JDBC+Hibernate将Blob数据写入Oracle

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  oracle|数据Oracle的Blob字段比较特殊,他比long字段的性能要好很多,可以用来保存例如图片之类的二进制数据。

  写入Blob字段和写入其它类型字段的方式非常不同,因为Blob自身有一个cursor,你必须使用cursor对blob进行操作,因而你在写入Blob之前,必须获得cursor才能进行写入,那么如何获得Blob的cursor呢?

  这需要你先插入一个empty的blob,这将创建一个blob的cursor,然后你再把这个empty的blob的cursor用select查询出来,这样通过两步操作,你就获得了blob的cursor,可以真正的写入blob数据了。

  看下面的JDBC的demo,把oraclejdbc.jar这个二进制文件写入数据库表javatest的content字段(这是一个blob型字段)

import java.sql.*;
import java.io.*;
import oracle.sql.*;
public class WriteBlob {

public static void main(String[] args) {

 try {
  DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
  Connection conn = DriverManager.getConnection("jdbc:oracle:thin:localhost:1521:orcl","fankai","fankai");
  conn.setAutoCommit(false);

  BLOB blob = null;

  PreparedStatement pstmt = conn.prepareStatement("insert into javatest(name,content) values(?,empty_blob())");
  pstmt.setString(1,"fankai");
  pstmt.executeUpdate();
  pstmt.close();

  pstmt = conn.prepareStatement("select content from javatest where name= ? for update");
  pstmt.setString(1,"fankai");
  ResultSet rset = pstmt.executeQuery();
  if (rset.next()) blob = (BLOB) rset.getBlob(1);

  String fileName = "oraclejdbc.jar";
  File f = new File(fileName);
  FileInputStream fin = new FileInputStream(f);
  System.out.println("file size = " + fin.available());

  pstmt = conn.prepareStatement("update javatest set content=? where name=?");

  OutputStream out = blob.getBinaryOutputStream();

  int count = -1, total = 0;
  byte[] data = new byte[(int)fin.available()];
  fin.read(data);
  out.write(data);
  /*
  byte[] data = new byte[blob.getBufferSize()]; 另一种实现方法,节省内存
  while ((count = fin.read(data)) != -1) {
   total += count;
   out.write(data, 0, count);
  }
  */

  fin.close();
  out.close();

  pstmt.setBlob(1,blob);
  pstmt.setString(2,"fankai");

  pstmt.executeUpdate();
  pstmt.close();

  conn.commit();
  conn.close();
 } catch (SQLException e) {
   System.err.println(e.getMessage());
  e.printStackTrace();
 } catch (IOException e) {
  System.err.println(e.getMessage());
 }
}

}

  仔细看上例,分三步:

  1、插入空blob

into javatest(name,content) values(?,empty_blob());

  2、获得blob的cursor

select content from javatest where name= ? for update;

  注意!!!必须加for update,这将锁定该行,直至该行被修改完毕,保证不产生并发冲突。

  3、update javatest set content=? where name=

  用cursor往数据库写数据

  这里面还有一点要提醒大家:

  JDK1.3带的JDBC2.0规范是不完善的,只有读Blob的接口,而没有写Blob的接口,JDK1.4带的JDBC3.0加入了写Blob的接口。你可以使用JDBC3.0的接口,也可以直接使用Oracle的JDBC的API,我在上例中使用了Oracle的JDBC的API。

  另外要注意的是:

java.sql.Blob

oracle.sql.BLOB

  注意看blob的大小写,是不一样的。写程序的时候不要搞混了。

  下面看看用Hibernate怎么写,原理是一样的,也要分三步,但是代码简单很多

  这是Cat对象定义

package com.fankai;

import java.sql.Blob;

public class Cat {
 private String id;
 private String name;
 private char sex;
 private float weight;
 private Blob image;
 public Cat() { }

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

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

 public char getSex() { return sex; }
 public void setSex(char sex) { this.sex = sex; }

 public float getWeight() { return weight; }
 public void setWeight(float weight) { this.weight = weight; }

 public Blob getImage() { return image; }
 public void setImage(Blob image) { this.image = image;}
}


  这是Cat.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
<class name="com.fankai.Cat" table="cat">
<!--jcs-cache usage="read-only"/-->
<id name="id" unsaved-value="null">
<generator class="uuid.hex"/>
</id>
<property name="name" length="16" not-null="true"/>
<property name="sex" length="1" not-null="true"/>
<property name="weight" />
<property name="image" />
</class>
</hibernate-mapping>

  下面是完整的用Hibernate写入Blob的例子,相比JDBC,已经简单轻松多了,也不用写那些Oracle特殊的sql了:

package com.fankai;

import java.sql.Blob;
import net.sf.hibernate.*;
import oracle.sql.*;
import java.io.*;

public class TestCatHibernate {
 public static void testBlob() {
  Session s = null;
  byte[] buffer = new byte[1];
  buffer[0] = 1;
  try {
   SessionFactory sf = HibernateSessionFactory.getSessionFactory();
   s = sf.openSession();
   Transaction tx = s.beginTransaction();
   Cat c = new Cat();
   c.setName("Robbin");
   c.setImage(Hibernate.createBlob(buffer));
   s.save(c);
   s.flush();
   s.refresh(c, LockMode.UPGRADE);
   BLOB blob = (BLOB) c.getImage();
   OutputStream out = blob.getBinaryOutputStream();
   String fileName = "oraclejdbc.jar";
   File f = new File(fileName);
   FileInputStream fin = new FileInputStream(f);
   int count = -1, total = 0;
   byte[] data = new byte[(int)fin.available()];
   fin.read(data);
   out.write(data);
   fin.close();
   out.close();
   s.flush();
   tx.commit();

  } catch (Exception e) {
   System.out.println(e.getMessage());
  } finally {
   if (s != null)
   try {
    s.close();
   } catch (Exception e) {}
  }
 }
}



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