HTTP 500 error when accessing a custom servlet injected into Selenium grid

Prvn

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May 2, 2018, 10:04:32 AM5/2/18

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I have a basic servlet that extends RegistryBasedServlet class. I did `mvn package` and made sure I am only using the packaged jar with dependencies. Then I started the selenium server with the following command

java -cp gridservlet-0.0.1-SNAPSHOT.jar:selenium-server-standalone-3.8.1.jar org.openqa.grid.selenium.GridLauncherV3 -role hub -port 8007 -maxSession 1 -newSessioaitTimeout 600000 -timeout 50 -servlets com.servlet.ClacServlet

But when I access http://localhost:8007/grid/admin/ClacServlet/ . I get the following exception

HTTP ERROR 500

Problem accessing /grid/admin/ClacServlet/. Reason:

    Server Error

Caused by:

javax.servlet.ServletException: com.servlet.ClacServlet-7dc222ae@5c7dbcc9==com.servlet.ClacServlet,jsp=null,order=-1,inst=false
	at org.seleniumhq.jetty9.servlet.ServletHolder.initServlet(ServletHolder.java:658)
	at org.seleniumhq.jetty9.servlet.ServletHolder.getServlet(ServletHolder.java:498)
	at org.seleniumhq.jetty9.servlet.ServletHolder.ensureInstance(ServletHolder.java:785)
	at org.seleniumhq.jetty9.servlet.ServletHolder.prepare(ServletHolder.java:770)
	at org.seleniumhq.jetty9.servlet.ServletHandler.doHandle(ServletHandler.java:530)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.seleniumhq.jetty9.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.seleniumhq.jetty9.server.handler.ContextHandler.doHandle(ContextHandler.java:1253)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168)
	at org.seleniumhq.jetty9.servlet.ServletHandler.doScope(ServletHandler.java:473)
	at org.seleniumhq.jetty9.server.session.SessionHandler.doScope(SessionHandler.java:1564)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166)
	at org.seleniumhq.jetty9.server.handler.ContextHandler.doScope(ContextHandler.java:1155)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.seleniumhq.jetty9.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
	at org.seleniumhq.jetty9.server.Server.handle(Server.java:561)
	at org.seleniumhq.jetty9.server.HttpChannel.handle(HttpChannel.java:334)
	at org.seleniumhq.jetty9.server.HttpConnection.onFillable(HttpConnection.java:251)
	at org.seleniumhq.jetty9.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
	at org.seleniumhq.jetty9.io.FillInterest.fillable(FillInterest.java:104)
	at org.seleniumhq.jetty9.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
	at org.seleniumhq.jetty9.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:679)
	at org.seleniumhq.jetty9.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:597)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.InstantiationException: com.servlet.ClacServlet
	at java.lang.Class.newInstance(Class.java:427)
	at org.seleniumhq.jetty9.server.handler.ContextHandler$Context.createInstance(ContextHandler.java:2535)
	at org.seleniumhq.jetty9.servlet.ServletContextHandler$Context.createServlet(ServletContextHandler.java:1326)
	at org.seleniumhq.jetty9.servlet.ServletHolder.newInstance(ServletHolder.java:1273)
	at org.seleniumhq.jetty9.servlet.ServletHolder.initServlet(ServletHolder.java:614)
	... 24 more
Caused by: java.lang.NoSuchMethodException: com.servlet.ClacServlet.<init>()
	at java.lang.Class.getConstructor0(Class.java:3082)
	at java.lang.Class.newInstance(Class.java:412)
	... 28 more

Caused by:

java.lang.InstantiationException: com.servlet.ClacServlet
	at java.lang.Class.newInstance(Class.java:427)
	at org.seleniumhq.jetty9.server.handler.ContextHandler$Context.createInstance(ContextHandler.java:2535)
	at org.seleniumhq.jetty9.servlet.ServletContextHandler$Context.createServlet(ServletContextHandler.java:1326)
	at org.seleniumhq.jetty9.servlet.ServletHolder.newInstance(ServletHolder.java:1273)
	at org.seleniumhq.jetty9.servlet.ServletHolder.initServlet(ServletHolder.java:614)
	at org.seleniumhq.jetty9.servlet.ServletHolder.getServlet(ServletHolder.java:498)
	at org.seleniumhq.jetty9.servlet.ServletHolder.ensureInstance(ServletHolder.java:785)
	at org.seleniumhq.jetty9.servlet.ServletHolder.prepare(ServletHolder.java:770)
	at org.seleniumhq.jetty9.servlet.ServletHandler.doHandle(ServletHandler.java:530)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.seleniumhq.jetty9.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.seleniumhq.jetty9.server.handler.ContextHandler.doHandle(ContextHandler.java:1253)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168)
	at org.seleniumhq.jetty9.servlet.ServletHandler.doScope(ServletHandler.java:473)
	at org.seleniumhq.jetty9.server.session.SessionHandler.doScope(SessionHandler.java:1564)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166)
	at org.seleniumhq.jetty9.server.handler.ContextHandler.doScope(ContextHandler.java:1155)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.seleniumhq.jetty9.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
	at org.seleniumhq.jetty9.server.Server.handle(Server.java:561)
	at org.seleniumhq.jetty9.server.HttpChannel.handle(HttpChannel.java:334)
	at org.seleniumhq.jetty9.server.HttpConnection.onFillable(HttpConnection.java:251)
	at org.seleniumhq.jetty9.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
	at org.seleniumhq.jetty9.io.FillInterest.fillable(FillInterest.java:104)
	at org.seleniumhq.jetty9.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
	at org.seleniumhq.jetty9.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:679)
	at org.seleniumhq.jetty9.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:597)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NoSuchMethodException: com.servlet.ClacServlet.<init>()
	at java.lang.Class.getConstructor0(Class.java:3082)
	at java.lang.Class.newInstance(Class.java:412)
	... 28 more

Caused by:

java.lang.NoSuchMethodException: com.servlet.ClacServlet.<init>()
	at java.lang.Class.getConstructor0(Class.java:3082)
	at java.lang.Class.newInstance(Class.java:412)
	at org.seleniumhq.jetty9.server.handler.ContextHandler$Context.createInstance(ContextHandler.java:2535)
	at org.seleniumhq.jetty9.servlet.ServletContextHandler$Context.createServlet(ServletContextHandler.java:1326)
	at org.seleniumhq.jetty9.servlet.ServletHolder.newInstance(ServletHolder.java:1273)
	at org.seleniumhq.jetty9.servlet.ServletHolder.initServlet(ServletHolder.java:614)
	at org.seleniumhq.jetty9.servlet.ServletHolder.getServlet(ServletHolder.java:498)
	at org.seleniumhq.jetty9.servlet.ServletHolder.ensureInstance(ServletHolder.java:785)
	at org.seleniumhq.jetty9.servlet.ServletHolder.prepare(ServletHolder.java:770)
	at org.seleniumhq.jetty9.servlet.ServletHandler.doHandle(ServletHandler.java:530)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.seleniumhq.jetty9.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.seleniumhq.jetty9.server.handler.ContextHandler.doHandle(ContextHandler.java:1253)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168)
	at org.seleniumhq.jetty9.servlet.ServletHandler.doScope(ServletHandler.java:473)
	at org.seleniumhq.jetty9.server.session.SessionHandler.doScope(SessionHandler.java:1564)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166)
	at org.seleniumhq.jetty9.server.handler.ContextHandler.doScope(ContextHandler.java:1155)
	at org.seleniumhq.jetty9.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.seleniumhq.jetty9.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
	at org.seleniumhq.jetty9.server.Server.handle(Server.java:561)
	at org.seleniumhq.jetty9.server.HttpChannel.handle(HttpChannel.java:334)
	at org.seleniumhq.jetty9.server.HttpConnection.onFillable(HttpConnection.java:251)
	at org.seleniumhq.jetty9.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
	at org.seleniumhq.jetty9.io.FillInterest.fillable(FillInterest.java:104)
	at org.seleniumhq.jetty9.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
	at org.seleniumhq.jetty9.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:679)
	at org.seleniumhq.jetty9.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:597)
	at java.lang.Thread.run(Thread.java:745)

⇜Krishnan Mahadevan⇝

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May 2, 2018, 10:06:54 AM5/2/18

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What does the constructor of your servlet look like ?

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My Technical Scribbings @ http://rationaleemotions.wordpress.com/

Prvn

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May 2, 2018, 10:08:16 AM5/2/18

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Hello Krishnan,

public class ClacServlet extends RegistryBasedServlet {

private static final long serialVersionUID = 4615464862476676155L;

public ClacServlet(GridRegistry registry) {

super(registry);

}

@Override

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

doPost(req, resp);

}

@Override

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

processServlet(req, resp);

}

...

..

.....

⇜Krishnan Mahadevan⇝

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May 2, 2018, 10:16:23 AM5/2/18

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Your constructor looks fine. The exception is talking about a missing method. Are you sure you aren't mixing up selenium versions ? If you built a jar of jars then you don't need to be referring to selenium jar in your class path.

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Prvn

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May 2, 2018, 10:31:18 AM5/2/18

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I am using selenium server standalone jar 3.8.1 and in the servlet project I am using Maven dependency selenium-server 3.8.1

Yes I am building the servlet jar with selenium server and testNG as dependency. So are you saying in my java -cp command I dont have to specify selenium server jar?

⇜Krishnan Mahadevan⇝

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May 2, 2018, 10:32:59 AM5/2/18

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Yes if you have an uber jar then you don't need to be including the selenium jar. Can you give it a whirl and post back your findings ?

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Prvn

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May 2, 2018, 11:32:25 AM5/2/18

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Ok. this is what I did

1. In my pom of the GridServlet there are two dependencies selenium-server and testng. selenium-server version is 3.8.1 (I also tried with 3.11.0)

2. Then I did mvn package

3. I see a jar with name gridservlet-0.0.1-SNAPSHOT-jar-with-dependencies.jar

4. Now I ran the command java -cp gridservlet-0.0.1-SNAPSHOT.jar org.openqa.grid.selenium.GridLauncherV3 -role hub -port 8007 -servlets com.servlet.ClacServlet

5. I see that the servlet was injected successfully. when the grid was started

6. Now In the browser I did http://localhost:8007/grid/admin/ClacServlet and still see HTTP error 500

Krishnan Mahadevan

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May 2, 2018, 12:30:29 PM5/2/18

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Praveen,

I took a closer look at the codebase.

It looks like you would need to be adding a default constructor to your constructor and try again.

Even though the Selenium Grid basically has a 1 arg constructor for the RegistryBasedServlet class, the codebase doesn’t seem to be leveraging that constructor via reflection for instantiation of your servlet into the root servlet container.

Selenium grid seems to be trying to invoke the default constructor for instantiation and the registry is being added to the RegistryBasedServlet via an attribute in the servlet context.

I hope that adds clarity. My apologies for not calling this out earlier. Been a bit out of touch with the grid servlets ☺

Thanks & Regards

Krishnan Mahadevan

"All the desirable things in life are either illegal, expensive, fattening or in love with someone else!"

My Scribblings @ http://wakened-cognition.blogspot.com/

My Technical Scribbings @ http://rationaleemotions.wordpress.com/

.
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Prvn

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May 2, 2018, 1:27:50 PM5/2/18

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Krishnan,

If I have a default no argument constructor then it says "Implicit super constructor RegistryBasedServlet() is undefined. Must explicitly invoke another constructor"

What do you mean by "adding a default constructor to your constructor "?

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⇜Krishnan Mahadevan⇝

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May 2, 2018, 1:42:27 PM5/2/18

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Add both the constructors. The no arg default constructor to facilitate instantiation and the 1 arg constructor to keep the parent class happy.

You can have your default constructor call into the 1 arg constructor via a "this()" call.

.

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Prvn

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May 2, 2018, 1:49:44 PM5/2/18

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I tried that earlier. Pls see the code below. But when I do this() it says "Recursive constructor invocation ClacServlet()"

public class ClacServlet extends RegistryBasedServlet {

private static final long serialVersionUID = 4615464862476676155L;

public ClacServlet(GridRegistry registry) {

super(registry);

}

public ClacServlet() {

this();

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Krishnan Mahadevan

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May 2, 2018, 1:52:34 PM5/2/18

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Praveen,

I meant something like below:

public class ClacServlet extends RegistryBasedServlet {

private static final long serialVersionUID = 4615464862476676155L;

public ClacServlet(GridRegistry registry) {

super(registry);

}

public ClacServlet() {

this(null);

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Krishnan Mahadevan
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My Scribblings @ http://wakened-cognition.blogspot.com/
My Technical Scribbings @ http://rationaleemotions.wordpress.com/

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Prvn

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May 2, 2018, 2:01:59 PM5/2/18

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Thanks a lot. It worked :)

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