name="javax.persistence.jdbc.password" value="pwd"/>
    </properties>
     -->

  </persistence-unit>

</persistence>

DAO

package com.sample.inventory.entity.manager;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.TypedQuery;

import org.springframework.stereotype.Component;
import org.springframework.transaction.annotation.Transactional;

import com.sample.inventory.entity.dto.Inventory;

@Component
public class InventoryDao {
    // Injected database connection:
//    @PersistenceUnit(unitName="inventory")
//  private EntityManagerFactory entityManagerFactory;

    @PersistenceContext 
    private EntityManager em;// = entityManagerFactory.createEntityManager();

    // Stores a new guest:
    @Transactional
    public void persist(Inventory inventory) {
        em.persist(inventory);
    }

    // Retrieves all the guests:
    public List<Inventory> getAllItems() {
        TypedQuery<Inventory> query = em.createQuery(
            "SELECT i FROM Inventory i ORDER BY i.item_id", Inventory.class);
        return query.getResultList();
    }
}

异常

Nov 23, 2014 12:11:05 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at com.stuffworks.inventory.entity.manager.InventoryDao.getAllItems(InventoryDao.java:31)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:91)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:744)

我无法识别代码中的错误。我也跟着在PersistenceContext EntityManager injection NullPointerException中提到了，但EntityManagerFactory也没有被注入。