From Gossip@caterpillar

EJB3 Gossip: Lob 物件



 


關於BLOB、CLOB，可以先參考一下 將 檔案存入資料庫 這篇文章。

在Hibernate中，您可以直接對Blob、Clob作映射，例如在T_USER表格中，若有BLOB與CLOB欄位分別為photo與resume，則您可以如下設計一個User類別：
  • User.java
package onlyfun.caterpillar;

import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;

@Entity
@Table(name="T_USER")
public class User implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String name;
    private Long age;

    @Lob
    private byte[] photo;
    
    @Lob
    private char[] resume;

    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    public Long getAge() { return age;  }
    public void setAge(Long age) { this.age = age; }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    public byte[] getPhoto() { return photo; }
    public void setPhoto(byte[] photo) { this.photo = photo; }

    public char[] getResume() { return resume; }
    public void setResume(char[] resume) { this.resume = resume; }
}

無論是映射至BLOB或CLOB的欄位，在JPA中都是使用@Lob來標註，而JPA會自動根據屬性來判斷是要採用BLOB或CLOB的處理方式儲存至表格中，若屬性是byte[]型態，則以BLOB方式處理，若屬性是char[]型態，則使用CLOB方式處理。

一個儲存檔案至表格的範例如下：
        FileInputStream inputStream =
            new FileInputStream("c://workspace//caterpillar.jpg");
        byte[] photo = new byte[inputStream.available()];
        inputStream.read(photo);
        inputStream.close();

        User user = new User();
        user.setName("caterpillar");
        user.setAge(new Long(35));
        user.setPhoto(photo);
        user.setResume("Bla....Bla....resume text!!".toCharArray());

        EntityManager entityManager =
                JPAUtil.getEntityManagerFactory().createEntityManager();
        EntityTransaction etx = entityManager.getTransaction();
        etx.begin();
        entityManager.persist(user);
        etx.commit();
        entityManager.close();


而一個取出檔案的範例如下：
        EntityManager entityManager =
                JPAUtil.getEntityManagerFactory().createEntityManager();
        EntityTransaction etx = entityManager.getTransaction();
        etx.begin();
        User user = entityManager.find(User.class, id);
        etx.commit();
        entityManager.close();

        FileOutputStream outputStream =
            new FileOutputStream("c://workspace//caterpillar2.jpg");

        outputStream.write(user.getPhoto());
        outputStream.close();