ResultSet Handling

✅ What is ResultSet?

In Java, when you use JDBC to connect to a database and run a SELECT query, the data returned by that query is stored in a special object called ResultSet.

👉 ResultSet is like a temporary table in Java that holds rows of data returned from the database.

🔄 How Does ResultSet Work?

When you run a SQL query using Statement or PreparedStatement, you write:

ResultSet rs = statement.executeQuery("SELECT * FROM students");

This line:

• Runs the query: SELECT * FROM students

• Stores the results (rows) inside a ResultSet object called rs

Imagine your students table looks like this:

Now all this data is temporarily held in memory inside rs.

🧭 ResultSet Uses a Cursor

• A cursor is a pointer that moves row by row inside the ResultSet.

• Initially, it sits before the first row.

• You must use rs.next() to move it to the first row.

while (rs.next()) {
    // now pointing to one row
}

Each time you call rs.next():

• It moves the cursor to the next row.

• Returns true if a row is available.

• Returns false when there are no more rows.

🧱 How to Get Column Values

Once the cursor points to a row, you can use getter methods to get the values of that row's columns.

Example:

int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");

You can also use column indexes (starting from 1), but names are safer and easier to read.

int id = rs.getInt(1); // 1st column

🔁 Full Code Example

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/testdb", "root", "password");
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT id, name, age FROM students");

while (rs.next()) {
    int id = rs.getInt("id");
    String name = rs.getString("name");
    int age = rs.getInt("age");

    System.out.println(id + " " + name + " " + age);
}

1  Alice   20  
2  Bob     21  
3  Charlie 22

⚙️ Common ResultSet Methods

🛡️ Best Practices

• ✅ Always close ResultSet after you're done: rs.close();

• ✅ Use PreparedStatement instead of plain Statement for security

• ✅ Handle exceptions using try-catch

• ❌ Don’t forget to close your Connection and Statement too.

🧠 Summary