SSM框架—java.lang.NullPointerException,空指標異常處理
阿新 • • 發佈:2019-02-07
Servlet.service() for servlet [GoodShop] in context with path [/goshop] threw exception [Request processing failed;
nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
在測試SSM專案時,一直報空指標異常,明明配置檔案與程式碼都沒有錯,為什麼會這樣呢?
五月 30, 2018 1:17:53 下午 org.apache.catalina .core.StandardWrapperValve invoke
嚴重: Servlet.service() for servlet [GoodShop] in context with path [/goshop] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at com.xh.goshop.controller.GetRoleController .handleRequest(GetRoleController.java:35)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.springframework .web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1539)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1495)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
第一次空指標異常出現在Service層,沒有在物件上加上註解@Autowired:
@Service("roleService")
public class RoleService implements IRoleService {
@Autowired //當時沒有加這個註解,自動裝配Bean
private RoleMapper roleMapper;
@Override
public Role getRoleById(Long id) {
// TODO Auto-generated method stub
return roleMapper.getRole(id);
}
}
第二次空指標異常出現在Controller層,原因是我把它改成測試類了,以至於在model方法中沒有初始化Spring Ioc容器,因此獲取不到bean例項,報空指標異常。
//將Spring IoC容器執行在Junit上,減少開銷
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations="classpath:spring-mybatis.xml")
@Controller//標記這個類是通過註解來對映URL
public class GetRoleController {
//@Resource
//private RoleService roleService = null;
@RequestMapping("/hello")//前端哪個請求對映到這個方法
public ModelAndView model(HttpServletRequest request, HttpServletResponse response) throws Exception {
// ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:spring-mybatis.xml");
// IRoleService roleService = ctx.getBean("roleService",RoleService.class);
ModelAndView mv = new ModelAndView();
Long id = 1L;
System.out.println("檢測roleService是否為");
System.out.println(roleService);
Role role = roleService.getRoleById(id);
mv.addObject("userinfo", role.getRoleName());
mv.setViewName("/hello.jsp");
return mv;
}
// @Test
// public void test() {
// System.out.println("檢測roleServices是否為空");
// System.out.println(roleService);
// Long id = 1L;
// Role role = roleService.getRoleById(id);
// System.out.println(role.getNote());
// }
}
把上面程式碼中的Test類獨立出來,對比Spring IoC容器初始化的方式,如下:
//將Spring IoC容器執行在Junit上,減少開銷
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations="classpath:spring-mybatis.xml")
public class GetRoleController {
@Resource
private RoleService roleService = null;
@Test
public void test() {
System.out.println("檢測roleServices是否為空");
System.out.println(roleService);
Long id = 1L;
Role role = roleService.getRoleById(id);
System.out.println(role.getNote());
}
}
總結:空指標異常處理,檢視是否加上註解@Autowired或@Resource,不要把測試用的Spring IoC容器初始化方式混淆。