Prof. Dr. Stefan Böttcher Exercises for the course Databases and Information Systems I WS 2006/2007 Special exercise JDBC 1. Preliminary configurations 1.1. Register ODBC database Chose Arbeitsplatz Systemsteuerung Verwaltung Datenquellen(ODBC) and then the tab Benutzer-DSN. If the name "odbc2access" is not yet registered: Select the button "Hinzufügen, and then chose from the list of drivers the driver "Microsoft Access-Driver (*.mdb)". Click "Fertigstellen". Chose "odbc2access" as name of the data source. Click "Auswählen" in the panel Datenbanken and select the database db2000.mdb which is contained in the zip-file, Click OK repeatedly to leave the ODBC data source administrator. 1.2 Configure variables The batch file j5pool.bat configures the variables PATH and CLASSPATH. This batch file has to be executed in each DOS-shell. Open a DOS-shell, execute the batchfile and compile and execute the program dbinit.java: working directory > j5pool working directory > javac dbinit.java working directory > java dbinit 1.3 Overview of examples The program dbinit.java generates a small example database. It demonstrates how to create and to delete tables and how to insert entries in to the database. The program dbselect.java demonstrates how to execute queries on the database with JDBC and how to process the results in the java program. The programs dbinf.java and dbtab.java demonstrate how to access meta information of the database and of the database tables. The programs exinit.java, exselect.java, exselect.java, exinf.java and extab.java demonstrate the same issues on an excel spreadsheet instead of an access database. The program excel2db.java shows the conversion of an excel spreadsheet into an access table and vice versa. 2. Exercises 2.1. Creating a database and executing queries E1.1. Compile and execute dbinit.java and dbselect.java to initialize and query the database Page 1 of 7
E1.2. Add two stmt.executeupdate commands in dbinit.java to insert the following information: "Dell supplies a pc400, price: 1800, duration: 2 days" and "Reich orders a pc500 ". Compile and execute dbinit.java once again and then execute dbselect.java to verify the modifications. E1.3. Add the query: Who supplies (at least) one item that has been ordered by Reich to the program dbselect.java and output the results via JDBC. Modify if necessary the database to verify the correctness of your modifications. 2.2. Querying meta data E2: Implement a program that outputs the complete content of all tables of the database. (Hint: Combine dbinf.java and dbtab.java) 2.3. Searching for Strings in the whole database E3: Implement a program that searches for a given String (e.g. pc400 ) in the whole database, i.e., that outputs each tuple of the database that contains the given String, no matter in which table or in which table-column this string is contained. Page 2 of 7
3. Examples 3.1. Initializing a database: source code dbinit.java public class dbinit try ergebnis = makedb( con ) ; // darf nicht von einer Exception aus makedb übersprungen werden! catch (Exception e) System.out.println( e ) ; public static String makedb( Connection con ) try Statement stmt = con.createstatement() ; try "drop table Liefert" ); catch (Exception e) "create table Liefert( Lieferant char(10), Teil char(10), " + " Preis int, Lieferzeit int ) " ); "Insert into Liefert values('vobis ','pc400',1700,3)" ); "Insert into Liefert values('dell ','pc500',2000,6)" ); "Insert into Liefert values('ibm ','pc500',2500,6)" ); "Insert into Liefert values('vobis ','pc500',2000,3)" ); "Insert into Liefert values('ibm ','pc600',3500,4)" ); "Insert into Liefert values('vobis ','pc600',2500,3)" ); Page 3 of 7
try "drop table Auftrag" ); catch (Exception e) "create table Auftrag( Kunde char(10), PC char(10) ) " ); "Insert into Auftrag values('arm ','pc400') " ); "Insert into Auftrag values('meier','pc500') " ); "Insert into Auftrag values('reich','pc600') " ); stmt.close(); // Statement schließen ausgabe += "\ndatenbank initialisiert.\n" ; catch (Exception e) ausgabe += "\n" + "Fehler: " + e ; return ausgabe ; // makedb zuende // class zuende 3.2. Selecting data: source code dbselect.java public class dbselect try ergebnis = selecttab( con, "2200" ) ; catch (Exception e) System.out.println( e ) ; public static String selecttab( Connection con, String limit ) try Statement stmt = con.createstatement() ; ResultSet rsliefert = stmt.executequery( "SELECT * FROM Liefert WHERE Preis < " + limit ) ; Page 4 of 7 // Strings in SQL müßten zusätzlich in einfache Hochkommas:
// "SELECT * FROM Liefert WHERE Teil = '" + limit + "'" ) ; ausgabe += "\n\nliefert:\n( Lieferant Teil" + " Preis Lieferzeit )" ; while (rsliefert.next()) // hole nächstes Tupel aus Result-Set ausgabe += "\n" + rsliefert.getstring("lieferant") + " " + rsliefert.getstring("teil") + " " + rsliefert.getint("preis") + " " + rsliefert.getint("lieferzeit") ; rsliefert.close() ; // Result-Set schließen stmt.close() ; // Statement schließen catch (Exception e) ausgabe += "\nfehler bei Anfrage an die Datenbank:\n" + e ; return ausgabe ; // selecttab zuende // class zuende Page 5 of 7
3.3. Querying database meta data: source code dbinf.java public class dbinf try ergebnis = accessdb( con ) ; catch (Exception e) System.out.println( e ) ; public static String accessdb( Connection con ) try DatabaseMetaData md = con.getmetadata(); // Metadaten holen // Hilfsvariable final String[] tabellen = "TABLE"; // Hole Tabellennamen ResultSet tablesnames =md.gettables(null,null,null,tabellen); while (tablesnames.next()) // Hole Tabellenname String tablename = new String(tablesNames.getString(3)); ausgabe += tablename + "\n" ; catch (Exception e) ausgabe += e ; return ausgabe; // accessdb // dbinf Page 6 of 7
3.4. Querying table meta data: source code dbtab.java public class dbtab try ergebnis = accesstab( con, "Auftrag" ) ; catch (Exception e) System.out.println( e ) ; public static String accesstab( Connection con, String tabelle ) int spalte; try Statement stmt = con.createstatement(); // Statement anlegen ResultSet rs = stmt.executequery("select * from " + tabelle); // Hole Meta-Daten für dieses Result Set ResultSetMetaData rsmd= rs.getmetadata(); int spaltenanzahl = rsmd.getcolumncount(); for( spalte=1 ; spalte <= spaltenanzahl ; spalte++ ) ausgabe += rsmd.getcolumnlabel( spalte ) + "\t\t" ; ausgabe += "\n-------------------------------------\n" ; while (rs.next()) for( spalte=1 ; spalte <= spaltenanzahl ; spalte++ ) ausgabe += rs.getstring(spalte) + "\t" ; ausgabe += "\n" ; catch (Exception e) ausgabe += e ; return ausgabe; // accesstab // dbtab Page 7 of 7