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
.
package org.kodejava.jdbc;
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 URL = "jdbc:mysql://localhost/kodejava";
private static final String USERNAME = "root";
private static final String PASSWORD = "";
public static void main(String[] args) {
try (Connection connection =
DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
Statement statement = connection.createStatement();
ResultSet resultSet = statement.executeQuery(
"SELECT isbn, title, published_year, price FROM books");
// The ResultSetMetaData is where all metadata related
// information for a result set is stored.
ResultSetMetaData metadata = resultSet.getMetaData();
int nullable = metadata.isNullable(1);
// Check the nullable status of a column (`isbn`)
if (nullable == ResultSetMetaData.columnNullable) {
System.out.println("`isbn` can have a null value.");
} else if (nullable == ResultSetMetaData.columnNoNulls) {
System.out.println("`isbn` does not allowed to have a " +
"null value.");
} else if (nullable == ResultSetMetaData.columnNullableUnknown) {
System.out.println("Nullability unknown.");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
Maven dependencies
<dependency>
<groupId>com.mysql</groupId>
<artifactId>mysql-connector-j</artifactId>
<version>8.0.32</version>
</dependency>
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