JDBC Objects in Java

Generator PDF 417 in Java JDBC Objects

Db = DriverManagergetConnection(url,userID,password); } catch (ClassNotFoundException error) { Systemerrprintln("Unable to load the JDBC/ODBC bridge" + error); Systemexit(1); } catch (SQLException error) { Systemerrprintln("Cannot connect to the database" + error); Systemexit(2); } try { String query = "SELECT FirstName,LastName FROM Customers"; DataRequest = DbcreateStatement(); Results = DataRequestexecuteQuery (query); } catch ( SQLException error ){ Systemerrprintln("SQL error" + error); Systemexit(3); } boolean Records = Resultsnext(); if (!Records ) { Systemoutprintln("No data returned"); Systemexit(4); } try { do { FirstName = ResultsgetString ( 1 ) ; LastName = ResultsgetString ( 2 ) ; printrow = FirstName + " " + LastName; Systemoutprintln(printrow); } while (Resultsnext() ); DataRequestclose(); } catch (SQLException error ) { Systemerrprintln("Data display error" + error); Systemexit(5); }

Until the release of JDBC 21 API, the virtual cursor could only be moved down the ResultSet object But today the virtual cursor can be moved backwards or even positioned at a specific row The JDBC 21 API also enables a J2ME application to specify the number of rows to return from the DBMS Six methods of the ResultSet object are used to position the virtual cursor, in addition to the next() method discussed in the previous section These are first(), last(), previous(), absolute(), relative(), and getRow()

The first() method moves the virtual cursor to the first row in the ResultSet Likewise, the last() method positions the virtual cursor at the last row in the ResultSet The previous() method moves the virtual cursor to the previous row The absolute() method positions the virtual cursor at the row number specified by the integer passed as a parameter to the absolute() method The relative() method moves the virtual cursor the specified number of rows contained in the parameter The parameter is a positive or negative integer, where the sign represents the direction the virtual cursor is moved For example, a 4 moves the virtual cursor back four rows from the current row Likewise, a 5 moves the virtual cursor forward five rows from the current row And the getRow() method returns an integer that represents the number of the current row in the ResultSet The Statement object that is created using the createStatement() of the Connection object must be set up to handle a scrollable ResultSet by passing the createStatement() method one of three constants These constants are TYPE_FORWARD_ONLY, TYPE_SCROLL_INSENSITIVE, and TYPE_SCROLL_SENSITIVE The TYPE_FORWARD_ONLY constant restricts the virtual cursor to downward movement, which is the default setting TYPE_SCROLL_INSENSITIVE and TYPE_ SCROLL_SENSITIVE constants permit the virtual cursor to move in both directions TYPE_SCROLL_INSENSITIVE makes the ResultSet insensitive to data changes made by another J2ME application in the table whose rows are reflected in the ResultSet The TYPE_SCROLL_SENSITIVE constant makes the ResultSet sensitive to those changes Listing 10-14 illustrates how to reposition the virtual cursor in the ResultSet This listing, which is a modification of the previous code segments used as examples in this chapter, retrieves customers first names and last names from the Customers table of the CustomerInformation database Since Listing 10-14 moves the virtual cursor in multiple directions, the TYPE_SCROLL_INSENSITIVE constant is passed to the createStatement() This enables the use of virtual cursor control methods in the third try {} block Initially, the virtual cursor moves to the first row of the ResultSet and then to the last row before being positioned at the second to last row of the ResultSet Next, the virtual cursor is positioned in the tenth row of the ResultSet using the absolute() method Finally, the relative() method is called twice The first time the relative() method is called, the virtual cursor is moved back two rows from the current row, which places the virtual cursor at row eight The relative( ) method is again called to return the virtual cursor back to its original row by moving the virtual cursor two rows forward If you use any of these methods and end up positioning the cursor before the first record or beyond the last record, there won t be any errors thrown

Listing 10-14 Using a scrollable virtual cursor String url = "jdbc:odbc:CustomerInformation"; String userID = "jim"; String password = "keogh"; String printrow; String FirstName; String LastName; Statement DataRequest;

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