An Ajax4JSF bug

The other day I had this exception:

15:16:47,296 ERROR [[Faces Servlet]] Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
 at org.ajax4jsf.org.w3c.tidy.Node.trimInitialSpace(Node.java:946)
 at org.ajax4jsf.org.w3c.tidy.Node.trimSpaces(Node.java:1012)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl$ParseInline.parse(ParserImpl.java:1125)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl.parseTag(ParserImpl.java:203)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl$ParseRowGroup.parse(ParserImpl.java:2809)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl.parseTag(ParserImpl.java:203)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl$ParseTableTag.parse(ParserImpl.java:2629)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl.parseTag(ParserImpl.java:203)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl$ParseInline.parse(ParserImpl.java:1587)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl.parseTag(ParserImpl.java:203)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl$ParseBody.parse(ParserImpl.java:978)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl.parseTag(ParserImpl.java:203)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl$ParseHTML.parse(ParserImpl.java:486)
 at org.ajax4jsf.org.w3c.tidy.ParserImpl.parseDocument(ParserImpl.java:3409)
 at org.ajax4jsf.org.w3c.tidy.Tidy.parse(Tidy.java:363)
 at org.ajax4jsf.org.w3c.tidy.Tidy.parse(Tidy.java:261)
 at org.ajax4jsf.org.w3c.tidy.Tidy.parseDOM(Tidy.java:604)
 at org.ajax4jsf.webapp.tidy.TidyParser.parseHtmlByTidy(TidyParser.java:182)
 at org.ajax4jsf.webapp.tidy.TidyParser.parseHtml(TidyParser.java:265)
 at org.ajax4jsf.webapp.FilterServletResponseWrapper.parseContent(FilterServletResponseWrapper.java:594)
 at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:367)
 at org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290)
 at org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:388)
 at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:515)
 at org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:56)
 at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
 at org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:60)
 at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
 at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
 at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
 at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
 at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
 at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
 at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
 at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
 at java.lang.Thread.run(Unknown Source)

I was using JSF 1.2_13-b01-FCS with RichFaces 3.3.2.SR1. The problem turned out to be with the generated HTML content which Ajax4JSF was sending as a response. We were using a4j:repeat to generate a HTML table, and one row of this table was shown using an AJAX request. However, the default rendering behaviour of a4j:outputPanel is the using of some element (span or div, I don't remember which is the actual default), and the html tidy code above had problems with handling those elements between table rows. You just have to define layout="none" for the outputPanel, then it works fine.

The bug is since then reported: https://jira.jboss.org/jira/browse/AJSF-158

Using action bindings in facelets template components

When creating Facelets template components, you might face difficulties when trying to pass action bindings as component or template parameters. The problem is that the method binding gets evaluated at the place it is used, so if you write:

  <my:actionComponent action="#{backing.method}"/>

the method is invoked and the result value will be available for named 'action' inside the template. To change this behaviour, I created a method in a backing named 'ELEvaluator':

 public void evaluateMethodBinding(String el) {
  ValueExpression ve = FacesContext.getCurrentInstance().getApplication().getExpressionFactory()
   .createValueExpression(FacesContext.getCurrentInstance().getELContext(), "#{" + el + "}", Object.class);
  ve.getValue(FacesContext.getCurrentInstance().getELContext());
 }

Inside the template component I use:

    action="#{ELEvaluator.evaluateMethodBinding(action)}" 

And when passing the action parameter, I have to pass a normal String, without the '#{}' stuff:

 <my:actionComponent [...] action="backing.method(params)"/>

See also: http://seamframework.org/Community/FaceletsParamForActionMethod