问候 SO 社区
我在使用 Hibernate JPA 时遇到了问题:每当我调用 entityManger.merge(entity) 时，Hibernate 尝试插入它。我从 OpenJPA 迁移过来，它工作正常，但无论我做什么都无法使其工作。
我一直在 SO 和 Google 中寻找问题的解决方案，或者至少为我指明正确方向的解决方案，但没有运气。与我的问题最接近的帖子尚未得到答复:entitymanager merge insert instead of update JPA Hibernate
我正在尝试插入一个实体Organization其中有一个单向 @OneToOne与User的关系实体。我已添加Casecade.Persist所以User实体仅在创建/保留 Organization 时受到影响。持久操作按预期工作。然而，正如之前提到的，merge不按预期工作，相反，它尝试保留/插入。
有人可以帮我解决这个问题吗？
我想仅使用 JPA Hibernate，并远离 Hibernate 特定实现，以防我需要迁移到另一个 JPA 提供程序。
环境:
这是一个Maven项目，我正在使用Wildfly 10
下面是我的代码:
我使用MappedSuperClass对于常见的 SQL 字段:
@MappedSuperclass
public abstract class BaseEntity implements Serializable{
protected static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
protected Long id;
//[UPDATE] I omitted the version field thinking it wasn't relevant, but now I believe this is the root of my problem. If I remove this field merge works as expected.
@Version
Long version
// getters and setters
}
我尝试插入的实体:
@Entity
public class Organization extends BaseEntity{
@Column
private String name;
@Column
private String description;
@OneToOne(cascade = CascadeType.PERSIST)
@JoinColumn(unique = true, insertable = true)
private User user;
// getters and setters
}
User实体:
@Entity
public class User extends BaseEntity implements Serializable {
private static final long serialVersionUID = 1L;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 100)
private String username;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 256)
private String password;
@Size(max = 45)
private String firstName;
@Size(max = 45)
private String lastName;
//getters and setters
}
我尝试将实体合并到 JAX-RS 中休息方法:
@Path("{id}")
@PUT
@Consumes("application/json")
@Produces("application/json")
public Organization edit(Organization entity,
@PathParam("id") Long id) {
//Omitting how I got the userId as it is not relevant to the situation at hand
entity.setUser(entityManager.find(User.class, userId));
super.edit(entity);
return entity;
}
注意:
- 上面的实体对象(我在请求中作为 JSON 对象传递并由 Jackson 编码)包含所有必要的字段，[特别是主键 (id)]。
- 这两个实体和 MappedSuperClass 都位于 persistence.xml 中
我启用了hibernate.show_sql在persistence.xml为了看看发生了什么:
<property name = "hibernate.show_sql" value = "true" />
下面是我得到的异常的堆栈跟踪:
17:58:08,804 INFO [stdout] (default task-4) Hibernate: insert into Organization (createdBy, lastUpdatedBy, version, description, name, user_id) values (?, ?, ?, ?, ?, ?)
17:58:09,302 WARN [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-4) SQL Error: 1062, SQLState: 23000
17:58:09,303 ERROR [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-4) Duplicate entry '1' for key 'UK_5lqexr38qf28ptx0lhuhqor9w'
17:58:09,401 ERROR [org.jboss.as.ejb3.invocation] (default task-4) WFLYEJB0034: EJB Invocation failed on component OrganizationFacadeREST for method public com.scholarjet.model.Organization com.scholarjet.service.OrganizationFacadeREST.edit(com.scholarjet.model.Organization,java.lang.Long): javax.ejb.EJBException: javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not execute statement
at org.jboss.as.ejb3.tx.CMTTxInterceptor.handleExceptionInOurTx(CMTTxInterceptor.java:187)
at org.jboss.as.ejb3.tx.CMTTxInterceptor.invokeInOurTx(CMTTxInterceptor.java:277)
at org.jboss.as.ejb3.tx.CMTTxInterceptor.required(CMTTxInterceptor.java:327)
at org.jboss.as.ejb3.tx.CMTTxInterceptor.processInvocation(CMTTxInterceptor.java:239)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.interceptors.CurrentInvocationContextInterceptor.processInvocation(CurrentInvocationContextInterceptor.java:41)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.invocationmetrics.WaitTimeInterceptor.processInvocation(WaitTimeInterceptor.java:43)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.security.SecurityContextInterceptor.processInvocation(SecurityContextInterceptor.java:100)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.interceptors.ShutDownInterceptorFactory$1.processInvocation(ShutDownInterceptorFactory.java:64)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.interceptors.LoggingInterceptor.processInvocation(LoggingInterceptor.java:66)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ee.component.NamespaceContextInterceptor.processInvocation(NamespaceContextInterceptor.java:50)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.interceptors.AdditionalSetupInterceptor.processInvocation(AdditionalSetupInterceptor.java:54)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.ContextClassLoaderInterceptor.processInvocation(ContextClassLoaderInterceptor.java:64)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.InterceptorContext.run(InterceptorContext.java:356)
at org.wildfly.security.manager.WildFlySecurityManager.doChecked(WildFlySecurityManager.java:636)
at org.jboss.invocation.AccessCheckingInterceptor.processInvocation(AccessCheckingInterceptor.java:61)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.InterceptorContext.run(InterceptorContext.java:356)
at org.jboss.invocation.PrivilegedWithCombinerInterceptor.processInvocation(PrivilegedWithCombinerInterceptor.java:80)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61)
at org.jboss.as.ee.component.ViewService$View.invoke(ViewService.java:195)
at org.jboss.as.ee.component.ViewDescription$1.processInvocation(ViewDescription.java:185)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61)
at org.jboss.as.ee.component.ProxyInvocationHandler.invoke(ProxyInvocationHandler.java:73)
at com.scholarjet.service.OrganizationFacadeREST$$$view4.edit(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.jboss.weld.util.reflection.Reflections.invokeAndUnwrap(Reflections.java:436)
at org.jboss.weld.bean.proxy.EnterpriseBeanProxyMethodHandler.invoke(EnterpriseBeanProxyMethodHandler.java:127)
at org.jboss.weld.bean.proxy.EnterpriseTargetBeanInstance.invoke(EnterpriseTargetBeanInstance.java:56)
at org.jboss.weld.bean.proxy.InjectionPointPropagatingEnterpriseTargetBeanInstance.invoke(InjectionPointPropagatingEnterpriseTargetBeanInstance.java:67)
at org.jboss.weld.bean.proxy.ProxyMethodHandler.invoke(ProxyMethodHandler.java:100)
at com.scholarjet.service.OrganizationFacadeREST$Proxy$_$$_Weld$EnterpriseProxy$.edit(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:139)
at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:295)
at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:249)
at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:236)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:395)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:202)
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:284)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:263)
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:174)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202)
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:793)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not execute statement
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1692)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1602)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1608)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:1171)
at org.jboss.as.jpa.container.AbstractEntityManager.merge(AbstractEntityManager.java:565)
at com.scholarjet.service.AbstractFacade.edit(AbstractFacade.java:32)
at com.scholarjet.service.OrganizationFacadeREST.edit(OrganizationFacadeREST.java:110)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.jboss.as.ee.component.ManagedReferenceMethodInterceptor.processInvocation(ManagedReferenceMethodInterceptor.java:52)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.InterceptorContext$Invocation.proceed(InterceptorContext.java:437)
at org.jboss.as.weld.ejb.Jsr299BindingsInterceptor.doMethodInterception(Jsr299BindingsInterceptor.java:82)
at org.jboss.as.weld.ejb.Jsr299BindingsInterceptor.processInvocation(Jsr299BindingsInterceptor.java:93)
at org.jboss.as.ee.component.interceptors.UserInterceptorFactory$1.processInvocation(UserInterceptorFactory.java:63)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.invocationmetrics.ExecutionTimeInterceptor.processInvocation(ExecutionTimeInterceptor.java:43)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.jpa.interceptor.SBInvocationInterceptor.processInvocation(SBInvocationInterceptor.java:47)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.InterceptorContext$Invocation.proceed(InterceptorContext.java:437)
at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:64)
at org.jboss.as.weld.ejb.EjbRequestScopeActivationInterceptor.processInvocation(EjbRequestScopeActivationInterceptor.java:83)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ee.concurrent.ConcurrentContextInterceptor.processInvocation(ConcurrentContextInterceptor.java:45)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.InitialInterceptor.processInvocation(InitialInterceptor.java:21)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61)
at org.jboss.as.ee.component.interceptors.ComponentDispatcherInterceptor.processInvocation(ComponentDispatcherInterceptor.java:52)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.component.pool.PooledInstanceInterceptor.processInvocation(PooledInstanceInterceptor.java:51)
at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
at org.jboss.as.ejb3.tx.CMTTxInterceptor.invokeInOurTx(CMTTxInterceptor.java:275)
... 84 more
Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:59)
at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:109)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:95)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:207)
at org.hibernate.dialect.identity.GetGeneratedKeysDelegate.executeAndExtract(GetGeneratedKeysDelegate.java:57)
at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:42)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2792)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3363)
at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:81)
at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:597)
at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:232)
at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:213)
at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:256)
at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:317)
at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:272)
at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:178)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:109)
at org.hibernate.jpa.event.internal.core.JpaMergeEventListener.saveWithGeneratedId(JpaMergeEventListener.java:56)
at org.hibernate.event.internal.DefaultMergeEventListener.saveTransientEntity(DefaultMergeEventListener.java:255)
at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:235)
at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:173)
at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:69)
at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:840)
at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:822)
at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:827)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:1161)
... 116 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '1' for key 'UK_5lqexr38qf28ptx0lhuhqor9w'
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:389)
at com.mysql.jdbc.Util.getInstance(Util.java:372)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:973)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3835)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3771)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2435)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2582)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2535)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1911)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2145)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2081)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2066)
at org.jboss.jca.adapters.jdbc.WrappedPreparedStatement.executeUpdate(WrappedPreparedStatement.java:537)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:204)
... 138 more
[更新]
在 PUT 请求中提交的 JSON 对象:
{
"id": 1,
"name": "2 My Org 1",
"description": "2 Org 1 Description 1"
}
就toString而言输出，我还没有覆盖(覆盖？)toString该对象的方法。所以现在它返回默认值 toString Object中的方法:
com.francisco.model.Organization@1
如果有帮助，我在调用 super.edit(entity) 的行中放置了一个断点并运行调试器。这是entity的内容:
我还应该注意到 super.edit(entity)只需调用:
entityManager.merge(entity)
最佳答案
I omitted the version field thinking it wasn't relevant, but now I believe this is the root of my problem. If I remove this field merge works as expected.
这是因为 @Version 和乐观锁定的工作原理。
我总是不喜欢将@Version属性暴露给外界，因为它允许一些外部事件在我需要抛出OptimisiticLockException的情况下强制更新当多个 session 同时修改同一行时。
您想要做的是利用传输对象模式并将传入数据覆盖在实际数据库对象之上:
@Path("{id}")
@PUT
@Consumes("application/json")
@Produces("application/json")
public Organization edit(OrganizationDTO dto,
@PathParam("id") Long id) {
// lookup entity from database
Organization org = entityManager.find( Organization.class, entity.getId() );
// map changable values to the entity
org.setName( dto.getName() );
org.setDescription( dto.getDescription() );
org.setUser( entityManager.find( User.class, userId ) );
dto.setUser( org.getUser() );
// merge changes
entityManager.merge( org );
// return dto
return dto;
}
我相信您可以利用ObjectMapper来进行映射覆盖，而不必对其进行硬编码；我将把它作为练习。
但问题的根源在于，您试图将传入的 JSON 数据视为一个完整的 Organization 对象，并尝试在数据库中更新它，而实际上它是部分的数据。
如果版本值已在您的初始 JSON 中提供，hibernate 将按照您的预期使用合并，假设提供的版本值与数据库中的值匹配。不匹配的非空值将引发 OptimisticLockException。
关于java - EntityManager 合并插入新实体，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36657920/