javax.el.E​​LException：java.util.AbstractList.add中的java.lang.UnsupportedOperationException

Question

On Wildfly 9 (JSF 2.2, EL 3.0) I have two nested <ui:repeat> tags and want to use the var attribute of the outer one as method argument for the inner:

<ui:repeat value="#{bean.getEntries()}" var="entry">
    <ui:repeat value="#{bean.getPosts(entry)}" var="post">
        <p id="text">#{post.text}</p>
    </ui:repeat>
</ui:repeat>

bean.getEntries() returns List<Entry> and bean.getPosts(Entry entry) returns List<Post> as one would expect.

But instead of some <p> tags filled with posts I get an exception:

11:24:26,574 SEVERE [javax.enterprise.resource.webcontainer.jsf.application] (default task-2) Error Rendering View[/index.xhtml]: javax.el.ELException: /WEB-INF/templates/diary.xhtml @14,73 value="#{sessionBean.getPublicPosts(elEntry)}": java.lang.UnsupportedOperationException
at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:114)
at com.sun.faces.facelets.component.UIRepeat.getValue(UIRepeat.java:279)
at com.sun.faces.facelets.component.UIRepeat.getDataModel(UIRepeat.java:255)
at com.sun.faces.facelets.component.UIRepeat.setIndex(UIRepeat.java:523)
at com.sun.faces.facelets.component.UIRepeat.process(UIRepeat.java:577)
at com.sun.faces.facelets.component.UIRepeat.encodeChildren(UIRepeat.java:1110)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
at com.sun.faces.facelets.component.RepeatRenderer.encodeChildren(RepeatRenderer.java:104)
at com.sun.faces.facelets.component.UIRepeat.process(UIRepeat.java:621)
at com.sun.faces.facelets.component.UIRepeat.encodeChildren(UIRepeat.java:1110)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:456)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:655)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:86)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:72)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:282)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:261)
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:80)
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:172)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:199)
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:774)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: javax.el.ELException: java.lang.UnsupportedOperationException
at javax.el.ELUtil.invokeMethod(ELUtil.java:312)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:537)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:256)
at com.sun.el.parser.AstValue.getValue(AstValue.java:136)
at com.sun.el.parser.AstValue.getValue(AstValue.java:204)
at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:226)
at org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
... 49 more
Caused by: java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:148)
at java.util.AbstractList.add(AbstractList.java:108)
at org.bollin.diary.util.SessionBean.getPublicPosts(SessionBean.java:124)
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:497)
at javax.el.ELUtil.invokeMethod(ELUtil.java:308)
... 57 more

11:24:26,580 ERROR [io.undertow.request] (default task-2) UT005023: Exception handling request to /diary/index.jsf: javax.servlet.ServletException
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:667)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:86)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:72)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:282)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:261)
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:80)
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:172)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:199)
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:774)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:148)
at java.util.AbstractList.add(AbstractList.java:108)
at org.bollin.diary.util.SessionBean.getPublicPosts(SessionBean.java:124)
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:497)
at javax.el.ELUtil.invokeMethod(ELUtil.java:308)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:537)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:256)
at com.sun.el.parser.AstValue.getValue(AstValue.java:136)
at com.sun.el.parser.AstValue.getValue(AstValue.java:204)
at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:226)
at org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
at com.sun.faces.facelets.component.UIRepeat.getValue(UIRepeat.java:279)
at com.sun.faces.facelets.component.UIRepeat.getDataModel(UIRepeat.java:255)
at com.sun.faces.facelets.component.UIRepeat.setIndex(UIRepeat.java:523)
at com.sun.faces.facelets.component.UIRepeat.process(UIRepeat.java:577)
at com.sun.faces.facelets.component.UIRepeat.encodeChildren(UIRepeat.java:1110)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
at com.sun.faces.facelets.component.RepeatRenderer.encodeChildren(RepeatRenderer.java:104)
at com.sun.faces.facelets.component.UIRepeat.process(UIRepeat.java:621)
at com.sun.faces.facelets.component.UIRepeat.encodeChildren(UIRepeat.java:1110)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:456)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:655)
... 27 more

Answer 1

java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:148)
    at java.util.AbstractList.add(AbstractList.java:108)
    at org.bollin.diary.util.SessionBean.getPublicPosts(SessionBean.java:124)

The List implementation being used in line 124 of SessionBean class, inside the getPublicPosts() method, doesn't support calling the add() method.

That can happen when it's an unmodifiable list such as ones returned by Collections#unmodifiableList() and Arrays#asList() .

Wrap it in a modifiable list before modifying it.

modifiableList = new ArrayList<>(unmodifiableList);

Note that this problem is not strictly related to JSF nor EL, it's just basic Java. You can reproduce exactly the same problem using a simple Java application class with a main() method. In future questions it's wise to first do that in order to exclude JSF/EL from being the probable cause.

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Unrelated to the concrete problem, this signals another design problem: performing business logic in a Javabean getter method. This is performance wise a really bad idea as it's in this specific construct invoked during every iteration round. Move the business logic into a method which is called only once in the desired scope, such as a @PostConstruct annotated method. See also How and when should I load the model from database for h:dataTable .