java重复堆栈问题

Question

重复堆栈问题
运行报错如下：

前端jsp代码如下

<form action="FlightSearchServlet" method="post">
    <div>
        <label for="airline">Airline：</label>
        <input type="text" id="airline" name="airline">
    </div>
    <div>
        <label for="start_city">Start From：</label>
        <input type="text" id="start_city" name="start_city">
    </div>
    <div>
        <label for="end_city">To：</label>
        <input type="text" id="end_city" name="end_city">
    </div>
    <div>
        <button type="submit">Search</button>
    </div>
</form>
<div id="searchResult">
    <%-- Here to show the searchResult --%>
    <c:forEach items="${flights}" var="flight">
        <div class="flight">
            <div>Airline: ${flights.Airline}</div>
            <div>Flight Number：${flight.FlightNo}</div>
            <div>Departure：${flight.DepartureTime}</div>
            <div>Arrival：${flight.ArrivalTime}</div>
            <div>Start From：${flight.StartCity}</div>
            <div>To：${flight.EndCity}</div>
        </div>
    </c:forEach>
</div>

servlet代码如下

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    String airline = request.getParameter("airline");
    String StartCity = request.getParameter("start_city");
    String EndCity = request.getParameter("end_city");
    List<Flight> flights = FlightDao.search(airline, StartCity , EndCity);
    request.setAttribute("flights", flights);
    RequestDispatcher dispatcher = request.getRequestDispatcher("FlightSearchServlet");
    dispatcher.forward(request,response);
    response.setHeader("refresh","URL=FlightSearchServlet");

}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.getRequestDispatcher("/WEB-INF/flightQuery.jsp").forward(req,resp);
}

如果把这句代码删了就没问题，但是我不知道为什么这句会重复执行并且报堆栈错误

RequestDispatcher dispatcher = request.getRequestDispatcher("FlightSearchServlet");
    dispatcher.forward(request,response);

Answer 1

以下内容部分参考ChatGPT模型：

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问题的原因是在servlet中使用了RequestDispatcher来转发请求，但是转发的目标是当前的servlet，而不是jsp页面。所以在转发后又会再次执行servlet，导致重复执行。

解决方法是将转发的目标改为jsp页面，即修改以下代码：

RequestDispatcher dispatcher = request.getRequestDispatcher("FlightSearchServlet");
dispatcher.forward(request,response);
response.setHeader("refresh","URL=FlightSearchServlet");

改为：

RequestDispatcher dispatcher = request.getRequestDispatcher("/WEB-INF/flightQuery.jsp");
dispatcher.forward(request,response);

这样就可以避免重复执行了。

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