获取ApplicationContext对象的几种方法

方法一:在初始化时保存ApplicationContext对象
代码:
ApplicationContext ac = new FileSystemXmlApplicationContext("applicationContext.xml");
ac.getBean("beanId");
说明:这种方式适用于采用Spring框架的独立应用程序,需要程序通过配置文件手工初始化Spring的情况。

方法二:通过Spring提供的工具类获取ApplicationContext对象
代码:
import org.springframework.web.context.support.WebApplicationContextUtils;
ApplicationContext ac1 = WebApplicationContextUtils.getRequiredWebApplicationContext(ServletContext sc);
ApplicationContext ac2 = WebApplicationContextUtils.getWebApplicationContext(ServletContext sc);
ac1.getBean("beanId");
ac2.getBean("beanId");
说明:
这种方式适合于采用Spring框架的B/S系统,通过ServletContext对象获取ApplicationContext对象,然后在通过它获取需要的类实例。

上面两个工具方式的区别是,前者在获取失败时抛出异常,后者返回null。

其中 servletContext sc 可以具体 换成 servlet.getServletContext()或者 this.getServletContext() 或者 request.getSession().getServletContext(); 另外,由于spring是注入的对象放在ServletContext中的,所以可以直接在ServletContext取出 WebApplicationContext 对象: WebApplicationContext webApplicationContext = (WebApplicationContext) servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);

方法三:继承自抽象类ApplicationObjectSupport
说明:抽象类ApplicationObjectSupport提供getApplicationContext()方法,可以方便的获取到ApplicationContext。
Spring初始化时,会通过该抽象类的setApplicationContext(ApplicationContext context)方法将ApplicationContext 对象注入。

方法四:继承自抽象类WebApplicationObjectSupport
说明:类似上面方法,调用getWebApplicationContext()获取WebApplicationContext

方法五:实现接口ApplicationContextAware
说明:实现该接口的setApplicationContext(ApplicationContext context)方法,并保存ApplicationContext 对象。
Spring初始化时,会通过该方法将ApplicationContext对象注入。
在applicationContext.xml加载该bean类:
<bean id="SpringContextTools" class="com.momo.platform.util.SpringContextUtils" />

package com.momo.platform.util;


import java.io.IOException;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.xml.ResourceEntityResolver;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ConfigurableApplicationContext;

public class SpringContextUtils implements ApplicationContextAware {

	public static final String BEAN_ID = "Platform_SpringContext";

	private static ApplicationContext applicationContext;

	/**
	 * ApplicationContextAware接口的context注入函数.
	 */
	public void setApplicationContext(ApplicationContext context) throws BeansException {
//		System.out.println("==========================applicationContext注入==================================");
		applicationContext = context;
	}

	public static ApplicationContext getApplicationContext() {
		if (applicationContext == null){
			throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextUtil");
		}	
		return applicationContext;
	}

	@SuppressWarnings("unchecked")
	public static <T> T getBean(String name) throws BeansException {
		if(applicationContext == null){
			System.out.println("==========================================ApplicationContext没有注入成功!==================================");
		}
		return (T) applicationContext.getBean(name);
	}

	/**
	 * 向spring的beanFactory动态地装载bean
	 * 
	 * @param configLocationString  要装载的bean所在的xml配置文件位置。
	 * spring配置中的contextConfigLocation,同样支持诸如"/WEB-INF/ApplicationContext-*.xml"的写法。
	 */
	public static void loadBean(String configLocationString) {
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(
				(BeanDefinitionRegistry) ((ConfigurableApplicationContext) getApplicationContext()).getBeanFactory());
		beanDefinitionReader.setResourceLoader(getApplicationContext());
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(getApplicationContext()));
		try {
			String[] configLocations = new String[] { configLocationString };
			for (int i = 0; i < configLocations.length; i++) {
				beanDefinitionReader.loadBeanDefinitions(getApplicationContext().getResources(configLocations[i]));
			}
		} catch (BeansException e1) {
			e1.printStackTrace();
		} catch (IOException e2) {
			e2.printStackTrace();
		}
	}

}
















在web应用中一般用ContextLoaderListener加载webapplication,如果需要在action之外或者control类之外获取webapplication思路之一是,单独写个类放在static变量中,
类似于:
public class AppContext {

  private static AppContext instance;

  private AbstractApplicationContext appContext;

  public synchronized static AppContext getInstance() {
    if (instance == null) {
      instance = new AppContext();
    }
    return instance;
  }

  private AppContext() {
    this.appContext = new ClassPathXmlApplicationContext(
        "/applicationContext.xml");
  }

  public AbstractApplicationContext getAppContext() {
    return appContext;
  }
}

不过这样,还是加载了2次applicationcontext,servlet一次,路径加载一次;觉得不如直接用路径加载,舍掉servlet加载
在网上也找了些其他说法:实现ApplicationContextAware,,, 接口,或者servletcontextAware接口,还要写配置文件。有的竟然要把配置文件里的listener,换成自己的类,这样纯粹多此一举。不过有的应用不是替换,是在补一个listener,
我在一版的jpetstore(具体那一版不知道)里发现了这个:
[web.xml]里
     
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
   
    <listener>
        <listener-class>com.ibatis.jpetstore.util.SpringInit</listener-class>
    </listener>
其中SpringInit实现接口ServletContextListener :

package com.ibatis.jpetstore.util;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;


public class SpringInit implements ServletContextListener {
   

    private static WebApplicationContext springContext;
   
    public SpringInit() {
        super();
    }
   
    public void contextInitialized(ServletContextEvent event) {
        springContext = WebApplicationContextUtils.getWebApplicationContext(event.getServletContext());
    }
   

    public void contextDestroyed(ServletContextEvent event) {
    }
   
    public static ApplicationContext getApplicationContext() {
        return springContext;
    }

   
}

在其中的一个bean的构造里SpringInit获取applicationcontext,代码:
  public OrderBean() {
    this(
            (AccountService) SpringInit.getApplicationContext().getBean("accountService"),
            (OrderService) SpringInit.getApplicationContext().getBean("orderService") );
  }

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