CH 16 JDBC

8/3/2019 CH 16 JDBC

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ACEP/ Sun Java 2/ Session 16/ 1 of 39

ava a a ase

Connectivity

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Session Objectives JDBC API JDBC Drivers JDBC Products

JDBC Design Considerations Two-Tier Client-Server Model Three-Tier Client-Server Model Basic Steps to JDBC

Setting up a connection to thedatabase

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Session Objectives

(Contd«) Creating and Executing SQL Statements ResultSet & ResultSetMetaData Object

Database Security

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JDBC API JDBC API stands for Java Database

Connectivity Application Programming

Interface. Defines how an application opens aconnection, communicates with thedatabase, execute SQL statementsand retrieves the results.

Developed by JavaSoft. Both ODBC and JDBC are based on

call level interface.

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JDBC API (Contd«) JDBC is a port of ODBC to Java programming

language. The major difference being ODBC is written in ³C´. The pointers are made use of extensively. But Java

does not pointers. JDBC was designed to be compact and focussed

only on the execution of SQL statements and thereby

retrieving the results, but ODBC has multiplemechanisms for performing a single task and hasadditional data handling capabilities.

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Functioning of JDBC API

GUI

JDBC API

Network

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JDBC Driver Ensures that the application interacts

with the databases.

Ensures that the requests, made bythe application, are presented to thedatabase in a language, understoodby the database.

Receives the requests from the client,

converts it into the format familiar tothe database and then presents it to

the database.

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JDBC Products There are three components to the JDBC:

o java.sql package

This consists of the following interfaces: Callable Interface Connection DatabaseMetaData Driver PreparedStatement

ResultSet ResultSetMetaData Statement

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java.sql. Package

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JDBC Products

(Contd«)o The classes included in this package

are: Date DriverManager DriverPropertyInfo Time TimeStamp Type

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JDBC Products

(Contd«) The exceptions included in this

package are: DataTruncation SQLException SQLWarning

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JDBC Products

(Contd«) Test Suite

o Used to test the functionality of a JDBCDriver.

o Ensures that all the classes and methodsdefined in the JDBC API are implemented.

o Once the driver passes through all thetests, the test suite can be designated asJDBC COMPLAINT.

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JDBC Products (Contd«) JDBC-ODBC bridge

o Is a JDBC driver designed to allow Javaapplications communicate with the

database using ODBC driver.

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JDBC Design

Considerations The four types of drivers are:

o JDBC-ODBC Bridge Once the request is passed by the

JDBC to the ODBC driver, it is theresponsibility of the ODBC driver tocommunicate it with the database.

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JDBC Design Considerations

(Contd«) Native API Java

o The Native-API-Partly-Java Driver makesuse of local native libraries to

communicate with the database.o It is done by making calls to the local

installed native call level interface.o The Call Level Interface [CLI] libraries are

written in C.

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(Contd«) JDBC Network

o The native CLI libraries are placed on theremote server and the driver uses a

network protocol to communicate betweenthe application and the driver.

o The driver is split into two parts: onecontaining all Java portion that can bedownloaded to the client and the server

portion containing both Java and nativemethods.

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(Contd«) Native Protocol

o These drivers are 100% Java and use noCLI libraries.

o This driver is capable of communicatingdirectly with the database without anyneed of translation.

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Two-Tier Client-Server

Model The architecture of any client server

environment is by default a two-tier

system. The client is the first tier and theserver the second tier.

In a two-tier JDBC environment, thedatabase application is the client and

the DBMS is the server. The client communicates directly with

the server without any server.

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Two-Tier Client-Server Model [

Contd« ] Advantage

It is the leastcomplicated systemto implement.

This architecturemaintains a constantconnection betweenthe client and thedatabase.

This system isusually faster than athree-tier implementation

Disadvantages Most of the drivers

require that nativelibraries be loaded on theclient machine.

Local configuration has tobe maintained for nativecode.

Applets can open up

connection to the server from which they aredownloaded

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Three-Tier Client-Server

Model A third server is employed to handlerequests from the client and then passthem to the database server.

This third server acts as a proxy for allclient requests.

All the client requests are routed throughthe proxy server thereby creating a moresecure environment for the database.

The driver translates the request into anetwork protocol and then requests viathe proxy server.

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BasicS

teps to JDBC There are about seven steps to usingJDBC access a database. The sevensteps are as mentioned below:o Import java.sql packageo Loading and registering the driver o Establishing a connection to the

database server o Creating a statemento Executing the statemento Retrieving the resultso Closing the statement and connection

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Setting up a connection to the

database For using JDBC, we require a databaseserver and database driver.

JDBC consists of the following classes:o DriverManager Class

java.sql.DriverManager class provides withmethods to load drivers.

This class is basically used for managing JDBCdrivers installed in the system.

This class contains the following methods: getDrivers( ) getConnection( ) getLoginTimeout( ) & setLoginTimeout( ) getLogStream & setLogStream

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Creating and Executing SQL

Statement Queries

o Queries are one of the most importantforms of SQL statements.

o In JDBC, all queries return results in theform of ResultSet objects.

o The most efficient way to execute a queryis to use the Statement executeQuery( )method.

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Creating and Executing SQL Statement [

Contd« ]Example In SQL

SELECT emp_no, emp_name, emp_age FROMemployee;

o The above query returns the employeenumber, name and age from the employeedatabase.

In JDBC

String stg = ³SELECT emp_no, emp_name,emp_age FROM employee´;

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StatementThe Java code for the above would look likethis:

String stg = ³SELECT emp_no, emp_name,emp_age FROM employee´;Statement st = conn.createStatement( );ResultSet rst = st.executeQuery(stg);

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Statement Updates

o Update statements do not return theresults as ResultSets instead return an

integer representing the number of rowsaffected by that statement.

o For updates, the Statement object andexecuteUpdate( ) methods are used.

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Creating and Executing SQL Statement [

Contd « ] Suppose we want to add some value in the inventorydatabase where price is equal to 200.

In SQLINSERT INTO inventory VALUES(500) WHERE price

= 200; In JDBC is:

String stg = ³INSERT INTO inventory´ +³VALUES(500)´ + ³WHERE price = 200´;Statement st = conn.createStatement( );

int rowcount = st.executeUpdate(stg);

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Creating and Executing SQL Statement

(Contd«)

Data Definition Language [DDL]o Data Definition Language statements

are used to create tables, add columnsto the existing tables, delete tables, etc.

o DDL statements do not perform anyquery and hence do not return anyResultSet. DDL statements alwaysreturn a value of 0.

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(Contd«) The following code creates a new

table called ³employee´ In SQL:

CREATE TABLE test (emp_nameVARCHAR(25),emp_no int,emp_age int);

In JDBC:String stg = (³CREATE TABLE employee´ +³(emp_name VARCHAR(25), ³emp_no init´,

³emp_age int´);Statement st = conn.createStatement( );st.execute(stg);

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Creating and Executing SQL Statement(Contd«)

LIKE Operator o The LIKE operator is used with the SQL statements,

to compare two strings.o The % and _ are used as pattern matching

characters

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(Contd«) In SQL

SELECT emp_name FROM employee WHEREemp_no LIKE µE00%¶ In JDBC

String stg = ³SELECT emp_name FROMemployee´ + ³WHERE emp_no LIKE µE00%¶´; Other than the above-mentioned tasks, SQL

is used to ALTER TABLE, DROP TABLE,INSERT values, DELETE rows from the table.

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Creating and Executing SQL Statement(Contd«)

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(Contd«)

Time and Date LiteralsThe code given below depicts the JDBC code that is

used to select all the employees employee id in theemployee table working from 1st December 1989. String stg = ³SELECT emp_no FROM employee´ + ³WHERE

doj = { d µ 1989 ± 12 ± 30¶ }´);

Statement st = conn.createStatement( );

st.execute(stg);

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(Contd«)

Outer Joinso Ex ample

Suppose we want to know the list of alloutstanding orders and want to include the user name, the code in JDBC is as shown below:

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(Contd«)o S ELECT users.usr_name,

users.usr_id, orders.ord_no FROM users, orders WHERE users.usr_id =

orders.usr_id;o In the above code, we find the field

usr_id is common between users andorders table. It is used commonly toestablish the relationship betweenboth.

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ResultSet & ResultSetMetaDataObject

How is the result of the query returned after execution of database query?o It is returned as tables of data according to

rows and columns.

How is this data accessed?o It is accessed using ResultSet interface.

The getMetaData( ) method is one suchthat returns the ResultSetMetaData object

containing the information about the row.

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ResultSetMetaData objecto An object that provides constants and methods used

to obtain information about theR

esultSet object. The ResultSet object uses the getColumnCount( )method to return the number of columns in thetabular data accessed by the ResultSet.

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The column name is returned using thegetColumnName( ) method.

The column¶s SQL type is returnedusing the getColumnType( ) method.

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Database

Security Database security is of vital importance. Data should be available whenever required.

JDBC depends on the database server for providing security. The JDBC makes use of Secure Socket Layer

(SSL) in their product lines.

This provides encrypted communicationbetween database driver and server.

Documents

CH 16 JDBC