Question

使用JSP和servlet以及NetBeans IDE。

我通过href传递一个参数，如下所示。

<a href="coursematerial.jsp?param1=${row.COURSEID}"><c:out value="${row.COURSEID}"/>

现在在下一个jsp中，我想保存我传递的参数。我可以这样做并将保存的参数发送到表单中的隐藏输入吗？我尝试使用

<input type="hidden" name="courseid" value=<%= request.getParameter("param1")%> >

但由于在填充表单之前还有另一个href，因此将该值检索为null。

有没有办法将所需参数保存为会话（没有脚本但使用JSTL）并在不将其作为href传递的情况下进行检索？

Answer 1

我不知道是否可以使用jstl。但是你可以使用闪存范围。该属性将根据您的要求仍然存在下一个jsp。使用此简单代码实现闪存范围。

例如，要向flash作用域添加消息，只需使用常规语法添加请求作用域属性，然后让fiter处理它：

request.setAttribute("flash.message", "Here is the news...");

然后可以使用EL或scriptlet语法在重定向目标JSP中访问上述属性（省略'flash。'前缀）：

${message}
or
<%= request.getAttribute("message") %>

以下是过滤器的代码：

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

/**
 * Ensures that any request parameters whose names start
 * with 'flash.' are available for the next request too. 
 */
public class FlashScopeFilter implements Filter {

    private static final String FLASH_SESSION_KEY = "FLASH_SESSION_KEY";

    @SuppressWarnings("unchecked")
    public void doFilter(ServletRequest request, ServletResponse response, 
                    FilterChain chain) throws IOException, ServletException {

        //reinstate any flash scoped params from the users session 
        //and clear the session
        if (request instanceof HttpServletRequest) {
            HttpServletRequest httpRequest = (HttpServletRequest) request;
            HttpSession session = httpRequest.getSession(false);
            if (session != null) {
                Map<String, Object> flashParams = (Map<String, Object>) 
                                    session.getAttribute(FLASH_SESSION_KEY);
                if (flashParams != null) {
                    for (Map.Entry<String, Object> flashEntry : flashParams.entrySet()) {
                        request.setAttribute(flashEntry.getKey(), flashEntry.getValue());
                    }
                    session.removeAttribute(FLASH_SESSION_KEY);
                }
            }
        }

        //process the chain
        chain.doFilter(request, response);

        //store any flash scoped params in the user's session for the 
        //next request
        if (request instanceof HttpServletRequest) {
            HttpServletRequest httpRequest = (HttpServletRequest) request;
            Map<String, Object> flashParams = new HashMap();
            Enumeration e = httpRequest.getAttributeNames();
            while (e.hasMoreElements()) {
                String paramName = (String) e.nextElement();
                if (paramName.startsWith("flash.")) {
                    Object value = request.getAttribute(paramName);
                    paramName = paramName.substring(6, paramName.length());
                    flashParams.put(paramName, value);
                }
            }
            if (flashParams.size() > 0) {
                HttpSession session = httpRequest.getSession(false);
                session.setAttribute(FLASH_SESSION_KEY, flashParams);
            }
        }
    }

    public void init(FilterConfig filterConfig) throws ServletException {
        //no-op
    }

    public void destroy() {
        //no-op
    }
}

http://smartkey.co.uk/development/implementing-flash-scope-in-java-web-applications/

JSTL和href传递参数

1 个答案: