JDBC and Java Access to DBMS

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JDBC and Java Access to DBMS

• University of California, Berkeley
• School of Information
• IS 257 Database Management

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Lecture Outline

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

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Lecture Outline

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

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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

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Object Relational Extended SQL (Illustra)

• CREATE TABLE tablename OF TYPE TypenameOF 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

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Object-Relational SQL in ORACLE

• CREATE (OR REPLACE) TYPE typename AS OBJECT
  (attr_name, attr_type, )
• CREATE TABLE OF typename

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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

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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

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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.

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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
• )

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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.

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Inheritance

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

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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

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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.

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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.

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Lecture Outline

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

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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 Microsofts ODBC

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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
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JDBC

• Provides a standard set of interfaces for any
  DBMS with a JDBC driver using SQL to specify
  the databases operations.

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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
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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(
"jdbcoraclethin_at_dream.sims.berkel
ey.edu1521dev", mylogin",
myoraclePW") // Do an SQL statement...
Statement stmt con.createStatement()
ResultSet rs stmt.executeQuery("SELECT NAME
FROM DIVECUST")
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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(Syst
em.out)
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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

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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

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JDBC GetXXX() methods
SQL data type Java Type GetXXX()
CHAR String getString()
VARCHAR String getString()
LONGVARCHAR String getString()
NUMERIC Java.math.BigDecimal GetBigDecimal()
DECIMAL Java.math.BigDecimal GetBigDecimal()
BIT Boolean getBoolean()
TINYINT Byte getByte()


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JDBC GetXXX() Methods
SQL data type Java Type GetXXX()
SMALLINT Integer (short) getShort()
INTEGER Integer getInt()
BIGINT Long getLong()
REAL Float getFloat()
FLOAT Double getDouble()
DOUBLE Double getDouble()
BINARY Byte getBytes()
VARBINARY Byte getBytes()
LONGVARBINARY Byte getBytes()

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JDBC GetXXX() Methods
SQL data type Java Type GetXXX()
DATE java.sql.Date getDate()
TIME java.sql.Time getTime()
TIMESTAMP Java.sql.Timestamp getTimeStamp()







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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 byte41024 // 4K buffer int len while
((len gifData.read(buf,0,buf.length)) ! -1)
out.write(buf, 0, len)
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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)

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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")
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JDBC for MySQL
try //All DB access is within the
try/catch block... // make a connection to
MySQL on Dream Connection con
DriverManager.getConnection(
"jdbcmysql//dream.sims.berkeley.ed
u/ (this is really one line)
MyDatabase?userMyLoginpasswordMySQLPW")
// 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