2.1 Load the DBMS Connect to the DBMS by use of the (static) class method forname 2 on the class Class 3. The syntax is: Class:forName("jdbc:DatabaseS

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1 A brief overview of JDBC Andreas Sjögren Department of computer engineering Mälardalen university April 12, Introduction JDBC [2] is an API (Application Programmers Interface) for connections to relation databases from Java. In the real sense the name JDBC has no meaning, but sometimes people refer to it as Java DataBase Connectivity. If we are using several databases and using JDBC we do not have towrite several programs for every database. Instead we can use the same program with different database managers (DBMS). In this small paper we give a brief introduction to JDBC and present some small examples. This introduction is just a very brief overview of some of the basic features of JDBC 1 and we will assume some acquaintance with the database language SQL and with the programming language Java. More information about JDBC could be found in, for instance, the tutorial [2] (ifyou do not have used JDBC before we strongly suggest you go through this tutorial). First we have to establish a connection to the database, how to do this is presented in section 2. In section 3, we shows how we can execute SQL statements on the database and process the result. Finally, in section 4, we give an example which summarize the different JDBC features we have presented in the previous sections. 2 Connect to the database The first thing wehave to do is to connect to the database. Use a DriverManager [1] or a DataSource [1]. This is done in two stages: 1. Load the DBMS 2. Create the connection 1 In reality JDBC is in most cases used to collect data from a database and only make some small updates to the database. In rare cases we possibly want to create new tables from the Java program. So, this basic knowledge will possibly be enough. 1

2 2.1 Load the DBMS Connect to the DBMS by use of the (static) class method forname 2 on the class Class 3. The syntax is: Class:forName("jdbc:DatabaseSpecif icdriver" Use the statement in a try-catch construct, since the method could throw ClassNotFoundException. An example is: Class.forName("RmiJdbc.odbc" catch(classnotfoundexception e) e.printstacktrace( 2.2 Create the connection To establish a connection to the given database URL we use, for example, the class method getconnection in the class DriverManager and we store the connection in a Connection [1] object. The syntax is: Connection c = DriverManager:getConnection(URL The statement can throw SQLException therefore we use a try-catch construct. URL is a database URL of the form jdbc:subprotocol:subname. An example: Connection c = DriverManager.getConnection("jdbc:odbc=db1.mdb" catch(sqlexception e) e.printstacktrace( 3 Execute statements on the database To execute an SQL statement and obtaining the results produced by the statement we have to create an SQL command and send it to the database. We can use the interface Statement [1] to create the command. We use the same Connection-object as in the establishment of the connection above. The syntax is: Statement stmt = c:createstatement( Now we can send the command to the database by use of one execute() method which is implemented in the Connection class. There are different execute methods (see [1]), for instance: 2 forname returns the Class object associated with the class or interface with the given string name [1]. 3 Instances of the class Class represent classes and interfaces in a running Java application [1]. 2

3 FrogName MeasureCM Color Location GreenFrog 7 Green Wetlands BullFrog 20 Green Rivers MinkFrog 6 Green ForestLakes WoodFrog 6 Brown Forests Kermit 45 Green MuppetShow Figure 1: A table of different types of frogs in an SQL database ffl executeupdate(string) executes an SQL INSERT, UPDATE, DELETE statements or DDL (Data Definition Language) statements, such as CREATE, DROP or ALTER. ffl executequery(string) executes an SQL statement that returns a single ResultSet object, for instance SELECT statements to collect data from the database. 3.1 Create a table To create tables we use the executeupdate method described above. For instance the following code: "CREATE TABLE FROGS(" +"FrogName VARCHAR2(32)," +"MeasureCM integer," +"Color VARCHAR2(32)," +"Location VARCHAR2(32))" creates the table in Figure 1. To create the first row we write: +"values('greenfrog', 7, 'Green', 'Wetlands')" 3.2 Collect data from the table To collect data from a table in the database connection we use the executequery method described above. We store the result in an object which implements the ResultSet interface [1]. For instance: ResultSet rs = stmt.executequery("select FrogName from FROGS" selects all the frogs (all rows) in the table of Figure 1. To process the rows we use the next() method in ResultSet. For example: while(rs.next()) String f = rs.getstring("frogname" int l = rs.getint("measurecm" 3

4 System.out.println( "A "+ f +" is in average "+ l +" cm long" We can also use index the reach a specific row. For instance, we could alternatively write: String f = rs.getstring(1 to select the name of the frogs. 3.3 Update the table To update a table we use the executequery method again. For example, to set the location for the frog Kermit in the table of Figure 1 to Treasure Island we write: "update FROGS set Location = 'TreasureIsland'" To select the updated row from the table and print therowwe write: ResultSet rset = stmt.executequery( "select FrogName,Location from FROGS" while (rset.next()) System.out.println(rset.getString("FrogName") System.out.println(rset.getInt("MeasureCM") 4 Example In this section we summarize, through an example, the different JDBC features we have presented in the previous sections. import java.sql.*; public class Frog public static void main(string[] args) //Load the DBMS Class.forName("RmiJdbc.odbc" catch(classnotfoundexception e) e.printstacktrace( 4

5 //create the connection Connection c = DriverManager.getConnection("jdbc:odbc=db1.mdb" //create the SQL statement Statement stmt = c.createstatement( //create the table "CREATE TABLE FROGS(" +"FrogName VARCHAR2(32)", +"MeasureCM integer", +"Color VARCHAR2(32)", +"Location VARCHAR2(32))" //insert data to the table +"values('greenfrog', 7, 'Green', 'Wetlands')" +"values('woodfrog', 6, 'Brown', 'Forests')" +"values('kermit', 45, 'Green', 'MuppetShow')" +"values('gonzo', 55, 'Blue', 'MuppetShow')" //remove the ``false'' frog from the table //(yes we know that the species of gonzo is unknown, // but he is certainly not a frog...) "delete * from FROGS" +"where FrogName = 'Gonzo'" //change the location of kermit "update FROGS set Location = 'TreasureIsland'" //select the row into a set ResultSet rset = stmt.executequery( "select FrogName,Location from FROGS" //extract information from the set, print the rows while (rset.next()) 5

6 System.out.println(rset.getString("FrogName") System.out.println(rset.getInt("MeasureCM") catch(sqlexception e) e.printstacktrace( And as always, beware of bugs in the above code, I have only proved it correct not tried it 4. References [1] Sun microsystems, Java 2 Platform, API Specification, 1.3 edition, April [2] Sun microsystems, JDBC Database Access, 1.3 edition, April Donald Knuth, March , in Notes on the van Emde Boas construction of priority deques: An instructive use of recursion 6