3 jdbc api

JDBC API

JDBC API

• this is a part of the JDBC Specification that provides an abstraction (interface) to program java applications accessing the JDBC service

• we know that the JDBC Service is implemented into the JDBC Driver• the JDBC API is described into two parts:1. JDBC CORE API2. JDBC Extension APIJDBC CORE API: THIS part of the API supports accessing the extended

services such as:• Connection pool• Accessing distributed transactionUnderstanding JDBC API• WE want to use JDBC API in our java application to access the tabular

datastore such as DB Server.

Why should I use Database server?

• Because to manage the persistence data, why persist the data because to persist our business data, to do this we need CRUD sql operations.

• To connect to the database server, we should interact with jdbc drivers, to do CRUD operations we should follow SQL (STRUCTURED QUERY LANGUAGE) because database server only understand one language called sql .

• We understand the java application would mainly want to interact with database server for CRUD (create, read, update and delete) operations.

• We also know that the SQL is used to describe the CRUD operations to database server, that means the Core (central part) of using the JDBC API is to submit the SQL statement to the JDBC Driver; requesting it to execute with DATABASE SERVER and carry the result back.

• Note:• I have developed one java application, I want to store the data into the database server, to store

or to interact with database server I have to use only one language that is SQL statement; but database server is located somewhere else, so I need one vehicle( bus i.e jdbc driver) to carry my sql statements, so we are using jdbc driver to carry our data with sql statements, so travel over the different networks we should follow the network API CALL interface. Next I have submitted my SQL ( data) to JDBC drivers, jdbc driver safely takes my (sql) data to the database server.

• Here jdbc driver acts as a courier boy.

The Basic steps of working with JDBC API

• We know that the java application wants to work with JDBC to access the tabular datastore

• We also know that the application wants to access the tabular datastore managing the persistence data.

• Thus the basic requirement in this process will be to perform the CRUD operations

• The following are the basic steps involved to implement for accessing the datastore performing CRUD operations:

•

• Here our intention is to execute the statement i.e. Step 3: but to perform step 3 we should have step 2, to do the step 2 we should have make the establish the connection to database server

Step1: obtaining the connection to DB:

• STEP1 : is just like a connecting to the mail box, first we have to use login, password to connect to our Mail inbox

• STEP1 : is just like a connecting to the mail box, first we have to use login, password to connect to our Mail inbox

• We know that any database server demands to establish a session/connectivity before accessing any of its services.

• Thus even working with JDBC , we start with establishing the DB Session.

• Creating a Database session is costlier job it includes:• Authentication• Allocating the resources for the session.• Note: the DB Session can not be shared between the

clients/threads.

Q: How establish/obtain connection to DB with respect to java/JDBC?

• We have multiple approaches to do this• Lets start with the basic (primary) approach i.e

using driver object direction.

APPROACH 1:

• Obtaining the connection to db using Driver object directly: in this approach we use the connect() method of the Driver object for getting the connection to the server.

Q: What is Driver object?Ans: it is a part of JDBC Driver responsible for establishing a session to the database server.Q: What is java.sql.Driver?Ans:It is an interface part of JBC API designed to represent the Driver object. (to the java application)The following method of Driver object is used to establish the session to the database server:Connection connect(String jdbcUrl, Properties props) throws SQLException{-----;}This method is declared in java.sql.Driver interface, implemented by the Driver object. Thus connect() is Non-

static method.That means to invoke the connect() method we need the following three (3) pre-requisit:1. Driver Object2. jdbcUrl3. PropertiesThus we can implement this step in following two steps:Step 1: create a Driver object instanceStep 2: invoke the connect() method.

Step 1: create a Driver object instance

• We know that the Driver class (i.e: implementation of java.sql.Driver interface)is provided by the 3rd party vendor.

• Thus the Driver class Name varies from one JDBC Driver to other:• Example:• For sun JDBC-ODBC Bridge Driver• sun.jdbc.odbc.JdbcOdbcDriver• For Oracle OCI & thin Driver• oracle.jdbc.driver.OracleDriver• (or)• oracle.jdbc.driver.OracleDri ver• For MySQL Connector driver• com.mysql.jdbc.Driver• Pre-requisite: (I.E we must know the following before learning the step1)

Q: How many ways we can instantiate a java object (with respect to JRE)?Ans:We have only 4 ways to do this:new keywordnewInstance() method of java.lang.Class objectclone()Deserialization And (2) are used for initial state , defined into the class constructor.• new keyword:Use new keyword when you know the class name while developing time .newInstance():

• Supports instantiating the object whose class name is known dynamically at run time.• (3.) clone(): • To create a new object with a copy of state of existing object• (4.) deserialization:• To create a object with the state from serialized bytes.• From this pre-requisite discussion we understand the Driver class instance can be

created using any of the following options:• Using new keyword• newInstance() method of java.lang.Class• using new keyword;• we may want to write the code as shown below:• java.sql.Driver d=new Oracle.jdbc.driver.OracleDriver();• the above statement (for creating Driver class object) is simple but makes our program

tightly bounded to OracleDriver. • Migrating to some other driver such as MYSQL Driver needs changes in the java

program.

• Note:

• Tightly bounded: In case any changes in a program and main logic may be destroyed is called tightly bounded.• Loosely coupled : In case without changing the program then it is called loosely coupled.• Example program:• //Message.java• public interface Message• {• String getMessage();• }• //Oraclemsg.java• public class Oraclemsg implements Message• {• public String getMessage()• {• return "I'm from Oraclemsg"; • }• }• //MYSQLmsg.java• public class MYSQLmsg implements Message• {• public String getMessage()• {• return "I'm from MYSQLmsg"; • }• }

• //Test.java with using newInstance() method of java.lang.Class• public class Test• {• public static void main(String args[]) throws Exception• {• String classname=args[0];• Class c=Class.forName(classname);• Object o=c.newInstance();• Message msg=(Message)o;• System.out.println(msg.getMessage()); • }• }• /*

• output:• D:\webtechnologies\jdbc\prog\newInstance>javac *.java• • D:\webtechnologies\jdbc\prog\newInstance>java Test Oraclemsg• I'm from Oraclemsg• • D:\webtechnologies\jdbc\prog\newInstance>java Test MYSQLmsg• I'm from MYSQLmsg• • D:\webtechnologies\jdbc\prog\newInstance>• */• • /* (or) we can write the main() by using new operator

• //Test.java with using new operator• public class Test• {• public static void main(String args[])• {• Message msg;• msg=new OracleMsg();// i can't call MYSQLmsg class method, and i got confused which class object

want to • //create the object so here new operator is not recommended, if you use new operator it leads to

write • //hardcode• System.out.println(msg.getMessage()); • //if u want to create MYSQLmsg class method again we need to create the object something like below• msg=new MYSQLmsg();• System.out.println(msg.getMessage()); • }• }• */

• Q: How work with the Class.newInstance() method to create a object?• Ans:• We want to implement the following two statements to do this:• //Statement 1:• Class c=Class.forName(className);• // Statement 2:• Object o=c.newInstance();• Q: what happens when at statement 1 (i.e Class.forName())?• Ans:• • The following operations are performed inside the forName() method:• Find is the .class with the given name is loaded into the JVM• If Yes: return the Class object representing the given class loaded. • : Load the class into the JVM:• If Failed throw the respective exception• If successful return the Class object representing Class loaded.

Q: What is the role of the Class object in the JVM?

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Fig: newInstanceJVM.JPG

Q: What is the role of the Class object in the JVM?

• Fig: newInstanceJVM.JPG• We know that for every type loaded into the

JVM a java.lang.Class instance will be created.• This object is responsible to represent the

type definition loaded into the JVM to the java application. So that the java Application can dynamically introspect the types.

Q: What happens when we invoke the newInstance()?

• Ans:• The newInstance() method of Class object creates a

new instance of the class this object is representing• This uses a no-argument class constructor to

instance the object.• From the above discussion we prefer to instantiate

the Driver object using the newInstance() method of Class object, as it provides a convenience to dynamically shift between the implementations.

Note:

• In case of private constructor:• //Abc.java• public class Abc• {• private Abc()• {• System.out.println("private Constructor()");• }• public static Abc getInstance()• {• //some logic• • return(new Abc());• }• }• //Test.java• public class Test• {• public static void main(String args[])• {• //creating the object in case of private constructor• Abc a=Abc.getInstance();• }• }• /*• Output:• D:\material\java(E DRIVE)\java\constructor\private>javac *.java• • D:\material\java(E DRIVE)\java\constructor\private>java Test• private Constructor()• */

• But in case we are creating the object inside the class (Ex: Abc.java then no problem directly we can create by using new operator: like below:

• //Abc.java• public class Abc• {• private Abc()• {• System.out.println("private Constructor()");• }• public static void main(String args[])• {• Abc a=new Abc();• }• }• /*• • D:\material\java(E DRIVE)\java\constructor\private\inside>javac *.java• • D:\material\java(E DRIVE)\java\constructor\private\inside>java Abc• private Constructor()• */•

List 1.1: Sample code for Step 1.1: creating a Driver class instance

• String

driverClassName=”oracle.jdbc.driver.OracleDriver=”oracle.jdbc.driver.OracleDriver”;

Class c=Class.forname(driverClassName);Driver d=(Driver)c.newInstance();•

Step 1.2: Invoking the connect() method:

• • We know that the connect() method is non-static thus

we need a Driver object reference which we got in the step 1.1

• However still we also need to prepare the inputs to the connect(0 method so thtat we can invoke it.

• The following are the two inputs for connect() method:

1. jdbcUrl(String)2. dbProperties(java.util.Properties)

jdbcUrl(String)

• as the name described this is a simple string used by JDBC to locate the

• database server that we it to connect.• That means we are informing to the Driver object that

where the Database server is located.• Why should we inform Driver object only? Because this

Driver object only knows how to connect to the Database server. Url contains the address (location) of the Database server.

• The JDBC URL describes the location of the resource (DataBase Server) to JDBC.

jdbcUrl(String)

• From the URL Format we understand locating the database server includes the information (inputs) that varies from one DB to other and also one JDBC Driver to other.

• Example:• • In case of Type-1 Driver:• i.e: JdbcOdbcDriver we use the following URL format:• jdbc:odbc:<ODBC DSN>• Fig: jdbcurl2.JPG

In case of Type 1 driver: jdbcurl2.JPG

In case of JDBC Type-2 Driver:Jdbc:oracle:oci:@<TNS_SERVICE_NAME>

Fig: jdbcurl3.JPG

Note:

• If I want to connect to Oracle DB Server, I have to write the information about Oracle Driver in Driver object and I have to inform to the OCN Native Driver which port should I connect( ex: 1521) because ports only connects to the Instance (like DB Names) probably ports may connects more than one instance (ex: port 1521 may connect Inventory and finance instances (DB).

• Once I have declared port name (TNS Service), I should inform to which Data Base I have to connect

In case of JDBC Type-4 Driver:

2. dbProperties: second (2nd) argument (parameter) of connect() method

• Apart from providing the URL for locating the database server we also require to supply necessary parameters such as username and password to the database server for authentication and establishing the session.

• The parameter require for establishing the session to DB differ from one database to other.

• The java.util.Properties is an implementation of Map which is suitable to describe the multiple data elements each of them with a unique name.

•

MapKey Value

User System

Password manager

• Thus the 2nd argument of connect() method is Properties