Java and the Java DataBase Connectivity (JDBC) API. Todd Kaufman April 25, 2002

Transcription

1 Java and the Java DataBase Connectivity (JDBC) API Todd Kaufman April 25, 2002

2 Agenda BIO Java JDBC References Q&A

3 Speaker 4 years Java experience 4 years JDBC experience 3 years J2EE experience BS from The Ohio State University

4 Trilegiant tri-lee-junt Membership Services company (NetMarket.com, PrivacyGuard.com, TravelersAdvantage.com) Offline businesses with online portal Many legacy systems High maintenance

5 Agenda Bio Java JDBC References Q&A

6 Why Java? Platform independence Object Oriented No memory worries? APIs Security Available Tools Industry Acceptance

7 State of the Union Latest Releases Java 2 Standard Edition Java DataBase Connectivity API Java 2 Enterprise Edition Over 1 million J2SE 1.4 downloads less than a month after release Java Community Process is the standards body responsible for new APIs

8 Agenda Bio Java JDBC References Q&A

9 JDBC Overview Interface Specification only JCP defines the interfaces and how they should be implemented Independent vendors implement the underlying drivers and sell or distribute them Provides a means for connecting, querying, updating, inserting, deleting, retrieving meta-data, etc...

10 How it works

11 JDBC Driver Types Type 1 - JDBC-ODBC Bridge Only use if there is no other driver to your database other than ODBC Performance hit due to JDBC -> ODBC call conversion Type 2 - Native API Only use if the implementation outperforms type 3 and 4 drivers Sometimes slow due to JDBC -> native conversion (Oracle s OCI)

12 Driver Types (cont.) Type 3-3 Tiered Use when an application server or middleware is in between the JDBC client and database Type 4 - All Java Use when no native code should be installed on the client and you are in a two tiered environment

13 Driver Types (cont.)

14 Step One: Load the Driver Explicitly Load the JDBC driver class into the VM Class.forName( oracle.jdbc.driver.oracledriver ); Set the jdbc.drivers property java -Djdbc.drivers=oracle.jdbc.driver.OracleDriver MyJDBCProgram

15 Step Two: Get a connection Grab a connection from the DriverManager Connection conn = DriverManager.getConnection( jdbc:oracle:thin@ machine:1521:sid, tkaufman, pass );

16 Step 3: Execute a Query Create the Statement from the Connection object Statement stmt = conn.createstatement(); Execute a query from this Statement ResultSet rs = stmt.executequery( SELECT sysdate FROM dual );

17 Retrieve the Results Advance to the first entry in the ResultSet rs.next(); Retrieve the data into an appropriate object Timestamp dbtime = rs.gettimestamp(1); or Timestamp dbtime = rs.gettimestamp( sysdate );

18 Close all Open Objects Free db resources (connections, cursors, etc..) by closing the objects in reverse order rs.close(); stmt.close(); conn.close(); That s all Let s see it work...

19 Retrieving Multiple Rows Execute the query as normal ResultSet rs = stmt.executequery( SELECT * FROM customer ); Advance to the first row and get data rs.next(); firstname = rs.getstring(1); Advance to the second row and get data rs.next(); firstname = rs.getstring(1); etc...

20 Retrieving Multiple Rows (cont.)

21 ResultSet.wasNull() What value will be returned when the database value is null 0 for integers? null for Strings? Use ResultSet.wasNull() to check the last retrieved value String temp = rs.getstring(1); if (rs.wasnull()) name = null else name = temp;

22 Executing Inserts, Updates, and Deletes Use Statement.executeUpdate instead of executequery int count = stmt.executeupdate( UPDATE customer SET first_name = Todd, last_name = Kaufman WHERE id = ); Integer returned is the number of rows updated, deleted, or inserted Let s see it in action

23 PreparedStatement use Use when executing the same statement repeatedly with different values PreparedStatement ps = conn.preparestatement( UPDATE customer SET first_name =?, last_name =? WHERE id =? ); ps.setstring(1, Todd ); ps.setstring(2, Kaufman ); ps.setint(3, ); int count = ps.executeupdate(); Repeat 2-4 as needed

24 CallableStatement use Use CallableStatement when executing a stored procedure call CallableStatement cs = conn.preparecall( {? = call UPDATE_CUSTOMER(?,?,?)} ); cs.registeroutparameter(1, Types.INT); cs.setstring(2, Todd ); cs.setstring(3, Kaufman ); cs.setint(4, ); cs.executeupdate(); int newid = cs.getint(1);

25 Commits and Rollbacks Commits/Rollbacks are on a per connection basis Default to auto - commit Only commit after every connection.close() method Adjustable via Connection.setAutoCommit(boolean)

26 Commits and Rollbacks (cont.) Explicitly perform commits/rollbacks through connection.commit() and connection.rollback() Only applicable if Connection.setAutoCommit(false) has been called previously.

27 Batch Retrieval ResultSet objects are a Java façade to a database cursor What happens when resultset.next() is called? If the result set exists in memory then array traversal If the result set is not in memory then the database cursor is used to bring the next batch into memory

28 Batch Retrieval (cont.)

29 Batch Retrieval (cont.) We need to control the tradeoff between memory footprint vs. remote access performance Use Statement.setFetchSize(int) Gives the JDBC driver a hint as to how many results to bring into memory Determine appropriate value by comparing DB access time with memory footprint and garbage collection time

30 Batch Updates Repeated Statement.execute() calls results in a similar issue Use Statement.addBatch() inside a loop and then Statement.executeBatch() to flush everything to the database Make sure that transaction management is still handled correctly using commits and rollbacks

31 Scrollable ResultSets Introduced in JDBC 2.0 Allows for navigation forward through rs.next() and rs.relative(int) navigation backward through rs.previous() and rs.relative(int) navigation to a specific row through rs.absolute(int) navigation to the first and last rows through rs.first() and rs.last()

32 Database MetaData Typically not needed Useful when the application is unsure of what DBMS it is connecting to Often used by tool vendors Can retrieve information about schemas, tables, columns, stored procedures, supported features, etc...

33 ResultSet MetaData Like DatabaseMetaData it provides information about the ResultSet object Used mainly to retrieve column names and types dynamically Generic querying class can output the contents of an entire table without knowing the table name at compile time Basically a describe command for a result set

34 javax.sql.datasource Introduced in JDBC 2.0 Moves connection instantiation (and pooling) outside of application Grab a connection from a DataSource Context ctx = new InitialContext(); DataSource ds = (DataSource)ctx.lookup( jdbc/timedb ); Connection conn = ds.getconnection( tkaufman, pass );

35 Where is JDBC Going? JDBC 3.0 Savepoints PreparedStatement pooling Auto generated keys Improved BLOB, CLOB, ARRAY, and REF support Multiple open result sets JDBC 4.0?

36 Agenda Bio Java JDBC References Q&A

37 References Books Learning Java by Niemeyer, et al. JDBC API Tutorial and Reference 2nd Edition by White, et al. Sites General Java - JDBC - Java/JDBC Performance and Tips -

38 Agenda Bio Java JDBC References Q&A

39 Q & A tkaufman@trilegiant.com