Develop Reference

Profile GAE application in local dev server with VisualVM

I have an app that consumes so much memory, I would like to profile it, but I'm unable to start the app and pass the argument -agentpath; after I add this argument it waits for the profiler to connect, and so the GAE application doesn't startup. I get this message
Profiler Agent: Waiting for connection on port 5140 (Protocol version: 15)
I'm using maven to start up GAE application.
Sample command to start up:
java -agentpath:C:/visualvm_139/profiler/lib/deployed/jdk16/windows-amd64/profilerinterface.dll=C:\visualvm_139\profiler\lib,5140 -javaagent:C:\Users\User\.m2\repository\com\google\appengine\appengine-java-sdk\1.9.59\appengine-java-sdk\appengine-java-sdk-1.9.59\lib\agent\appengine-agent.jar -Dappengine.fullscan.seconds=5 -classpath C:\Users\User\.m2\repository\com\google\appengine\appengine-java-sdk\1.9.59\appengine-java-sdk\appengine-java-sdk-1.9.59\lib\appengine-tools-api.jar com.google.appengine.tools.development.DevAppServerMain -p 8888 C:\Users\User\eclipse\workspace\App\

An alternative solution would be using;
-Xdebug
-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=y
which would block the app until a debug client is attached on port 8000.

If you are having trouble using VisualVM with App Engine, you can try another approach, such as using Stackdriver to monitor different aspects of your Java VM, such as memory usage.
This link has all the useful information on how to set up a Stackdriver agent and use its monitoring functions to determine where the memory leaks come from.

If you don't need to profile startup of your application (from the description it looks like you don't), just start your application normally (without -agentpath). Start VisualVM, open your application and go to Profiler tab.
if you need to profile startup of your application use Startup profiler. It will tell you, what you should do.

Is it possible to run java command line app from python in AWS EC2?

I am working on some machine learning for chemical modelling in python. I need to run a java app (from command line through python subprocess.call) and a python webserver. Is this possible on AWS EC2?
I currently have this setup running on my mac but I am curious on how to set it up on aws.
Thanks in advance!

Since you're just making a command line call to the Java app, the path of least resistance would just be to make that call from another server using ssh. You can easily adapt the command you've been using with subprocess.call to use ssh -- more or less, subprocess.call(['ssh', '{user}#{server}', command]) (although have fun figuring out the quotation marks). As an aside on those lines, I usually find using '-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null' stabilizes scripted SSH calls in my environment.
The more involved thing will be setting up the environments to properly run the components you need. You'll need to set up ssh configs so that your django app can ssh over and set up -- probably with private key verification. Then, you'll need to make sure that your EC2 security groups are set up to allow the ssh access to your java server on port 22, where sshd listens by default.
None of this is that hairy, but all the same, it might be stabler to just wrap your Java service in a HTTP server that your Django app can hit. Anyway, hope this is helpful.

Streaming log files to remote client

I have a Java app running on a remote server (debian linux). The app logs runtime informations to files.
Once in a while, the support needs to analyze the logs using a client tool (not running on the server, but on the support's desktop). The tool then needs remote access to
old log files on the server
the current log file (growing in real time)
I'm searching a good (=standard, flexible, secure, well debugged etc) way to stream these past and present log messages to my client tool.
How would go about doing this?
Does a library exist, which provides this service?
Can syslog be adapted to do this?
Edit: For privacy reasons, the log files should be stored on the remote server only and not generally sent to a central logging service.

Why not use Log4j's capability as a publisher of log files to a remote server via TCP? Log4j is a standard Java logging tool (well-known/well-documented) and setting up the remote connectivity is pretty straightforward.
I've used this in the past to transmit across networks and collate log files from multiple machines in one common searchable directory structure (very useful in grid environments when you don't know where your processes could be running)
See this page for more details.

The simplest approach is likely to setup samba on the Linux box so you can access the logs remotely as they are updated without having to copy them.
You could use rsync. This allows you to securely copy changes to files between machines. i.e. an appending file would only copy the changes since the last rsync. Note: you have to run it repeatedly to keep seeing updates.
If the tools could be modified to support SSH e.g. via VFS, then you could access the remote files as if they were local.

JMX client accessible locally only

I want to create a JMX agent that has to be accessible from local host only.
Please advise how can I do that.
Also help with a Simple JMX client on same machine that will connect to that JMX agent.
If somehow we can get away with specifying an explicit port, that will be helpful.

You might find this helpful. It uses the attach API for Oracle's JVM to connect to a running Java process and have it start a local only JMX agent. You would setup whatever MBeans you want to expose as usual. I get the impression that this code is similar to what JConsole does for connecting to local JVM processes. You might also want to investigate the source for Jmxterm which leverages JConsole for connecting to local JVM processes.

NativeProcess API Java Debugging?

What is your way to debug Java side when nativeProcess.standardInput.write method is invoked by Flex side? I know that it is possible but don't know how?

To be able to attach your Eclipse debugger to a running Java process you need to start that process with the following Java options…
-Xdebug -Xrunjdwp:transport=dt_socket,address=8001,server=y,suspend=n
Once you have done this and have restarted the server, you can use your Eclipse to attach to the running process. From Eclipse go to the Debug manager and create a new Remote Java Application configuration for the process you want to connect to. Set the port number to 8001, the same as that of the options. You will also need to enter the hostname for the machine running the Java process. That is pretty much it…