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JDBC Overview

JDBC Overview. Autumn 2001 Lecturer: C. DeJong. Relational Databases. widespread use used via SQL (Structured Query Language) freely available powerful text-based. What is JDBC?. An API for Java database connectivity A collection of Java classes from Sun

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JDBC Overview

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  1. JDBC Overview Autumn 2001 Lecturer: C. DeJong

  2. Relational Databases • widespread use • used via SQL (Structured Query Language) • freely available • powerful • text-based

  3. What is JDBC? • An API for Java database connectivity • A collection of Java classes from Sun • A set of interfaces for database programming • java.sql.*

  4. Steps for setting up JDBC • install Java and JDBC (available from java.sun.com) • install a driver • install a relational database • MySQL, PostgreSQL (free!) • Oracle, Sybase, IBM’s DB2 (commercial)

  5. Establishing a connection • Load the database driver • Make the connection

  6. Loading the driver • driver should be provided with database • one line of code: Class.forName(<driver class name>); • ex: Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

  7. Make the connection • Returns a Connection object • Syntax: Connection con = DriverManager.getConnection( url, "myLogin", "myPassword");

  8. URL for connecting • should be in documentation with JDBC driver • starts with “jdbc:” • can connect across a network

  9. Statements • used to send SQL to the database • syntax: Statement stmt = con.createStatement();

  10. Using statements • creating a table stmt.executeUpdate( "CREATE TABLE COFFEES " + "(COF_NAME VARCHAR(32), SUP_ID INTEGER, PRICE FLOAT, " + "SALES INTEGER, TOTAL INTEGER)");

  11. Using statements • inserting data stmt.executeUpdate( "INSERT INTO COFFEES " + "VALUES ('Colombian', 101, 7.99, 0, 0)");

  12. Sample query • in SQL: SELECT COF_NAME, PRICE FROM COFFEES

  13. Query result COF_NAME PRICE ------------------ ----- Colombian 7.99 French_Roast 8.99 Espresso 9.99 Colombian_Decaf 8.99 French_Roast_Decaf 9.99

  14. Retrieving data with ResultSet • Statements can run a query on a database • This returns an object. • This object is a ResultSet.

  15. Running the query in Java Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery( "SELECT COF_NAME, PRICE FROM COFFEES");

  16. Inspecting the ResultSet while (rs.next()) { String s = rs.getString("COF_NAME"); float n = rs.getFloat("PRICE"); System.out.println(s + " " + n); }

  17. Output • The output will look something like this: Colombian 7.99 French_Roast 8.99 Espresso 9.99 Colombian_Decaf 8.99 French_Roast_Decaf 9.99

  18. alternative syntax while (rs.next()) { String s = rs.getString(1); float n = rs.getFloat(2); System.out.println(s + " " + n); } • note: starts at 1, not 0!

  19. some ResultSet retrieval methods • getString() • getInt() • getFloat() • getObject() • … many others

  20. Closing • When finished, call close() on • ResultSet objects • Statement objects • Connection objects • … or you may have a memory leak!

  21. Exceptions • Most methods on classes in the java.sql package throw java.sql.SQLException • SQLException.getMessage() shows database error • SQLException is a checked exception • so: try/catch/finally or throws

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