|
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)代码: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blobinto javatest(name,content) values(?,empty_blob());2、获得blob的cursorselect 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.Bloboracle.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对象定义代码: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代码:<?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：代码: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) {}}}}
|
