import java.io.Writer;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import oracle.sql.CLOB;

import com.icss.common.CommonConfig;
/**
 * <title>kmdp</title>
 * <description>更新大字段专用类</description>
 * @author yinjin
 * <copyright></copyright>
 * @version 1.0
 * 2005-7-29 15:06:18
 */
public class LobUpdateUtil
{
 /**
  * 用于weblogic环境下的clob字段更新，在其他web环境下可以不用这个方法
  * @param content clob字段的内容
  * @param tableName 表名
  * @param fieldName Clob字段名
  * @param sqlWhere 带where关键字的where条件
  * @author 殷晋
  */
 public static void updateClob(String content,String tableName,String fieldName,String sqlWhere)
 {
  
  String sqlSelect = "SELECT "+ fieldName +" FROM "+ tableName + sqlWhere + " FOR UPDATE ";
  String sqlUpdate = "UPDATE "+ tableName +" SET "+ fieldName +" = empty_clob() "+ sqlWhere;
  Connection conn = null;
  try {               
   conn = getConnection();
   conn.setAutoCommit(false);   
   PreparedStatement pst = conn.prepareStatement(sqlUpdate);    
   pst.executeUpdate();
   
   Statement st = conn.createStatement();
   ResultSet rs = st.executeQuery(sqlSelect);
   if(rs.next())
   {
    CLOB m_clob = ((oracle.jdbc.OracleResultSet)rs).getCLOB(fieldName.toUpperCase());
       Writer wr = m_clob.getCharacterOutputStream();
       wr.write(content);
       wr.flush();
       wr.close();
   }
   conn.commit();
   rs.close();
   pst.close();
   st.close();
  } catch (Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();      
  }
  finally{      
   colseConnection(conn);
  }  
 }
 /**
  * 获取数据库链接，根据conmon_config.xml配置
  * @return 数据库链接
  */
 private static Connection getConnection()
 {
  try {
   String driverClassName = CommonConfig.getValue("uwf.database.defaultProvider.driver");
   String dbUrl = CommonConfig.getValue("uwf.database.defaultProvider.serverURL");
   String username = CommonConfig.getValue("uwf.database.defaultProvider.username");
   String password = CommonConfig.getValue("uwf.database.defaultProvider.password");
   Class.forName(driverClassName);
   Connection conn = null;
   conn = DriverManager.getConnection(dbUrl, username, password);
   return conn;
  } catch (ClassNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   return null;
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   return null;
  }
  
 }
 /**
  * 关闭数据库连接
  * @param conn 等待关闭的数据库链接
  */
 private static void colseConnection(Connection conn)
 {
  try {
   if(conn != null && !conn.isClosed())
   {
    conn.close();
    conn = null;
   }
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   conn = null;
  }
 }
}