春季EntityManager.persist问题

Question

我使用一个Spring框架(Boot+web+jpa)作为REST服务，并且需要持久化一个名为Sensor的实体。因为我使用Hibernate，所以我想继续使用EntityManager。从Spring文档和Stackoverflow中回答的一些问题中，我可以看到我应该配置LocalEntityManagerFactoryBean或LocalContainerEntityManagerFactoryBean。

现在，我能够读取persist.xml，并通过依赖注入@PersistenceUnit(unitName="...") EntityManagerFactory来持久化实体，以防出现LocalContainerEntityManagerFactoryBean。但是，每次我尝试用new Sensor()持久化LocalEntityManagerFactoryBean时，Spring都会抛出一个错误，如下所示。

// LocalEntityManagerFactoryBean
@Bean
public LocalEntityManagerFactoryBean entityManagerFactory() {
    LocalEntityManagerFactoryBean em = new LocalEntityManagerFactoryBean();
    em.setPersistenceUnitName("myunit");
    JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
    em.setJpaVendorAdapter(vendorAdapter);
    return em;
}

持久化(transaction.begin和end在调用方方法中)：

private Sensor getSensor(SimpleData sd) {
    List<Sensor> sensors = entityManager.createQuery("select s from Sensor s where s.deviceId = :devid", Sensor.class)
                                     .setParameter("devid", sd.getDeviceId())
                                     .getResultList();
    Sensor sensor = null;
    if(sensors.isEmpty()) {
        sensor = new Sensor();
        sensor.setDeviceId(sd.getDeviceId());
        sensor.setName(sd.getName());
        entityManager.persist(sensor); // Throws an exception
        deviceIdMapper.put(sensor.getDeviceId(), sensor.getId());
        logger.trace("Cannot find the sensor in db, adding: "+sensor.getDeviceId());
    } else {
        sensor = sensors.get(0);
        deviceIdMapper.put(sensor.getDeviceId(), sensor.getId());
        logger.trace("Found a sensor from the db: "+sd.getDeviceId());
    }
    deviceIdMapper.putIfAbsent(sensor.getDeviceId(), sensor.getId());
    logger.trace(sensor);
    return sensor;
}

例外：

javax.persistence.PersistenceException: org.hibernate.property.access.spi.PropertyAccessException: Error accessing field [protected int com.database.Sensor.id] by reflection for persistent property [com.database.Sensor#id] : com.database.Sensor@6de9600a
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:154)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:181)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:188)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:807)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:785)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:350)
at com.sun.proxy.$Proxy108.persist(Unknown Source)
at com.DataListener.getSensor(DataListener.java:69)
at com.DataListener.lambda$0(DataListener.java:87)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
at com.DataListener.processData(DataListener.java:86)
at com.DataListener.onMessage(DataListener.java:49)
at org.apache.activemq.ActiveMQMessageConsumer.dispatch(ActiveMQMessageConsumer.java:1321)
at org.apache.activemq.ActiveMQSessionExecutor.dispatch(ActiveMQSessionExecutor.java:131)
at org.apache.activemq.ActiveMQSessionExecutor.iterate(ActiveMQSessionExecutor.java:202)
at org.apache.activemq.thread.PooledTaskRunner.runTask(PooledTaskRunner.java:129)
at org.apache.activemq.thread.PooledTaskRunner$1.run(PooledTaskRunner.java:47)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: org.hibernate.property.access.spi.PropertyAccessException: Error accessing field [protected int com.database.Sensor.id] by reflection for persistent property [com.database.Sensor#id] : com.database.Sensor@6de9600a
at org.hibernate.property.access.spi.GetterFieldImpl.get(GetterFieldImpl.java:75)
at org.hibernate.tuple.entity.AbstractEntityTuplizer.getIdentifier(AbstractEntityTuplizer.java:224)
at org.hibernate.persister.entity.AbstractEntityPersister.getIdentifier(AbstractEntityPersister.java:4931)
at org.hibernate.persister.entity.AbstractEntityPersister.isTransient(AbstractEntityPersister.java:4631)
at org.hibernate.engine.internal.ForeignKeys.isTransient(ForeignKeys.java:226)
at org.hibernate.event.internal.AbstractSaveEventListener.getEntityState(AbstractSaveEventListener.java:540)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:102)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:62)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:800)
... 20 more
Caused by: java.lang.IllegalArgumentException: Can not set int field com.database.Sensor.id to com.database.Sensor
at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.ensureObj(UnsafeFieldAccessorImpl.java:58)
at java.base/jdk.internal.reflect.UnsafeIntegerFieldAccessorImpl.getInt(UnsafeIntegerFieldAccessorImpl.java:56)
at java.base/java.lang.reflect.Field.getInt(Field.java:594)
at org.hibernate.property.access.spi.GetterFieldImpl.get(GetterFieldImpl.java:62)
... 28 more

传感器类：

@Entity
public class Sensor {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected int id;
    protected String deviceId;
    protected String name;

    @OneToMany(mappedBy = "owner", cascade=CascadeType.ALL)
    private List<SimpleData> simpleDevices = new ArrayList<>();

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDeviceId() {
        return deviceId;
    }

    public void setDeviceId(String deviceId) {
        this.deviceId = deviceId;
    }


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public List<SimpleData> getSimpleDevices() {
        return simpleDevices;
    }

    public void setSimpleDevices(List<SimpleData> simpleDevices) {
        this.simpleDevices = simpleDevices;
    }

}

有两个问题：

1. 为什么会出错？
2. 如果我不提供DataSource for LocalContainerEntityManagerFactoryBean，Spring会抛出一个错误？LocalEntityManagerFactoryBean使用来自persistence.xml的DataSource吐露为什么LocalContainerEntityManagerFactoryBean不做同样的操作？：

编辑1

我想我找到了解决办法。如果我从依赖项中删除spring devtools，它就解决了这个问题。事实上，当我使用spring devtools时，由于某种Sensor问题，我无法阅读ClassLoader。也许是什么虫子？：

java.lang.ClassCastException: class com.database.Sensor cannot be cast to class com.database.Sensor (com.database.Sensor is in unnamed module of loader 'app'; com.database.Sensor is in unnamed module of loader org.springframework.boot.devtools.restart.classloader.RestartClassLoader @6228d409)

编辑2这里是SimpleData类

@Entity
public class SimpleData {

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

    private double value;

    @JsonIgnore
    private Date time;

    @Transient
    private String deviceId;

    @JsonIgnore
    @Transient
    private String name;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="sensor_id")
    private Sensor owner;

    public double getValue() {
        return value;
    }

    public void setValue(double value) {
        this.value = value;
    }

    public Date getTime() {
        return time;
    }

    public void setTime(Date time) {
        this.time = time;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDeviceId() {
        return deviceId;
    }

    public void setDeviceId(String deviceId) {
        this.deviceId = deviceId;
    }

    public Sensor getOwner() {
        return owner;
    }

    public void setOwner(Sensor owner) {
        this.owner = owner;
    }
}

编辑3

好的，我做了一个小测试程序来重现这个问题：https://github.com/hjparker/spring-boot-devtools-issue。

一旦服务器启动，您就可以向localhost:8080发出GET请求，这将引发一个错误。在build.gradle中注释出spring devtools将解决这个问题。我发现这与spring tools (https://docs.spring.io/spring-boot/docs/current/reference/html/using-boot-devtools.html)中的重新启动类加载程序有关，每次重新启动spring时都会重新加载开发代码。但我认为文件的某些部分不会自动重新加载，从而导致类异常，例如，带有CL1 !=的实体加载了CL2。有人能解释一下我是不是做错了什么吗？

Answer 1

由hibernate/Spring管理的实体类或Bean类的反序列化器似乎没有被spring devtools重新启动类加载器正确地重新加载。通过在META-INF/spring-devtools.properties中设置以下属性，我必须显式地包含对重新启动类加载器执行反序列化的类

restart.include.hibernate=hibernate.*
restart.include.spring-orm=spring-orm.*

资料来源：

https://github.com/AxonFramework/AxonFramework/issues/344

https://docs.spring.io/spring-boot/docs/current/reference/html/using-boot-devtools.html#using-boot-devtools-customizing-classload

Answer 2

需要更新访问修饰符私有而不是受保护，似乎Java持久性试图获取不在包中的id，在某些子类上也没有调用id。

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String deviceId;
private String name;

访问修饰符文档