JDBC and Java Access to DBMS

JDBC and Java Access to DBMS University of California, Berkeley School of Information IS 257: Database Management

Review: Object-Relational DBMS OR features in Oracle OR features in PostgreSQL Extending OR databases (examples from PostgreSQL) Java and JDBC Lecture Outline

Object-Relational DBMS OR features in Oracle OR features in PostgreSQL Extending OR databases (examples from PostgreSQL) Java and JDBC Lecture Outline

Object Relational Data Model • Class, instance, attribute, method, and integrity constraints • OID per instance • Encapsulation • Multiple inheritance hierarchy of classes • Class references via OID object references • Set-Valued attributes • Abstract Data Types

Object Relational Extended SQL (Illustra) • CREATE TABLE tablename {OF TYPE Typename}|{OF NEW TYPE typename} (attr1 type1, attr2 type2,…,attrn typen) {UNDER parent_table_name}; • CREATE TYPE typename (attribute_name type_desc, attribute2 type2, …, attrn typen); • CREATE FUNCTION functionname (type_name, type_name) RETURNS type_name AS sql_statement

Object-Relational SQL in ORACLE • CREATE (OR REPLACE) TYPE typename AS OBJECT (attr_name, attr_type, …); • CREATE TABLE OF typename;

Example • CREATE TYPE ANIMAL_TY AS OBJECT (Breed VARCHAR2(25), Name VARCHAR2(25), Birthdate DATE); • Creates a new type • CREATE TABLE Animal of Animal_ty; • Creates “Object Table”

Constructor Functions • INSERT INTO Animal values (ANIMAL_TY(‘Mule’, ‘Frances’, TO_DATE(‘01-APR-1997’, ‘DD-MM-YYYY’))); • Insert a new ANIMAL_TY object into the table

PostgreSQL Classes • The fundamental notion in Postgres is that of a class, which is a named collection of object instances. Each instance has the same collection of named attributes, and each attribute is of a specific type. Furthermore, each instance has a permanent object identifier (OID) that is unique throughout the installation. Because SQL syntax refers to tables, we will use the terms table and class interchangeably. Likewise, an SQL row is an instance and SQL columns are attributes.

Creating a Class • You can create a new class by specifying the class name, along with all attribute names and their types: CREATE TABLE weather ( city varchar(80), temp_lo int, -- low temperature temp_hi int, -- high temperature prcp real, -- precipitation date date );

PostgreSQL • Postgres can be customized with an arbitrary number of user-defined data types. Consequently, type names are not syntactical keywords, except where required to support special cases in the SQL92 standard. • So far, the Postgres CREATE command looks exactly like the command used to create a table in a traditional relational system. However, we will presently see that classes have properties that are extensions of the relational model.

Inheritance CREATE TABLE cities ( name text, population float, altitude int -- (in ft) ); CREATE TABLE capitals ( state char(2) ) INHERITS (cities);

Inheritance • In Postgres, a class can inherit from zero or more other classes. • A query can reference either • all instances of a class • or all instances of a class plus all of its descendants

Non-Atomic Values - Arrays • The preceding SQL command will create a class named SAL_EMP with a text string (name), a one-dimensional array of int4 (pay_by_quarter), which represents the employee's salary by quarter and a two-dimensional array of text (schedule), which represents the employee's weekly schedule • Now we do some INSERTSs; note that when appending to an array, we enclose the values within braces and separate them by commas.

PostgreSQL Extensibility • Postgres is extensible because its operation is catalog-driven • RDBMS store information about databases, tables, columns, etc., in what are commonly known as system catalogs. (Some systems call this the data dictionary). • One key difference between Postgres and standard RDBMS is that Postgres stores much more information in its catalogs • not only information about tables and columns, but also information about its types, functions, access methods, etc. • These classes can be modified by the user, and since Postgres bases its internal operation on these classes, this means that Postgres can be extended by users • By comparison, conventional database systems can only be extended by changing hardcoded procedures within the DBMS or by loading modules specially-written by the DBMS vendor.

Review Object-Relational DBMS OR features in Oracle OR features in PostgreSQL Extending OR databases (examples from PostgreSQL) Java and JDBC Lecture Outline

Java and JDBC • Java is probably the high-level language used in most software development today one of the earliest “enterprise” additions to Java was JDBC • JDBC is an API that provides a mid-level access to DBMS from Java applications • Intended to be an open cross-platform standard for database access in Java • Similar in intent to Microsoft’s ODBC

JDBC Architecture • The goal of JDBC is to be a generic SQL database access framework that works for any database system with no changes to the interface code Java Applications JDBC API JDBC Driver Manager Driver Driver Driver Oracle MySQL Postgres

JDBC Resultset Resultset Resultset Statement PreparedStatement CallableStatement Connection Application DriverManager Oracle Driver ODBC Driver Postgres Driver Oracle DB ODBC DB Postgres DB • Provides a standard set of interfaces for any DBMS with a JDBC driver – using SQL to specify the databases operations.

JDBC Simple Java Implementation import java.sql.*; import oracle.jdbc.*; public class JDBCSample { public static void main(java.lang.String[] args) { try { // this is where the driver is loaded //Class.forName("jdbc.oracle.thin"); DriverManager.registerDriver(new OracleDriver()); } catch (SQLException e) { System.out.println("Unable to load driver Class"); return; }

JDBC Simple Java Impl. try { //All DB access is within the try/catch block... // make a connection to ORACLE on Dream Connection con = DriverManager.getConnection( "jdbc:oracle:thin:@dream.sims.berkeley.edu:1521:dev", “mylogin", “myoraclePW"); // Do an SQL statement... Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("SELECT NAME FROM DIVECUST");

JDBC Simple Java Impl. // show the Results... while(rs.next()) { System.out.println(rs.getString("NAME")); } // Release the database resources... rs.close(); stmt.close(); con.close(); } catch (SQLException se) { // inform user of errors... System.out.println("SQL Exception: " + se.getMessage()); se.printStackTrace(System.out); } } }

JDBC • Once a connection has been made you can create three different types of statement objects • Statement • The basic SQL statement as in the example • PreparedStatement • A pre-compiled SQL statement • CallableStatement • Permits access to stored procedures in the Database

JDBC Resultset methods • Next() to loop through rows in the resultset • To access the attributes of each row you need to know its type, or you can use the generic “getObject()” which wraps the attribute as an object

JDBC “GetXXX()” methods

JDBC GetXXX() Methods

Large Object Handling • Large binary databytes can be read from a resultset as streams using: • getAsciiStream() • getBinaryStream() • getUnicodeStream() ResultSet rs = stmt.executeQuery(“SELECT IMAGE FROM PICTURES WHERE PID = 1223”)); if (rs.next()) { BufferedInputStream gifData = new BufferedInputSteam( rs.getBinaryStream(“IMAGE”)); byte[] buf = new byte[4*1024]; // 4K buffer int len; while ((len = gifData.read(buf,0,buf.length)) != -1) { out.write(buf, 0, len); } }

JDBC Metadata • There are also methods to access the metadata associated with a resultSet • ResultSetMetaData rsmd = rs.getMetaData(); • Metadata methods include… • getColumnCount(); • getColumnLabel(col); • getColumnTypeName(col)

JDBC access to MySQL • The basic JDBC interface is the same, the only differences are in how the drivers are loaded public class JDBCTestMysql { public static void main(java.lang.String[] args) { try { // this is where the driver is loaded Class.forName("com.mysql.jdbc.Driver").newInstance(); } catch (InstantiationException i) { System.out.println("Unable to load driver Class"); return; } catch (ClassNotFoundException e) { System.out.println("Unable to load driver Class"); …

JDBC for MySQL try { //All DB access is within the try/catch block... // make a connection to MySQL on Dream Connection con = DriverManager.getConnection( "jdbc:mysql://dream.sims.berkeley.edu/ (this is really one line) MyDatabase?user=MyLogin&password=MySQLPW"); // Do an SQL statement... Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("SELECT NAME FROM DIVECUST"); • Otherwise everything is the same as in the Oracle example • For connecting to the machine you are running the program on, you can use “localhost” instead of the machine name

JDBC and Java Access to DBMS