The JAVA Way: JDBC and SQLJ

Transcription

1 The JAVA Way: JDBC and SQLJ David Toman School of Computer Science University of Waterloo Introduction to Databases CS348 David Toman (University of Waterloo) JDBC/SQLJ 1 / 21

2 The JAVA way to Access RDBMS JDBC: Java version of ODBC Hamilton, et al: JDBC Database Access with JAVA. A Tutorial and annotated Reference. Addison Wesley SQLJ: Embedded SQL in Java database/articles/sqlj.html Examples, etc., again courtesy of IBM: David Toman (University of Waterloo) JDBC/SQLJ 2 / 21

3 JDBC Overview JAVA API patterned after ODBC ) uses OO features to handle sets by iterators Standardized ) should work with any RDBMS What does it do for us? 1 establishes connection with the database 2 manages SQL statements 3 processes results/diagnostic messages David Toman (University of Waterloo) JDBC/SQLJ 3 / 21

4 JDBC Drivers and Connections Connection to the DBMS is made using two pieces of software: 1 JDBC driver (supplied by the DBMS vendor) COM.ibm.db2.jdbc.app.DB2Driver: IBM DB2 jdbc:oracle:oci8:@database : ORACLE 8 sun.jdbc.odbc.jdbcodbcdriver : JDBC to ODBC ) use Class.forName to load it. 2 JDBC Driver Manager (in JDK1.1) ) makes the actual connection: DriverManager.getConnection("jdbc:db2:db") ) uses an URL to identify the database ) picks the right driver based on the URL David Toman (University of Waterloo) JDBC/SQLJ 4 / 21

5 JDBC Example // DB2 UDB JDBC Samples // // (c) Copyright International Business Machines // Corporation, 1996, All Rights Reserved. import java.sql.*; class Appl { static { try { // register the driver with DriverManager Class.forName("COM.ibm.db2.jdbc.app.DB2Driver"); catch (Exception e) { e.printstacktrace(); David Toman (University of Waterloo) JDBC/SQLJ 5 / 21

6 JDBC (connection) public static void main(string argv[]) { Connection con = null; // URL is jdbc:db2:dbname String url = "jdbc:db2:cs448"; try { if (argv.length == 0) { // connect with default id/password con = DriverManager.getConnection(url); else if (argv.length == 2) { String userid = argv[0]; String passwd = argv[1]; // connect with user-provided username and password con = DriverManager.getConnection(url, userid, passwd); else { System.out.println("\nUse: java Appl [name passwd]\n"); System.exit(0); David Toman (University of Waterloo) JDBC/SQLJ 6 / 21

7 Statements et al. get a statement : stmt = con.createstatement() or stmt = con.preparestatement(string) where String may contain parameters (?) supply input parameters : stmt.setxxx(i,val) (or stmt.setnull()) and execute it: ResultSet stmt.executequery() int = stmt.executeupdate() David Toman (University of Waterloo) JDBC/SQLJ 7 / 21

8 Errors Much nicer than in ODBC/Embedded SQL in C: use JAVA Exception handling mechanisms. The methods used in JDBC may throw SQLException ) you HAVE to catch it. Provides: 1 SQL state: exception.getsqlstate() 2 Text Message: exception.getmessage() 3 Vendor code: exception.geterrorcode() 4... to get next exception : exception.getnextexception() David Toman (University of Waterloo) JDBC/SQLJ 8 / 21

9 Retrieving Answers JDBC returns answers to queries using ResultSet: essentially an implicit cursor. returned by rs = stmt.executequery() get tuple/no more tuples: boolean rs.next() get value of attributes: XXX rs.getxxx(int) (by column number) or XXX rs.getxxx(string) (by attribute name) close: rs.close() No indicator variables: uses JAVA s NULL. David Toman (University of Waterloo) JDBC/SQLJ 9 / 21

10 Retrieving Answers JDBC returns answers to queries using ResultSet: essentially an implicit cursor. returned by rs = stmt.executequery() get tuple/no more tuples: boolean rs.next() get value of attributes: XXX rs.getxxx(int) (by column number) or XXX rs.getxxx(string) (by attribute name) close: rs.close() No indicator variables: uses JAVA s NULL. David Toman (University of Waterloo) JDBC/SQLJ 9 / 21

11 JDBC query // get a statement handle Statement stmt = con.createstatement(); // retrieve data from the database ResultSet rs = stmt.executequery("select * from publication"); System.out.println("Received results:"); // display the result set // rs.next() returns false when there are no more rows while (rs.next()) { String a = rs.getstring(1); String str = rs.getstring(2); System.out.print(" pubid= " + a); System.out.print(" title= " + str); System.out.print("\n"); rs.close(); stmt.close(); David Toman (University of Waterloo) JDBC/SQLJ 10 / 21

12 JDBC update // get a statement handle stmt = con.preparestatement("update author set name = SHILI where aid =?"); //set up the paremeter(s) stmt.setint(1,1); // update the database int rowsupdated = stmt.executeupdate(); System.out.println("Changed "+rowsupdated+" row(s)."); stmt.close(); con.close(); catch( Exception e ) { e.printstacktrace(); David Toman (University of Waterloo) JDBC/SQLJ 11 / 21

13 Transactions and Connections Transactions managed by database connection: con.commit() ) commits the transaction con.rollback() ) aborts the transaction con.close() ) closes the database connection (and releases DBMS resources) David Toman (University of Waterloo) JDBC/SQLJ 12 / 21

14 SQLJ Overview Embedded SQL for Java Only Static SQL (use JDBC for dynamic SQL) Type checking ) allows disconnected operation Magic keyword in SQLJ: #sql <sqlj command> Error handling: ) exception-based (same as in JDBC) SQLJ compiles foo.sqlj to foo.java. ) connects to the database ) uses exemplar schema David Toman (University of Waterloo) JDBC/SQLJ 13 / 21

15 Connections and Contexts embedded SQL implicitly talks to a context ) essentially a database connection ) Exemplar Schema for every context context declarations #sql context MyContext; contexts may be used explicitly: #sql [MyContext]... ; context omitted! default context David Toman (University of Waterloo) JDBC/SQLJ 14 / 21

16 SQLJ Example // DB2 UDB SQLJ Samples // // (c) Copyright International Business Machines // Corporation, All Rights Reserved. import java.sql.*; import sqlj.runtime.*; #sql iterator App_Cursor1 (String empno, String firstnme) ; #sql iterator App_Cursor2 (String) ; class App { static { try { // register the driver with DriverManager Class.forName("COM.ibm.db2.jdbc.app.DB2Driver"); catch (Exception e) { e.printstacktrace(); David Toman (University of Waterloo) JDBC/SQLJ 15 / 21

17 SQLJ (cont.) public static void main(string argv[]) { try { Connection con = null; // URL is jdbc:db2:dbname String url = "jdbc:db2:cs448"; DefaultContext ctx = DefaultContext.getDefaultContext(); if (ctx == null) { try { // connect with default id/password con = DriverManager.getConnection(url); ctx = new DefaultContext(con); catch (SQLException e) { System.out.println("Error: no default context"); System.err.println(e) ; System.exit(1); DefaultContext.setDefaultContext(ctx); David Toman (University of Waterloo) JDBC/SQLJ 16 / 21

18 SQLJ Statements Embedded SQL statements: #sql [context] { embedded sql ; ) embedded sql must be a static SQL statement ) host variables connect SQL and JAVA David Toman (University of Waterloo) JDBC/SQLJ 17 / 21

19 SQLJ update try { // update the database #sql { UPDATE author set name = :string where aid = :aid ; // rollback the update #sql { ROLLBACK work ; catch( Exception e ) { e.printstacktrace(); David Toman (University of Waterloo) JDBC/SQLJ 18 / 21

20 Cursors, Iterators, etc. iterator object declarations #sql iterator Iter (a1,..., ak); used for queries: where ai is a type and identifier (name) #sql Iter = { SELECT b1,...,bk FROM... ; binding of columns: 1 positional: #sql { FETCH :Iter INTO :v1,...,:vk ; more rows: Iter.endFetch() not true 2 named: value of column a i : vi = Iter.ai() next row: Iter.next() is true David Toman (University of Waterloo) JDBC/SQLJ 19 / 21

21 SQLJ query try { #sql iterator cursor1(string pubid, String title); #sql cursor1 = { SELECT pubid, title from publicaion ; System.out.println("Received results:"); while (cursor1.next()) { str1 = cursor1.pubid(); str2 = cursor1.title(); System.out.print (" pubid= " + str1); System.out.print (" title= " + str2); System.out.print ("\n"); cursor1.close(); #sql { SELECT count(*) into :count1 from author ; System.out.println("There are "+count1+" authors."); catch( Exception e ) { e.printstacktrace(); David Toman (University of Waterloo) JDBC/SQLJ 20 / 21

22 Summary SQL in JAVA: static: SQLJ + SQLJ precompiler ) adopts most of static embedded SQL dynamic: JDBC ) responsible for the rest... SQLJ and JDBC cooperate Cursors handled by Iterators Errors are handled by JAVA Exceptions David Toman (University of Waterloo) JDBC/SQLJ 21 / 21