hibernate注解使用

Love The Way You Lie 2022-03-06 10:04 187阅读 0赞

hibernate默认使用xml映射文件来关联实体和数据库表，随着系统的越来越复杂，每增加一个实体类，就需要配置一个xml映射文件，一般的系统少说也有十几个实体类，多的可能会有上百个实体，如此数量繁多的xml配置，在开发中也是很难维护的，实体一改动，配置文件就需要做相应的调整，通过xml配置的方式在实际中，也越来越不推荐使用，而是通过注解的方式。

hibernate注解，默认情况下，只需要配置@Id,@Table,@Entity等主要的属性，其余的属性和字段如果没有特别的要求，可以不用设置，如果属性createDate需要映射createdate字段，那么只需要通过如下表示：

@Column(name="createdate")  
public Date createDate;

下面我们使用hibernate注解配置实现关系映射。

实体类：

BaseEntity.java

package com.xxx.hibernate4.entity;
    
    import java.io.Serializable;
    import java.util.Date;
    
    import javax.persistence.Column;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.persistence.MappedSuperclass;
    @MappedSuperclass
    public class BaseEntity implements Serializable{
    	/**
    	 * 
    	 */
    	private static final long serialVersionUID = 1L;
    	@Id
    	@GeneratedValue(strategy=GenerationType.IDENTITY)
    	protected Integer id;
    	@Column(name="createdate")
    	protected Date createDate;
    	@Column(name="modifydate")
    	protected Date modifyDate;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public Date getCreateDate() {
    		return createDate;
    	}
    	public void setCreateDate(Date createDate) {
    		this.createDate = createDate;
    	}
    	public Date getModifyDate() {
    		return modifyDate;
    	}
    	public void setModifyDate(Date modifyDate) {
    		this.modifyDate = modifyDate;
    	}
    	
    }

User.java

package com.xxx.hibernate4.entity;
    
    import javax.persistence.Entity;
    import javax.persistence.Table;
    
    @Entity
    @Table(name="xx_user")
    public class User extends BaseEntity {
    	/**
    	 * 
    	 */
    	private static final long serialVersionUID = 1L;
    	private String username;
    	private String password;
    	private String mobile;
    	private int age;
    	public String getUsername() {
    		return username;
    	}
    	public void setUsername(String username) {
    		this.username = username;
    	}
    	public String getPassword() {
    		return password;
    	}
    	public void setPassword(String password) {
    		this.password = password;
    	}
    	public String getMobile() {
    		return mobile;
    	}
    	public void setMobile(String mobile) {
    		this.mobile = mobile;
    	}
    	public int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    	@Override
    	public String toString() {
    		return "User [username=" + username + ", password=" + password + 
                    ", mobile=" + mobile + ", age=" + age + ", id="
    				+ id + "]";
    	}
    	
    	
    }

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd" >
    <hibernate-configuration>
      <session-factory>
          <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
          <property name="connection.url">jdbc:mysql:///hibernate4?useUnicode=true&characterEncoding=UTF-8</property>
          <property name="connection.username">hadoop</property>
          <property name="connection.password">hadoop</property>
          <property name="connection.pool_size">1</property>
          <property name="dialect">org.hibernate.dialect.MySQL57InnoDBDialect</property>
          <property name="show_sql">true</property>
          <property name="format_sql">true</property>
          <property name="hbm2ddl.auto">update</property>
          <mapping class="com.xxx.hibernate4.entity.User"/>
      </session-factory>
    </hibernate-configuration>

hibernate.cfg.xml配置文件中mapping以前是引入的user.hbm.xml配置文件，现在改为了class="com.xxx.hibernate4.entity.User" 直接指向了实体类。

App.java

package com.xxx.hibernate4;
    import java.util.Date;
    
    import org.hibernate.HibernateException;
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.Transaction;
    import org.hibernate.cfg.Configuration;
    
    import com.xxx.hibernate4.entity.BaseEntity;
    import com.xxx.hibernate4.entity.User;
    
    @SuppressWarnings("deprecation")
    public class App {
    	public static SessionFactory sessionFactory;
    	public static final ThreadLocal<Session> session = new ThreadLocal<>();
    	static {
    		try {
    			Configuration cfg = new Configuration().configure();
    			sessionFactory = cfg.buildSessionFactory();
    		} catch (HibernateException e) {
    			e.printStackTrace();
    			System.err.println("Initialize SessionFactory fail "+e);
    		}
    	}
    	
    	public static Session getSession() {
    		Session sess = (Session)session.get();
    		if(sess==null) {
    			sess = sessionFactory.openSession();
    			session.set(sess);
    		}
    		return sess;
    	}
    	
    	public static void closeSession() {
    		Session sess = (Session)session.get();
    		if(sess!=null) {
    			sess.close();
    		}
    		session.set(null);
    		sessionFactory.close();
    	}
    	
    	public static void add(BaseEntity entity) {
    		Session sess = getSession();
    		Transaction tx = sess.beginTransaction();
    		entity.setCreateDate(new Date());
    		entity.setModifyDate(new Date());
    		sess.save(entity);
    		tx.commit();
    		closeSession();
    	}
    	
    	public static void search(String className) {
    		Session sess = getSession();
    		Integer id = 1;
    		Object object = sess.get(className, id);
    		System.out.println(object);
    		closeSession();
    	}
    	
        public static void main( String[] args ){
        	
        	User user = new User();
        	user.setUsername("hadoop");
        	user.setPassword("hadoop");
        	user.setAge(20);
        	user.setMobile("15011186303");
        	add(user);
        	
        	//search("com.xxx.hibernate4.entity.User");
        }
    }

运行打印信息：

三月 18, 2019 5:37:23 下午 org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
    INFO: HCANN000001: Hibernate Commons Annotations {4.0.5.Final}
    三月 18, 2019 5:37:23 下午 org.hibernate.Version logVersion
    INFO: HHH000412: Hibernate Core {4.3.10.Final}
    三月 18, 2019 5:37:23 下午 org.hibernate.cfg.Environment <clinit>
    INFO: HHH000206: hibernate.properties not found
    三月 18, 2019 5:37:23 下午 org.hibernate.cfg.Environment buildBytecodeProvider
    INFO: HHH000021: Bytecode provider name : javassist
    三月 18, 2019 5:37:23 下午 org.hibernate.cfg.Configuration configure
    INFO: HHH000043: Configuring from resource: /hibernate.cfg.xml
    三月 18, 2019 5:37:23 下午 org.hibernate.cfg.Configuration getConfigurationInputStream
    INFO: HHH000040: Configuration resource: /hibernate.cfg.xml
    三月 18, 2019 5:37:23 下午 org.hibernate.cfg.Configuration doConfigure
    INFO: HHH000041: Configured SessionFactory: null
    三月 18, 2019 5:37:23 下午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
    WARN: HHH000402: Using Hibernate built-in connection pool (not for production use!)
    三月 18, 2019 5:37:23 下午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
    INFO: HHH000401: using driver [com.mysql.jdbc.Driver] at URL [jdbc:mysql:///hibernate4?useUnicode=true&useSSL=false&characterEncoding=UTF-8]
    三月 18, 2019 5:37:23 下午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
    INFO: HHH000046: Connection properties: {user=hadoop, password=****}
    三月 18, 2019 5:37:23 下午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
    INFO: HHH000006: Autocommit mode: false
    三月 18, 2019 5:37:23 下午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
    INFO: HHH000115: Hibernate connection pool size: 1 (min=1)
    三月 18, 2019 5:37:24 下午 org.hibernate.dialect.Dialect <init>
    INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQL57InnoDBDialect
    三月 18, 2019 5:37:24 下午 org.hibernate.engine.transaction.internal.TransactionFactoryInitiator initiateService
    INFO: HHH000399: Using default transaction strategy (direct JDBC transactions)
    三月 18, 2019 5:37:24 下午 org.hibernate.hql.internal.ast.ASTQueryTranslatorFactory <init>
    INFO: HHH000397: Using ASTQueryTranslatorFactory
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
    INFO: HHH000228: Running hbm2ddl schema update
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
    INFO: HHH000102: Fetching database metadata
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
    INFO: HHH000396: Updating schema
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.TableMetadata <init>
    INFO: HHH000261: Table found: hibernate4.xx_user
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.TableMetadata <init>
    INFO: HHH000037: Columns: [password, modifydate, mobile, createdate, id, age, username]
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.TableMetadata <init>
    INFO: HHH000108: Foreign keys: []
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.TableMetadata <init>
    INFO: HHH000126: Indexes: [primary]
    三月 18, 2019 5:37:24 下午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
    INFO: HHH000232: Schema update complete
    Hibernate: 
        insert 
        into
            xx_user
            (createdate, modifydate, age, mobile, password, username) 
        values
            (?, ?, ?, ?, ?, ?)
    三月 18, 2019 5:37:24 下午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
    INFO: HHH000030: Cleaning up connection pool [jdbc:mysql:///hibernate4?useUnicode=true&useSSL=false&characterEncoding=UTF-8]

通过注解，我们省去了很多xml配置，大大减轻了工作量，如果修改了实体类，增加或者修改属性，无需担心实体和表的映射问题。

另外@Column属性，可以修改varchar长度的，比如mobile一般默认是11位的，这里我们通过@Column(length=11)来设置mobile的长度，节省存储空间。

@Column(length=11)  
private String mobile;

设置前生成的表结构：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW5pZmk_size_16_color_FFFFFF_t_70][]

限制长度11之后表结构：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW5pZmk_size_16_color_FFFFFF_t_70 1][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW5pZmk_size_16_color_FFFFFF_t_70]: /images/20220303/13183585de4947619400247f3496bb0e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW5pZmk_size_16_color_FFFFFF_t_70 1]: /images/20220303/21580bb78edd4cfdbc5b44ff5d2083a6.png