Suppose I launch a Java application:
java -cp whatever.jar com.example.Start
Process launches ok and keeps running with PID 1314.
Now I would like the system to fire a method by users request.
How can I use bash to signal the running PID and have it fire a method?
My thought is to have bash echo data to the Java processes via a named pipe, which I'm pretty sure Java has support for.
To communicate with a Java process, you would normally use RMI from another process (this could be in the same JAR)
However, if you want a pure bash/unix utilities solution, you could have the application listen on a port for commands and send back responses. This means you could use plain telnet to send commands and get output. One example of this is to use a http server with wget or you could have a simple socket based solution.
Related
I have installed a terminal client utility on my linux terminal that enables me to talk to an external remote device. How do i execute such stuff using the java runtime?
For example if i want to execute a query on a mongodb installation, I can open a terminal and move to the mongo client mode by executing the "mongo --port 27017" command and get connected to the mongo server and then execute the commands from the mongo client mode from the terminal window. How can i do this from java run time.
[akhilv#dc1devpavxsrv01 bin]$ ./mongo --port 27017
MongoDB shell version: 2.6.5
connecting to: 127.0.0.1:5000/test
rpset:PRIMARY> use quartz
switched to db quartz
rpset:PRIMARY> show collections
quartz__calendars
quartz__jobs
quartz__locks
quartz__triggers
system.indexes
rpset:PRIMARY>
rpset:PRIMARY> exit
bye
[akhilv#dc1devpavxsrv01 bin]$
The above is the actual stuff that I want to be doing from the Runtime. I first execute the command ./mongo --port 27017 from my raw terminal and i am moved into the mongo client mode. Then i execute the use quartz, show collections etc, which are understood only by my mongo client mode.
I am trying to execute "use quartz" and "show collections" commands to he executed from the java code using the Runtime. I am not very specific about Runtime, but need to be using something within java as i cannot go for client libraries from mongo or any other vendors.
Please help
It is possible to do that by forking external processes from java and capture its I/O channels. So basicly from java you would have to invoke shell command, campture and parse its output. See some details on Process class.
http://docs.oracle.com/javase/7/docs/api/java/lang/Process.html
The most interesting methods for you are waitFor() getInputStream() and getOutputStream()
This is very similar how android applications can use root access - the same way :)
I need to access and run Linux commands on a remote CentOS machine through Java code. Please suggest me any API to access run the commands and also I need to get the output of the commands to be printed on the Java console.
Check out JSch - it allows you to connect via SSH, execute commands remotely and transfer files.
You can use Java ProcessorBuilder and Process classes to start an ssh process that executes remote command i.e. start an ssh process (e.g. ssh username#REMOTE_MACHINE 'CMD_ON_REMOTE_MACHINE') and read the output of the executed command using getInputStream() method of Process class.
I want to control a remote system in Java via SSH using JSCH.
The front end is a simple button GUI which triggers the execution of a command.
Some of the controls are time critical, there should be no big delay between button press and command execution.
My problem:
Every time a new channel is opened, the back-end needs about 8 seconds to initialize until the command is executed. (The back-end interface is implemented with RBSH afaik)
If I run a normal session via a console client, everything runs fine without bigger delays.
My question:
Is there a way to initialize a channel to execute some commands and read the output(and only the command output) back sequentially?
I already figured out that session.openChannel("shell") could give the desired functionality, but I cant figure out how to do that properly.
EDIT: I'm not tied to JSCH. If there's another library which can do that, I'm also open for that
You want an "exec" channel rather than a "shell" channel. SCP uses an exec channel, so look at one of the SCP examples or one of the SCP libraries on the Internet.
Alternately, if you control the remote server, you could define a "subsystem" for the command that you want to run, and run it through a subsystem channel. The big difference between an exec channel and a subsystem is who specifies the command to be executed. An exec channel will execute a command provided by the client. With a subsystem, the client just requests the subsystem by name, and the server runs the correct command (or provides the service in some other way). SFTP uses a subsystem called "sftp-server", so you could look at how Jsch's SFTP classes are implemented.
I know Java can act as a client for reading/writing named pipes, but I need another program which acts as a server.
In this case the program I am communicating with must act as the client, rather than the server. Is it possible for Java to act in server mode for named pipes?
EDIT: In named pipes (Windows) there are client and server modes. A server must first be established before a client can connect to it. I have a legacy application which acts as a 'client', this means that it connects to what it assumes is an already established named pipe.
I have a new java application which I would like to have communicate with this legacy app using named pipes. I have only found examples of how to use Java named pipes in connection to previously established named pipes.
Well on linux and mac you can always have java emit to the console one line at a time. Example:
In one terminal window to this:
mkfifo myPipe
java -jar mydataserver.jar > mkfifo
In a second terminal window do this:
while read line; do echo "What has been passed through the pipe is \
${line}"; done<myPipe
Yes, you can create named pipe on the Java server using JNA library https://github.com/java-native-access/jna
It is clearly shown in the following test: https://github.com/java-native-access/jna/blob/master/contrib/platform/test/com/sun/jna/platform/win32/Kernel32NamedPipeTest.java
API of JNA wrapper is the same as Win32 hence you will be able to use all the features and power of named pipes on Windows.
I am trying to make a terminal emulator in Java. The java program will accept the commands from user, and show its output to them. I can emulate simple commands like 'ls', but I don't know how to handle commands like 'cd'. This is because, I am using exec() method for executing terminal commands. So, all the commands are executed at current directory. The commands like 'cd ..' are executed, but then they have no persistent effect, because each command is separately executed by exec().
Any Ideas How I can emulate a whole session??
If you are executing commands with exec(), you are not writing a terminal emulator; you are writing a shell. In that case, you will need to keep track of things the shell keeps track of, like environment variables and working directory.
If you really want to write a terminal emulator, you would be talking to a shell process through a pseudo-terminal. Then your program would just be keeping track of the things a terminal keeps track of, like the line state and what appears on the screen.
Working with a pseudo-terminal from Java will be a little tricky, because most of the documentation assumes you are using a C api. man pty should get you started. Your Java process will have to open the master side of the pseudo-terminal with FileStream objects. I'm not sure there is a way within Java to get a child process to open the slave side of the pseudo-terminal; you might have to invoke a shell command with exec() that starts another shell command with standard input/output/error redirected to the slave side of the pseudo terminal.
JSch is a pure Java implementation of SSH2.
JSch allows you to connect to an sshd server and use port forwarding, X11 forwarding, file transfer, etc., and you can integrate its functionality into your own Java programs.
http://www.jcraft.com/jsch/
You should really give a try to Ganymed.
Ganymed SSH-2 for Java is a library which implements the SSH-2
protocol in pure Java (tested on J2SE 1.4.2 and 5.0). It allows one to
connect to SSH servers from within Java programs. It supports SSH
sessions (remote command execution and shell access), local and remote
port forwarding, local stream forwarding, X11 forwarding, SCP and
SFTP.
http://www.ganymed.ethz.ch/ssh2/
Ganymed along with apache FTP client you can also download and upload files.
Also there is a inbuilt example code for terminal emulation in Ganymed.
The following is a link to a project which is did using Ganymed along with apache FTP client.
GITHUB
Happy Coding!!