Why am I getting \"java.sql.SQLException: Operation not allowed after ResultSet closed\" when closing my MySQL Connection in Java?

Issue with Closing MySQL Connection in Java

Problem:

An exception, "java.sql.SQLException: Operation not allowed after ResultSet closed," arises when closing a connection to a MySQL database, indicating an issue with ResultSet handling after connection termination.

Code Excerpt:

<code class="java">public static ResultSet sqlquery(String query) {
    ResultSet rs = null;
    Connection connection = null;
    Statement st = null;
    try {
        // Establish connection and execute query
    } finally {
        // Attempt to close connection and ResultSet objects
    }
    return rs;
}</code>

Explanation:

JDBC does not retrieve all query results to the ResultSet immediately. Instead, it provides an object that facilitates result retrieval. However, this object becomes invalid upon connection closure.

Solution:

To avoid this issue, the code should create an object to store the query results before closing the connection. This involves using a RowMapper to map ResultSet rows to objects and populate a collection that is returned as the method's result.

Resolved Code:

<code class="java">public static <T> List<T> sqlquery(String query, RowMapper<T> rowMapper) {
    Connection connection = null;
    Statement st = null;
    ResultSet rs = null;
    try {
        // Establish connection and execute query
    } finally {
        // Handle possible exceptions gracefully
    }
    while (rs.next()) {
        list.add(rowMapper.mapRow(rs));
    }
    return list;
}</code>

Additional Notes:

• Using a RowMapper makes the code more reusable and versatile for handling various data types.
• Consider parameterizing queries to prevent SQL injection attacks.
• Spring-jdbc provides a robust solution for handling JDBC operations effortlessly.

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