bottomrule not working in a self-made environment

Question

I have this environment for consistent tables in my LaTeX documents:

\newenvironment{defaultTable}[2] {
 \@float{table}[h]
 \noindent
 \tabularx{\textwidth}{#1}
 \specialrule{0.5pt}{10pt}{0pt}
 \rowcolor[gray]{.9}
 \gdef\mycaption{#2}
} {
 \bottomrule
 \endtabularx
 \emph{\caption{\mycaption}}
 \end@float
}

Unfortunately, the line with \bottomrule leads to this error, which i don't understand:

! Misplaced \noalign. \bottomrule
->\noalign 
               {\ifnum 0=`}\fi \@aboverulesep =\aboverulesep
\global... l.27 \end{defaultTable}

When I use it inside the environment it works though

\begin{defaultTable}{X X}{Blablah Table}
(..)
\bottomrule
\end{defaultTable}

What am I doing wrong?

Answer 1

This error can be avoided by using the environ package. For example, here's a working modifiation of your code using \NewEnviron of that package:

\documentclass{article}
\usepackage{tabularx} 
\usepackage{booktabs} 
\usepackage[table]{xcolor}
\usepackage{environ}
\makeatletter
\NewEnviron{defaultTable}[2] {
 \@float{table}[h]
 \noindent
 \tabularx{\textwidth}{#1}
 \specialrule{0.5pt}{10pt}{0pt}
 \rowcolor[gray]{.9}
 \gdef\mycaption{#2}
 \BODY
 \bottomrule}[
 \endtabularx
 \emph{\caption{\mycaption}}
 \end@float
]
\makeatother
\begin{document}

\begin{defaultTable}{X X}{Test Table}
1 & 2 \\
\end{defaultTable}

\end{document}

Note: either end also the last row by \\ (or do it after \BODY). (In the original environment definition \\ before \bottomrule doesn't help.)