在服务器启动时加载spring配置

Question

 <context:annotation-config />
 <context:component-scan base-package="com.firstapp.dao"/>

 <bean id="datasource" 
      class="org.springframework.jdbc.datasource.DriverManagerDataSource">  
     <property name="driverClassName" 
     value="oracle.jdbc.driver.OracleDriver"  />  
     <property name="url" value="jdbc:oracle:thin:@localhost:1521:xe" />  
     <property name="username" value="system" />  
     <property name="password" value="oracle" />  
 </bean>  

<bean id="jdbcTemplate" 
      class="org.springframework.jdbc.core.JdbcTemplate">  
      <property name="dataSource" ref="datasource"></property>  
 </bean>  

 public class UserDAO 
  {
   @Autowired
   private JdbcTemplate jdbcTemplate;
   ....}

  public class UserService  
   {
      private UserDAO  userDAO  = new UserDAO ();       
    ....}

<context-param>
  <param-name>contextConfigLocation</param-name>
  <param-value>/WEB-INF/applicationContext.xml</param-value>
</context-param>

<listener>
  <listener-class>
     org.springframework.web.context.ContextLoaderListener
  </listener-class>
</listener>

Answer 1

我打赌您的userDAO类没有定义为Spring bean。在这种情况下，您有两种选择：用XML定义bean或对其进行注释。

选项1:XML

ApplicationContext.xml

<bean id="userDao" class="[package of UserDAO class].UserDAO">
    <property name="jdbcTemplate" ref="jdbcTemplate"/>
</bean>

<context:annotation-config/>
<context:component-scan base-package="[package of UserDAO class]"/>

@Component
public class UserDAO {
    @Autowired
    private JdbcTemplate jdbcTemplate;
}

@Component // must be a bean as well
public class DummyClass {
    private final UserDAO userDao;

    @Autowired
    public DummyClass(UserDAO userDao) {
        this.userDao = userDao;
    }
}

选项3：从应用程序上下文中手动提取Bean

我想强调的是，不推荐使用这种方法，您应该避免使用它，并正确使用依赖注入。如果您需要使用那种方法--您的应用程序的体系结构可能是错误的。

SpringBeanutil.java

@Component
public class SpringBeanUtil implements ApplicationContextAware {
    private static ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        context = applicationContext;
    }

    public static <T> T getBean(Class<T> beanClass) {
        return context.getBean(beanClass);
    }
}

public class UserDAO {
    private JdbcTemplate jdbcTemplate = SpringBeanUtil.getBean(JdbcTemplate.class);
}