最终编辑：对不起，我确定这篇文章很难理解，我正在对其进行更新以备后继。我没弄清楚@PersistenceContext批注是什么问题，我最终放弃了，只是继续使用CrudRepository。
从CrudRepository实现的存储库接口：
public interface RepositoryCar extends CrudRepository<Car, Long> {
}
建立服务接口（不是必需的，但这是更好的做法）：
public interface ServiceInterface {
Car addCar(Car car);
Car findCar(long carId);
}
创建实现子类@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;
}
}
所以这是我的帖子集，我仍然很好奇为什么未以某种方式使用我的@PersistenceContext，但是我所有的端点都正确设置了，我还是很想听听一个解释。我只是继续使用CrudRepository，但是有多种方法可以做到这一点。
以下原始帖子：
我正在尝试发出一个PostRequest并使用Spring Boot存储有关我的Car对象的信息。我遵循的是以前做过的指南，但是起了作用，因此我试图重新阅读该指南和之前的示例，但是似乎缺少一些东西。我收到一个一般性错误500，但我不确定从这里去哪里。
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;
}
}
我的汽车资料库：
@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Application.yml：
spring:
jpa:
generate-ddl: true
properties.hibernate.dialect: org.hibernate.dialect.MySQL5InnoDBDialect
datasource:
url: jdbc:mysql://localhost:3306/cars?useSSL=false
username: root
在前面的可行示例中，我使用了相同的application.yml，并且再次检查了我是否设置了密码，因此省略了该字段。
我做了一个数据库和表格。下面的SQL代码构成了表格。由于该表是自动生成的，因此使该表不再需要，我删除了该表，只是在所有这些操作的结尾都存在数据库：
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);
}
}
我想知道我的表是否以某种方式设置不正确，所以我复制粘贴了我先前的工作示例，它也给了我500错误，所以我不认为我的表是错误的，因为我确定我的先前表一个不同的应用程序的作品。
当我在PostMan中执行发帖请求时，我总是会返回错误500，因此我将其从EntityManger更改为仅存在于内存中的HashMap，并且工作正常，因此可以肯定是问题所在是EntityManager
这里是否缺少某些组件，或者我做错了什么？我在此上花了太多时间，但似乎我在照做过去的示例，但显然不是。
我的帖子请求：
{
"make" : "make",
"model" : "model",
"color" : "blue",
"year" : 2000
}
只是说
{
"timestamp": "2019-06-29T03:29:06.110+0000",
"status": 500,
"error": "Internal Server Error",
"message": "No message available",
"path": "/cars/"
}
非常感谢您的帮助。
编辑：正如Dmitriy所指出的，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。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：我很确定是问题出在我的build.gradle上，因为我不知道还有什么可能。说实话，我什至惊讶它甚至可以编译，但是无论如何这里都是这样：
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"
])
答案 0 :(得分：-1)
在类CarsRepository.java的代码中，您已经在方法上提供了注释@Transactional。请尝试使用它，如下所示：
@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：持久性上下文处理一组实体 其中包含要保留在某些持久性存储中的数据（例如 数据库）。特别是，上下文知道不同的状态 实体相对于两个实体可以具有（例如，托管，分离） 上下文和基础持久存储。