servlet是无法直接调用spring中的bean的，如果直接调用，一般都会报空指针异常。
为什么会这样？其实我们使用spring的目的就是为了让spring为我们来提供一个已经被注入好的一个实例。而servlet是不同的，servlet是有生命周期的，而这个并不归属spring管理，而是由web容器管理的。那么当servlet刚刚创建的时候，spring可以为servlet注入，当你访问的时候，由于servlet是单实例多线程的，所以，servlet信息被重置，刚刚被注入的对象又为null了。
那么该怎么处理这个问题呢？其实只要我在获得servlet的时候，用从Spring获得，而不是由web容器获得就可以了。而解决这个方法的思路就是，我们使用一个代理的servlet，利用这个代理的servlet去调用我们的业务servlet（其中这个业务servlet是被配置为spring中的bean），这样就可以实现其他bean注入，然后使用代理servlet调用
具体的配置及调用代码：
代理servlet：

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
/**
 * HttpServlet 代理
 * @author lwei
 * @since 2011-03-17
 * @version 1.0
 */
public class HttpServletProxy extends HttpServlet {
    /**
     * random serialVersionUID
     */
    private static final long serialVersionUID = -7208519469035631940L;
    Log logger = LogFactory.getLog(HttpServletProxy.class);
    private String targetServlet;
    private HttpServlet proxy;
    public void init() throws ServletException {
        this.targetServlet = getInitParameter("targetServlet");
        getServletBean();
        proxy.init(getServletConfig());
        System.out.println(targetServlet + " was inited by HttpServletProxy  successfully......");
    }
    private void getServletBean() {
        WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
        this.proxy = (HttpServlet) wac.getBean(targetServlet);
    }
    @Override
    public void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException, RuntimeException {
        proxy.service(request, response);
    }
}
业务servlet



import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.origin.mobile.factory.IDemoFactory;
/**
 * @author 卢旭昶
 */
public class UserCheckServlet extends HttpServlet {
    /**
     * random serialVersionUID
     */
    private static final long serialVersionUID = 3075635113536622929L;
    private IDemoFactory idemoFactory;//UserService 是spring托管的bean，通过set方法注入
    public void setIdemoFactory (IDemoFactory idemoFactory) {
        this.idemoFactory = idemoFactory;
    }
    public UserCheckServlet() {
        super();
    }
    public void init() throws ServletException {
        super.init();
    }
    @Override
    public void service(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
            throws ServletException, IOException, RuntimeException {
        String str = idemoFactory.testMobile();
        System.out.println("=======================str:"+str);
    }   
}


web.xml配置

	<servlet>
		<servlet-name>UserCheckProxy</servlet-name>
		<servlet-class>com.origin.mobile.servlet.HttpServletProxy</servlet-class>
		<init-param>
			<param-name>targetServlet</param-name>
			<param-value>userCheckServlet</param-value><!--业务servlet配置为spring的bean时的名字-->
		</init-param>
	</servlet>
	<servlet-mapping>
		<servlet-name>UserCheckProxy</servlet-name>
		<url-pattern>/UserCheck.do</url-pattern>
	</servlet-mapping>


spring配置文件

	<bean id="userCheckServlet" class="com.origin.mobile.servlet.UserCheckServlet">
		<property name="idemoFactory" ref="demoFactory"></property>
	</bean>