selenium RemoteWebDriver firefox producing NullPointerException

Question

I have a dedicated test server which runs selenium standalone server with no role specified. I have Xvfb and firefox running on that server.

My junit test can successfully connect and create driver object as follows:

   @Before
   public void setUp() throws Exception {
      DesiredCapabilities capabilities = DesiredCapabilities.firefox();

      driver = new RemoteWebDriver(new URL("http://192.168.132.102:4444/wd/hub/"), capabilities);
      driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);
   }

Everything is normal until I select some element from the reqested URL:

driver.get("http://www.google.com");   // works fine
logger.info(driver.getTitle());        // working fine also

However when i evaluate any method on the result (elem reference) of (in debugging session):

RemoteWebElement elem = ((RemoteWebDriver)driver).findElementById("gbqfq");
elem.getLocation(); // exception
elem.getText();     // exception
elem.getSize();     // exception

I get NullPointerException as follows:

Session ID: bf2eeaa9-3abd-42d5-9210-8255712b9e63
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
    at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:193)
    at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:145)
    at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:595)
    at org.openqa.selenium.remote.RemoteWebElement.execute(RemoteWebElement.java:268)
    at org.openqa.selenium.remote.RemoteWebElement.getText(RemoteWebElement.java:152)
    at match.selenium.testcases.ExampleTest.test2(ExampleTest.java:43)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:74)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:211)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:67)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
Caused by: java.lang.NullPointerException
    at org.openqa.selenium.remote.server.handler.GetElementText.call(GetElementText.java:29)
    at org.openqa.selenium.remote.server.handler.GetElementText.call(GetElementText.java:1)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at org.openqa.selenium.remote.server.DefaultSession$1.run(DefaultSession.java:170)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:744)

Is there any way to overcome this? I tried on my local machine with driver setting to new FirefoxDriver instance, but it works as expected. I cannot get it working on remote web driver unfortunately.

NOTE: I tried most of the select methods (byId, byClass, byTagname) but nothing changed.

Answer 1

尝试使用以下元素查找元素：WebElement findElement（By by）;