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!

---------------------------------------分割线-------------------------------------------------------

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");
        }
    }
 
}