Oracle中JDBC对BLOB和CLOB读取的专用处理和通用处理

设有表：
create table blobimg (id int primary key, contents blob);
一、BLOB入库的专用访问：
    1) 最常见于Oracle的JDBC示例中
    一般是先通过select  ... for update锁定blob列，然后写入blob值，然后提交。要用到特定的Oracle BLOB类。

          
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:testdb", "test", "test");
//处理事务
con.setAutoCommit(false);
Statement st = con.createStatement();
//插入一个空对象
st.executeUpdate("insert into BLOBIMG  values(1,empty_blob())");
//用for update方式锁定数据行
ResultSet rs = st.executeQuery(
          "select contents from  BLOBIMG  where  id=1  for update");
if (rs.next()) {
//使用oracle.sql.BLOB类，没办法了，变成专用的了
oracle.sql.BLOB blob = (oracle.sql.BLOB) rs.getBlob(1).;
//到数据库的输出流
OutputStream outStream = blob.getBinaryOutputStream();
//这里用一个文件模拟输入流
File file = new File("d:\\proxy.txt");
InputStream fin = new FileInputStream(file);
//将输入流写到输出流
byte[] b = new byte[blob.getBufferSize()];
int len = 0;
while ( (len = fin.read(b)) != -1) {
          outStream.write(b, 0, len);
}
//依次关闭
fin.close();
outStream.flush();
outStream.close();
}
con.commit();
con.close();

 

2) 再厉害一点的，是通过调用DBMS_LOB包中的一些函数来处理，效率好像也不错.
　不过，要使用到存储过程，用到专用类OracleCallableStatement。
　例：  

         
import java.sql.*;
import java.io.*;
import oracle.jdbc.driver.*;
import oracle.sql.*;
class TestBlobWriteByDBMS_LOB {

    public static void main (String args []) throws SQLException , 
    FileNotFoundException, IOException
    {
        DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());
        Connection conn = 
            DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:ora92","scott","tiger");
        conn.setAutoCommit(false);
        Statement stmt = conn.createStatement();
        stmt.execute( "delete from demo" );
        System.out.println( "deleted from demo" );
        stmt.execute( "insert into demo (id,theBlob) values (s_enr.nextval,empty_blob())" );
        conn.commit();
        System.out.println( "committed" );
        ResultSet rset = stmt.executeQuery ("SELECT theBlob FROM  demo where id = s_enr.currval  FOR UPDATE");
        System.out.println( "Executed Query" );
        if(rset.next())
        {
            System.out.println( "Fetched row " );
            BLOB l_mapBLOB = ((OracleResultSet)rset).getBLOB(1);
            File binaryFile = new File("e:\\free\\jo.jpg");
            FileInputStream instream=new  FileInputStream(binaryFile);
            int chunk = 32000;
            
            System.out.println( "Chunk = "+ chunk );
            
            byte[] l_buffer = new byte[chunk];
            int l_nread = 0;
            
            OracleCallableStatement cstmt =
                (OracleCallableStatement)conn.prepareCall( "begin dbms_lob.writeappend( :1, :2, :3 ); end;" );
            cstmt.registerOutParameter( 1, OracleTypes.BLOB );
            while ((l_nread= instream.read(l_buffer)) != -1) 
            {
                cstmt.setBLOB(  1, l_mapBLOB );
                cstmt.setInt(   2, l_nread );
                cstmt.setBytes( 3, l_buffer );
                cstmt.executeUpdate();
                l_mapBLOB = cstmt.getBLOB(1);
            }
            instream.close();
            conn.commit();
            rset.close();
            stmt.close();
            conn.close();
        }
    }
}

二、BLOB值读取的通用处理：
这个jdbc标准接口可以直接调用，因此比较简单，如下所示：     

   
Connection con = ConnectionFactory.getConnection();
con.setAutoCommit(false);
Statement st = con.createStatement();
ResultSet rs = st.executeQuery("select contents from  BLOBIMG  where  id=1");
if (rs.next()) {
    java.sql.Blob blob = rs.getBlob(1);
    InputStream ins = blob.getBinaryStream();
    //输出到文件
    File file = new File("d:\\output.txt");
    OutputStream fout = new FileOutputStream(file);
    //下面将BLOB数据写入文件
    byte[] b = new byte[1024];
    int len = 0;
    while ( (len = ins.read(b)) != -1) {
      fout.write(b, 0, len);
    }
    //依次关闭
    fout.close();
    ins.close();
}    
con.commit();
con.close();
 

三、BLOB值写入的通用处理：
　这时要借助于PreparedStatement的动态绑定功能，借用其setObject()方法插入字节流到BLOB字段。

        
public void insertFile(File f) throws Exception{ 
    FileInputStream fis=new FileInputStream(f,Connection conn); 
    byte[] buffer=new byte[1024]; 
    data=null; 
    int sept=0;int len=0; 
    while((sept=fis.read(buffer))!=-1){ 
        if(data==null){ 
        len=sept; 
        data=buffer; 
        }else{ 
            byte[] temp; 
            int tempLength; 
            tempLength=len+sept; 
            temp=new byte[tempLength]; 
            System.arraycopy(data,0,temp,0,len); 
            System.arraycopy(buffer,0,temp,len,sept); 
            data=temp; 
            len=tempLength; 
        } 
        if(len!=data.length()){ 
        byte temp=new byte[len]; 
        System.arraycopy(data,0,temp,0,len); 
        data=temp; 
        } 
    } 
    String sql="insert into fileData (filename,blobData) value(?,?)"; 
    PreparedStatement ps=conn.prepareStatement(sql); 
    ps.setString(1,f.getName()); 
    ps.setObject(2,data); 
    ps.executeUpdate();
}

四. CLOB读取的通用处理

         
public static String getClobString(ResultSet rs, int col) { 
    try { 
        Clob c=resultSet.getClob(2); 
        Reader reader=c.getCharacterStream(): 
        if (reader == null) { 
            return null; 
        } 
        StringBuffer sb = new StringBuffer(); 
        char[] charbuf = new char[4096]; 
        for (int i = reader.read(charbuf); i > 0; i = reader.read(charbuf)) { 
            sb.append(charbuf, 0, i); 
        } 
        return sb.toString(); 
    } catch (Exception e) { 
        return ""; 
    } 
}

当然还可以直接编写BLOB存取的存储过程供JDBC调用，那也非常方便。不过可能要用到外部LOB类型。这将在后边陆续进行介绍。
To be contd.

评论

1 楼 charlesgong 2010-05-05  

第三个例子中“data”的类型是什么？