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In this example we'll show how to use ResultSetMetaData.isNullable() method to know if a column can be null or not. This method return an integer which values defined in the constants of ResultSetMetaData.columnNullable, ResultSetMetaData.columnNoNulls and ResultSetMetaData.columnNullableUnknown.


import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;

public class IsNullableExample {
private static final String DRIVER = "com.mysql.jdbc.Driver";
private static final String URL = "jdbc:mysql://localhost/testdb";
private static final String USERNAME = "root";
private static final String PASSWORD = "";

public static void main(String[] args) throws Exception {
Connection connection = null;
try {
Class.forName(DRIVER);
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);

Statement statement = connection.createStatement();
ResultSet resultSet = statement.executeQuery("SELECT id, username FROM users");

//
// The ResultSetMetaData is where all metadata related information
// for a result set is stored.
//
ResultSetMetaData metadata = resultSet.getMetaData();
int nullability = metadata.isNullable(1);

//
// Check the nullability status of a column (ID)
//
if (nullability == ResultSetMetaData.columnNullable) {
System.out.println("Columns ID can have a null value");
} else if (nullability == ResultSetMetaData.columnNoNulls) {
System.out.println("Columns ID does not allowed to have a null value");
} else if (nullability == ResultSetMetaData.columnNullableUnknown) {
System.out.println("Nullability unknown");
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
connection.close();
}
}
}