当我尝试使用hibernate手动插入MySql表时,我收到此错误 . 我试图将一些默认数据插入我的应用程序,但手动插入时我得到Null指针异常 . 我是java编程的新手,所以无法理解如何修复此错误 . 如果有人可以帮助我,我真的很感激..
User_Role类:
package com.sanjay31321.sys.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity @Table(name="user_role")
public class User_Role {
@Id @Column @GeneratedValue(strategy=GenerationType.AUTO)
private int id;
@Column(name="role_name")
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
InsertUserRole
import org.springframework.beans.factory.annotation.Autowired;
import com.sanjay31321.sys.model.User_Role;
import com.sanjay31321.sys.service.UserRoleService;
public class InsertUserRole {
private static final Logger logger = LoggerFactory.getLogger(InsertUserRole.class);
@Autowired
private UserRoleService userRoleService;
public void insert() {
User_Role role = new User_Role();
role.setId(1);
role.setName("ROLE_ADMIN");
logger.info("id : "+ role.getId() + " | Role : " + role.getName());
userRoleService.addUserRole(role);
}
}
Error:
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:965)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
root cause
java.lang.NullPointerException
com.sanjay31321.sys.preset.data.InsertUserRole.insert(InsertUserRole.java:22)
com.sanjay31321.sys.preset.DefaultDataInstall.install(DefaultDataInstall.java:23)
com.sanjay31321.sys.controller.DefaultDataController.postinstall(DefaultDataController.java:31)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:601)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
DefaultDataController class
package com.sanjay31321.sys.controller;
import java.util.Locale;
import javax.validation.Valid;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import com.sanjay31321.sys.preset.DefaultDataInstall;
import com.sanjay31321.sys.preset.model.Install;
@Controller
public class DefaultDataController {
private static final Logger logger = LoggerFactory.getLogger(DefaultDataController.class);
@RequestMapping(value = "/install", method = RequestMethod.GET)
public String getinstall(Locale locale, Install install) {
logger.info("Welcome to Install Default Settings page ! GET METHOD : The client locale is {}.", locale);
return "install";
}
@RequestMapping(value="/install", method=RequestMethod.POST)
public String postinstall(@Valid Install install, BindingResult result, Locale locale){
logger.info("Welcome to Install Default Settings page ! POST METHOD : The client locale is {}.", locale);
DefaultDataInstall settings = new DefaultDataInstall();
settings.install();
return "install";
}
}
DefaultDataInstall class
package com.sanjay31321.sys.preset;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.sanjay31321.sys.preset.data.InsertCourse;
import com.sanjay31321.sys.preset.data.InsertFeedback;
import com.sanjay31321.sys.preset.data.InsertQuestion;
import com.sanjay31321.sys.preset.data.InsertQuestionSet;
import com.sanjay31321.sys.preset.data.InsertStudent;
import com.sanjay31321.sys.preset.data.InsertSubject;
import com.sanjay31321.sys.preset.data.InsertTeacher;
import com.sanjay31321.sys.preset.data.InsertUser;
import com.sanjay31321.sys.preset.data.InsertUserRole;
public class DefaultDataInstall {
private static final Logger logger = LoggerFactory.getLogger(DefaultDataInstall.class);
public void install() {
InsertUserRole role = new InsertUserRole();
role.insert();
logger.info("User Role data is installed");
}
}
我附上了你问过的课程 .
1 回答
我在github上看到你的代码 .
它显示该错误,因为
InsertUserRole
中的userRoleService
为空 . 所以你不能在它上面调用任何方法 .Why?
您在
DefaultDataInstall
中使用new
关键字创建InsertUserRole
对象 .@Autowired
当你这样做时不起作用它只有当DefaultDataInstall
也被spring实例化时才有效 . Spring只能在创建对象时才注入某个对象 .如何解决它 .
实例化
preset
包中的所有对象,即将它们标记为@Component
.另一种方法是在控制器中注入ApplicationContext并将其传递给您正在创建的对象,并从AppContext获取服务 .
将
ApplicationContext
对象传递给要使用spring bean的所有订单对象 .现在,您可以使用传递的服务来调用它们的方法