在 PostRequest 中使用 EntityManager 时出现错误 500

Question

最终编辑：抱歉，我确定这篇文章很难理解，我正在更新它以备后人之用。我从来没有弄清楚我的 @PersistenceContext 注释有什么问题，我最终放弃了，只是转而使用 CrudRepository。

我们从 CrudRepository 实现的存储库接口：

public interface RepositoryCar extends CrudRepository<Car, Long> {
}

制作一个服务接口（不是必需的，但这是更好的做法）：

public interface ServiceInterface {
    Car addCar(Car car);
    Car findCar(long carId);
}

制作实现子类@Service:

@Service
@Transactional
public class ServiceCar implements ServiceInterface{
    //autowire this so it can instantiate your CrudRepository class.
    @Autowired
    RepositoryCar repositoryCar;


    public Car addCar(Car car) {
        return repositoryCar.save(car);
    }

    public Car findCar(long carId) {
        Optional<Car> present=repositoryCar.findById(carId);
        if(present.isPresent())
        {
            return present.get();
        }
        else
            return null;
    }
}

这就是我的帖子集群，我仍然很好奇为什么我的@PersistenceContext 没有以某种方式被选中，但是我的所有端点都设置正确，我仍然很想听听解释。我只是继续前进并使用了 CrudRepository，但有多种方法可以做到这一点。

原帖如下：

我正在尝试使用 Spring Boot 发出 PostRequest 并存储有关我的 Car 对象的信息。我正在遵循我之前做过的指南并且它有效，所以我试图重新遵循该指南和我之前的示例，但我似乎遗漏了一些东西。我收到一般性错误 500，我不知道从哪里开始。

我的汽车课：

@Entity
@Table(name = "cars")
public class Car {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    private String make;
    private String model;
    private String color;
    private int year;

    public Car(String make, String model, String color, int year) {
        this.make = make;
        this.model = model;
        this.color = color;
        this.year = year;
    }
    //getters and setters

我的 CarController 类：

@RestController
@RequestMapping("/cars")
public class CarsController {
    CarsRepository repository;

    public CarsController(CarsRepository repository) {
        this.repository = repository;
    }

    @PostMapping
    public Car addCar(@RequestBody Car car) {
        repository.addCar(car);
        return car;
    }

    @GetMapping
    public CarsRepository getCars() {
        return repository;
    }
}

我的汽车存储库：

@Repository
public class CarsRepository {

    @PersistenceContext
    EntityManager entityManager;

    @Transactional
    public void addCar(Car car) {

        entityManager.persist(car);
    }

    public Car find(Long id) {
        return entityManager.find(Car.class, id);
    }
}

我的应用程序.yml：

spring:
  jpa:
    generate-ddl: true
    properties.hibernate.dialect: org.hibernate.dialect.MySQL5InnoDBDialect

  datasource:
    url: jdbc:mysql://localhost:3306/cars?useSSL=false
    username: root

在我之前的有效示例中，我使用了相同的application.yml，并且我仔细检查了我没有设置密码，因此我省略了该字段。

我做了一个数据库和表。下面的 SQL 代码创建了这个表。由于该表是自动生成的，因此不需要该表，我删除了该表并在所有这一切结束时让数据库存在：

CREATE TABLE car (
  id         BIGINT(20) NOT NULL AUTO_INCREMENT,
  make       VARCHAR(20),
  model      VARCHAR(20),
  color      VARCHAR(20),
  year       INT,
  PRIMARY KEY (id)
)
  ENGINE = innodb
  DEFAULT CHARSET = utf8;

我的主要 SpringBootApplication 类非常简单：

package study.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

我想知道我的表格是否以某种方式设置不正确，所以我复制粘贴了我之前的工作示例，它也给了我一个错误 500，所以我不认为我的表格不正确，因为我确定我之前的表格是不同的应用程序工作。

当我在 PostMan 中进行发布请求时，我总是返回错误 500，所以我将它从 EntityManger 更改为只是内存中的 HashMap，它工作正常，所以我确定是 EntityManager 是问题.

这里是否缺少某些组件，或者我做错了什么？我在这方面花费了太多时间，但看起来我在效仿我过去的例子，但显然不是。

我的发帖请求：

{
    "make" : "make",
    "model" : "model",
    "color" : "blue",
    "year" : 2000
}

而且回复没什么用，它只是说

{
    "timestamp": "2019-06-29T03:29:06.110+0000",
    "status": 500,
    "error": "Internal Server Error",
    "message": "No message available",
    "path": "/cars/"
}

感谢您的帮助，非常感谢。

编辑：我现在意识到我实际上在日志中收到了一些有用的错误消息，正如 Dmitriy 指出的那样。我收到 NullPointer 异常。这是整个堆栈跟踪：

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
        at study.example.CarsRepository.addCar(CarsRepository.java:19) ~[main/:na]
        at study.example.CarsController.addCar(CarsController.java:23) ~[main/:na]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_211]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_211]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_211]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_211]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:891) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:877) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.valves.RemoteIpValve.invoke(RemoteIpValve.java:685) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_211]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_211]
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.34.jar:8.5.34]
        at java.lang.Thread.run(Thread.java:748) [na:1.8.0_211]

编辑：我很确定问题出在我的 build.gradle 上，因为我看不出还有什么问题。老实说，如果这是问题所在，我很惊讶它甚至可以编译，但无论如何：

buildscript {
    ext {
        springBootVersion = "2.0.6.RELEASE"
        springVersion = "5.0.10.RELEASE"
        hibernateVersion = "5.2.17.Final"
        slf4jVersion = "1.7.25"
        junitVersion = "4.12"
        mysqlVersion = "5.1.40"
    }

    repositories {
        mavenCentral()
    }

    dependencies {
        classpath "org.springframework.boot:spring-boot-gradle-plugin:$springBootVersion"

    }
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

repositories {
    mavenCentral()
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:$springBootVersion")
    compile "com.fasterxml.jackson.dataformat:jackson-dataformat-csv:2.7.0"
    compile("mysql:mysql-connector-java:6.0.6")
    compile "org.springframework.boot:spring-boot-starter-tomcat"
    compile "org.hibernate:hibernate-core:$hibernateVersion"
    compile "org.slf4j:slf4j-api:$slf4jVersion"
    testCompile("org.springframework.boot:spring-boot-starter-test:$springBootVersion")

}

springBoot {
    buildInfo()
}

bootRun.environment([
        "WELCOME_MESSAGE": "hello"
])

Answer 1

在CarsRepository.java 类的代码中，您在方法上提供了注释@Transactional。尝试如下使用它：

@Repository
@Transactional
public class CarsRepository {

    @PersistenceContext
    EntityManager entityManager;

    public void addCar(Car car) {

        entityManager.persist(car);
    }

    public Car find(Long id) {
        return entityManager.find(Car.class, id);
    }
}

@PersistenceContext：一个持久化上下文处理一组实体 将数据保存在某个持久性存储中（例如 数据库）。特别是，上下文知道不同的状态 一个实体可以同时拥有（例如托管的、分离的） 上下文和底层持久性存储。