Velocity MethodInvocationExceptions not properly reported [SPR-6246]

[spring-projects-issues]

Will Glass-Husain opened SPR-6246 and commented

My velocity properties include the following
<entry key="runtime.references.strict" value="true" />

(I'm using Velocity 1.6.2)

This will throw a MethodInvocationException (runtime exception, as of Velocity 1.5) if a reference is incorrect.

When I have a bad reference in my page (example: $!user.firstName when $user is not available in the context), I get a runtime error reported in my browser. (This is good). The problem is that the Velocity error is not wrapped correctly due to an apparent bug in NestedServletException which does not wrap the cause.

The actual error reported:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalStateException: Can't overwrite cause
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:583)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:501)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

...

com.forio.servlet.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:37)

root cause

java.lang.IllegalStateException: Can't overwrite cause
java.lang.Throwable.initCause(Throwable.java:320)
org.springframework.web.util.NestedServletException.<init>(NestedServletException.java:65)
org.springframework.web.servlet.view.velocity.VelocityView.mergeTemplate(VelocityView.java:556)
org.springframework.web.servlet.view.velocity.VelocityLayoutView.doRender(VelocityLayoutView.java:162)

root cause

org.springframework.web.servlet.view.AbstractTemplateView.renderMergedOutputModel(AbstractTemplateView.java:174)
org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:257)
org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1183)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:902)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:807)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:571)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:501)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

This is due to the following code in VelocityView:

protected void mergeTemplate(
Template template, Context context, HttpServletResponse response) throws Exception {

try {
template.merge(context, response.getWriter());
}
catch (MethodInvocationException ex) {
throw new NestedServletException(
"Method invocation failed during rendering of Velocity view with name '" +
getBeanName() + "': " + ex.getMessage() + "; reference [" + ex.getReferenceName() +
"], method '" + ex.getMethodName() + "'",
ex.getWrappedThrowable());
}
}

specifically failing on the "initCause" line in NestedServletException:

public NestedServletException(String msg, Throwable cause) {
super(msg, cause);
// Set JDK 1.4 exception chain cause if not done by ServletException class already
// (this differs between Servlet API versions).
if (getCause() == null) {
initCause(cause);
}
}

I have solved this by creating a CustomVelocityView which just lets the MethodException pass through.

protected void mergeTemplate(Template template, Context context, HttpServletResponse response) throws
{
template.merge(context, response.getWriter());
}

Then I get the much more useful message:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.apache.velocity.exception.MethodInvocationException: Variable $user has not been set at layout/slide_login.vm[line 13, column 117]
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:583)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:501)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

---

Affects: 2.5 final

Referenced from: commits 0e85c66, bce723d, c63cdb2

[spring-projects-issues]

Dave Syer commented

Which JDK are you using? It works for me as it is with Sun JDK 1.6, and the message is slightly more friendly because it gives you the bean name as well.

[spring-projects-issues]

Will Glass-Husain commented

This is Sun JDK 1.5, running in debug mode with MyEclipse. NestedServletException appears to have issues.

[spring-projects-issues]

Dave Syer commented

Actually it looks like it might depebd on the version of the servlet API you have as well. What is that?

[spring-projects-issues]

Dave Syer commented

OK, I fixed it. It does depend on the Servlet API a bit (exception is created differently on 2.5 and 2.3). It also depends on the Velocity version - 1.6.2 sometimes pops null into the wrapped throwable of the MethodInvocationException, but I couldn't find a way to make 1.5 do that. Fix is to check the wrapped throwable for null before trying to initCause() on Throwable in VelocityView.