Java监听器如何调用dao_消息监听器无法注入bean

问题描述&＃xff1a;

在activemq的监听器中&＃xff0c;通过注解&＃64;Autowired或&＃64;Resource注入bean时&＃xff0c;获取到的bean为null。调用该bean的方法时会报空指针异常。

问题原因&＃xff1a;

当调用bean内方法时&＃xff0c;spring容器中还没有完成对注解bean的扫描&＃xff0c;dispatcher.xml中配置的注解bean的优先级没有框架中的contextListener的优先级高&＃xff0c;所以contextListener初始化的时候根据&＃64;Autowired扫描&＃xff0c;肯定是null的。

解决办法&＃xff1a;

在web.xml文件中增加一个监听器类&＃xff0c;该类实现ServletContextListener,ApplicationContextAware这两个接口。

&＃96;&＃96; com.activemq.common.InitComponent

当容器启动的时候&＃xff0c;会执行该类中的contextInitialized(ServletContextEvent servletContextEvent)方法。

我们要做的&＃xff0c;就是在该类中新增获取bean的方法。

package com.activemq.common;

import javax.jms.Connection;

import javax.jms.ConnectionFactory;

import javax.jms.Destination;

import javax.jms.JMSException;

import javax.jms.MessageConsumer;

import javax.jms.Session;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import org.apache.activemq.ActiveMQConnectionFactory;

import org.springframework.beans.BeansException;

import org.springframework.context.ApplicationContext;

import org.springframework.context.ApplicationContextAware;

import org.springframework.stereotype.Component;

&＃64;Component

public class InitComponent implements ServletContextListener,ApplicationContextAware{

private static ApplicationContext applicationContext;

public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {

InitComponent.applicationContext&＃61;applicationContext;

}

/**

* 程序运行时即初始化activemq消费组件

*/

public void contextInitialized(ServletContextEvent servletContextEvent) {

ConnectionFactory factory &＃61; new ActiveMQConnectionFactory("tcp://132.252.3.22:61616");

// ConnectionFactory factory &＃61; new ActiveMQConnectionFactory("tcp://localhost:61616");

Connection connection;

Session session;

Destination destination;

MessageConsumer messageConsumer;

try {

connection &＃61; factory.createConnection();

connection.start();

session &＃61; connection.createSession(Boolean.FALSE, Session.AUTO_ACKNOWLEDGE);

destination &＃61; session.createTopic("ZHXJ_QUEUE"); // 创建连接的消息队列

messageConsumer &＃61; session.createConsumer(destination);// 创建消息消费者

messageConsumer.setMessageListener(new StaffMsgListener());

} catch (JMSException e) {

e.printStackTrace();

}

}

&＃64;SuppressWarnings("unchecked")

public static T getBean(String name) {

checkApplicationContext();

return (T) applicationContext.getBean(name);

}

private static void checkApplicationContext() {

if (applicationContext &＃61;&＃61; null) {

throw new IllegalStateException("applicaitonContext未注入");

}

}

public void contextDestroyed(ServletContextEvent sce) {

}

}

此时&＃xff0c;获取bean的方式就变为&＃xff1a;

ConsumerDao consumerDao &＃61; InitComponent.getBean( "ConsumerDao" ); consumerDao.saveMessage(param);

注意&＃xff1a;

ConsumerDao接口上需要加上注解&＃xff1a;&＃64;Repository("ConsumerDao")