老师为什么我访问首页会空指针异常?

package com.mason.hospital.controller;

import com.mason.hospital.entity.Category;
import com.mason.hospital.entity.Department;
import com.mason.hospital.service.CategoryService;
import com.mason.hospital.service.DepartmentService;
import org.springframework.beans.factory.annotation.Autowired;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@WebServlet(urlPatterns = "/index.do")
public class IndexController extends HttpServlet {
    @Autowired
    CategoryService categoryService;
    @Autowired
    DepartmentService departmentService;
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        List<Category> categories = categoryService.selectAll();
        List<Department> departments = departmentService.selectAll();
        System.out.println("分类:"+categories);
        System.out.println("部门:"+departments);
        req.setAttribute("CLIST",categories);
        req.setAttribute("DLIST",departments);
        req.getRequestDispatcher("/hospital_detail.jsp").forward(req,resp);
    }
}

29-Jul-2019 16:04:43.424 涓ラ噸 [http-nio-8080-exec-2] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [com.mason.hospital.controller.IndexController] in context with path [/hospital] threw exception
 java.lang.NullPointerException
	at com.mason.hospital.controller.IndexController.service(IndexController.java:25)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.mason.hospital.global.EncodingFilter.doFilter(EncodingFilter.java:16)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:660)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)

我在后台页面都是正常能获取到分类和部门的数据的