Before establishing a connection between the front end i.e your Java Program and the back end i.e the database we should learn what precisely a JDBC is and why it came into existence. Now let us discuss what exactly JDBC stands for and will ease out with the help of real-life illustration to get it working.
What is JDBC?
JDBC is an acronym for Java Database Connectivity. It’s an advancement for ODBC ( Open Database Connectivity ). JDBC is a standard API specification developed in order to move data from frontend to the backend. This API consists of classes and interfaces written in Java. It basically acts as an interface (not the one we use in Java) or channel between your Java program and databases i.e it establishes a link between the two so that a programmer could send data from Java code and store it in the database for future use.
Illustration: Working of JDBC co-relating with real-time
Why JDBC Come into Existence?
As previously told JDBC is an advancement for ODBC, ODBC being platform-dependent had a lot of drawbacks. ODBC API was written in C, C++, Python, and Core Java and as we know above languages (except Java and some part of Python )are platform-dependent. Therefore to remove dependence, JDBC was developed by a database vendor which consisted of classes and interfaces written in Java.
Steps For Connectivity Between Java Program and Database
- Import the Packages
- Load the drivers using the forName() method
- Register the drivers using DriverManager
- Establish a connection using the Connection class object
- Create a statement
- Execute the query
- Close the connections
Let us discuss these steps in brief before implementing by writing suitable code to illustrate connectivity steps for JDBC/
Step 1: Import the Packages
Step 2: Loading the drivers
In order to begin with, you first need to load the driver or register it before using it in the program. Registration is to be done once in your program. You can register a driver in one of two ways mentioned below as follows:
2-A Class.forName()
Here we load the driver’s class file into memory at the runtime. No need of using new or create objects. The following example uses Class.forName() to load the Oracle driver as shown below as follows:
Class.forName(“oracle.jdbc.driver.OracleDriver”);
2-B DriverManager.registerDriver()
DriverManager is a Java inbuilt class with a static member register. Here we call the constructor of the driver class at compile time. The following example uses DriverManager.registerDriver()to register the Oracle driver as shown below:
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver())
Step 3: Establish a connection using the Connection class object
After loading the driver, establish connections as shown below as follows:
Connection con = DriverManager.getConnection(url,user,password)
- user: Username from which your SQL command prompt can be accessed.
- password: password from which the SQL command prompt can be accessed.
- con: It is a reference to the Connection interface.
- Url: Uniform Resource Locator which is created as shown below:
String url = “ jdbc:oracle:thin:@localhost:1521:xe”
Where oracle is the database used, thin is the driver used, @localhost is the IP Address where a database is stored, 1521 is the port number and xe is the service provider. All 3 parameters above are of String type and are to be declared by the programmer before calling the function. Use of this can be referred to form the final code.
Step 4: Create a statement
Once a connection is established you can interact with the database. The JDBCStatement, CallableStatement, and PreparedStatement interfaces define the methods that enable you to send SQL commands and receive data from your database.
Use of JDBC Statement is as follows:
Statement st = con.createStatement();
Note: Here, con is a reference to Connection interface used in previous step .
Step 5: Execute the query
Now comes the most important part i.e executing the query. The query here is an SQL Query. Now we know we can have multiple types of queries. Some of them are as follows:
- The query for updating/inserting a table in a database.
- The query for retrieving data.
The executeQuery() method of the Statement interface is used to execute queries of retrieving values from the database. This method returns the object of ResultSet that can be used to get all the records of a table.
The executeUpdate(sql query) method of the Statement interface is used to execute queries of updating/inserting.
Pseudo Code:
int m = st.executeUpdate(sql);
if (m==1)
System.out.println("inserted successfully : "+sql);
else
System.out.println("insertion failed");
Here sql is SQL query of the type String
Java
// This code is for establishing connection with MySQL// database and retrieving data// from db Java Database connectivity/* *1. import --->java.sql *2. load and register the driver ---> com.jdbc. *3. create connection *4. create a statement *5. execute the query *6. process the results *7. close */import java.io.*;import java.sql.*;class GFG { public static void main(String[] args) throws Exception { String url String username = "rootgfg"; // MySQL credentials String password = "gfg123"; String query = "select *from students"; // query to be run Class.forName( "com.mysql.cj.jdbc.Driver"); // Driver name Connection con = DriverManager.getConnection( url, username, password); System.out.println( "Connection Established successfully"); Statement st = con.createStatement(); ResultSet rs = st.executeQuery(query); // Execute query rs.next(); String name = rs.getString("name"); // Retrieve name from db System.out.println(name); // Print result on console st.close(); // close statement con.close(); // close connection System.out.println("Connection Closed...."); }} |
Output:
name of the student is retrieved from database
Step 6: Closing the connections
So finally we have sent the data to the specified location and now we are on the verge of completing our task. By closing the connection, objects of Statement and ResultSet will be closed automatically. The close() method of the Connection interface is used to close the connection. It is shown below as follows:
con.close();
Example:
Java
// Java Program to Establish Connection in JDBC// Importing databaseimport java.sql.*;// Importing required classesimport java.util.*;// Main classclass Main { // Main driver method public static void main(String a[]) { // Creating the connection using Oracle DB // Note: url syntax is standard, so do grasp String url = "jdbc:oracle:thin:@localhost:1521:xe"; // Username and password to access DB // Custom initialization String user = "system"; String pass = "12345"; // Entering the data Scanner k = new Scanner(System.in); System.out.println("enter name"); String name = k.next(); System.out.println("enter roll no"); int roll = k.nextInt(); System.out.println("enter class"); String cls = k.next(); // Inserting data using SQL query String sql = "insert into student1 values('" + name + "'," + roll + ",'" + cls + "')"; // Connection class object Connection con = null; // Try block to check for exceptions try { // Registering drivers DriverManager.registerDriver( new oracle.jdbc.OracleDriver()); // Reference to connection interface con = DriverManager.getConnection(url, user, pass); // Creating a statement Statement st = con.createStatement(); // Executing query int m = st.executeUpdate(sql); if (m == 1) System.out.println( "inserted successfully : " + sql); else System.out.println("insertion failed"); // Closing the connections con.close(); } // Catch block to handle exceptions catch (Exception ex) { // Display message when exceptions occurs System.err.println(ex); } }} |
Output:
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