Java - 当我尝试关闭数据库资源时无法访问语句

Question

每当我尝试关闭资源 rs.close() 或 stmt.close() 甚至 conn.close() 时，我都会收到一条错误消息，提示“无法访问语句”。奇怪的是，它在其他方法中也有效。也许我忘记了什么？

   public static boolean exists(int av) {

    try {

        Connection conn = DriverManager.getConnection(DBURL, DBUSER, DBPASS);
        Statement stmt = conn.createStatement();
        String query = "SELECT id FROM audiovisuals WHERE id='" + av + "' LIMIT 1";
        ResultSet rs = stmt.executeQuery(query);

        if(!rs.isBeforeFirst()) {
           return false;
        }
        else {
            return true;
        }

        rs.close();
        stmt.close();
        conn.close();

    } catch (SQLException e) {

        String error = "SQLException: " + e.getMessage() + "\nSQLState: " + e.getSQLState() + "\nVendorError: " + e.getErrorCode();
        return false;

    }

}

Answer 1

我在这里假设您收到了无法访问的语句，因为您将调用放在了 return 语句之后。您需要将关闭调用放在finally block 中。所以你的方法看起来像这样:

 Connection conn = null;
 Statement stmt = null;
 ResultSet rs = null;
 try {

    conn = DriverManager.getConnection(DBURL, DBUSER, DBPASS);
    stmt = conn.createStatement();
    String query = "SELECT id FROM audiovisuals WHERE id='" + av + "' LIMIT 1";
    rs = stmt.executeQuery(query);

    if(!rs.isBeforeFirst()) {
       return false;
    }
    else {
        return true;
    }

} catch (SQLException e) {

    String error = "SQLException: " + e.getMessage() + "\nSQLState: " + e.getSQLState() + "\nVendorError: " + e.getErrorCode();
    return false;

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