获取webapplicationContext以及servletContext的几种方式

   webapplicationContext是spring的核心context，所有的bean在初始化后都会在里面，当项目被加载，applicationContext.xml已经被加载了一次，如果此时用new ClassPathXmlApplicationContext.getBean("applicationContext.xml")的方式获取bean对象，applicationContext就相当于被加载了两次，所以就会起冲突，如果要在程序中获取webapplicationContext有以下几种方式。

一 通过webapplicationContextUtils.getRequiredWebApplicationContext(servletContext);

import javax.servlet.ServletContext;

import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

public final class WebAppUtils {
	private static volatile WebApplicationContext wac;
	private static volatile ServletContext servletContext;

	public static void setServletContext(ServletContext servletContext) {
		if (WebAppUtils.servletContext == null)
			synchronized (WebAppUtils.class) {
				if (WebAppUtils.servletContext == null)
					WebAppUtils.servletContext = servletContext;
			}
	}

	public static ServletContext getServletContext() {
		return servletContext;
	}

	public static WebApplicationContext getInstance() {
		if (wac == null) {
			synchronized (WebAppUtils.class) {
				if ((wac == null) && (servletContext != null)) {
					wac =       WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
				}
		
			}
		}

		return wac;
	}
}

这里需要获取servletContext,获取servletContext有两种方法

1.直接写一个filter，当filter在初始化的时候调用init()方法的时候，就会把servletConfig传进去，然后可以使用filterConfig.getServletContext();获取到servletContext 并设置到webapplication里面去就好了，代码如下。

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

import com.nsu.pmes.utils.cache.memory.WebAppUtils;

/**
 * 过滤器获取servletContext 用户获取webapplicationContext容器获取bean对象
 * @author lixin
 *
 */
public class DelegatingVisitFilterProxy implements Filter {


	public void init(FilterConfig filterConfig) throws ServletException {
	       ServletContext servletConfig= filterConfig.getServletContext();
		WebAppUtils.setServletContext(servletConfig);
	
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		chain.doFilter(request, response);
	
	}

	public void destroy() {
	}
	
}

2.还有一种获取servletContext的方法比较简单，
 直接通过 servletContext SC=ContextLoader.getCurrentWebApplicationContext().getServletContext();可以获取到

3.用Httprequest对象获取到 

servletContext SC=request.getsession().getServletContext

二借用ApplicationContextAware,ApplicationContext的帮助类能够自动装载ApplicationContext，只要你将某个类实现这个接口，并将这个实现类在Spring配置文件中进行配置，Spring会自动帮你进行注入 ApplicationContext.ApplicationContextAware的代码结构如下：

1 public interface ApplicationContextAware {  
2 
3         void setApplicationContext(ApplicationContext applicationContext) throws BeansException;  
4 
5 }  

就这一个接口。可以这样简单的实现一个ApplicationContextHelper类：

 1 public class ApplicationHelper implements ApplicationContextAware {  
 2 
 3 
 4     private ApplicationContext applicationContext; 
 5 
 6     public void setApplicationContext(ApplicationContext applicationContext)  
 7             throws BeansException {  
 8             this.applicationContext = applicationContext;  
 9     }  
10 
11 
12     public  ApplicationContext getApplicationContext(){
13         return this.applicationContext;  
14     }  
15 }