Hibernate注解-使用注解示例

Hibernate的注解是什么？ 简单的说，本来放在hbm.xml文件里的映射信息，现在不用配置文件做了，改由注解来完成

• Product.hbm.xml
  
  这是Product.hbm.xml，用于提供类与表的映射，以及属性与表字段的映射关系
  

  <?xml version="1.0"?>
  <!DOCTYPE hibernate-mapping PUBLIC
          "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
          "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    
  <hibernate-mapping package="com.how2java.pojo">
      <class name="Product" table="product_">
          <id name="id" column="id">
              <generator class="native">
              </generator>
          </id>
          <property name="name" />
          <property name="price" />
      </class>
        
  </hibernate-mapping>

• 注解方式
  现在直接在类上使用注解，来达到相同的配置效果。
  

  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.Table;
   
  @Entity
  @Table(name = "product_")
  public class Product {
      int id;
      String name;
      float price;
       
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      @Column(name = "id")  
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
      @Column(name = "name")
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
      @Column(name = "price")
      public float getPrice() {
          return price;
      }
      public void setPrice(float price) {
          this.price = price;
      }
        
  }

• hibernate.cfg.xml 配置文件改动
  
  为了能够让hibernate支持这种注解的方式，还需要做一个改动:
  把hibernate.cfg.xml配置文件中的
  

  <mapping resource="pojo/Product.hbm.xml" />

  注释掉，采用：
  

  <mapping class="pojo.Product" />

  这种写法，其他所有代码都不用改变，这样就可以一样实现hibernate的CRUD操作
  

  <?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>
          <!-- Database connection settings -->
          <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
          <property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8</property>
          <property name="connection.characterEncoding">utf-8</property>
          <property name="connection.username">root</property>
          <property name="connection.password">admin</property>
          <!-- SQL dialect -->
          <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
          <property name="current_session_context_class">thread</property>
          <property name="show_sql">true</property>
          <property name="hbm2ddl.auto">update</property>
  <!--    <mapping resource="pojo/Product.hbm.xml" /> -->
          <mapping class="pojo.Product" />
   
      </session-factory>
    
  </hibernate-configuration>