Adding new parameter to current URL using JSTL

问题:

My application allows user to change language in any given moment and that cause me some trouble. For example if user specify page by URL: /category/8?page=3 and then would try to change the language by ?language=en it will erase previous parameters and take him to first page.

How can I get a current URL and add another parameter to it? I'd like to achieve something like this: /category/8?page=3&language=en when current ULR is /category/8?page=3 and user tried to change a language.

I tried using ${pageContext.request.requestURL} but that's not what I look for as it returns jsp page.

回答1:

Here's a tag file I use. Save it as /WEB-INF/tags/replaceParam.tag:

<%@ tag pageEncoding="UTF-8" trimDirectiveWhitespaces="true" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ attribute name="name" required="true" type="java.lang.String" %>
<%@ attribute name="value" required="true" type="java.lang.String" %>

<c:url value="">

    <%-- 
      replaces or adds a param to a URL
      if $name in query then replace its value with $value. 
      copies existing 
    --%>

    <c:forEach items="${paramValues}" var="p">
        <c:choose>
            <c:when test="${p.key == name}">
                <c:param name="${name}" value="${value}"/>
            </c:when>
            <c:otherwise>
                <c:forEach items="${p.value}" var="val">
                    <c:param name="${p.key}" value="${val}"/>
                </c:forEach>
            </c:otherwise>
        </c:choose>
    </c:forEach>

    <%-- if $name not in query, then add --%>
    <c:if test="${empty param[name] }">
        <c:param name="${name}" value="${value}"/>
    </c:if>

</c:url>

Usage in another page (ex url is /category/9?page=3):

<%@ taglib prefix="my" tagdir="/WEB-INF/tags" %>

<my:replaceParam name='language' value='en' />

output is /category/8?page=3&language=en