1

I'm getting a NullPointerException when trying to use @FindBy because the object reference is only declared and not instantiated.

What is the usage? The docs give example declaration but no instance creation I saw.

code:

package dur.bounceme.net.SeleniumBase;

import java.util.List;
import java.util.logging.Logger;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.FindBy;

class WelcomePage {

    private static final Logger LOG = Logger.getLogger(App.class.getName());
    private WebDriver webDriver = null;

    @FindBy(partialLinkText = "Books")
    private WebElement books;

    @FindBy(tagName = "a")
    List<WebElement> links;

    private WelcomePage() {
    }

    WelcomePage(WebDriver webDriver) {
        this.webDriver = webDriver;
        LOG.info(webDriver.getCurrentUrl());
    }

    static WelcomePage init(WebDriver webDriver) {
        return new WelcomePage(webDriver);
    }

    void populateCatalogue() {
        LOG.info("start..");
        LOG.info(links.toString());
        LOG.info("..done");
    }

}

runtime exception, NPE:

thufir@dur:~/NetBeansProjects/com.toscrape.books.selenium$ 
thufir@dur:~/NetBeansProjects/com.toscrape.books.selenium$ r

> Task :run
1545512623646   mozrunner::runner       INFO    Running command: "/usr/lib/firefox/firefox" "-marionette" "--headless" "-foreground" "-no-remote" "-profile" "/tmp/rust_mozprofile.SCFlr3V6QNyv"
*** You are running in headless mode.
1545512626080   addons.webextension.screenshots@mozilla.org     WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid host permission: resource://pdf.js/
1545512626080   addons.webextension.screenshots@mozilla.org     WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid host permission: about:reader*
1545512631280   Marionette      INFO    Listening on port 44731
1545512631388   Marionette      WARN    TLS certificate errors will be ignored for this session
Dec 22, 2018 1:03:51 PM org.openqa.selenium.remote.ProtocolHandshake createSession
INFO: Detected dialect: W3C
JavaScript warning: http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js, line 1: Using //@ to indicate sourceMappingURL pragmas is deprecated. Use //# instead
Dec 22, 2018 1:03:54 PM dur.bounceme.net.SeleniumBase.WelcomePage <init>
INFO: http://books.toscrape.com/
Dec 22, 2018 1:03:54 PM dur.bounceme.net.SeleniumBase.WelcomePage populateCatalogue
INFO: start..
Exception in thread "main" java.lang.NullPointerException
        at dur.bounceme.net.SeleniumBase.WelcomePage.populateCatalogue(WelcomePage.java:34)
        at dur.bounceme.net.SeleniumBase.App.initSelenium(App.java:25)
        at dur.bounceme.net.SeleniumBase.App.main(App.java:13)

> Task :run FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':run'.
> Process 'command '/usr/lib/jvm/java-8-openjdk-amd64/bin/java'' finished with non-zero exit value 1

* Try:
Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':run'.
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:96)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:65)
        at org.gradle.api.internal.tasks.execution.ActionEventFiringTaskExecuter.execute(ActionEventFiringTaskExecuter.java:44)
        at org.gradle.api.internal.tasks.execution.TimeoutTaskExecuter.execute(TimeoutTaskExecuter.java:53)
        at org.gradle.api.internal.tasks.execution.SnapshotAfterExecutionTaskExecuter.execute(SnapshotAfterExecutionTaskExecuter.java:38)
        at org.gradle.api.internal.tasks.execution.OutputDirectoryCreatingTaskExecuter.execute(OutputDirectoryCreatingTaskExecuter.java:51)
        at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:59)
        at org.gradle.api.internal.tasks.execution.ResolveTaskOutputCachingStateExecuter.execute(ResolveTaskOutputCachingStateExecuter.java:49)
        at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:61)
        at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:101)
        at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:91)
        at org.gradle.api.internal.tasks.execution.FinalizePropertiesTaskExecuter.execute(FinalizePropertiesTaskExecuter.java:44)
        at org.gradle.api.internal.tasks.execution.ResolveTaskArtifactStateTaskExecuter.execute(ResolveTaskArtifactStateTaskExecuter.java:62)
        at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:55)
        at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:54)
        at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:35)
        at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.run(EventFiringTaskExecuter.java:49)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:301)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:293)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:175)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:91)
        at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
        at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:44)
        at org.gradle.execution.plan.LocalTaskNodeExecutor.execute(LocalTaskNodeExecutor.java:43)
        at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:337)
        at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:325)
        at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:318)
        at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:304)
        at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker$1.execute(DefaultPlanExecutor.java:134)
        at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker$1.execute(DefaultPlanExecutor.java:129)
        at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.execute(DefaultPlanExecutor.java:202)
        at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.executeNextNode(DefaultPlanExecutor.java:193)
        at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.run(DefaultPlanExecutor.java:129)
        at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
        at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
        at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
Caused by: org.gradle.process.internal.ExecException: Process 'command '/usr/lib/jvm/java-8-openjdk-amd64/bin/java'' finished with non-zero exit value 1
        at org.gradle.process.internal.DefaultExecHandle$ExecResultImpl.assertNormalExitValue(DefaultExecHandle.java:396)
        at org.gradle.process.internal.DefaultJavaExecAction.execute(DefaultJavaExecAction.java:37)
        at org.gradle.api.tasks.JavaExec.exec(JavaExec.java:79)
        at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
        at org.gradle.api.internal.project.taskfactory.StandardTaskAction.doExecute(StandardTaskAction.java:48)
        at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:41)
        at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:28)
        at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:704)
        at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:671)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$1.run(ExecuteActionsTaskExecuter.java:117)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:301)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:293)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:175)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:91)
        at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:106)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:85)
        ... 35 more


* Get more help at https://help.gradle.org

BUILD FAILED in 18s
4 actionable tasks: 4 executed
thufir@dur:~/NetBeansProjects/com.toscrape.books.selenium$ 

Is PageFactory in play here? Admittedly, a follow-up to my previous xpath efforts.

1

To understand the magic happening you should first understand a Proxy pattern. There is a post on SO where you can get some insight on what the Proxy patter is.

So, when you call PageFactory.init(...) you initiate a mechanism that is called a Reflection that allows the code analyze itself in runtime.

What is actually happening under the hood is that Selenium code analyzes the fields which are provided in the class that is passed to PageFactory.initElements(this.webDriver, this);. Basically it takes the object that is referred as this in your case and looks up for all the fields in the class that object has and in its superclasses.

Then it wraps the fields which are annotated into proxy objects. When you create a Proxy you need to provide an invocation handler that would handle invocations of the methods of proxy object. Below is Selenium code that implements such handler:

public class LocatingElementHandler implements InvocationHandler {
    private final ElementLocator locator;

    public LocatingElementHandler(ElementLocator locator) {
        this.locator = locator;
    }

    public Object invoke(Object object, Method method, Object[] objects) throws Throwable {
        WebElement element;
        try {
            element = this.locator.findElement();
        } catch (NoSuchElementException var7) {
            if ("toString".equals(method.getName())) {
                return "Proxy element for: " + this.locator.toString();
            }

            throw var7;
        }

        if ("getWrappedElement".equals(method.getName())) {
            return element;
        } else {
            try {
                return method.invoke(element, objects);
            } catch (InvocationTargetException var6) {
                throw var6.getCause();
            }
        }
    }
}

So when you use PageFactory.init(...), all your further calls to the fields are dispatched using the code above where the web element is looked up using your locator you have specified in annotation. Thus you do not get NullPointerException.

If you do not use init() then Selenium does not wrap your fields with proxy objects so that the fields are null's which causes NPE obviously.

0

I added a line to constructor which does some magic which I don't understand. But, it works:

package dur.bounceme.net.SeleniumBase;

import java.util.List;
import java.util.logging.Logger;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;

class WelcomePage {

    private static final Logger LOG = Logger.getLogger(App.class.getName());
    private WebDriver webDriver = null;

    @FindBy(partialLinkText = "Books")
    private WebElement books;

    @FindBy(tagName = "a")
    List<WebElement> links;

    private WelcomePage() {
    }

    WelcomePage(WebDriver webDriver) {
        this.webDriver = webDriver;
        PageFactory.initElements(this.webDriver, this);
        LOG.info(webDriver.getCurrentUrl());
    }

    static WelcomePage init(WebDriver webDriver) {
        return new WelcomePage(webDriver);
    }

    void populateCatalogue() {
        LOG.info("start..");
        LOG.info(links.toString());
        for (WebElement webElement : links) {
            LOG.info(webElement.getText());
        }
        LOG.info("..done");
    }

}

after stumbling upon a snippet. Comments and other solutions welcomed and appreciated.

Particularly if you will explain what the PageFactory line actually does.

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