在servlet、filter、Taglib中获取Spring Bean

在servlet容器中使用spring框架时spring的上下文（WebApplicationContext）被在保存在 ServletContext中。在servlet、filter或jsp标签中获取spring bean的关键在于如何获取ServletContext。

servlet中：
public void init(ServletConfig config){
     servletContext= config.getServletContext();
}

filter中：
public void init(FilterConfig config) throws ServletException {
      ServletContext  servletContext  =config.getServletContext();
}

jsp taglib中：
ServletContext servletContext = this.pageContext.getServletContext();

spring的上下文（WebApplicationContext）存在ServletContext以 WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE为key的属性中，可通过如下方式获取：

Object ob = servletContext .getAttribute(     WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
WebApplicationContext context = (WebApplicationContext) ob;

或者

WebApplicationContext context =WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);

或者WebApplicationContextUtils.getWebApplicationContext(servletContext);

      在WebApplicationContext中获取bean:
protected Object getBean(String name){
      return this.getWebApplicationContext().getBean(name);
}

      一个抽像的servlet基类：
import javax.servlet.ServletContext;
import javax.servlet.ServletConfig;
import javax.servlet.Servlet;
import org.springframework.web.context.WebApplicationContext;
 
public abstract class BaseServlet implements Servlet {
 
    protected ServletContext servletContext;

    public void init(ServletConfig config){
         servletContext= config.getServletContext();
    }
 
    public ServletContext getServletContext(){
         return servletContext;
    }
 
    public void destroy(){
 
    }
 
    public String getServletInfo(){
         return "";
    }
 
    protected WebApplicationContext getWebApplicationContext()

throws RuntimeException{
         Object ob = servletContext.getAttribute(WebApplicationContext

                      .ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
        WebApplicationContext context = (WebApplicationContext) ob;
        return context;
    }
 
    protected Object getBean(String name){
        return this.getWebApplicationContext().getBean(name);
    }
 
    public ServletConfig getServletConfig(){
        return null;
    }
}