知识大全 JDBC存取Oralce数据库的注意几点事项

Posted 2022-07-16 数据库

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　　Be careful with date type column 　　　　Just like Y K when you try to give a value to a column which type is date you should determine the year area with YYYY not YY 　　　　Suppose there is a user Named Bob Male borned on Jan st 　　　　Insert into test (user_name user_birthday sex) values( Bob to_date( YYMMDD M );　　　　Ok now let s check Bob s birthday:　　　　Select to_char(birthday YYYYMMDD ) as birthday from test where user_name= Bob ;　　　　Birthday　　　　　　　　Ok its st century now don t fet it 　　　　How to operate on Clob:　　　　Clob type is to save single byte character data up to gigabytes 　　　　If you are a newer to use clob you must find it s not so easy to operate on it! Ok take it easy from now on I ll give an example to insert update retrieve clob type values from test 　　　　→ Insert new value for clob type column:　　　　Because it is now allowed to insert string directly into Clob type column we must insert an Empty_clob into the table 　　　　Suppose we have established a connection to database and the reference of the Connection object it conn 　　　　String sql = insert into test (user_name user_birthday sex biography) values( Bob to_date( yyyymmdd ) M EMPTY_CLOB()) ;　　　　PreparedStatement stmt = conn prepareStatement(sql);　　　　Stmt execute();　　　　Now an Empty_Clob object has be signed to biography 　　　　To give real value of biography column use the following code fragment:　　　　sql = select biography from test where user_name= Bob for update ;　　　　stmt = conn prepareStatement(sql);　　　　ResultSet rs = stmt executeQuery();　　　　Please remembered the for update clause it s very important This particular clause means you told the database to prepare the biography of Bob for update 　　　　oracle sql CLOB clob = (oracle sql CLOB)((oracle jdbc OracleResultSet)rs) getCLOB( biography );　　　　java io OutputStream clobWriter = clob getAsciiOutputStream();　　　　byte[] temp = currentBiography getBytes();　　　　(supposed currentBiography is the value to be update to database)　　　　clobWriter write(temp);　　　　clobWriter flush();　　　　clobWriter close();　　　　rs close();　　　　stmt close();　　　　mit();　　　　　　Ok the biography has been updated 　　　　→ When you retrieve clob from database remember to use InputStream 　　　　oracle sql CLOB clob = (oracle sql CLOB)rs getClob( biography );　　　　java io InputStream asciiStream = clob getAsciiStream();　　　　byte[] tempBody = new byte[ ]; //set to K;　　　　int readLen = asciiStream read(tempBody );　　　　String tempString = (new String(tempBody)) substring( readLen);　　　　Be careful with PreparedStatement　　When you use PreparedStatement to pre pile and execute SQL String you must close it after transaction ending Otherwise you ll got an exception named ORA : maximum cursors exceeded!　　　　I m not sure about cursor there is a parameter in the init ora file which will used by oracle database In this file max cursors is defined 　　　　Actually when try to prepare statement and execute in a loop block You may also cause ORA exception 　　　　So only prepare statement once for particular sql strings set Use set XXX(int index XXX value) method to set column values cha138/Article/program/Oracle/201311/17137