@Autowired objects getting null value

问题

Trying to set up a project but fail at Autowiring objects through Spring.

package se.hsr.web;

public class TestRunner {

    public static void main(String[] args) {
        ContactDAO cd = new ContactDAOImpl();
        Contact contact = new Contact();
        contact.setFirstname("Zorro");
        cd.addContact(contact);
    }

}

package se.hsr.web;

Running this gives me a NullPointerException when cd.addContact is invoked. The ContactDaoImpl:

import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

@Repository
public class ContactDAOImpl implements ContactDAO {

    @Autowired
    private SessionFactory sessionFactory;

    public void addContact(Contact contact) {
        sessionFactory.getCurrentSession().save(contact);
    }

My servlet file:

    <?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:p="http://www.springframework.org/schema/p"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:context="http://www.springframework.org/schema/context"
    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">

    <context:component-scan
        base-package="se.hsr.web"/>

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass"
            value="org.springframework.web.servlet.view.JstlView" />
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <bean id="propertyConfigurer"
        class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
        p:location="/WEB-INF/jdbc.properties" />

    <bean id="dataSource"
        class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"
        p:driverClassName="${jdbc.driverClassName}"
        p:url="${jdbc.databaseurl}" p:username="${jdbc.username}"
        p:password="${jdbc.password}" />  

     <bean id="sessionFactory"
        class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation">
            <value>classpath:hibernate.cfg.xml</value>
        </property>
        <property name="configurationClass">
            <value>org.hibernate.cfg.AnnotationConfiguration</value>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">${jdbc.dialect}</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>

    <bean id="contactDAOImpl"
        class="se.hsr.web.ContactDAOImpl"/>

    <context:annotation-config/>

</beans>

My hibernate.cfg.xml file:

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <mapping class="se.hsr.web.Contact" />
    </session-factory>

</hibernate-configuration>

My web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <display-name>HSRMVC</display-name>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>HSR</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>HSR</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

I suppose the error is that the SessionFactory isn't getting initialized via @Autowired correctly, but why is that? Could it be a simple directory structure/filepath problem or is it something more complicated?

Thanks in advance.

UPDATE: ContactDAOImpl class:

@Repository
public class ContactDAOImpl extends HibernateDaoSupport implements ContactDAO{

    @Autowired
    @Qualifier("sessionFactory")
    private SessionFactory sessionFactory;

    public void addContact(Contact contact) {
        sessionFactory.getCurrentSession().save(contact);
    }

回答1:

In order to use Spring features (autowiring, call to post construct methods or aspects) you need to let Spring instanciate the instances instead of using new.

For instance:

public static void main(String[] args) {
    ApplicationContext context = AnnotationConfigApplicationContext("se.hsr.web")
    ContactDAO cd = (ContactDAO)context.getBean("contactDAOImpl");
    Contact contact = new Contact();
    contact.setFirstname("Zorro");
    cd.addContact(contact);
}

AnnotationConfigApplicationContext will scan the classes in the classes in the se.hsr.web package to for classes with Spring annotations. It requires Spring 3.0 to work. Before that you should add the following line in your applicationContext.xml file:

<context:component-scan base-package="se.hsr.web" />

回答2:

You need this at the top of your test class:

@RunWith(SpringJUnit4ClassRunner.class)
// ApplicationContext will be loaded from "/applicationContext.xml" and "/applicationContext-test.xml"
// in the root of the classpath
@ContextConfiguration(locations={"/applicationContext.xml", "/applicationContext-test.xml"})
public class MyTest {

I assumed JUnit4; my oversight.

You do need the context configuration tag in an application context somewhere, but I don't see anyplace in your code where you're actually opening an application context file and creating an ApplicationContext. Usually that's done in a set up method for your test. You'll have better luck if you actually create an ApplicationContext somewhere. Try reading the XML from your CLASSPATH in a setup method and see if that helps.

回答3:

You need this in your Spring configuration for autowiring to work

xmlns:context="http://www.springframework.org/schema/context" 
....
<context:annotation-config/>

回答4:

Add @Component/@Repository to the DAO/DAOImpl.

回答5:

you are creating the POJO outside of the spring context.

if you really want to be able to instanciate "manually", you can fix this, by adding <context:spring-configured /> to your configuration, and then annotating ContactDAOImpl with @Configurable

回答6:

You need to retrieve the ContactDAO instance from Spring context. You are initing yourself with new keyword.

See the below link;

@Autowired annotation not able to inject bean in JUnit class

or if not unit test

ClassPathResource resource = new ClassPathResource("beans.xml");
BeanFactory factory = new XmlBeanFactory(resource);
beanFactory.getBean("nameOfYourBean");

http://static.springsource.org/spring/docs/2.0.x/reference/beans.html

来源：https://stackoverflow.com/questions/4816283/autowired-objects-getting-null-value