NPE PropertyOrFieldReference$AccessorLValue due to concurrency issue [SPR-14850]

[spring-projects-issues]

Thijs Vonk opened SPR-14850 and commented

We're seeing 'strange' NullpointerExceptions while using ThymeLeaf and having heavy load on the machine.

2016-10-26 15:17:23,200 [trace=7cd2c0bf5bcb66db,span=7cd2c0bf5bcb66db] ERROR       TemplateEngine:1085 - [THYMELEAF][http-nio-8080-exec-12] Exception processing template "sections/default": Exception evaluating SpringEL expression: "article.detailUrl" (includes/ankeilers/standard:5)
2016-10-26 15:17:23,229 [trace=,span=] ERROR  [dispatcherServlet]:182  - Servlet.service() for servlet dispatcherServlet threw exception
java.lang.NullPointerException: null
	at org.springframework.expression.spel.ast.PropertyOrFieldReference$AccessorLValue.getValue(PropertyOrFieldReference.java:377)
	at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:88)
	at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:120)
	at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:267)
	at org.thymeleaf.spring4.expression.SpelVariableExpressionEvaluator.evaluate(SpelVariableExpressionEvaluator.java:139)
	at org.thymeleaf.standard.expression.VariableExpression.executeVariable(VariableExpression.java:154)
	at org.thymeleaf.standard.expression.SimpleExpression.executeSimple(SimpleExpression.java:59)
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:103)
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:133)
	at org.thymeleaf.standard.expression.Expression.execute(Expression.java:120)
	at org.thymeleaf.standard.processor.attr.AbstractStandardSingleAttributeModifierAttrProcessor.getTargetAttributeValue(AbstractStandardSingleAttributeModifierAttrProcessor.java:67)
	at org.thymeleaf.spring4.processor.attr.SpringHrefAttrProcessor.getTargetAttributeValue(SpringHrefAttrProcessor.java:68)
	at org.thymeleaf.processor.attr.AbstractSingleAttributeModifierAttrProcessor.getModifiedAttributeValues(AbstractSingleAttributeModifierAttrProcessor.java:59)
	at org.thymeleaf.processor.attr.AbstractAttributeModifierAttrProcessor.processAttribute(AbstractAttributeModifierAttrProcessor.java:62)
	at org.thymeleaf.processor.attr.AbstractAttrProcessor.doProcess(AbstractAttrProcessor.java:87)
	at org.thymeleaf.processor.AbstractProcessor.process(AbstractProcessor.java:212)
	at org.thymeleaf.dom.Node.applyNextProcessor(Node.java:1017)
	at org.thymeleaf.dom.Node.processNode(Node.java:972)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.NestableNode.computeNextChild(NestableNode.java:695)
	at org.thymeleaf.dom.NestableNode.doAdditionalProcess(NestableNode.java:668)
	at org.thymeleaf.dom.Node.processNode(Node.java:990)
	at org.thymeleaf.dom.Document.process(Document.java:93)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1155)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1060)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1011)
	at org.thymeleaf.spring4.view.ThymeleafView.renderFragment(ThymeleafView.java:335)
	at org.thymeleaf.spring4.view.ThymeleafView.render(ThymeleafView.java:190)
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1246)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1029)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:973)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:895)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:858)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:281)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.springframework.web.filter.ShallowEtagHeaderFilter.doFilterInternal(ShallowEtagHeaderFilter.java:87)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:115)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)

Looking at similar NPE issues #17614 and how this was fixed
I fixed this locally by doing the following in spring-expression v4.2.7
replace

line:372
@Override
public TypedValue getValue() {
	TypedValue value = this.ref.getValueInternal(this.contextObject, this.evalContext, this.autoGrowNullReferences);
	if (this.ref.cachedReadAccessor instanceof CompilablePropertyAccessor) {
		CompilablePropertyAccessor accessor = (CompilablePropertyAccessor) this.ref.cachedReadAccessor;
				this.ref.exitTypeDescriptor = CodeFlow.toDescriptor(accessor.getPropertyType());
	}
	return value;
}

with

@Override
public TypedValue getValue() {
	TypedValue value = this.ref.getValueInternal(this.contextObject, this.evalContext, this.autoGrowNullReferences);
	PropertyAccessor accessorToUse = this.ref.cachedReadAccessor;
	if (accessorToUse instanceof CompilablePropertyAccessor) {
		CompilablePropertyAccessor accessor = (CompilablePropertyAccessor) accessorToUse;
				this.ref.exitTypeDescriptor = CodeFlow.toDescriptor(accessor.getPropertyType());
	}
	return value;
}

---

Affects: 4.2.7, 4.2.8

Issue Links:

• NPE in PropertyOrFieldReference due to concurrency issue when caching SpelExpression objects [SPR-13023] #17614 NPE in PropertyOrFieldReference due to concurrency issue when caching SpelExpression objects

Backported to: 4.2.9

[spring-projects-issues]

Thijs Vonk commented

Looking at the code for 4.3.x and master I suspect this problem may also still occur there. No hard evidence though

[spring-projects-issues]

Thijs Vonk commented

Juergen, how was this fixed? I'm looking for the commit's but can't find any.

[spring-projects-issues]

Juergen Hoeller commented

Thijs Vonk sorry, not pushed/backported yet... coming later tonight or tomorrow, along with a bunch of other commits.

The fix itself looks just like in your patch, analogous to the older fixes in other locations.