stmt.executeUpdate("update tablename set content=empty_clob() where id=320");//请空原来的内容
PreparedStatement updateStmt = cnOra.prepareStatement("UPDATE tablename SET CONTENT=? WHERE ID=320");
updateStmt.setCharacterStream(1,new FileReader("c:\\test.htm"),file.length() );
updateStmt.executeUpdate();
updateStmt=null;
PreparedStatement updateStmt = cnOra.prepareStatement("UPDATE tablename SET CONTENT=? WHERE ID=320");
updateStmt.setCharacterStream(1,new FileReader("c:\\test.htm"),file.length() );
updateStmt.executeUpdate();
updateStmt=null;
插入操作:
<%
Connection con = DriverManager.getConnection(...); //该行从略
String content = request.getParameter("content"); //大文本数据
con.setAutoCommit(false); //*
String sql = "insert into test values(1, empty_clob())";
Statement stmt = con.createStatement();
stmt.executeUpdate(sql);
con.commit(); //*
sql = "select content from test where id=1 for update";
ResultSet rs = stmt.executeQuery(sql);
if (rs.next()) {
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob(1);
clob.putString(1, content);
sql = "update test set content=? where id=" + seq;
PreparedStatement pstmt = con.prepareStatement(sql);
pstmt.setClob(1, clob);
pstmt.executeUpdate();
}
%>以上需要注意的几点是:
1)clob类型的数据不能直接insert,要先通过empty_clob()方法给它分配一个locator(同理,blob的用empty_blob()函数分配locator).然后把它select出来(此时它当然没有数据,但结果集不是空的),得到一个Clob的对象,修改该对象的内容让它满足我们的需要,再通过update方法更新该行记录.2) 通过select修改含lob类型的记录时一定要锁定该行(通过for update关键字实现),否则oracle会报错.3) 刚插入的记录就select for update, 会出现"违反读取顺序"错误,解决办法是将自动提交功能置为false,即不允许自动提交,然后commit它,再select,就可以了. 这就是上面那段代码里//*两行的作用.
table_name in varchar2,
field_id in varchar2,
field_name in varchar2,
v_id in number,
v_pos in number,
v_clob in varchar2)
is
lobloc clob;
c_clob varchar2(32767);
amt binary_integer;
pos binary_integer;
query_str varchar2(1000);
begin
pos:=v_pos*32766+1;
amt := length(v_clob);
c_clob:=v_clob;
query_str :='select '||field_name||' from '||table_name||' where '||field_id||'= :id for update ';
--initialize buffer with data to be inserted or updated
EXECUTE IMMEDIATE query_str INTO lobloc USING v_id;
--from pos position, write 32766 varchar2 into lobloc
dbms_lob.write(lobloc, amt, pos, c_clob);
commit;
exception
when others then
rollback;
end;
/
用法说明:
在插入或修改以前,先把其它字段插入或修改,CLOB字段设置为空empty_clob(),
然后调用以上的过程插入大于2048到32766个字符。
如果需要插入大于32767个字符,编一个循环即可解决问题。查询CLOB的PL/SQL函数:getclob
create or replace function getclob(
table_name in varchar2,
field_id in varchar2,
field_name in varchar2,
v_id in number,
v_pos in number) return varchar2
is
lobloc clob;
buffer varchar2(32767);
amount number := 2000;
offset number := 1;
query_str varchar2(1000);
begin
query_str :='select '||field_name||' from '||table_name||' where '||field_id||'= :id ';
--initialize buffer with data to be found
EXECUTE IMMEDIATE query_str INTO lobloc USING v_id;
offset:=offset+(v_pos-1)*2000;
--read 2000 varchar2 from the buffer
dbms_lob.read(lobloc,amount,offset,buffer);
return buffer;
exception
when no_data_found then
return buffer;
end;
/用法说明:用select getclob(table_name,field_id,field_name,v_id,v_pos) as partstr from dual;
可以从CLOB字段中取2000个字符到partstr中,
编一个循环可以把partstr组合成dbms_lob.getlength(field_name)长度的目标字符串。