Hibernate学习笔记 --- 使用Hibernate连接数据库

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    Hibernate用来操作数据库,它对开发人员隐藏了底层JDBC的操作及不同数据库的差异,通过它,开发人员基本上只用关心自己的对象就可以了

    构建一个最基本的Hibernate应用需要四个部分:

  1.数据类。数据类同数据库的表存在对应关系,使用Hibernate操作数据类时,Hibernate会将之转换为对数据库中对应表的操作;

  2.ORM配置文件,用于配置数据类及数据库中表的对应关系;

       3.Hibernate配置文件,用于配置JDBC数据源、ORM配置文件路径等信息;

  4.程序启动类,用于加载Hibernate并启动整个应用;

  以一个基于maven的项目为例,其项目结构示例如下,该项目将创建一个电影表用来管理电影数据

              

    首先,在pom.xml中配置Hibernate相关的依赖

 1     <dependencies>
 2         <!-- Hibernate依赖 -->
 3         <dependency>
 4             <groupId>org.hibernate</groupId>
 5             <artifactId>hibernate-core</artifactId>
 6             <version>5.2.11.Final</version>
 7         </dependency>
 8 
 9         <!-- JDBC驱动的依赖,不使用mysql换成对应的驱动 -->
10         <dependency>
11             <groupId>mysql</groupId>
12             <artifactId>mysql-connector-java</artifactId>
13             <version>8.0.8-dmr</version>
14         </dependency>
15     </dependencies>
16 
17     <build>
18         <resources>
19             <resource>
20                 <directory>${basedir}/src/main/resources</directory>
21             </resource>
22             <!-- 由于ORM配置文件放在src/main/java目录下,maven默认不会将该目录下非java文件打包,还需做该配置 -->
23             <resource>
24                 <directory>${basedir}/src/main/java</directory>
25                 <includes>
26                     <include>**/*.hbm.xml</include>
27                 </includes>
28             </resource>
29         </resources>
30     </build>

 

    其次,编写数据类Movie.java,其内包含ID、电影名称及描述信息

 1 package study.hibernate.model;
 2 
 3 /**
 4  * 电影数据类
 5  * @author yaoyao
 6  *
 7  */
 8 public class Movie {
 9     private int id;
10     
11     private String name;
12     
13     private String description;
14 
15     public int getId() {
16         return id;
17     }
18 
19     public void setId(int id) {
20         this.id = id;
21     }
22 
23     public String getName() {
24         return name;
25     }
26 
27     public void setName(String name) {
28         this.name = name;
29     }
30 
31     public String getDescription() {
32         return description;
33     }
34 
35     public void setDescription(String description) {
36         this.description = description;
37     }
38     
39 }

    接着,编写ORM配置文件Movie.hbm.xml,用于告诉Hibernate,该数据类同数据库中哪个表对应,该表的数据结构是什么样的

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="study.hibernate.model">
    <!-- 此处配置的class name与上面的package合并得到完整的类名 -->
    <class name="Movie" table="Movie">
    
        <!-- MOVIE_ID列作为MOVIE表的主键,同Movie类的id属性关联 -->
        <id name="id" column="MOVIE_ID" />
        
        <!-- string类型对应的数据库类型为VARCHAR(255),可以存储255个字符 -->
        <property name="name" type="string" column="NAME" />
        
        <!-- desc属性比较长,字段类型需设置为text,最多可以存储2^32 - 1个字符 -->
        <property name="description" type="text" column="DESCRIPTION" />
    </class>
    
</hibernate-mapping>

    接下来,编写Hibernate配置文件,配置JDBC、ORM配置文件 路径等相关信息

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 5 
 6 <hibernate-configuration>
 7     <session-factory>
 8         <!-- 数据库JDBC配置 -->
 9         <property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
10         <property name="connection.url">jdbc:mysql://localhost:3306/MOVIE_DB?serverTimezone=GMT%2B8&amp;useUnicode=true&amp;characterEncoding=UTF-8</property>
11         <property name="connection.username">root</property>
12         <property name="connection.password">root</property>
13 
14         <!-- JDBC数据库连接池大小 -->
15         <property name="connection.pool_size">10</property>
16 
17         <!-- SQL dialect -->
18         <!-- <property name="dialect">org.hibernate.dialect.H2Dialect</property> -->
19         <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
20 
21         <!-- Disable the second-level cache  -->
22         <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>
23 
24         <!-- Echo all executed SQL to stdout -->
25         <property name="show_sql">true</property>
26 
27         <!-- 每次启动的时候,会把表先删除重新创建 -->
28         <property name="hbm2ddl.auto">create</property>
29 
30         <!-- 数据类和表关联关系文件存放路径,Hibernate会在整个classpath下查找该文件 -->
31         <mapping resource="study/hibernate/model/Movie.hbm.xml"/>
32 
33     </session-factory>

    最后,编写程序启动类Launcher.java,加载Hibernate并启动应用程序

 1 package study.hibernate;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.boot.MetadataSources;
 6 import org.hibernate.boot.registry.StandardServiceRegistry;
 7 import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
 8 
 9 import study.hibernate.model.Movie;
10 
11 public class Launcher {
12     public static void main(String[] args) {
13         StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
14                 .configure()
15                 .build();
16         SessionFactory sessionFactory = null;
17         Session session = null;
18         try {
19             sessionFactory = new MetadataSources( registry ).buildMetadata().buildSessionFactory();
20             session = sessionFactory.openSession();
21             
22             Movie movie = new Movie();
23             movie.setId(1);
24             movie.setName("速度与激情8");
25             movie.setDescription("多米尼克(范·迪塞尔 Vin Diesel 饰)与莱蒂(米歇尔·罗德里格兹 Michelle Rodriguez 饰)共度蜜月,布莱恩与米娅退出了赛车界,这支曾环游世界的顶级飞车家族队伍的生活正渐趋平淡。然而,一位神秘女子Cipher(查理兹·塞隆 Charlize T heron 饰)的出现,令整个队伍卷入信任与背叛的危机,面临前所未有的考验。");
26             
27             session.beginTransaction();
28             session.save(movie);
29             session.getTransaction().commit();
30         } catch (Exception e) {
31             e.printStackTrace();
32         } finally {
33             if (session != null) {
34                 session.close();
35             }
36             
37             if(sessionFactory != null) {
38                 sessionFactory.close();
39             }
40         }
41     }
42 }

 

  运行程序,并查看数据,发现数据库中已经创建了movie表并且其内已经插入了一条数据

mysql> use MOVIE_DB;
Database changed
mysql> select name from Movie;
+------------------+
| name             |
+------------------+
| 速度与激情8      |
+------------------+
1 row in set (0.00 sec)

mysql>

 

学习过程中遇到的一些问题:

1.MYSQL使用的是5.7版本,而JDBC使用的最新的8.0.8版本,启动的时候提示时区信息不可识别

Caused by: java.sql.SQLException: The server time zone value \'Öйú±ê׼ʱ¼ä\' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:121)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:81)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:55)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:65)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:70)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:853)
    at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:440)
    at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:241)
    at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:221)
    at org.hibernate.engine.jdbc.connections.internal.DriverConnectionCreator.makeConnection(DriverConnectionCreator.java:38)
    ... 28 more

  该问题在hibrnate.cfg.xml中指定时区(GMT+8,其中+需用%2B转义)信息即可:jdbc:mysql://localhost:3306/MOVIE_DB?serverTimezone=GMT%2B8&amp;useUnicode=true&amp;characterEncoding=UTF-8

2.Hibernae官方基础示例中配置的方言为org.hibernate.dialect.H2Dialect,需更改为正确的方言配置org.hibernate.dialect.MySQL5Dialect,否则会提示DDL语句执行失败

WARN: GenerationTarget encountered exception accepting command : Error executing DDL via JDBC Statement
org.hibernate.tool.schema.spi.CommandAcceptanceException: Error executing DDL via JDBC Statement
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:67)
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.applySqlString(SchemaCreatorImpl.java:440)
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.applySqlStrings(SchemaCreatorImpl.java:424)
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.createFromMetadata(SchemaCreatorImpl.java:315)
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.performCreation(SchemaCreatorImpl.java:166)
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.doCreation(SchemaCreatorImpl.java:135)
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.doCreation(SchemaCreatorImpl.java:121)
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:155)
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:72)
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:313)
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:452)
    at org.hibernate.boot.internal.MetadataImpl.buildSessionFactory(MetadataImpl.java:170)
    at study.hibernate.Launcher.main(Launcher.java:19)

3.Hibernate.cfg.xml中的<property name="hbm2ddl.auto">create</property>配置只会自动创表,不会帮忙把schemal一起创建出来,因此程序运行前必须手动创建:create database MOVIE_DB;

 

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