无法在 Java Web 应用程序中创建类型的对象
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【中文标题】无法在 Java Web 应用程序中创建类型的对象【英文标题】：Could not create object of a type in java web application 【发布时间】：2019-09-08 01:06:08 【问题描述】：我一直在开发一个 java 应用程序，但遇到了一个我找不到答案的问题。我的应用程序是 postgresql 中学生的数据库，该应用程序是在 maven 中使用 MCV 模式制作的，而对于 Web 部分，我使用 Spring 和 hibernate，因为 IDE 使用 Intellij。
我可以毫无问题地启动它，但是在访问 localhost 页面时出现以下错误：
“出现意外错误（类型=内部服务器错误，状态=500）。 无法提取结果集； SQL [不适用]；嵌套异常是 org.hibernate.exception.SQLGrammarException: could not extract ResultSet"
在 intelij 中出现以下错误：
"2019-04-17 20:38:43.283 错误 14120 --- [nio-8010-exec-7] oaccC[.[.[/].[dispatcherServlet]：Servlet.service() 用于 servlet [dispatcherServlet ] 在路径 [] 的上下文中抛出异常 [请求处理失败；嵌套异常是 org.springframework.dao.InvalidDataAccessResourceUsageException：无法提取 ResultSet；SQL [n/a]；嵌套异常是 org.hibernate.exception.SQLGrammarException：不能extract ResultSet] 的根本原因是 org.postgresql.util.PSQLException: ERROR: 关系“老师”不存在”
我不明白为什么这种关系不存在，因为我的表上有 @ManyToOne 与老师有关，而在 postgresql 中是相同的关系。
我的教师示范课是：
package project.M.Entities;
import javax.persistence.*; import java.io.Serializable;
@Entity @Table(name = "Teacher") public class Teacher implements
Serializable
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@Column(name="name", nullable = false)
private String name;
@Column(name="address", nullable = true)
private String address;
@Column(name="email",nullable = false)
private String email;
@Column(name="age")
private Integer age;
@Column(name="passsword",nullable = false)
private String password;
public Teacher(Integer idTask, String description, String filepath, String str, String ema, Integer it)
public Teacher(int id, String name, String password, String address, String email, int age)
this.id = id;
this.name = name;
this.address = address;
this.email = email;
this.age = age;
this.password = password;
public Teacher( String name,String password, String address, String email, int age)
this.name = name;
this.address = address;
this.email = email;
this.age = age;
this.password = password;
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;
public String getAddress()
return address;
public void setAddress(String address)
this.address = address;
public String getEmail()
return email;
public void setEmail(String email)
this.email = email;
public int getAge()
return age;
public void setAge(int age)
this.age = age;
public String getPassword()
return password;
public void setPassword(String password)
this.password = password;
@Override
public String toString()
return "Teacher" +
"id=" + id +
", name='" + name + '\'' +
", address='" + address + '\'' +
", email='" + email + '\'' +
", age=" + age +
", password='" + password + '\'' +
'';
它连接到我的模型所在的课程类
package project.M.Entities; import javax.persistence.Column;
import javax.persistence.Entity; import
javax.persistence.GeneratedValue; import
javax.persistence.GenerationType; import javax.persistence.Id; import
javax.persistence.JoinColumn; import javax.persistence.ManyToOne;
import javax.persistence.Table; import
javax.validation.constraints.NotNull; import java.io.Serializable;
@Entity @Table(name = "courses") public class Course implements
Serializable
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@Column(name="name",nullable = false)
private String name;
//@Column()
//private Integer TeacherID;
@ManyToOne
@JoinColumn(name = "teacherID",referencedColumnName = "id")
@NotNull
private project.M.Entities.Teacher teacher;
public Course(Integer id, String name, Teacher teacher)
this.id = id;
this.name = name;
this.teacher = teacher;
public Integer getId()
return id;
public void setId(Integer id)
this.id = id;
public String getName()
return name;
public void setName(String name)
this.name = name;
public project.M.Entities.Teacher getTeacher()
return teacher;
public void setTeacherID(Teacher teacherID)
this.teacher = teacherID;
@Override
public String toString()
return "Course" +
"id=" + id +
", name='" + name + '\'' +
", teacher=" + teacher +
'';
关于我对老师的服务：
package project.C;
import project.M.Entities.Teacher;
import project.M.Services.TeacherService;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.ModelAndView;
import javax.inject.Inject;
import java.util.List;
@Controller
public class TeacherController
@Inject
TeacherService teacherService;
@RequestMapping(value ="" ,method = RequestMethod.GET)
public ModelAndView getTeachers()
List<Teacher> teacherList = teacherService.getAllTeachersWithCourses();
ModelAndView mav = new ModelAndView("TeacherView");
mav.addObject("teachersWithCoursesListId", teacherList);
return mav;
@RequestMapping(value = "", method = RequestMethod.POST)
public ModelAndView postTeacher(@ModelAttribute(value = "newTeacher") Teacher newTeacher)
teacherService.create(newTeacher);
return new ModelAndView("redirect:teachers");
@RequestMapping(value ="", method = RequestMethod.DELETE)
public ModelAndView deleteTeacher(@ModelAttribute(value = "newTeacher") Teacher newTeacher)
teacherService.delete(newTeacher);
return new ModelAndView("redirect:teachers");
/*
@RequestMapping(value = "", method = RequestMethod.POST)
@ResponseBody
public void set(@RequestParam("idTeacher") Integer idTask, @RequestParam("name") String description, @RequestParam("password") String filepath, @RequestParam("address") String str, @RequestParam("email") String ema,@RequestParam("age")Integer it)
// assign parameters to taskDocumentEntity by constructor args or setters
Teacher document = new Teacher(idTask,description,filepath,str,ema,it);
teacherService.create(document);
*/
对于 TeacherService，我有以下
package project.M.Services;
import project.M.Entities.Teacher; import
project.M.Repository.TeacherRepository; import java.util.List; import
java.util.Optional;
import javax.inject.Inject;
import org.springframework.stereotype.Service;
@Service public class TeacherService
private int count;
@Inject
TeacherRepository teacherRepository;
public List<Teacher> getAllTeachersWithCourses()
return teacherRepository.findAll();
public void create(Teacher newTeacher)
System.out.println("aaaa"+newTeacher);
teacherRepository.save(newTeacher);
public void delete(Teacher newTeacher)
teacherRepository.delete(newTeacher);
public void update(Teacher old,Teacher st)
if(old==null)
System.out.println("eror at update");
else
teacherRepository.delete(old);
teacherRepository.save(st);
我尝试访问的 TeacherView 是：
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org" xmlns:th1="http://www.w3.org/1999/xhtml">
<head>
<title>Teachers</title>
<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css" />
<link href="//maxcdn.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.min.css" rel="stylesheet" />
</head>
<body>
<table border="1">
<thead>
<tr>
<th>teacher.ID</th>
<th>teacher.NAME</th>
<th>teacher.PASSWORD</th>
<th>teacher.EMAIL</th>
<th>teacher.AGE</th>
<th>course entire data</th>
</tr>
</thead>
<tbody>
<tr th:each="teacher : $ teachersWithCoursesList ">
<td th:text="$ teacher.id ">ID</td>
<td th:text="$ teacher.name "></td>
<td th:text="$ teacher.password "></td>
<td th:text="$ teacher.email "></td>
<td th:text="$ teacher.age "></td>
<td th1:text="$ teacher.courses ">
<p th:each="course: $ teacher.courses ">
<span th:text="$course.id"></span>
<span th:text="$course.name"></span>
</p>
</td>
</tr>
</tbody>
</table>
<br/>
<br/>
<br/>
<form th:object="$newTeacher" method="post">
<div class="col-sm-12">
<label>Name</label>
<input placeholder="Teacher Name" name="name"/>
</div>
<div class="col-sm-12">
<label>Password</label>
<input placeholder="Teacher password" name="password"/>
</div>
<div class="col-sm-12">
<label>Email</label>
<input placeholder="Teacher email" name="email"/>
</div>
<button type="submit" class = "btn btn-primary">ADD Teacher</button>
</form>
</body>
我的数据库是
还有数据库的 sql： 课程
-- Table: public."Courses"
-- DROP TABLE public."Courses";
CREATE TABLE public."Courses"
(
"idCourses" integer NOT NULL,
"Name" "char"[] NOT NULL,
"TeacherID" integer NOT NULL,
CONSTRAINT "Courses_pkey" PRIMARY KEY ("idCourses"),
CONSTRAINT "teacherID" FOREIGN KEY ("TeacherID")
REFERENCES public."Teacher" ("idTeacher") MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)
WITH (
OIDS = FALSE
)
TABLESPACE pg_default;
ALTER TABLE public."Courses"
OWNER to postgres;
-- Index: fki_teacherID
-- DROP INDEX public."fki_teacherID";
CREATE INDEX "fki_teacherID"
ON public."Courses" USING btree
("TeacherID")
TABLESPACE pg_default;
老师
-- Table: public."Teacher"
-- DROP TABLE public."Teacher";
CREATE TABLE public."Teacher"
(
"idTeacher" integer NOT NULL,
name "char"[] NOT NULL,
password "char"[] NOT NULL,
address "char"[],
email "char"[] NOT NULL,
age integer,
CONSTRAINT "Teacher_pkey" PRIMARY KEY ("idTeacher")
)
WITH (
OIDS = FALSE
)
TABLESPACE pg_default;
ALTER TABLE public."Teacher"
OWNER to postgres;
学生：
-- Table: public."Student"
-- DROP TABLE public."Student";
CREATE TABLE public."Student"
(
address "char"[],
email "char"[] NOT NULL,
"idStudent" integer NOT NULL,
name "char"[] NOT NULL,
password "char"[] NOT NULL,
age integer,
CONSTRAINT "Student_pkey" PRIMARY KEY ("idStudent")
)
WITH (
OIDS = FALSE
)
TABLESPACE pg_default;
ALTER TABLE public."Student"
OWNER to postgres;
成绩：
-- Table: public.grades
-- DROP TABLE public.grades;
CREATE TABLE public.grades
(
"IdCourses" integer NOT NULL,
"idStudent" integer NOT NULL,
"Grade" integer,
"Exam" integer,
"Midterm" integer,
"examDate" date,
"midtermDate" date,
"Id" bigint NOT NULL,
CONSTRAINT "IdGrades" PRIMARY KEY ("Id"),
CONSTRAINT "idCourses" FOREIGN KEY ("IdCourses")
REFERENCES public."Courses" ("idCourses") MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION,
CONSTRAINT "idStudent" FOREIGN KEY ("idStudent")
REFERENCES public."Student" ("idStudent") MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)
WITH (
OIDS = FALSE
)
TABLESPACE pg_default;
ALTER TABLE public.grades
OWNER to postgres;
-- Index: fki_idCourses
-- DROP INDEX public."fki_idCourses";
CREATE INDEX "fki_idCourses"
ON public.grades USING btree
("IdCourses")
TABLESPACE pg_default;
-- Index: fki_idStudent
-- DROP INDEX public."fki_idStudent";
CREATE INDEX "fki_idStudent"
ON public.grades USING btree
("idStudent")
TABLESPACE pg_default;
稍后编辑： 这是使用 2 个关系更新代码后的错误：
org.hibernate.tool.schema.spi.CommandAcceptanceException: Unable to execute command [alter table courses drop constraint FKkhvrych02e4jav7oqoemsf498]
at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:63) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.applySqlString(SchemaDropperImpl.java:370) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.applySqlStrings(SchemaDropperImpl.java:355) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.applyConstraintDropping(SchemaDropperImpl.java:327) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.dropFromMetadata(SchemaDropperImpl.java:229) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.performDrop(SchemaDropperImpl.java:153) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.doDrop(SchemaDropperImpl.java:125) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.internal.SchemaDropperImpl.doDrop(SchemaDropperImpl.java:111) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:137) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:65) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:308) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:483) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:888) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:57) ~[spring-orm-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:390) ~[spring-orm-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:377) ~[spring-orm-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1837) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1774) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1105) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at project.Assignment2Application.main(Assignment2Application.java:9) ~[classes/:na]
Caused by: org.postgresql.util.PSQLException: ERROR: relation "courses" does not exist
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2440) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2183) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:308) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:441) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:365) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.jdbc.PgStatement.executeWithFlags(PgStatement.java:307) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.jdbc.PgStatement.executeCachedSql(PgStatement.java:293) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.jdbc.PgStatement.executeWithFlags(PgStatement.java:270) ~[postgresql-42.2.5.jar:42.2.5]
at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:266) ~[postgresql-42.2.5.jar:42.2.5]
at com.zaxxer.hikari.pool.ProxyStatement.execute(ProxyStatement.java:95) ~[HikariCP-3.2.0.jar:na]
at com.zaxxer.hikari.pool.HikariProxyStatement.execute(HikariProxyStatement.java) ~[HikariCP-3.2.0.jar:na]
at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:51) ~[hibernate-core-5.2.1.Final.jar:5.2.1.Final]
... 35 common frames omitted
【问题讨论】：
【参考方案1】：在您的 Course 课程中，您没有遵守 Java Bean 命名约定。
你有一个字段teacher，getter getTeacher，但是setter setTeacherID。
将设置器重命名为 setTeacher
更新
同一字段上的@JoinColumn 不正确。 我可以在数据库中看到 Teacher_idTeacher，并且在您的代码中看到不同的值
要检查的另一件事是您的数据库用户是否拥有对您使用的表的所有必要授权。如果用户无权访问某张表，可能会正确生成查询，但还是会收到sql语法错误
更新2
以下任何一项：
外壳问题。您正在创建“教师”，但生成的查询会查找教师。见org.postgresql.util.PSQLException: ERROR: relation "app_user" does not exist
默认架构不匹配公共 Change database schema used by Spring Boot 或者在@Table 中指定架构
最重要的是，您的映射仍然不正确，id 列名称与 db 不匹配。
【讨论】：
谢谢你，这是一个错误，当我试图查看它是否在没有类之间的连接的情况下工作时。我重命名了它，但错误仍然没有任何改变。 更新了答案。如果问题仍然存在，请使用生成的 Sql 更新您的问题。 更新帖子。很抱歉，我为数据库放置了错误的图像。【参考方案2】：1) 让 JPA 为您构建表和 DDL。
spring.jpa.generate-ddl
spring.jpa.hibernate.ddl-auto
https://docs.spring.io/spring-boot/docs/current/reference/html/howto-database-initialization.html
2) 在页面中，您正在访问teacher.courses，但您的Teacher 实体中没有课程的关系对象。
课程
@ManyToOne(fetch = FetchType.LAZY, optional = false)
@JoinColumn(name = "TeacherID", nullable = false)
private Teacher teacher;
老师
@OneToMany(cascade = CascadeType.ALL,
fetch = FetchType.LAZY,
mappedBy = "teacher")
private List<Course> courses = new ArrayList<>();
如需完整的工作示例，请查看https://www.callicoder.com/hibernate-spring-boot-jpa-one-to-many-mapping-example/
【讨论】：
嗨，我听从了你的建议，让 spring 来构建我的数据库。我也用上面的序列完成了代码。当我运行它时，错误是一样的，即使正在构建数据库并且正在运行tomcat。 您可以使用新代码和错误堆栈跟踪更新您的问题。要获取数据，请使用CrudRepository。使用@AutoWired 而不是@Inject以上是关于无法在 Java Web 应用程序中创建类型的对象的主要内容，如果未能解决你的问题，请参考以下文章
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