I have a problem with a JSF project.
- GlassFish Server 3.1.2
- Mojarra 2.1.6
I’m trying to show a table containing the request header fields. Therefor I’ve written this managed bean:
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;
import javax.faces.context.FacesContext;
import javax.servlet.http.HttpServletRequest;
@ManagedBean
@RequestScoped
public class RequestHeader extends LinkedHashMap<String, List<String>> {
private List<String> keys;
@PostConstruct
public void init() {
final HttpServletRequest request = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest();
keys = Collections.list(request.getHeaderNames());
for (final String key : keys) {
final List<String> value = Collections.list(request.getHeaders(key));
final List<String> oldValue = get(key);
if (oldValue == null) {
put(key, value);
} else {
oldValue.addAll(value);
}
}
}
public List<String> keys() {
return keys;
}
}
This is my JSF page:
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:c="http://java.sun.com/jsp/jstl/core">
<h:head>
<title>HTTP request headers</title>
</h:head>
<h:body>
<h:dataTable value="#{requestHeader.keys()}" var="k" border="1">
<f:facet name="header">HTTP request headers</f:facet>
<h:column>
<f:facet name="header">Key</f:facet>
<h:outputText value="#{k}" />
</h:column>
<h:column>
<f:facet name="header">Value</f:facet>
<!-- This forEach seems to be ignored. -->
<c:forEach items="#{requestHeader[k]}" var="v">
<h:outputText value="#{v}" /><br />
</c:forEach>
</h:column>
</h:dataTable>
</h:body>
</html>
Instead of having the values in the second column of the table, the cells are empty:
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>HTTP request headers</title>
</head>
<body>
<table border="1">
<thead>
<tr><th colspan="2" scope="colgroup">HTTP request headers</th></tr>
<tr>
<th scope="col">Key</th>
<th scope="col">Value</th>
</tr>
</thead>
<tbody>
<tr>
<td>user-agent</td>
<td></td>
</tr>
<tr>
<td>host</td>
<td></td>
</tr>
<tr>
<td>accept</td>
<td></td>
</tr>
<tr>
<td>accept-language</td>
<td></td>
</tr>
<tr>
<td>accept-encoding</td>
<td></td>
</tr>
<tr>
<td>cache-control</td>
<td></td>
</tr>
<tr>
<td>connection</td>
<td></td>
</tr>
</tbody>
</table>
</body>
</html>
I did several tests. <h:outputText value="#{requestHeader[k]}" /> and c:forEach on other lists will work.
Why won’t it work this way?
Taghandlers like JSTL tags runs during view build time, while the UI components like JSF
<h:xxx>tags runs during view render time. So they doesn’t run in sync as you’d expect from the coding. In your code, at the moment the<c:forEach>runs, the<h:dataTable>hasn’t run at all and thus itsvarattribute is not been set and thus#{k}is not available when the<c:forEach>runs and thus it retrieves an empty/non-existent collection.You need an UI component instead if you want a nested iteration inside another UI component. One of them is Facelets
<ui:repeat>.In case you’re still on JSF 1.x, use Tomahawk’s
<t:dataList>instead, or simply another<h:dataTable>.See also:
Unrelated to the concrete problem: you don’t need a backing bean here at all. All request headers are already as a
Mapavailable by the implicit EL object#{header}.All with all, your approach can be simplified as follows, without any backing bean:
See also: