How to Handle SQLException in JDBC? - Coding

Java Database Connectivity (JDBC) serves as the backbone for Java applications when interacting with databases. While establishing connections and executing queries, we developers often encounter SQLExceptions, which are inevitable in the real world. Handling those exceptions is crucial in the development of applications. Now let’s understand more about SQL Exception.

Understanding SQL Exception

Exception is a type of condition when a program encounters a problem in execution and quits with a problematic error message. In JDBC, when the program has trouble with a data source, it throws SQLException.

Note: An SQLException can occur in the JDBC Driver or inside the database.

SQL Exception methods in Java:

METHOD NAME	DESCRIPTION
getErrorCode()	Gets the error number associated with the exception.
getMessage()	This method gets the JDBC driver’s error message for
getSQLState()	Gets the XOPEN SQLstate string. This method can return null.
getNextException()	In the exception chain, gets the next Exception object
printStackTrace()	Prints the current exception, or throwable, and it’s backtrace to a standard error stream.
printStackTrace(PrintStream s)	To the print the stream we have specified, prints this throwable and its backtrace.
printStackTrace(PrintStream s)	Prints this throwable and it’s backtrace to the print writer you specify.

The below-described code describes how to handle SQL Exception.

Initial part of the code is to connect to the sql server i.e. username and password are declared.
The resultantSet is initialized and declared.
Once the server gets connected then the query gets executed.

Java

import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.PreparedStatement; 
import java.sql.SQLException; 
  
public class SQLExceptionExample { 
    public static void main(String[] args) { 
        Connection connection = null; 
        PreparedStatement preparedStatement = null; 
  
        try { 
            // Load the JDBC driver 
            Class.forName("com.mysql.cj.jdbc.Driver"); 
  
            // establish a connection to the database 
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/your_database", "username", "password"); 
  
            // Your SQL query with an intentional error (table name is misspelled) 
            String sql = "SELECT * FROM non_existent_table"; 
  
            // create a PreparedStatement 
            preparedStatement = connection.prepareStatement(sql); 
  
            // execute the query (this will throw an SQLException in case of an error) 
            preparedStatement.executeQuery(); 
        } catch (SQLException | ClassNotFoundException e) { 
            // handle the SQL exception 
            handleSQLException(e); 
        } finally { 
            // close the resources in the finally block 
            try { 
                if (preparedStatement != null) { 
                    preparedStatement.close(); 
                } 
                if (connection != null) { 
                    connection.close(); 
                } 
            } catch (SQLException e) { 
                handleSQLException(e); 
            } 
        } 
    } 
  
    private static void handleSQLException(SQLException e) { 
        // handle the SQL exception 
        int errorCode = e.getErrorCode(); 
        String sqlState = e.getSQLState(); 
        String errorMessage = e.getMessage(); 
  
        System.out.println("SQL Error Code: " + errorCode); 
        System.out.println("SQL State: " + sqlState); 
        System.out.println("Error Message: " + errorMessage); 
  
        e.printStackTrace(); 
    } 
} 

Note: To load the JDBC Driver, first connect to the database (SQL) and fetch that link to establish the connection.

Output:

The Output of the above code will intentionally create SQL Exception error since there is no non-existence table in the database. This code lets you to understand the SQL Exception Methods.

Source Code:
Below is the entire source code which follows the connection steps.

Java

import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 
  
public class SQLException_Example { 
    // Define JDBC Driver 
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; 
  
    // Database URL, username, and password 
    static final String dburl = "jdbc:mysql://localhost/STOREDB"; 
    static final String dbuser = "root"; 
    static final String dbpass = "root"; 
  
    public static void main(String[] args) throws SQLException { 
        Connection con = null; 
        Statement stmt = null; 
  
        try { 
            // Connecting to the server and database 
            con = DriverManager.getConnection(dburl, dbuser, dbpass); 
              
            // Initialize Statement 
            stmt = con.createStatement(); 
              
            // SQL Query 
            String query = "SELECT * FROM ITEM"; 
  
            // Execute Query And Get ResultSet 
            ResultSet rset = stmt.executeQuery(query); 
            while (rset.next()) { 
                System.out.print("ID: " + rset.getInt(1)); 
                System.out.print(" Product: " + rset.getString(2)); 
                System.out.println(" Price: " + rset.getString(3)); 
            } 
        } catch (SQLException e) { 
            // Catch SQLException, print error and stack trace 
            System.err.println("Cannot connect! "); 
            e.printStackTrace(); 
        } finally { 
            // Finally block to ensure closing connection 
            System.out.println("Closing the connection."); 
            if (con != null) try { con.close(); } catch (SQLException ignore) {} 
        } 
    } 
} 

The above program establishes a connection to the MySQL database (STOREDB) using the provided URL, username, and password.
To load the JDBC Driver, first connect to the database (SQL) and fetch that link to establish the connection.
A Statement object is created to execute SQL queries.
The SELECT query is executed, and the results are stored in a ResultSet.
The program iterates through the result set and prints the values of the ID, Product, and Price columns.
If a SQLException occurs during the execution of the program, it is caught, and its details are printed.
The details that are printed is included in the output of methods of SQL Exception.
The finally block ensures that the connection is closed, whether an exception occurs or not.

Output:

All values of database prints

The output will be displayed based on the Java code written. This article only deals with handling SQL Exceptions in JDBC.

Reffered: https://www.geeksforgeeks.org

Java

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