WEB/DB1 DATABASE PROGRAMMING 3JDBC by the ASU Scholars

WEB/DB2 ADVANCED DATABASE CONCEPTS JDBC Susan D. Urban and Suzanne W. Dietrich Department of Computer Science and Engineering Arizona State University Tempe, AZ

WEB/DB3 OPEN DATABASE CONNECTIVITY (ODBC) Standard application programming interface (API) for accessing a database. A separate module or driver is required for each database to be accessed. Based on the standard Call Level Interface (CLI) of the SQL Access Group (part of the X/Open Standard). Can use the API to execute SQL statements, update tables, and retrieve metadata.

WEB/DB4 ODBC ISSUES IN A JAVA ENVIRONMENT ODBC uses C to access the data source. This poses issues with implementation. Hence, it cannot be used in conjunction with Java. OBDC’S API cannot be used by translating the API to Java since there is no pointer concept in Java. ODBC requires the driver manager to be installed on every client installation.

WEB/DB5 JAVA DATABASE CONNECTIVITY (JDBC) Java API for connecting programs written in Java to databases. Based on ODBC. Allows Java programs to send SQL statements to any relational database. Platform independent. JDBC drivers written in Java can be accessed from any computer in a heterogeneous network. A JDBC-ODBC bridge can be used to access databases using the ODBC interface.

WEB/DB6 TWO-TIER JDBC ARCHITECTURES Java application or applet talks directly to the data source. Client sends requests to the server through user interfaces. JDBC Driver communicates with the data source to access the data. Sun Microsystems Inc. 1999

WEB/DB7 THREE-TIER JDBC ARCHITECTURES Uses a third tier between the client and the server. Controls updates that are made to the database. Secure and robust. Sun Microsystems Inc. 1999

WEB/DB8 DEVELOPING JDBC APPLICATIONS Import JDBC classes (java.sql.*) Load the JDBC Driver. Connect to the database. Use the JDBC API to access the database. Disconnect from the database.

WEB/DB9 ESTABLISHING A CONNECTION TO A DATABASE The first step in accessing data from any relational database using JDBC is to establish a connection with the data source. The Connection object is used to get meta data and execute SQL statements. The getConnection method returns a Connection object that represents a session with a specific database. The parameters in the getConnection method are URL, username and password. Username and password are optional. The URL consists of the protocol “jdbc”, sub-protocol “odbc”, and the Data Source Name (DSN).

WEB/DB10 EXAMPLE TO CONNECT TO A DATABASE /* dbName is the registered name of the ODBC data source */ String url = "jdbc:odbc:" + dbName ; try { /* Load the jdbc-odbc driver */ Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); /* Open a connection to the odbc data source */ con =DriverManager.getConnection(url,"",""); }

WEB/DB11 STATEMENTS A Statement Object is used to send SQL queries to a database. A Statement object should be created using the connection method createStatement().

WEB/DB12 TYPES OF STATEMENTS There are three types of statement objects: Simple statements Used to execute SQL statements without any parameters. Statement stmt = connection.createStatement(); Prepared Statements Used when a statement will be called several times and is stored as a pre-compiled statement with IN parameters. PreparedStatement pstmt = con.prepareStatement(“update employee set salary=? where ssn=?”); Callable Statements Used with calls to database stored procedures and SQL statements with OUT parameters.

WEB/DB13 EXECUTING SIMPLE STATEMENTS The execution of a statement returns results into a ResultSet object. The ResultSet object is then used to access query results. ResultSet rs = null; The executeQuery() method is used to execute an SQL statement through the statement object. rs = stmt.executeQuery("SELECT a, b, c FROM Table1"); The close() method is used to close the ResultSet. rs.close();

WEB/DB14 GETTING DATA FROM A ResultSet The next() method is used to traverse through tuples in the ResultSet object. The data stored in a ResultSet object is retrieved through a set of get methods that allows access to the various columns of the current row. The results are printed out on a screen using the Servlet output stream. while(rs.next()) { out.println(rs.getString(“SSN”)); }

WEB/DB15 DATABASE METADATA Metadata is the information in the database that is associated with the database schema: Table names Column names Column types The metadata associated with a database can be queried using JDBC. The metadata associated with the result set object of a statement execution can also be queried.

WEB/DB16 DATABASE METADATA RETRIEVAL Create a metadata object. DatabaseMetaData dbmd ; Retrieve metadata from the database through the connection established. dbmd = con.getMetaData(); The getTables() method of the metadata object is used to retrieve information about the tables in a database. The information is stored in a result set object. ResultSet rsTables = dbmd.getTables(null, null, null, null);

WEB/DB17 GETTING THE METADATA The getString() method of the ResultSet object is used to locate a specific table. String tableName = rsTables.getString("TABLE_NAME"); The getColumns() method is used to retrieve information about the columns and column types in a table, with the results stored in a ResultSet object. ResultSet rsColumns = dbmd.getColumns(null,null,tableName,null); while (rsColumns.next()) { … }