Moving away from parameterized getters - jsf

Question

I'm planning to use an application scoped bean (as a common bean) to return a value of rowsPerPageTemplate attribute of <p:dataTable> like 5,10,15,20 - a comma-separated list of values indicating the page size of <p:dataTable>.
<p:dataTable var="row" value="#{viewScopedBean}"
lazy="true"
pageLinks="10"
rows="10"
rowsPerPageTemplate="#{pageTemplate.getCommonTemplate(viewScopedBean.rowCount)}">
...
</p:dataTable>
The pageTemplate bean :
#ManagedBean
#ApplicationScoped
public final class PageTemplate {
private static final int pageSize = 10;
public PageTemplate() {}
private static String getTemplate(int rowCount) {
if (pageSize >= rowCount) {
return String.valueOf(pageSize);
}
int sum = 0;
int pages = (int) Math.ceil(rowCount / (double) pageSize);
pages = pages >= 100 ? 100 : pages;
String templateString = "";
for (int i = 0; i < pages; i++) {
sum += pageSize;
templateString += sum + ",";
}
return new String(templateString.substring(0, templateString.length() - 1));
}
public String getCommonTemplate(int rowCount) {
return getTemplate(rowCount);
}
}
The bean and XHTML are self-explanatory. A parameterized method getCommonTemplate() is being referenced to by an EL expression #{} and consequently being invoked more than once.
Although the logic contained by the method is very cheap, it should not be the best practice to wrap this kind of logic around a getter method in a bean.
Can the code inside the getCommonTemplate() method be moved in a place where it is guaranteed to be executed only once (this should not the currently used bean for <p:dataTable> - ViewScopedBean, since the code contained by the getCommonTemplate() method should be shared across all beans that use <p:dataTable>)?

Answer 1

If the #{viewScopedBean.rowCount} is available during view build time (i.e. set in #PostConstruct), then you can use <c:set> to evaluate an EL expression once and store it in request, view, session or application scope (when no scope is specified, it defaults to none scoped and acts as "alias").
<c:set var="rowsPerPageTemplate" value="#{pageTemplate.getCommonTemplate(viewScopedBean.rowCount)}" scope="view" />
<p:dataTable ...
rowsPerPageTemplate="#{rowsPerPageTemplate}">
...
</p:dataTable>
However, if it's not available during view build time (which is apparently true in your case with LazyDataModel), then your best bet is to cache the results in #{pageTemplate}.
private static final Map<Integer, String> TEMPLATES_BY_ROW_COUNT = new HashMap<>();
public String getCommonTemplate(int rowCount) {
String template = TEMPLATES_BY_ROW_COUNT.get(rowCount);
if (template == null) {
template = getTemplate(rowCount);
TEMPLATES_BY_ROW_COUNT.put(rowCount, template);
}
return template;
}