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。
