Spring 對 Lob 的支援...

如果要將 將檔案存入資料庫，我們在JDBC中可以使用CLOB與BLOB來分別針對文字檔案與二進位檔案進行儲存，Spring中可以透過JdbcTemplate來處理CLOB與BLOB。

舉個例子來說，假設您的MySQL資料庫表格如下：

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CREATE TABLE test ( id INT AUTO_INCREMENT PRIMARY, txt TEXT, image BLOB );

假設我們現在分別讀進一個文字檔案與二進位檔案，並想將之儲存至資料庫中，則我們可以使用JdbcTemplate，例如：

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final File binaryFile = new File("c:\\workspace\\wish.jpg"); final File txtFile = new File("c:\\workspace\\test.txt"); final InputStream is = new FileInputStream(binaryFile); final Reader reader = new FileReader(txtFile); JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource); final LobHandler lobHandler = new DefaultLobHandler(); jdbcTemplate.execute("INSERT INTO test (txt, image) VALUES(?, ?)", new AbstractLobCreatingPreparedStatementCallback(lobHandler) { protected void setValues(PreparedStatement pstmt, LobCreator lobCreator) throws SQLException, DataAccessException { lobCreator.setClobAsCharacterStream(pstmt, 1, reader, (int) txtFile.length()); lobCreator.setBlobAsBinaryStream(pstmt, 2, is, (int) binaryFile.length()); } }); reader.close(); is.close();

JdbcTemplate中傳入了AbstractLobCreatingPreparedStatementCallback的實作，並傳入一 個 LobHandler，對於MySQL（MS SQL Server或Oracle 10g），這邊使用DefaultLobHandler即可，對於Oracle 9i特定的LOB處理，我們可以使用OracleLobHandler。

如果要從資料庫中將資料讀取出來，並另存為檔案，我們可以使用以下的程式：

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final Writer writer = new FileWriter("c:\\workspace\\test_bak.txt"); final OutputStream os = new FileOutputStream(new File("c:\\workspace\\wish_bak.jpg")); jdbcTemplate.query("SELECT txt,image FROM test WHERE id = ?", new Object[] {new Integer(1)}, new AbstractLobStreamingResultSetExtractor() { protected void streamData(ResultSet rs) throws SQLException, IOException, DataAccessException { FileCopyUtils.copy(lobHandler.getClobAsCharacterStream(rs, 1), writer); FileCopyUtils.copy(lobHandler.getBlobAsBinaryStream(rs, 2), os); } }); writer.close(); os.close();

 

在使用Spring搭配Hibernate時，可以簡化對Lob型態的處理，只要在SessionFactory建構時指定LobHandler，例如：
* beans-config.xml

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<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN" "http://www.springframework.org/dtd/spring-beans.dtd"> <beans> <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName"> <value>com.mysql.jdbc.Driver</value> </property> <property name="url"> <value>jdbc:mysql://localhost:3306/demo</value> </property> <property name="username"> <value>root</value> </property> <property name="password"> <value>123456</value> </property> </bean> <bean id="lobHandler" class="org.springframework.jdbc.support.lob.DefaultLobHandler"/> <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean" destroy-method="close"> <property name="dataSource"> <ref bean="dataSource"/> </property> <property name="lobHandler"> <ref bean="lobHandler"/> </property> <property name="mappingResources"> <list> <value>onlyfun/caterpillar/User.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect"> org.hibernate.dialect.MySQLDialect </prop> </props> </property> </bean> <bean id="hibernateTemplate" class="org.springframework.orm.hibernate3.HibernateTemplate"> <property name="sessionFactory"> <ref bean="sessionFactory"/> </property> </bean> </beans>

在這邊指定LobHandler時，對於MySQL、DB2、MS SQL Server、Oracle 10g，使用DefaultLobHandler即可，而對於Oracle 9i，則可以使用OracleLobHandler。

接下來的操作與一般對HibernateTemplate的操作無異，例如您的資料庫表格為：

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CREATE TABLE user ( id INT auto_increment PRIMARY Key, txt TEXT, image BLOB );

Spring的ClobStringType可以將CLOB映射至String，而BlobByteArrayType可以將BLOB映射至byte[]，所以我們可以設計一個User類別如下：

* User.java

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package onlyfun.caterpillar;   public class User { private Integer id; private String txt; private byte[] image; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public byte[] getImage() { return image; } public void setImage(byte[] image) { this.image = image; } public String getTxt() { return txt; } public void setTxt(String txt) { this.txt = txt; }   }

Use.hbm.xml沒什麼特別的：

* User.hbm.xml

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<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">   <hibernate-mapping> <class name="onlyfun.caterpillar.User" table="user">   <id name="id" column="id"> <generator class="native"/> </id>   <property name="txt" column="txt"/>   <property name="image" column="image"/> </class> </hibernate-mapping>

以下是個簡單的儲存與讀取Lob的程式片段示範：

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ApplicationContext context = new FileSystemXmlApplicationContext("beans-config.xml"); InputStream is = new FileInputStream(new File("c:\\workspace\\wish.jpg")); byte[] b = new byte[is.available()]; is.read(b); is.close(); User user = new User(); user.setTxt("long...long...text"); user.setImage(b); HibernateTemplate hibernateTemplate = (HibernateTemplate) context.getBean("hibernateTemplate"); hibernateTemplate.save(user); user = (User) hibernateTemplate.execute(new HibernateCallback() { public Object doInHibernate(Session session) throws HibernateException, SQLException { User user = (User) session.load(User.class, new Integer(1)); Hibernate.initialize(user); return user; } }); System.out.println(user.getTxt()); b = user.getImage(); OutputStream os = new FileOutputStream(new File("c:\\workspace\\wish_bak.jpg")); os.write(b); os.close();

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