Ive been trying unsuccessfully to connect two client debuggers to
a Debuggee program in context of JPDA. Is this possible or
are there workarounds to make it happen?
I am using eclipse as the IDE (edit for typo).
Think of a server program as a Hello World
which Prints out:
System.out.println("I have the String"); //1
System.out.println("You will have to pass through the breakpoints before you shall see");
System.out.println("breakpoints");
System.out.println("before you shall see"); //4
We can put breakpoints at lines 1 and 4.
Step 1:
The params passed to the program in Run Configuration:
-Xdebug -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=y
(server=y tells vm to behave like a server, suspend=y implies that prog execution will be suspended till debugger latches on to it)
and Run the program.
Step 2: Go to Debug as , Debug config ,Remote Java application and
create a new instance:
Project: Same as before
Connection type: Socket Attach(Socket Attach)
Host:LocalHost
Port:8000
Now when I debug Prog execution stops at the specified breakpoint.
What I cant do is create another instance of this remote debugger that
can latch on to the server(prog 1), I get a connection refused when I do that. Let me know if anyone else has faced this problem
and if a workaround exists.
Thanks!
Thanks
AFAIK there can be only one instance of debugger connected to a java program any given time. Once you started you program in debug, Eclipse connects to the debugged program blocking all other connection attempts. If you want to connect remotely you can run the program not in debug mode and add the parameters:
-Xdebug -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=y
to java parameters manually, then you should be able to connect with another debugger.
I don't know how things were in 2010, but in 2014 this is doable. I'm debugging an applet and a servlet at the same time eventough they use different JVM, to do so just start your remote debug process in eclipse like socket Listen, the start the first java applicaction with:
-Xdebug -Xrunjdwp:transport=dt_socket,address=127.0.0.1:8787,suspend=y
Then start the same eclipse remote debug process and start another java process with the same options, you should see the processes spawn like this:
You can see the two different JVM listening in the same port (nevermind the name of the 'applet' process)
Related
I developed a java code to connect to a device and issue few POST commands. This runs well in eclipse. But when I build and run on command-line it always times out.
I am running eclipse in the same machine as command line .I am using java 8.
Network problems are best tackled by first keeping Java out of it. So as a first step, you can open up the console and try to do a telnet connection to the socket address you used in your program by entering
telnet targetserver.example.com 12345
If that times out as well, the source of your problem is not within Java.
You haven't provided much (e.g. source as requested) but my guess into the blue is that you're sitting behind a proxy that is configured in Eclipse. Eclipse passes that information to the started application so the connection works. Starting the application on the console lacks this information, so the network connection is attempted directly without going via the proxy.
I wrote a Java servlet filter on my local machine and deployed it a remote (machine) web server. Unfortunately, it's been very difficult and time-consuming trying to trace errors reported by Apache Tomcat 5.5, my JSP/servlet engine. I can't keep writing System.out.println(...), saving, deploying, testing JSP pages, and so on. It's taking too long. There has to be a better, faster way.
Is it possible to remotely debug servlet filters? I don't have a web server on my local machine, which is why I'm asking about remote debugging. Specifically, I'm looking for a way to debug, line-by-line, the servlet filter, on-the-fly, as it's happening on the remote web server. Does such a method exist?
Or, is there a better method than writing to standard output. It's taking too long and I feel that must be a more efficient means of debugging Java servlet filters.
Note: I'm using Eclipse for development.
Thank you very much for any help.
Update
Thank you all for your help. I really appreciate it.
I added the JVM argument to Tomcat, restarted Tomcat. Then, on the machine with Eclipse, I entered in the appropriate info in the Debug config, put the breakpoint in, and tested. Unfortunately, it did not work. In the config, I left it as Socket Attach, clicked apply, and that was it. I pressed the debug button and it said the connection was refused. I tried ports 8000 and 8001 and both did not work.
Let me explain what I'm trying to do, that might be better.
I have a login page called login.jsp. On that page, is a form whose action attribute is servlet/LoginServlet. When the user submits the form, it calls servlet/LoginServlet, which is mapped to a class in the web.xml file. Let's call this class com.mysite.mypkg.classA. In class A, it calls a method from another class called com.custom.mypkg.classB. I want to put a breakpoint in classB.
So, using the url with login.jsp page in the Eclipse debugger won't call it. I tried using servlet/LoginServlet and that also did not work.
What should I put in for the URL? Or, do I debug this type of setup?
Thank you.
Update 2
I found this site here, which is pretty comprehensive. I ran netstat -a and noticed that the debug port is not listed. Windows Firewall is turned off, but there could be another thing blocking the port, who knows. Anyway, I placed the VM argument here and it's not working.
Thank you.
For remote debugging you need to start the server in debug mode. There are couple of ways doing that.
1 > start the server using
catinlina.bat jpda start
2 > Add an jvm argument to the tomcat java process
-Xdebug -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n
Once the server is started in debug mode , you need to change the perspective of the project in eclipse to debug.
Then go to Run - > Debug configuration.
Double click remote java application and enter the details such as
Remote IP address
Debug port . Default tomcat debug port is 8000. If you use jvm argument, use the port mentioned in the jvm argument.
Click Apply
Go to the java file you want to debug.
Put a break point in the source code and run the scenario you want to test (Eg Web application using browser)
Also , ensure that the code in the java file is in sync with code deployed on remote server.
Happy Debugging!!!
Peace.
Sanket Raut
You can attach a debugger to a running Tomcat instance, provided that you gave it the right command line options when you launched it.
The Tomcat Development Wiki explains how to do this, and as a bonus gives you instructions on how to set up to debug from the Eclipse or NetBeans IDEs.
Of course, attaching a debugger to a running Tomcat has both security and performance implications*.
* And OH&S issues - you might get badly scratched if you tried this on the wrong kind of tomcat ...
You should run your remote tomcat with the following starup parameter:
bin/catalina.bat jpda start
Then in Eclipse on your local machine go to Run -> Debug Configurations -> Remote Java Application, create new configuration here, use IP of the remote machine as a host and 8000 as a port there
Run this configuration and use the breakpoints in Eclipse for debugging
It might sound a bit too naive, but I always had a tough time to debug a java class during server startup. Here is the scenario:
The java application is hosted on a tomcat server.
Suppose there is a class which is invoked while the tomcat server starts up.
As soon as I stop the tomcat instance for a restart, the eclipse debug stops and I can start the debug only once the application is up and running.
Now how do I debug this class on eclipse?
Thanks for you help in advance.
You need to pass the "wait for debugger to connect" flag to tomcat. So the startup will wait until you have connected and thus you won't miss the breakpoint.
Take for example those java options to make tomcat listen for a debugger:
-Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,address=8797,server=y,suspend=y
The wait for a debugger connection flag is the suspend=y entry in the above line.
Debugging of classes during startup should work without problems. For example, suppose you implement a ServletContextListener class. The belonging contextInitialized method is called during Tomcat startup (or to be more precise: while your app gets deployed).
You can set breakpoints in this class. At that point, Tomcat is already started completely and there shouldn't be any problems with debugging.
I came to know of the remote debugging procedure under Idea recently. What I do is copy the configuration of remote debug under Run | Debug Configuration in Idea to the command line java execution parameters. The actual command line parameters are:
-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000
If it is a script, I add these commands to it. By doing so, the command line displays the message:
Listening for transport dt_socket at address: 8000
So the debugging can happen using the local source code. However, I don't properly understand how remote debugging work. Anyone who knows how remote debugging actually works, please give me an explanation.
Thank you!
Remote debugging means that you can run your Java code anywhere, either on the local or remote machine. When it's running in the debug mode, you can connect to it from the IDE using TCP network connection and perform debugging. IDE needs to have the source code for the running classes so that you can place breakpoints inside this code and perform stepping, inspecting variables, etc.
If you are interested in technical details, refer to the JPDA documentation.
Consider a scenario where you want to fix something in your application but your application only can run over a server machine because of other dependencies.
That is where Remote Debugging come into picture. You Just connect the sever by providing the hostname and port and connect it with your respective environment.
How It works:
Application to be debugged will attach a socket to itself and then will start listening debug instructions.
Debugger will bind itself to that socket and then send instructions.
This is best way to test your code which are in different environment .
we need to have below points for sure before you are using remote debug .
we are using JBOSS in our servers.
configure - JBOSS_HOME/bin/run.conf
JAVA_OPTS="${JAVA_OPTS} -Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n"
now add the server IP and port number into the intellij remote debugging .
4.your should have the latest version of the project in local that is in synch with the server else debug will not be allowed.
you need to start the intellij server for the project .
Then start the remote debug .
place a debug point in local and when we start testing in the server , when it hits the debug point it will stop and wait untill you process it .
The other point is , it will hold all the request in the queue and will not allow anyone to go through the break point which may stop other users to test it .
I need to attach a debugger to a remote instance of WAS and know that debugging is enabled. The problem is getting WID or whatever IDE I wanted connected to the server so I can step through the code.
I tried using Netbeans to connect and I get handshake failed, connection interrupted. The debugger is listening on port 7777. If I go into the WID admin console, I need a username and password. Would I need the same to attach a debugger, if so, where can I specify that?
Walter
Can you not add the following line to the startup script's parameters of WAS:
-Xnoagent -Djava.compiler=NONE -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=7777
And then attach your Netbeans remote debugger on port 7777
WAS can be configured for remote debugging via the web administration console.
It is also possible to configure this without starting WAS - via one of the profile XML files. But I don't remember the details and don't have WAS handy to check.
I think I simply need to enable the service at startup then I should be able to connect? I have to get permission first to do so.