DB2\Oracle数据库对clob的处理

spring定义了一个以统一的方式操作各种数据库的Lob类型数据的LobCreator(保存的时候用),同时提供了一个LobHandler为操作二进制字段和大文本字段提供统一接口访问。
举例，例子里面的t_post表中post_text字段是CLOB类型,而post_attach是BLOG类型：

//db2数据库
public class PostJdbcDao extends JdbcDaoSupport implements PostDao {
private LobHandler lobHandler;
private DataFieldMaxValueIncrementer incre;
public LobHandler getLobHandler() {
   return lobHandler;
}
public void setLobHandler(LobHandler lobHandler) {
   this.lobHandler = lobHandler;
}
public void addPost(final Post post) {  
   String sql = " INSERT INTO t_post(post_id,user_id,post_text,post_attach)"
     + " VALUES(?,?,?,?)";
   getJdbcTemplate().execute(
     sql,
     new AbstractLobCreatingPreparedStatementCallback(
       this.lobHandler) {
      protected void setValues(PreparedStatement ps,
        LobCreator lobCreator) throws SQLException {
       ps.setInt(1, incre.nextIntValue()); 
       ps.setInt(2, post.getUserId()); 
       lobCreator.setClobAsString(ps, 3, post.getPostText());
       lobCreator.setBlobAsBytes(ps, 4, post.getPostAttach());
      }
     });
}
}

设置相对应的配置文件(Oracle 9i版本),Oracle的数据库最喜欢搞搞特别的东西啦：

<bean id="nativeJdbcExtractor"
   class="org.springframework.jdbc.support.nativejdbc.CommonsDbcpNativeJdbcExtractor"
   lazy-init="true" />
<bean id="oracleLobHandler"
   class="org.springframework.jdbc.support.lob.OracleLobHandler"
   lazy-init="true">
   <property name="nativeJdbcExtractor" ref="nativeJdbcExtractor" />
</bean>
<bean id="dao" abstract="true">
   <property name="jdbcTemplate" ref="jdbcTemplate" />
</bean>
<bean id="postDao" parent="dao"
   class="com.baobaotao.dao.jdbc.PostJdbcDao">
   <property name="lobHandler" ref="oracleLobHandler" />
</bean>

Oracle 10g或其他数据库如下设置：

<bean id="defaultLobHandler"
   class="org.springframework.jdbc.support.lob.DefaultLobHandler"
   lazy-init="true" />
<bean id="dao" abstract="true">
   <property name="jdbcTemplate" ref="jdbcTemplate" />
</bean>
<bean id="postDao" parent="dao"
   class="com.baobaotao.dao.jdbc.PostJdbcDao">
   <property name="lobHandler" ref="defaultLobHandler" />
</bean>

读取BLOB/CLOB块,举例：

public List getAttachs(final int userId){
   String sql = "SELECT post_id,post_attach FROM t_post where user_id =? and post_attach is not null";
   return getJdbcTemplate().query(
       sql,new Object[] {userId},
       new RowMapper() {
        public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
        Post post = new Post();
        int postId = rs.getInt(1);
         byte[] attach = lobHandler.getBlobAsBytes(rs, 2);
         post.setPostId(postId);
         post.setPostAttach(attach);
         return post;
        }
       });
}