No operations allowed after statement closed

Question

I am getting the Exception with the signature No operations allowed after statement closed. inside my Java code where I am trying to insert values into the database. The error signature says that my Statement object gets closed and I am trying to use it again in my code , but what I am struggling to understand is why is this happening as I am not closing any connections anywhere in my code.

Here is the Java code.

public class DataBaseAccessUtils {

    private static String jdbcUrl = 
            AppConfig.findMap("BXRequestTracker").get("jdbcUrl").toString();
    private static Connection connection = null;
    private static Statement statement = null;

    public static void insertHostname(String hostname, String rid, String fleet, String locale)
    {
        locale.toUpperCase();
        String sql = "UPDATE " + locale + "REQUESTTRACKER SET " + fleet 
                + "='" + hostname + "' WHERE RID='" + rid + "'";
        try {
            statement.execute(sql);
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public static Statement connectToDatabase() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(DataBaseAccessUtils.jdbcUrl);
            statement = connection.createStatement();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
        return statement;
    }

Also I have observed that the error does not come when there is a single threaded execution , it comes up when multiple threads are trying to update the database simultaneously.

Answer 1

Create a Utility class for connection management to manage it at single point in whole application.

Don't load the DataSource every time you need a new connection.

Sample code:

public class ConnectionUtil {

    private DataSource dataSource;

    private static ConnectionUtil instance = new ConnectionUtil();

    private ConnectionUtil() {
        try {
            Context initContext = new InitialContext();
            dataSource = (DataSource) initContext.lookup("JNDI_LOOKUP_NAME");
        } catch (NamingException e) {
            e.printStackTrace();
        }
    }

    public static ConnectionUtil getInstance() {
        return instance;
    }

    public Connection getConnection() throws SQLException {
        Connection connection = dataSource.getConnection();
        return connection;
    }

    public void close(Connection connection) throws SQLException {
        if (connection != null && !connection.isClosed()) {
            connection.close();
        }
        connection = null;
    }

}

Always close the connection and handle it in try-catch-finally

        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            conn = ConnectionUtil.getInstance().getConnection();

            ...
        } finally {
            if (rs != null) {
                rs.close();
            }
            if (stmt != null) {
                stmt.close();
            }
            if (conn != null) {
                ConnectionUtil.getInstance().close(conn);
            }
        }

Answer 2

statement is static, so it's shared among instances (and threads). One thread is probably trying to use that object after another one has closed it.

It is generally a bad idea to share database connections and statements between threads since JDBC does not require connections to be thread-safe.