I have created and am working on a server-application that monitors for specific folders and takes appropriate actions whenever files are being added.
Now I come to the point where I want to be able to shutdown the program, for example for applying a patch.
The server runs simply in a command prompt, how can I signal that I want to perform maintenance on it? I do not think reading System.in is feasible as I am also outputting text in the prompt.
Regards.
You could try reading System.in as System.in and System.out are different file descriptors. What this means is that by writing things in console you are not writing in the same place than when you are typing, so console output should not matter for reading commands in the prompt.
A second application can be used to communicate with the server application. You can use Java Management Extensions or implement your own client/server communication using sockets.
Another way to achieve this is that server periodically checks for existence of an specific file somewhere on hard disk. If server finds that specific file, it will shut down.
Related
Note: being asked here because I guarantee the Security stack will close it for being a programming question.
I have a web application (in this case, Java on Tomcat) for which I occasionally need to allow the user to upload files. Even though I generally have trustworthy users, in my business we assume anybody and everybody could potentially be an insider threat (or just plain dumb). Therefore, I would like to have the uploaded file go directly to a "quarantine" directory, programmatically fire off a scan, and only if the scan succeeds, copy it to the intended destination folder for processing.
The only fly in the ointment is figuring out (a) how to fire off a scan, on demand, programmatically (let's assume we're using the McAfee suite of tools) and (b) how to get notification back when the scan is complete. Is it possible? If so, has anyone done it and can give me pointers?
We do this. We have a queue system so workers can pickup the file operations and perform them async. but The general flow is to scan the file using a command, and update the database to track status.
write the file to a dir
note the file information in a database with location=x; scanned=no;
read the docs for mcaffee, but there should be a way to run a scan via the command line or via an SDK. I'd probably run it via command line to scan the file, and assume the command will return some information (0 or !=0 on error or bad results)
If the file scanner returns non-zero, then set scanned=infected;
if the file scanner returns clean, then set scanned=clean;
Set the processing code to only process files that are scanned=clean;
Note: #David Conrad found the instructions for running the command line scanner https://kc.mcafee.com/corporate/index?page=content&id=KB75478 ; upvote that guy.
I made a simple chat room application consists of a client.jar and server.jar. After running the .jar file in cmd window, I need to type in some specified command in client part and carriage return to run the application, such as "#connect": connect to the server, "#send XXX": send XXX message to server and broadcast to other connected clients...
Here comes the problems. Actually I want to test how the application works well when there exist concurrency. So I think I need try to let two or more client parts send the command repeatedly and fast. But obviously i cannot achieve manually.
Is there any ways can let the system get the command and send it automatically at high speed? I guess using batch file is suitable for this issue, but I am not sure or how to implement it...
I have a CentOS server which is currently running a java jar application. I need to write a php script to communicate with this running program via its input stream. The java program outputs its output to a log file so I don't need access to the output stream.
I don't want to restart the program, just access the running process and interact with it.
Can someone point me in the right direction?
If portability is not a big matter for you, why not creating your own pipe(s)? I don't know much about the java application but have a look at the "mkfifo" function/command.
First, find the ProcessID of the application. You may do it using:
ps -Af | grep java
Since you are using java, you may feel more convenient with the jps command for finding the PID.
I'll assume PID of the running application is 12345. It suffices to issue the command:
cat >/proc/12345/fd/0
And whatever you type in will be put in the standard input of that application. Note that fd contains the file descriptors used by the application, and I suppose the 0-th file descriptor would always be stdin.
Using PHP for writing into the file (and thus being consumed by the application as input) is possible as well.
I recently implemented Java 7's WatchService and it works perfectly. Now I wondered if there is a way to get all the Events which occured since the last run of my program. For example:
I run my program, create some files, edit some files and I get all the corresponding Events
I close my program
I create a file named foo.txt
I start my program, and the first event i get is an ENTRY_CREATE for foo.txt
I thought about saving the lastModifiedDate and searching for files and directorys newer than the last execution of my program. Is there another (and better) way to do this?
There is no better way to do this if your program is meant to scan for all file changes (apart from storing files in a content / source control repository, but that would be external to your program).
Java 7's WatchService is only a more performant way than continuously looping and comparing file dates / folder contents, hence you need to implement your own logic to solve your own problem.
There is no way to do this in Java, or in any other programming language.
The operating system doesn't (and can't) buffer file system events on the off-chance that someone might start a program to process them. The event monitor / delivery system captures the events for a running application that is listening for them. When nothing is listening, the events are not captured.
You could write a small daemon (system service on Windows) which runs continuously and listens for file system changes. It could write these to a file. When your application runs, rather than listening for changes itself, it could just read the file. As events happen while it runs, the daemon will continue to receive them and send them through the file to the application.
You would need to ensure that the file was organised in such a way that it could be written to and read from safely at the same time, and that it did not grow indefinitely.
Is there a way I can start a command-line application from java and then send strings (commands) to its input stream and display its response from its output stream?
I'm using an application with a pretty sophisticated command line interface (vlc). The application has an interpreter that responds to a set of commands. For example, after I start the app, I can start or stop a movie by issuing the command 'pause' on the command line.
I'd like to write a java application that executes the program and issues commands to the program. I've seen many examples of java apps starting an application and getting the output stream of the app displaying the output of the app. But I've never seen an example, in which the java app would send requests to the sub-application.
Is there a way I can do this using java?
Thanks in advance!
So long as the spawned process listens on stdin for input, sure.
You'd launch a Process in the usual way (Runtime.exec()) - I won't document it here, as you say you've seen plenty of examples.
Then once you have a handle to the spawned process, you call the confusingly-named getOutputStream. This gives you an OutputStream, the other end of which is connected to the process' standard input. Hence, any bytes written to this stream can be consumed by your child process, just as if you were typing/piping input from a console.
I will point to a couple of resources that are always worth reading when dealing with Processes; cut-and-paste jobs from arbitrary Google results often don't cover the edge cases properly and can lead to deadlocks:
When Runtime.exec() won't (old, but still relevant)
Five common Java Process pitfalls