Description:

Using the AssetRenderer to display Journal/Web Content in a custom portlet results in a null pointer when the Web Content has an associated Template.

This is because the template parser com.liferay.portal.kernel.templateparser.BaseTransformer attempts to lookup the Template Parser with the following code:

Line 147 of BaseTransformer.java
templateParser =(TemplateParser)InstanceFactory.newInstance(templateParserClassName);

This results in the InstanceFactory getting the class loader from the current thread:
Line 47 of InstanceFactory.java
Thread currentThread = Thread.currentThread();

The class loader for the current thread will be the class loader for the custom portlet, thus the expected classes will not be available and an exception:
com.liferay.portal.kernel.templateparser.TransformException:
java.lang.ClassNotFoundException: com.liferay.portlet.journal.util.VelocityTemplateParser

will be generated.

Fortunately the InstanceFactory.newInstance(..) call can be passed a class loader, so modification of
Line 147 of BaseTransformer.java to:

templateParser=(TemplateParser)InstanceFactory.newInstance(
PortalClassLoaderUtil.getClassLoader(),
templateParserClassName);

i.e. passing in the PortalClassLoader fixes the issue.

Step to reproduce:

1. Create a structure and template for web content.
2. Add an instance of web content using the new structure and template.
3. Write a custom portlet that attempt to display the data using the AssetRenderer in FULL, i.e. AssetRenderer.TEMPLATE_FULL_CONTENT

example code:

<%
AssetRendererFactory af = AssetRendererFactoryRegistryUtil.getAssetRendererFactoryByClassName( JournalArticle.class.getName());

AssetRenderer assetRenderer=af.getAssetRenderer('articleId');
String renderPath=assetRenderer.render(portletRequest, portletResponse, AssetRenderer.TEMPLATE_FULL_CONTENT);
String renderPortletId = AssetRendererFactoryRegistryUtil.getAssetRendererFactoryByClassName( JournalArticle.class.getName()).getPortletId()
<liferay-util:include page="<%=renderPath%>" portletId="<%=renderPortletId %>" />

4. View custom portlet (sometimes it will work on the first view)
5. Refresh page - null pointer will occur in "html\portlet\journal\asset\full_content.jsp" at line 43 as the articleDisplay object is null due to the above exception.