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SQL Injection

  • A SQL Injection is an attack that consist of insertion ot injection of a SQL query via the input data from the client to the applicaiton.
  • SQL Injection is the code injection technique where the malicious SQL queries are inserted into an entry field and then executed by the application.

A successful SQL injection expert can easily exploit this vulnerability to gain access to the database. They can:

  • read sensitive data from database,
  • modify database data (insert, update, delete),
  • and even execute arbitrary SQL commands such as administrative operations (such as shut own the DBMS).

Types of SQL Injection

  1. Classic SQL Injection

    • Error based SQL Injection
      • It relies on error message thrown by the database server to obtain information about the structure of the database.
    • Union based SQL Injection
      • It forces UNION SQL operator to combine the results of one or more select statements into a single results which is then returned as a response.
  2. Blind SQL Injection

    • Boolean Based
      • It forces the application to return a different result depending on whether the query returns True or False result.

Prevention technique

  1. Prepared Statement (With parameterized query)

    • Paramaterized query force the developer to first refine all the SQL code and pass each parameter to query later.
    • This coding style allows the database to distinguish between code and data, regardless of what user input is supplied.
    • Prepared Statements ensure that an attacker is not able to change the intent of the query, even if SQL commands are inserted by an attackers.

    • Explaination: Can't be able to change the paramter later.

  2. Stored Procedure

    • Stored procedure are not always safe from SQL injection, however it tries to maintain certain standard of security.
    • Stored Procedure programming constructs have the same effect as the use of parameterized queries when incremented safely which is the norm for most stored procedure languages.
  3. White List Input Valdation

    • Whitelist validation is the practice of only accepting input that is known to be good.

      This can involve validating compliance with the expected type, length or size, numeric range, or other format standards before accepting the input for further processing.

  4. Escaping all user supplied input.

    • Escaping all user supplied input is the practice of escaping all user supplied input before passing it to the database.
    • While escaping, the input is converted to a format that is safe for the database to process.
    • The escaped input doesn't perform any operation on the database, even if the input contains malicious SQL commands.

Steps to Build JDBC Application using Prepared Statement


  1. Load and Register driver class.
  2. Establish Conection
    Connection con = Driver.Manager.getConnection( url , DbUsername , DbPassword );
  3. Creation of statement Object
    String INSERT_USERS_SQL = "INSERT INTO employee" +
            "  (id, first_name, last_name) VALUES " +
            " (?, ?, ?);"
    PreparedStatement preparedStatement = connection.prepareStatement(INSERT_USERS_SQL)
    preparedStatement.setInt(1, 1);
    preparedStatement.setString(2, "Arjun");
    preparedStatement.setString(3, "Adhikari");
  4. Send and Execute SQL Query
    Result rs = preparedStatement.executeUpdate();
  5. Process Result from ResultSet.
    If rs is result from Select Query, then we can use while loop to iterate through the result set.

    If rs is int (Non-Select Query).
    System.out.Println(rs + " rows affected"); 

  6. Close connection con.close();

Types of SQL Commands

  1. DDL(Data Definition Language)
  2. DQL(Data Query Language)
  3. DCL(Data Control Language)
  4. DML(Data Manipulation Language)
  5. (Data Administration)
  6. (Data Transaction)

What should I know as Java Developer ?

Select Queries (DQL)

Returns Result Set

Non-Select Queries (DML)

Returns Numeric Value

Methods to Execute SQL Query

  1. executeQuery()
  2. To execute SELECT queries.

    public result executeQuery(String sqlQuery) throws SQLException


    Result rs = st.executeQuery("SELECT * FROM employess");
        System.out.println(" ID : " rs.getInt(1));
  3. executeUpdate()

  4. Applicable for non-select operation(DML) public int executeUpdate(String sqlQuery) throws SQLException


    int affectedRow = st.executeUpdate("INSERT INTO employees(`id`) VALUES ('1')");

Returns the afftected rows.

  1. execute()
  2. For both SELECT and NON-SELECT operations.
  3. If you don't know SQL query until run-time, we can use execute().
  4. Return type => boolean
    🚀 True - SELECT Query
    🚀 false - Non-SELECT Query
    public boolean execute (String query) throws SQLException


    boolean b = st.execute(Dynamically provide SQLQuery);
    if(b == true) {
        ResultSet rs = st.getResultSet();
        int rowCount = st.getUpdateCount();