每当我运行程序时，它都会给出： 线程“主”中的异常java.lang.NullPointerException
我刚刚进入休眠状态，因此请向我建议一些摆脱此类异常的技术。
我已经使用maven依赖项将Jar文件加载到我的项目中。
此文件包含主要功能，我正在尝试建立会话并获取异常。
Login.java file
public class Login {
public static void main(String[] args) {
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
getStarted(session);
session.close();
sessionFactory.close();
}
}
这是我制作的hibernate.cfg.xml文件。
hibernate.cfg.xml file
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database Connection Settings -->
<property name="connection.driver_class">org.postgresql.Driver</property>
<property name="connection.url">jdbc:postgresql://localhost:5432/LMSHibernate</property>
<property name="connection.username">postgres</property>
<property name="connection.password">password</property>
<!-- JDBC connection pool (use the build-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<!-- Drop and re-create a database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<!-- Names the annotated entity class -->
<mapping class="com.lms.entities.Employee" />
</session-factory>
</hibernate-configuration>
结果：
Jan 18, 2019 6:12:38 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {5.3.7.Final}
Jan 18, 2019 6:12:38 PM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
Jan 18, 2019 6:12:40 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.0.4.Final}
Jan 18, 2019 6:12:40 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
Jan 18, 2019 6:12:40 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [org.postgresql.Driver] at URL [jdbc:postgresql://localhost:5432/LMSHibernate]
Jan 18, 2019 6:12:40 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {user=postgres, password=****}
Jan 18, 2019 6:12:40 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Jan 18, 2019 6:12:40 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 1 (min=1)
Jan 18, 2019 6:12:40 PM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Jan 18, 2019 6:12:41 PM org.hibernate.engine.jdbc.env.internal.LobCreatorBuilderImpl useContextualLobCreation
INFO: HHH000424: Disabling contextual LOB creation as createClob() method threw error : java.lang.reflect.InvocationTargetException
Jan 18, 2019 6:12:41 PM org.hibernate.type.BasicTypeRegistry register
INFO: HHH000270: Type registration [java.util.UUID] overrides previous : org.hibernate.type.UUIDBinaryType@7b420819
Jan 18, 2019 6:12:41 PM org.hibernate.tuple.PojoInstantiator <init>
INFO: HHH000182: No default (no-argument) constructor for class: com.lms.entities.Employee (class must be instantiated by Interceptor)
Jan 18, 2019 6:12:42 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@25cc7470] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Jan 18, 2019 6:12:42 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH10001008: Cleaning up connection pool [jdbc:postgresql://localhost:5432/LMSHibernate]
Exception in thread "main" java.lang.NullPointerException
at org.postgresql.jdbc2.AbstractJdbc2DatabaseMetaData.getColumns(AbstractJdbc2DatabaseMetaData.java:2502)
at org.postgresql.jdbc4.AbstractJdbc4DatabaseMetaData.getColumns(AbstractJdbc4DatabaseMetaData.java:99)
at org.hibernate.tool.schema.extract.internal.InformationExtractorJdbcDatabaseMetaDataImpl.populateTablesWithColumns(InformationExtractorJdbcDatabaseMetaDataImpl.java:350)
at org.hibernate.tool.schema.extract.internal.InformationExtractorJdbcDatabaseMetaDataImpl.getTables(InformationExtractorJdbcDatabaseMetaDataImpl.java:337)
at org.hibernate.tool.schema.extract.internal.DatabaseInformationImpl.getTablesInformation(DatabaseInformationImpl.java:120)
at org.hibernate.tool.schema.internal.GroupedSchemaMigratorImpl.performTablesMigration(GroupedSchemaMigratorImpl.java:65)
at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.performMigration(AbstractSchemaMigrator.java:207)
at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.doMigration(AbstractSchemaMigrator.java:114)
at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:183)
at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:72)
at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:310)
at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:467)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:708)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:724)
at com.lms.operations.Login.main(Login.java:20)