java - servlet 中似乎没有正确捕获 id 值

Question

如果我在实现 servlet 中任意分配一个“id”值，它就可以工作；但是，如果我不这样做，它会正确地从抽象类继承 id 值，并跳过“if”语句以转发到“then”语句中提供的 url。是什么赋予了？可以判断“id”变量出了什么问题:

抽象 servlet 片段:

 protected Integer id = null;

 private void _doProcess(final HttpServletRequest request, final HttpServletResponse response)
        throws IOException, ServletException {
    try {
        response.setContentType("text/html");
        writer = response.getWriter();
        final String idString = request.getParameter("id");
        if(StringUtil.isNotEmptyStringTrimmed(idString)){
            try {
                id = Integer.parseInt(idString.trim());
            } catch (NumberFormatException e) {
                id = null;
            }
        }

        doProcess(request,response);

    } finally {
        id = null;
    }

    try {
        writer.close();
    } catch (Exception e) {
        // no-op
    }
}

实现 servlet 片段:

 public void doProcess(final HttpServletRequest request, final HttpServletResponse response)
        throws IOException, ServletException {

    // set page title
    final HttpSession session = request.getSession();
    session.setAttribute("pageTitle", "Training Project 5: Author");

    if (id == null){
        request.setAttribute("authorNamesList", printAuthorNames());
        request.getRequestDispatcher("authorList.jsp").include(request,response);
    }else{
        final Author author = BEAN_FACTORY.getMember(id);
        session.setAttribute("authorId",author.getId());
        session.setAttribute("name", author.getName());
        session.setAttribute("bio", author.getBio());
        session.setAttribute("picture",author.getPicture());
        session.setAttribute("bookTitles", printBookTitles(author.getId()));
        request.getRequestDispatcher("authorPage.jsp").include(request,response);
    }
}

当上面的 servlet 'else' 代码不在条件语句中时，下面的 jsp 代码将起作用:

 <div id="right">
   <table class="display" summary="Author Information">         
     <tr>
         <td><span class="brown">Author Id: <c:out value="${authorId}"/></span></td>
     </tr>
     <tr>
         <td><span class="brown">Name: <c:out value="${name}"/></span></td>
     </tr>
     <tr>
         <td><span class="brown">Bio: <c:out value="${bio}"/></span></td>
     </tr>
     <tr>
         <td>
             <p>
                 <span class="brown"><img src="<c:out value="${picture}"/>" alt= ""/></span>
             </p>
         </td>
     </tr>

Answer 1

除非 id 是类字段，否则您不会向我们展示所有代码。也不清楚你所说的“它不起作用”是什么意思。预期内容为空？你有异常(exception)吗？