解析使用jdbc,hibernate处理clob/blob字段的详解

（1）不同数据库中对应clob,blob的类型:
mysql中 : clob对应text  blob对应blob
db2/oracle中 clob对应clob blob对应blob

（2）domain中对应类型:
clob 对应 string   blob 对应 byte[]
clob 对庆 java.sql.clob blob 对应 java.sql.blob

（3）hibernate配置文件中对应类型：
clob > clob   blob > binay

也可以直接使用数据库提供类型,例如:oracle.sql.clob,oracle.sql.blob。

2、jdbc操作clob (以oracle为例)
首先操作clob/blob不像操作varchar类型那样简单，插入步骤一般为两步：第一步插入一个空值，第二步锁住此行，更新clob/blob字段.

//插入空值
conn.setautocommit(false);
string sql = "insert into file(name,file_content) values("jack",empty_clob());
preparedstatement pstmt = conn.preparestatement(sql);
pstmt.executeupdate();
//锁住此行
string sql = "select file_content from file where name='jack' for update";
preparedstatement pstmt = conn.preparestatement(sql);
resultset rs = pstmt.executequery();
oracle.sql.clob clob = (oracle.sql.clob)rs.getclob(1);
java.io.outputstream writer = clob.getasciioutputstream();
byte[] temp = newfilecontent.getbytes();
writer.write(temp);
writer.flush();
writer.close();
//
pstmt.close();

读取内容:
oracle.sql.clob clob = rs.getclob("file_content");
if(null!=clob)
{
     reader is = clob.getcharacterstream();
     bufferedreader br = new bufferedreader(is);
     string s = br.readline();
    while (s != null)
    {
        content += s + "<br>"; 
        s = br.readline();
    }
}

3、jdbc操作blob

conn.setautocommit(false);
string sql = "insert into photo(name,photo) values("jack",empty_blob());
pstmt = conn.preparestatement(sql);
pstmt = conn.executeupdate();
//
sql = "select photo from photo where name='jack'";
pstmt = conn.preparestatement(sql);
rs = pstmt.executequery(sql);
if(rs.next())
     oracle.sql.blob blob = (oracle.sql.blob)rs.getblob(1);
//write to a file
file file = new file("c:\\test.rar");
fileinputstream fin = new fileinputstream(file);
outputstream out = blob.getbinaryoutputstream();
int count = -1, total = 0;
byte[] data = new byte[blob.getbuffersize()];
while ((count = fin.read(data)) != -1)
{
         total += count;
         out.write(data, 0, count);
}

4、hibernateth处理clob

myfile file = new myfile();
file.setname("jack");
file.setcontent(hibernate.createclob(""));
session.save(file);
session.flush();
session.refresh(file,lockmode.upgrade);
oracle.sql.clob clob = (oracle.sql.clob)file.getcontent();
writer pw = clob.getcharacteroutputstream();
pw.write(longtext);//写入长文本
pw.close();
session.close();

5、使用hibernate处理blob：

原理基本相同：
photo photo = new photo();
photo.setname("jack");
photo.setphoto(hibernate.createblob(""))://放一个空值
session.save(photo);
session.flush();
//
session.refresh(photo,lockmode.upgrade); //锁住此对象
oracle.sql.blob blob = photo.getphoto();//取得此blob的指针
outputstream out = blob.getbinaryoutputstream();   
//写入一个文件
file f = new file("c:\\test.rar");
fileinputstream fin = new fileinputstream(f);   
int count = -1, total = 0;
byte[] data = new byte[(int)fin.available()];
out.write(data);     
fin.close();
out.close();
session.flush();