Request Parameters in JSTL

Display All Request Parameters in JSTL

The following piece of JSTL code displays all request parameters on the page,
except for check-boxes and radio-buttons. They require the use of the paramValues implicit object.

<c:forEach items="${param}" var="par">
        Parameter Name/Value : <c:out value="${par.key} - ${par.value}"/>
</c:forEach>

To display session and request objects, use the following code:

<c:forEach items="${sessionScope}" var="par">
        Session object name/value : <c:out value="${par.key} - ${par.value}"/>
</c:forEach>

<c:forEach items="${requestScope}" var="par">
        Request object name/value : <c:out value="${par.key} - ${par.value}"/>
</c:forEach>

Other implicit objects include pageScope, applicationScope, header, headerValues, initParam, cookie and pageContext.

Sorting Request Parameters

A java TreeMap class that implements
SortedMap interface allows us to construct a sorted Map.
To sort request parameters, or any other implicit objects that implement the Map interface, I built a small bean class. Here is the source code listing:

    package beans;
    import java.util.Map;
    import java.util.TreeMap;

    public class SortMap{
    private Map map;

    public Map getMap() {
        return map;
    }
    public void setMap(Map map) {
        this.map = new TreeMap(map);
    }
}

The setMap method of the bean constructs a TreeMap object from the Map argument.

Now, it's easy to pass the map of request parameters to the new bean and obtain the key-value pairs from it:

 <jsp:useBean id="sorter" class= "beans.SortMap">
    <c:set target= "${sorter}" property="map" value="${param}"/>
</jsp:useBean>

<c:forEach items="${sorter.map}" var="par">
        Parameter name/value : <c:out value="${par.key} -  ${par.value}"/>
</c:forEach>

JSTL Pagination

The following code can be used to paginate database query results using JSTL.

The select statement results are stored in the queryResults variable. Here is the paginator code:

<c:set var="totalCount" scope="session" value="${queryResults.rowCount}"/>
    <c:set var="perPage" scope="session" value="20"/>
    <c:set var="totalPages" scope="session" value="${totalCount/perPage}"/>

    <c:set var="pageIndex" scope="session" value="${param.start/perPage+1}"/>

   <c:if test="${!empty param.start && param.start >(perPage-1) && param.start !=0 }">
          <a href="?start=<c:out value="${param.start - perPage}"/>">Prev </a>

    </c:if>

   <c:forEach
        var="boundaryStart"
        varStatus="status"
        begin="0"
        end="${totalCount - 1}"
        step="${perPage}">
        <c:choose>
            <c:when test="${status.count>0 && status.count != pageIndex}">
                             <a href="?start=<c:out value='${boundaryStart}'/>">

                                <c:out value="${status.count}"/> |
                            </a>
            </c:when>
        <c:otherwise>
                <c:out value="${status.count}"/> |
        </c:otherwise>

        </c:choose>
    </c:forEach>

    <c:if test="${empty param.start || param.start<(totalCount-perPage)}">
          <a href="?start=<c:out value="${param.start + perPage}"/>">Next </a>

    </c:if>

The code makes heavy use of the count property of the varStatus attribute.
This attribute keeps count of the current round of the iteration.