Transcript Introduction to Java Programming

Database Access through Java
CSE470 Software Engineering Fall 2000
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DBMS Overview
• A Database Management System (DBMS) is a
system that provides a convenient and efficient
way to store and retrieve data and manages issues
like security, concurrent access, etc. Today,
Relational Database Systems (RDBMS) are the
most extensively used DBMS.
• An RDBMS represents data as tables. Each table
has a specified set of fields. Each set of values for
the fields represents a record in the table. A
collection of related tables are grouped together as
a ‘database’ in the RDBMS.
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DBMS Overview…
• The de-facto standard for communicating
with a DBMS is through the use of
Structured Query Language (SQL)
Application
SQL
Results (e.g.,
records)
DBMS
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SQL Overview
• SQL provides the user a set of statements to
access the database. These statements can
be classified into two main types:
– Statements that specify/modify the structure of
the database, known as DDL (Data Definition)
statements (e.g., CREATE TABLE)
– Statements that retrieve, add or modify data in
the database, known as DML (Data
Manipulation) statements (e.g., SELECT)
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SQL Statements
• Some commonly used SQL statements are:
– CREATE TABLE : To define the structure of a table
– INSERT: To insert record(s) into a table
– DELETE: To delete records from a table
– UPDATE: To modify existing data in a table
– SELECT: To retrieve records from a table
[ Simple syntax for the CREATE TABLE and SELECT
statements are provided on the following slides. Examples
for these statements are also provided later in the
presentation. For more detailed syntax, refer to the MSDN
Library ]
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SQL – CREATE TABLE
• Syntax:
CREATE TABLE table-name (
field-name1 field-type1[,
field-name2 field-type2] …
)
• Field types are: INTEGER, CHAR,
DATETIME, etc.
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SQL – SELECT
• Syntax:
SELECT {* | field-name1
[, field-name2]…}
FROM table-name
[WHERE ( condition )]
• ‘*’ selects all fields in the table
• The WHERE clause is used to retrieve only those
records that meet a specific condition. Absence of
the WHERE clause retrieves all records in the
table
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JDBC™
• An API for Java applications, to access
databases and other tabular data
• Used to build all-Java database
applications
• Can interact with multiple database
management systems
• Often thought of as an acronym for ‘Java
Database Connectivity’
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JDBC Architecture
Java Application
JDBC API
JDBC Driver Manager
JDBC Driver
API
JDBC Driver Implementation
DBMS
Database Server
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The JDBC Driver
• Key component that enables communication
between the Java application and the data
source
• The driver makes it possible for the application
to:
– Establish a connection with the data source
– Send queries and update statements to the data
source
– Process results obtained from the data source
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How to Start using JDBC
• Check that your Java installation includes JDBC API.
The Java 2 SDK Standard Edition includes the JDBC 2.0
core API – the java.sql package. The javax.sql package
provides the JDBC Optional Package API. [We will use
the Java SDK installed on the Windows 2000 system].
• Check that a JDBC driver is installed. [We will use a
JDBC-ODBC bridge driver].
• Check that the DBMS you want to connect to, is setup.
[We will use the Microsoft SQL server “ALBORZ”].
• Check that the database you want to connect to has been
setup on the DBMS. [The system administrators have
setup the required databases].
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Using JDBC…
• If not already registered, register your database as an
(ODBC) data source [instructions are on the web page]
• Establish a connection
• Create Tables
• Enter data into Tables
• Process Data from Tables
• Close statements/connections when no longer required
SQL statements are used to create tables, enter/update
data in tables and to query the data.
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Establishing a Connection
• Load the JDBC driver
Example:
String driver = “sun.jdbc.odbc.JdbcOdbcDriver”;
Class.forName(driver);
• Make the connection
Example:
String url = “jdbc:odbc:alborz”;
String user = “sparty”;
String pswd = “xyz”;
Connection con = DriverManager.getConnection(url, user, pswd);
This statement creates a Connection object, con.
[Note: In the above example, “alborz” is the name of the data
source (DSN) as registered with the ODBC driver]
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Creating Tables
• Build the SQL statement to create a table
– SQL statement to be coded in the application:
CREATE TABLE PERSON (
FIRSTNAME CHAR(20),
LASTNAME CHAR(20) NOT NULL,
DOB DATETIME,
TELE INTEGER,
CONSTRAINT MYKEY
PRIMARY KEY(FIRSTNAME, LASTNAME))
– Corresponding Java code:
String createsql = “CREATE TABLE PERSON” +
“(FIRSTNAME CHAR(20), LASTNAME CHAR(20),” +
“DOB DATETIME, TELE INTEGER, CONSTRAINT” +
“MYKEY PRIMARY KEY (FIRSTNAME, LASTNAME))”;
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Creating Tables …
• Create a JDBC Statement
Example:
Statement stmt = con.createStatement();
This statement creates a Statement object, stmt that can
pass SQL statements to the DBMS using connection, con.
• Execute the JDBC Statement
Example:
stmt.executeUpdate(createsql);
[Note: The method executeUpdate() is used with statements like
CREATE, INSERT, UPDATE, etc., that affect either the data or
the structure of data stored in the database. For queries
(SELECT statements) the method executeQuery() is used]
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Entering Data into a Table
• Build the SQL INSERT statement
– SQL statement to be coded in the application:
INSERT INTO PERSON
VALUES (“Sparty”, “Spartan”, “1/1/1855”, 3531855)
– Corresponding Java code:
String insertsql = “INSERT INTO PERSON” +
“VALUES (‘Sparty’, ‘Spartan’, ‘1/1/1855’, 3531855)”;
• Create a JDBC Statement, if not already created
(as with CREATE TABLE)
• Execute the JDBC Statement with
executeUpdate()
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Retrieving Data from a Table
• Build the SQL SELECT statement
– SQL statement to be coded in the application:
SELECT * FROM PERSON
WHERE (DATEPART(YY, DOB) < 1900)
– Corresponding Java code:
String querysql = “SELECT * FROM PERSON” +
“WHERE (DATEPART(YY, DOB) < 1900)”;
• Create a JDBC Statement, if not already created
• Execute the JDBC Statement with executeQuery()
ResultSet rs = stmt.executeQuery(querysql);
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Processing Data (Result Sets)
• Use the first(), next() and last() methods of ResultSets
to scroll through the result set.
• Use the getXXX() methods to extract data from the
fields.
• The fields can be specified either by their names or
their position in the record.
• Example:
while (rs.next()) {
String name = rs.getString(1) + rs.getString(2);
Timestamp birthday = rs.getTimestamp(“DOB”);
Integer tele = rs.getInt(“TELE”);
System.out.println(name + “ “ + birthday + “ “ + tele);
}
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Closing Statements and Connections
• Statement objects that have been created, (for eg.,
using the createStatement() method), have to be
closed when they are no longer needed. The
close() method is used to close the statement.
E.g.:
stmt.close();
• All open connections also have to be closed, either
when they are no longer required, or before the
program terminates.
E.g.:
con.close()
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More SQL – Specifying Foreign Keys
Consider the following tables, STUDENTS & GRADES
• STUDENTS
ID
10001
…
NAME
Sparty
…
DOJ
1/1/1855
…
EMAIL
[email protected]
…
•GRADES
STU_ID
10001
COURSE
MTH101
GRADE
4.0
10001
…
CEM101
…
3.5
…
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Specifying Foreign Keys…
• The table GRADES has a foreign-key relationship
with table STUDENTS, i.e., for every value of
STU_ID in GRADES there must be a record with a
matching ID in STUDENTS
• The SQL statements to create the two tables will be as
follows:
– SQL to create table STUDENTS:
CREATE TABLE STUDENTS (
ID INTEGER,
NAME CHAR(30),
DOJ DATETIME,
EMAIL CHAR(30),
CONSTRAINT PK_STUDENTS PRIMARY KEY (ID))
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Specifying Foreign Keys…
– SQL to create table GRADES, with foreign key
CREATE TABLE GRADES (
STU_ID INTEGER,
COURSE CHAR(6),
GRADE DECIMAL(2,1),
CONSTRAINT PK_GRADES
PRIMARY KEY (STU_ID, COURSE),
CONSTRAINT FK_GRADES FOREIGN KEY (STU_ID)
REFERENCES STUDENTS)
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References
• JDBC API Tutorial and Reference, Second
Edition – White, Fisher, Cattell, Hamilton,
Hapner; Addison Wesley
• Understanding SQL and Java Together –
Melton, Eisenberg; Morgan Kauffman
Publishers
• Deitel & Deitel, “Java How To Program”
Third Edition, Prentice Hall Inc.
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Additional Notes:
JDBC Driver Implementation
• Various driver implementations are possible. Most
commonly used types are:
– Type 1 – JDBC-ODBC bridge: Implements JDBC by
invoking ODBC on the client machine
– Type 2 – Native-API Partly Java Driver: Implements JDBC
by making calls to a DBMS native-API on the client machine
– Type 3 – Net-Protocol All-Java Driver: Converts JDBC calls
to DBMS-independent net protocol messages. The server
then translates these messages to DBMS-specific calls
– Type 4 – Native-Protocol All-Java Driver: Converts JDBC
calls directly into the network protocol used by the DBMS
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