Why Does My Java JDBC Code Throw \'Operation not allowed after ResultSet closed\'?

Exception: "Operation not allowed after ResultSet closed"

You are encountering a Java JDBC MySQL exception due to the following code:

Statement statement;

public void connect() {
    statement = connection.createStatement();
}

Explanation of the Error:

The statement instance is shared among all database operations. When you execute a SELECT query, it returns a ResultSet object. Once the ResultSet is closed (either explicitly or implicitly), any further operations on the statement will fail with the exception "Operation not allowed after ResultSet closed."

Solution:

To resolve this issue, create a new Statement object for each database operation, such as:

public ResultSet query(String query) throws SQLException {
    if (query.toLowerCase().startsWith("select")) {
        return connection.createStatement().executeQuery(query);
    } else {
        connection.createStatement().executeUpdate(query);
    }
    return null;
}

This ensures that a new Statement is used for each query, preventing the issue of closing the ResultSet from affecting subsequent operations.

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