Java Database Connectivity JDBC  JDBC is an API, containing classes and interfaces in the java programming language, to execute SQL sentences over an external database.  Offers a standard interface for connecting to any database available.  Helps obtaining the data more easily and comfortable in a client-server environments through the Internet/Intranet.

2 What does JDBC do?  Allow a connection to a database server.  Allow sending SQL sentences.  Process the results of these Sentences.  The classes that allow this, are in the package java.sql (it has to be imported)

3 Loading the Driver  It is necessary to load a class with the driver of the Database (This is provided by the DBMS vendor)  Example: Class c = Class.forName(“com.informix.jdbc.IfxDriver"); Class.forName(“com.novell.sql.LDAPDriver”); Class.forName("com.mysql.jdbc.Driver");  This depends on the database that will be used  Then an instance of the class must be created. c.newInstance();

4 Establishing a Connection  In the examples the login and password will be discarded  A Connection Object represents a connection to a database  The class “DriverManager” tries to find a driver to connect to the database represented in the URL. Connection con = DriverManager.getConnection ( url,"login", "password");

5 Connection  URL Examples:  jdbc:mysql://localhost/test (for examples)  jdbc:oracle://oraserver  jdbc:odbc:mydatabase  jdbc:informix- sqli://hostname:port/dbname:INFORMIXSER VER=serverName (for CGE databases)  jdbc:ldap://server;baseDN=baseDN;useClearte xt=true

6...Connection  URL JDBC Syntaxis:  jdbc: :  is the name of the driver or mechanism of the connection. Example: odbc.  is the identification of the database. The format changes depending of the driver. Example: //server:port/db and parameters

7 Sending SQL sentences  JDBC allows to send any SQL sentence. although this is dependent to the database, the only risk is the incompatibility between different databases.

8...Sending SQL Sentences  JDBC provides 3 classes:  “Statement”: This object is used to send simple SQL sentences. It is created by the method: createStatement.  “PreparedStatement”: This object is used for sentences that needs one or more parameter. The sentence is pre-compiled and saved for a future use.  “CallableStatement”: It is used to execute procedures saved in the database.

9 The Statement class  Statement stmt = con.createStatement();  In this moment the statement exists but doesn't have a SQL sentence to execute. This can be sended using the methods:  executeUpdate(String), used to create/modify tables (there is no results), commonly used for the create,update,delete sentences.  executeQuery(String) to make queries, returns results in an object from the class ResulSet, tipically for a select statement.

10 excuteUpdate Examples  stmt.executeUpdate(“create table students (name varchar(32), id integer, address varchar(40), yearborn integer,...);  stmt.executeUpdate(“insert into students (‘Valeria Valencia ’, , ‘Calle bonita 223 Vitacura Stgo’, 1974,...);  stmt.executeUpdate(“update students set direccion = ‘?????’ where name = ‘Valeria Valencia’ ”);

11 excuteUpdate Examples CreateCoffees: Creates a Coffees table in the test database. CreateSuppliers: Creates a Suppliers table in the test Databes. DropCoffees: Delete both tables. MyConnection: encapsulates the connection to the database (to be used for other applications) InsertCoffees: Inserts rows in the table. InsertSupliers: Inserts rows in the table. InsertCoffeesDatos: Inserts rows from data readed from a file. ListCoffes, ListSuppliers: Show the content (uses executeQuery)

12 executeUpdate return The executeUpdate method returns an integer value corresponding to the number of rows that the SQL sentences modified. If it is a creation of a table, the return value is 0 If it is an insert of a value in a row the value is 1. The results is interesting when using the SQL sentence with the instruction: “update table set field = where

13 excuteQuery Examples  stmt.executeQuery(“select * from students “ + “where yearofborn = 1974”);  The results of a query is received in an ResultSet object.  ResultSet rs = stmt.executeQuery(....);  A ResultSet can be seen as an enumeration of rows that represents the results.  There are adequate methods to go through all the elements of this enumeration and obtain the values of the fields

14 The ResultSet ResultSet rs = stmt.executeQuery(“select name where address like Santiago”); while (rs.next()) { String s = rs.getString(“name”); int y = rs.getInt(“yearofborn”); System.out.println(s+” “+y); }  ResultSet rs contains a collection of rows with the results of the query instruction next advances a pointer which informs in what row are we now. At the beginning this is before the first row, so it is necessary to execute a next() method to point to the first row.

15 The getXXX Instruction  It can be used with two types of parameters:  getXXX(“Name of the field of the table”) example: getString(“name”)  getXXX(number of field of the table) example: getString(1)  getXXX tries to read what is on the field and converts it to the type specified in the “XXX”

16 The Instruction getXXX  Sometimes, even if the SQL data type does not exactly matches the XXX type a conversion is possible ( with getString & getObject almost everything can be retrieved)  In other cases the conversion is possible but with some loss of information (getByte for a numeric or longvarchar)  In other cases it is just impossible (use getLong for Time)

17 Prepared Statements  Everywhere a Statement has been used it is possible to use a PreparedStatement in order to make queries more efficient  An instruction containing a PreparedStatement will be translated to a native SQL statement of the database  Another advanatage is that it allows the usage of parameters  PreparedStatement us = con.prepareSatatement(“update alumnos set comuna = ? where direccion like = ?);  us.setString(1,’Vitacura’) us.setString(2,’Hualtatas’);

18 Prepared Statements: Example PreparedStatement updateSales; String updateString = "update COFFEES " + "set SALES = ? where COF_NAME like ?"; updateSales = con.prepareStatement(updateString); int [] salesForWeek = {175, 150, 60, 155, 90}; String [] coffees = {"Colombian", "French_Roast", "Espresso", "Colombian_Decaf", "French_Roast_Decaf"}; int len = coffees.length; for(int i = 0; i < len; i++) { updateSales.setInt(1, salesForWeek[i]); updateSales.setString(2, coffees[i]); updateSales.executeUpdate(); }

19 Transactions  A transaction consists in one or more sentences that have been executed and then confirmed (commit) or deleted (rolled back)  Auto-commit is pre-set.  if Auto-commit is deactivated, the methods commit or rollback have to be used in a explicit way.

20 Transactions  To use Transactions, the auto-commit must be disabled.  con.setAutoCommit(false)  PreparedStatement ps =..... ....  ps.executeUpdate()....  ps.excecuteUpdate()...  con.commit();

21 Stored Procedures  Is a group of SQL sentences that are grouped logically in a unit to do a specific work.  Exists in most of the DBMS, but they are dependent to this (The way of how these procedures are written or executed isn't so standard)  Generally receives parameters.  They are “written” with an Update and executed with a Query.

22 An Example To create a Stored procedure String crearSP = “create prodcedure SHOW_SUPPLIERS”+ “ as ”+ “select SUPPLIERS.SUP_NAME, COFFEES.COF_NAME”+ “from SUPPLIERS, COFFEES ”+ “where SUPPLIERS.SUP_ID = COFFEES.SUP_ID” Statement stmt = con.CreateStatement(); stmt.executeQuery(createSP); to call the Stored Procedure CallableStatement cs; cs = con.prepareCall(“{call SHOW_SUPPLIERS}”); ResultSet rs = cs.executeQuery();

23 Using metadata  The metadata is the information about the structure of a databaste or a ResultSet  It is obtained with the method getMetaData() stmt = con.createStatement(); ResultSet rs = stmt.executeQuery(query); ResultSetMetaData rsmd = rs.getMetaData(); int numberOfColumns = rsmd.getColumnCount(); int rowCount = 1; while (rs.next()) { System.out.println("Row " + rowCount + ": "); for (int i = 1; i <= numberOfColumns; i++) { System.out.print(" Column " + i + ": "); System.out.println(rs.getString(i)); } System.out.println(""); rowCount++; }

24 Using metadata  Example to know the tables of a database. DatabaseMetaData dbmd = con.getMetaData(); String dbmsName = dbmd.getDatabaseProductName(); ResultSet rs = dbmd.getTableTypes(); System.out.print("The following types of tables are "); System.out.println("available in " + dbmsName + ": "); while (rs.next()) { String tableType = rs.getString("TABLE_TYPE"); System.out.println(" " + tableType); }