无法打开JPA EntityManager进行交易；嵌套的异常是javax.persistence.PersistenceException

问题描述

运行代码时，出现此异常:

when i run my code, i get this exception:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    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:411)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1121)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:357)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2482)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2519)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
    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:411)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:208)
    at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriverManager(DriverManagerDataSource.java:153)
    at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriver(DriverManagerDataSource.java:144)
    at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnectionFromDriver(AbstractDriverBasedDataSource.java:155)
    at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnection(AbstractDriverBasedDataSource.java:120)
    at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:139)
    at org.hibernate.tool.hbm2ddl.SuppliedConnectionProviderConnectionHelper.prepare(SuppliedConnectionProviderConnectionHelper.java:51)
    at org.hibernate.tool.hbm2ddl.DatabaseExporter.<init>(DatabaseExporter.java:52)
    at org.hibernate.tool.hbm2ddl.SchemaExport.execute(SchemaExport.java:367)
    at org.hibernate.tool.hbm2ddl.SchemaExport.create(SchemaExport.java:304)
    at org.hibernate.tool.hbm2ddl.SchemaExport.create(SchemaExport.java:293)
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:517)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1857)
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
Aug 25, 2015 8:23:45 PM com.sun.jersey.spi.container.ContainerResponse mapMappableContainerException
SCHWERWIEGEND: The RuntimeException could not be mapped to a response, re-throwing to the HTTP container
org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Could not open connection
    at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:431)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:457)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:276)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
    at com.sun.proxy.$Proxy76.create(Unknown Source)

我不知道问题出在哪里.但是昨天我做得很好.

I don't know where is the problem. But yesterday i worked fine.

我的database.properties:

my database.properties:

jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/streaming
jdbc.username=root
jdbc.password=password

hibernate.dialect=org.hibernate.dialect.MySQLDialect
hibernate.showsql=true
hibernate.hbm2ddl.auto=create

我可以直接从命令行运行mysql.问题出在哪儿?是错的.我使用Spring 4，并以mysql作为数据库语言休眠.

It is possible for me to run mysql directly from command line. Where is the problem? Was is wrong.I use spring 4 and hibernate with mysql as database language.

有人有什么想法吗?

谢谢.

推荐答案

出现CommunicationsException:通信链接失败.

There is CommunicationsException: Communications link failure.

如果收到SQLException:连接被拒绝或连接超时或特定于MySQL

If you get a SQLException: Connection refused or Connection timed out or a MySQL specific

CommunicationsException: Communications link failure

这意味着数据库根本无法访问.可能有以下一种或多种原因:

then it means that the DB isn't reachable at all. This can have one or more of the following causes:

• JDBC URL中的IP地址或主机名错误.
• 本地DNS服务器无法识别JDBC URL中的主机名.
• JDBC URL中的端口号丢失或错误.
• 数据库服务器已关闭.
• 数据库服务器不接受TCP/IP连接.
• 数据库服务器已用尽连接.
• Java和DB之间的某些情况阻止了连接，例如防火墙或代理.

要解决一个问题，请遵循以下建议:

To solve the one or the other, follow the following advices:

• 使用ping验证并测试它们.
• 刷新DNS或在JDBC URL中使用IP地址.
• 基于MySQL DB的my.cnf进行验证.
• 启动数据库.
• 验证是否在没有--skip-networking选项的情况下启动mysqld.
• 重新启动数据库，并相应地修复代码，使其最终关闭连接.
• 禁用防火墙和/或配置防火墙/代理以允许/转发端口.

来源:更多详细信息

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