Struts2接收json参数,json参数是以流的形式在报文体中，所以不能直接获取参数，要从流中读取，如下：

public String getRequestBody(){
        ActionContext ctx = ActionContext.getContext();
        HttpServletRequest request = (HttpServletRequest)ctx.get(ServletActionContext.HTTP_REQUEST);   
        InputStream inputStream;
        String str = "";
        try {
            inputStream = request.getInputStream();
            String strMessage = "";
            BufferedReader reader;
            reader = new BufferedReader(new InputStreamReader(inputStream,"utf-8"));
            while ((strMessage = reader.readLine()) != null) {
                str += strMessage;
            }
            reader.close();
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }