applicationContext=null 错误总结

Spring版本:

Spring 4.2.5

问题:

private static DictMapper dictDao = SpringContextHolder.getBean(DictMapper.class);

通过SpringContextHolder获取上下文,applicationContext总是为null

问题分析:

1.SpringContextHolder采用配置文件的方式加载

<!-- 用于持有ApplicationContext,可以使用SpringContextHolder.getBean('xxxx')的静态方法得到spring bean对象 -->   <bean id="springContextHolder" class="com.xxx.common.utils.SpringContextHolder" />

2.web.xml 已配置

<listener><description>spring监听器</description><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener><!-- spring mvc servlet --><servlet><description>spring mvc servlet</description><servlet-name>springMvc</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><description>spring mvc 配置文件</description><param-name>contextConfigLocation</param-name><param-value>classpath:spring-mvc.xml</param-value></init-param><load-on-startup>1</load-on-startup></servlet>

3.项目启动时,为执行初始化  set方法

//实现ApplicationContextAware接口的context注入函数, 将其存入静态变量.    public void setApplicationContext(ApplicationContext applicationContext) {        SpringContextHolder.applicationContext = applicationContext;    }

问题解决方法:

参考文档:ApplicationContextAware方式获取上下文，但是最终却报错：NullPointerException?

在Spring配置文件中配置错误,修改为:

<!-- 用于持有ApplicationContext,可以使用SpringContextHolder.getBean('xxxx')的静态方法得到spring bean对象 -->   <bean id="springContextHolder" class="com.xxx.common.utils.SpringContextHolder"  lazy-init="false"/>

至此,重启项目 ,执行set方法,项目正常!

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SpringContextHolder类:

import java.util.Map;import org.springframework.context.ApplicationContext;import org.springframework.context.ApplicationContextAware;import org.springframework.stereotype.Component; /** * *以静态变量保存Spring ApplicationContext, 可在任何代码任何地方任何时候中取出ApplicaitonContext. * @author zhuh */public class SpringContextHolder implements ApplicationContextAware{     private static ApplicationContext applicationContext;          //实现ApplicationContextAware接口的context注入函数, 将其存入静态变量.    public void setApplicationContext(ApplicationContext applicationContext) {        SpringContextHolder.applicationContext = applicationContext;    }         //取得存储在静态变量中的ApplicationContext.    public static ApplicationContext getApplicationContext() {        checkApplicationContext();        return applicationContext;    }         //从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.    @SuppressWarnings("unchecked")    public static <T> T getBean(String name) {        checkApplicationContext();        return (T) applicationContext.getBean(name);    }          //从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.    //如果有多个Bean符合Class, 取出第一个.    @SuppressWarnings("unchecked")    public static <T> T getBean(Class<T> clazz) {        checkApplicationContext();        @SuppressWarnings("rawtypes")                Map beanMaps = applicationContext.getBeansOfType(clazz);        if (beanMaps!=null && !beanMaps.isEmpty()) {            return (T) beanMaps.values().iterator().next();        } else{            return null;        }    }     private static void checkApplicationContext() {        if (applicationContext == null) {            throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");        }    } }