Rendering a template on a background thread causes NPE

[donald-jackson]

In previous versions of Grails it was possible to generate templates on a background thread (things like emails, etc) for async generation. I'm not exactly sure which version this broke in.

A simple method like this:

    String renderTemplate(String key, String content, Map model) {
        Template template = groovyPagesTemplateEngine.createTemplate(content, key)
        Writable renderedTemplate = template.make(model);
        StringWriter stringWriter = new StringWriter();
        renderedTemplate.writeTo(stringWriter);
        return stringWriter.toString();
    }

Example call:

String template = renderTemplate("myTemplateId", '<h3>Hello, ${user} </h3>', [user: "Grails User"]);

Doing this on a background thread, causes the exception below. Looks like it relates to the WebOutputContext - however as you can see in my template generation this should have no dependency on a web context.

Steps to Reproduce

1. Clone https://github.com/donald-jackson/grails-template-error3211.git
2. Run-app
3. Visit http://localhost:8080/example/background
4. Visit http://localhost:8080/example/foreground - same code but on foreground thread, renders out the template.

Expected Behaviour

No exceptions, a template is rendered in the background

Actual Behaviour

java.lang.NullPointerException: null
        at org.grails.web.taglib.encoder.WebOutputContextLookup$WebOutputContext.getBinding(WebOutputContextLookup.java:89)
        at org.grails.gsp.GroovyPageWritable.doWriteTo(GroovyPageWritable.java:112)
        at org.grails.gsp.GroovyPageWritable.writeTo(GroovyPageWritable.java:82)
        at groovy.lang.Writable$writeTo$0.call(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
        at grails.template.demo.TemplateService.$tt__renderTemplate(TemplateService.groovy:20)
        at grails.template.demo.TemplateService$_renderTemplate_closure1.doCall(TemplateService.groovy)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springsource.loaded.ri.ReflectiveInterceptor.jlrMethodInvoke(ReflectiveInterceptor.java:1426)
        at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
        at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
        at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:294)
        at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
        at groovy.lang.Closure.call(Closure.java:414)
        at groovy.lang.Closure.call(Closure.java:430)
        at grails.transaction.GrailsTransactionTemplate$2.doInTransaction(GrailsTransactionTemplate.groovy:96)
        at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133)
        at grails.transaction.GrailsTransactionTemplate.execute(GrailsTransactionTemplate.groovy:93)
        at grails.template.demo.TemplateService.renderTemplate(TemplateService.groovy)
        at grails.template.demo.TemplateService$renderTemplate$0.callCurrent(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:52)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:154)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:182)
        at grails.template.demo.TemplateService.$tt__backgroundTask(TemplateService.groovy:26)
        at grails.template.demo.TemplateService$_backgroundTask_closure2.doCall(TemplateService.groovy)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springsource.loaded.ri.ReflectiveInterceptor.jlrMethodInvoke(ReflectiveInterceptor.java:1426)
        at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
        at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
        at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:294)
        at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
        at groovy.lang.Closure.call(Closure.java:414)
        at groovy.lang.Closure.call(Closure.java:430)
        at grails.transaction.GrailsTransactionTemplate$2.doInTransaction(GrailsTransactionTemplate.groovy:96)
        at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133)
        at grails.transaction.GrailsTransactionTemplate.execute(GrailsTransactionTemplate.groovy:93)
        at grails.template.demo.TemplateService.backgroundTask(TemplateService.groovy)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springsource.loaded.ri.ReflectiveInterceptor.jlrMethodInvoke(ReflectiveInterceptor.java:1426)
        at org.springframework.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:216)
        at org.springframework.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:201)
        at reactor.spring.context.config.ConsumerBeanAutoConfiguration$Invoker.apply(ConsumerBeanAutoConfiguration.java:333)
        at reactor.spring.context.config.ConsumerBeanAutoConfiguration$ServiceConsumer.accept(ConsumerBeanAutoConfiguration.java:297)
        at reactor.spring.context.config.ConsumerBeanAutoConfiguration$ServiceConsumer.accept(ConsumerBeanAutoConfiguration.java:284)
        at reactor.bus.EventBus$3.accept(EventBus.java:317)
        at reactor.bus.EventBus$3.accept(EventBus.java:310)
        at reactor.bus.routing.ConsumerFilteringRouter.route(ConsumerFilteringRouter.java:72)
        at reactor.bus.EventBus.accept(EventBus.java:591)
        at reactor.bus.EventBus.accept(EventBus.java:63)
        at reactor.core.dispatch.AbstractLifecycleDispatcher.route(AbstractLifecycleDispatcher.java:160)
        at reactor.core.dispatch.MultiThreadDispatcher$MultiThreadTask.run(MultiThreadDispatcher.java:74)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: reactor.core.support.Exceptions$ValueCause: Exception while signaling value: reactor.bus.Event.class : Event{id=null, headers=null, replyTo=null, key=background.task, data={}}
        at reactor.core.support.Exceptions.addValueAsLastCause(Exceptions.java:127)
        at reactor.bus.routing.ConsumerFilteringRouter.route(ConsumerFilteringRouter.java:77)
        ... 7 common frames omitted

Environment Information

• Operating System: Mac OS X 10.12
• Grails Version: 3.2.11
• JDK Version: 1.8.0_111

Example Application

• https://github.com/donald-jackson/grails-template-error3211.git

[sdelamo]

This issue is not present in Grails 3.3. Here is a sample repository which shows that the issue is fixed there:

https://github.com/grails-core-issues-forks/10789

Note: Grails 3.3 has decoupled GSP ( http://gsp.grails.rog - https://github.com/grails/grails-gsp )