I'm developing a java program that will read a file, for example; PSD file (example.psd), and I'll edit the bytes of the file. How can I call the adobe software and have it read the edited bytes through the java program without having to write out the file?
package sandbox;
import java.io.IOException;
public class Sandbox {
/**
* Example of how to run an executable from Java.
*
* #param args
*/
public static String readFileAsString(String fileName)throws Exception
{
String data = "";
data = new String(Files.readAllBytes(Paths.get(fileName)));
return data;
}
public static void main(String[] args) {
try {
Runtime runTime = Runtime.getRuntime();
String data = readFileAsString("C:\\Users\\pankaj\\Desktop\\example.psd");
String executablePath = "C:\\Users\\sdkca\\AppData\\Local\\Programs\\Adobe\\Adobe.exe";
Process process = runTime.exec(executablePath);
} catch (IOException e) {
e.printStackTrace();
}
}
}
I can call the adobe, and also read the bytes, how would I tell the adobe to read the bytes?
Take a look here:
Java open file with another program
If there is a default opener for the file in the local OS, then that
Desktop.getDesktop().open(...)
may do the trick
Although the titles are very similar, this questions is NOT a duplicate of Process output from apache-commons exec.
I am trying to get the output of a command by using apache-commons exec. Here is what I am doing
import org.apache.commons.exec.*;
import java.io.ByteArrayOutputStream;
public class Sample {
private static void runCommand(String cmd) throws Exception {
ByteArrayOutputStream stdout = new ByteArrayOutputStream();
PumpStreamHandler psh = new PumpStreamHandler(stdout);
CommandLine cl = CommandLine.parse(cmd);
DefaultExecutor exec = new DefaultExecutor();
exec.setStreamHandler(psh);
exec.execute(cl);
System.out.println(stdout.toString());
}
public static void main(String... args) throws Exception {
String cmd1 = "python -c \"print(10)\"";
String cmd2 = "python -c \"import datetime; print(datetime.datetime.now())\"";
runCommand(cmd1); // prints 10
runCommand(cmd2); // should print the current datetime, but does not!
}
}
The problem is that runCommand(cmd2) does not print anything to the output. When I try running the command on terminal, it works fine.
I have tried this program with and without the IDE so I'm sure this has nothing to do with the IDE console.
Here's a screenshot
Here's a screenshot of the terminal
Python command running on the terminal
It works fine on mine PC from IDEA. Try to recreate the project. Add more information about your environment.
Try to put your python code into .py file and run it like "python test.py".
A colleague was able to come up with a solution to this problem. Changing
CommandLine cl = CommandLine.parse(cmd);
to
CommandLine cl = new CommandLine("/bin/sh");
cl.addArguments("-c");
cl.addArguments("'" + cmd + "'", false);
solved the issue.
The complete code looks as follows:
import org.apache.commons.exec.*;
import java.io.ByteArrayOutputStream;
public class Sample {
private static void runCommand(String cmd) throws Exception {
ByteArrayOutputStream stdout = new ByteArrayOutputStream();
PumpStreamHandler psh = new PumpStreamHandler(stdout);
// CommandLine cl = CommandLine.parse(cmd);
CommandLine cl = new CommandLine("/bin/sh");
cl.addArguments("-c");
cl.addArguments("'" + cmd + "'", false);
DefaultExecutor exec = new DefaultExecutor();
exec.setStreamHandler(psh);
exec.execute(cl);
System.out.println(stdout.toString());
}
public static void main(String[] args) throws Exception {
String cmd1 = "python -c \"print(10)\"";
String cmd2 = "python -c \"import datetime; print(datetime.datetime.now())\"";
runCommand(cmd1); // prints 10
runCommand(cmd2);
}
}
I want to prevent the user from running my java application multiple times in parallel.
To prevent this, I have created a lock file when am opening the application, and delete the lock file when closing the application.
When the application is running, you can not open an another instance of jar. However, if you kill the application through task manager, the window closing event in the application is not triggered and the lock file is not deleted.
How can I make sure the lock file method works or what other mechanism could I use?
You could use a FileLock, this also works in environments where multiple users share ports:
String userHome = System.getProperty("user.home");
File file = new File(userHome, "my.lock");
try {
FileChannel fc = FileChannel.open(file.toPath(),
StandardOpenOption.CREATE,
StandardOpenOption.WRITE);
FileLock lock = fc.tryLock();
if (lock == null) {
System.out.println("another instance is running");
}
} catch (IOException e) {
throw new Error(e);
}
Also survives Garbage Collection.
The lock is released once your process ends, doesn't matter if regular exit or crash or whatever.
Similar discussion is at
http://www.daniweb.com/software-development/java/threads/83331
Bind a ServerSocket. If it fails to bind then abort the startup. Since a ServerSocket can be bound only once, only single instsances of the program will be able to run.
And before you ask, no. Just because you bind a ServerSocket, does not mean you are open to network traffic. That only comes into effect once the program starts "listening" to the port with accept().
I see two options you can try:
Use a Java shutdown hook
Have your lock file hold the main process number. The process should exist when you lanuch another instance. If it's not found in your system, you can assume that the lock can be dismissed and overwritten.
Creating a server socket, bounds to a specific port with a ServerSocket instance as the application starts is a straight way.
Note that ServerSocket.accept() blocks, so running it in its own thread makes sense to not block the main Thread.
Here is an example with a exception thrown as detected :
public static void main(String[] args) {
assertNoOtherInstanceRunning();
... // application code then
}
public static void assertNoOtherInstanceRunning() {
new Thread(() -> {
try {
new ServerSocket(9000).accept();
} catch (IOException e) {
throw new RuntimeException("the application is probably already started", e);
}
}).start();
}
You could write the process id of the process that created the lock file into the file.
When you encounter an existing lock file, you do not just quit, but you check if the process with that id is still alive. If not, you can go ahead.
You can create a Server socket like
new ServerSocket(65535, 1, InetAddress.getLocalHost());
at very beginning of your code. Then if AddressAlreadyInUse exception caught in main block you can display the appropriate message.
There are already available java methods in File class to achieve the same. The method is deleteOnExit() which ensure the file is automatically deleted when the JVM exits. However, it does not cater to forcible terminations. One should use FileLock in case of forcible termination.
For more details check, https://docs.oracle.com/javase/7/docs/api/java/io/File.html
Thus code snippet which could be used in the main method can be like :
public static void main(String args[]) throws Exception {
File f = new File("checkFile");
if (!f.exists()) {
f.createNewFile();
} else {
System.out.println("App already running" );
return;
}
f.deleteOnExit();
// whatever your app is supposed to do
System.out.println("Blah Blah")
}
..what other mechanism could I use?
If the app. has a GUI it can be launched using Java Web Start. The JNLP API provided to web-start offers the SingleInstanceService. Here is my demo. of the SingleInstanceService.
You can write something like this.
If file exists try to delete it. if it is not able to delete. We can say that application is already running.
Now create the same file again and redirect the sysout and syserr.
This works for me
Simple lock and advanced lock
I developed 2 solutions for this problem. I was also looking for an easy way of doing this without using any libraries and a lot of code.
My solutions are based on: https://stackoverflow.com/a/46705579/10686802 which I have improved upon. Therefore I would like to thank #akshaya pandey and #rbento
Simple file lock
package YOUR_PACKAGE_NAME;
import java.io.File;
import java.io.IOException;
/**
* Minimal reproducible example (MRE) - Example of a simple lock file.
* #author Remzi Cavdar - ict#remzi.info - #Remzi1993
*/
public class Main {
public static void main(String[] args) {
/*
* Prevents the user of starting multiple instances of the application.
* This is done by creating a temporary file in the app directory.
* The temp file should be excluded from git and is called App.lock in this example.
*/
final File FILE = new File("App.lock");
try {
if (FILE.createNewFile()) {
System.out.println("Starting application");
} else {
System.err.println("The application is already running!");
return;
}
} catch (IOException e) {
throw new RuntimeException(e);
}
/*
* Register a shutdown hook to delete the lock file when the application is closed. Even when forcefully closed
* with the task manager. (Tested on Windows 11 with JavaFX 19)
*/
FILE.deleteOnExit();
// Whatever your app is supposed to do
}
}
Advanced lock
package YOUR_PACKAGE_NAME;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
/**
* Minimal reproducible example (MRE) - Example of a more advanced lock system.
* #author Remzi Cavdar - ict#remzi.info - #Remzi1993
*/
public class Main {
public static void main(String[] args) {
/*
* Prevents the user of starting multiple instances of the application.
* This is done by creating a temporary file in the app directory.
* The temp file should be excluded from git and is called App.lock in this example.
*/
final File FILE = new File("App.lock");
if (FILE.exists()) {
System.err.println("The application is already running!");
return;
}
try (
FileOutputStream fileOutputStream = new FileOutputStream(FILE);
FileChannel channel = fileOutputStream.getChannel();
FileLock lock = channel.lock()
) {
System.out.println("Starting application");
} catch (FileNotFoundException e) {
throw new RuntimeException(e);
} catch (IOException e) {
throw new RuntimeException(e);
}
/*
* Register a shutdown hook to delete the lock file when the application is closed. Even when forcefully closed
* with the task manager. (Tested on Windows 11 with JavaFX 19)
*/
FILE.deleteOnExit();
// Whatever your app is supposed to do
}
}
Testing
Tested on: 31-10-2022
Tested OS: Windows 11 - Version 21H2 (OS Build 22000.1098)
Tested with: OpenJDK 19 - Eclipse Temurin JDK with Hotspot 19+36(x64)
I closed the application and also forcefully closed the application with task manager on Windows both times the lock file seems to be deleted upon (force) close.
I struggled with this same problem for a while... none of the ideas presented here worked for me. In all cases, the lock (file, socket or otherwise) did not persist into the 2nd process instance, so the 2nd instance still ran.
So I decided to try an old school approach to simply crate a .pid file with the process id of the first process. Then any 2nd process would quit if it finds the .pid file, and also the process number specified in the file is confirmed to be still running. This approach worked for me.
There is a fair bit of code, which I provide here in full for your use... a complete solution.
package common.environment;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.io.*;
import java.nio.charset.Charset;
public class SingleAppInstance
{
private static final #Nonnull Logger log = LogManager.getLogger(SingleAppInstance.class.getName());
/**
* Enforces that only a single instance of the given component is running. This
* is resilient to crashes, unexpected reboots and other forceful termination
* scenarios.
*
* #param componentName = Name of this component, for disambiguation with other
* components that may run simultaneously with this one.
* #return = true if the program is the only instance and is allowed to run.
*/
public static boolean isOnlyInstanceOf(#Nonnull String componentName)
{
boolean result = false;
// Make sure the directory exists
String dirPath = getHomePath();
try
{
FileUtil.createDirectories(dirPath);
}
catch (IOException e)
{
throw new RuntimeException(String.format("Unable to create directory: [%s]", dirPath));
}
File pidFile = new File(dirPath, componentName + ".pid");
// Try to read a prior, existing pid from the pid file. Returns null if the file doesn't exist.
String oldPid = FileUtil.readFile(pidFile);
// See if such a process is running.
if (oldPid != null && ProcessChecker.isStillAllive(oldPid))
{
log.error(String.format("An instance of %s is already running", componentName));
}
// If that process isn't running, create a new lock file for the current process.
else
{
// Write current pid to the file.
long thisPid = ProcessHandle.current().pid();
FileUtil.createFile(pidFile.getAbsolutePath(), String.valueOf(thisPid));
// Try to be tidy. Note: This won't happen on exit if forcibly terminated, so we don't depend on it.
pidFile.deleteOnExit();
result = true;
}
return result;
}
public static #Nonnull String getHomePath()
{
// Returns a path like C:/Users/Person/
return System.getProperty("user.home") + "/";
}
}
class ProcessChecker
{
private static final #Nonnull Logger log = LogManager.getLogger(io.cpucoin.core.platform.ProcessChecker.class.getName());
static boolean isStillAllive(#Nonnull String pidStr)
{
String OS = System.getProperty("os.name").toLowerCase();
String command;
if (OS.contains("win"))
{
log.debug("Check alive Windows mode. Pid: [{}]", pidStr);
command = "cmd /c tasklist /FI \"PID eq " + pidStr + "\"";
}
else if (OS.contains("nix") || OS.contains("nux"))
{
log.debug("Check alive Linux/Unix mode. Pid: [{}]", pidStr);
command = "ps -p " + pidStr;
}
else
{
log.warn("Unsupported OS: Check alive for Pid: [{}] return false", pidStr);
return false;
}
return isProcessIdRunning(pidStr, command); // call generic implementation
}
private static boolean isProcessIdRunning(#Nonnull String pid, #Nonnull String command)
{
log.debug("Command [{}]", command);
try
{
Runtime rt = Runtime.getRuntime();
Process pr = rt.exec(command);
InputStreamReader isReader = new InputStreamReader(pr.getInputStream());
BufferedReader bReader = new BufferedReader(isReader);
String strLine;
while ((strLine = bReader.readLine()) != null)
{
if (strLine.contains(" " + pid + " "))
{
return true;
}
}
return false;
}
catch (Exception ex)
{
log.warn("Got exception using system command [{}].", command, ex);
return true;
}
}
}
class FileUtil
{
static void createDirectories(#Nonnull String dirPath) throws IOException
{
File dir = new File(dirPath);
if (dir.mkdirs()) /* If false, directories already exist so nothing to do. */
{
if (!dir.exists())
{
throw new IOException(String.format("Failed to create directory (access permissions problem?): [%s]", dirPath));
}
}
}
static void createFile(#Nonnull String fullPathToFile, #Nonnull String contents)
{
try (PrintWriter writer = new PrintWriter(fullPathToFile, Charset.defaultCharset()))
{
writer.print(contents);
}
catch (IOException e)
{
throw new RuntimeException(String.format("Unable to create file at %s! %s", fullPathToFile, e.getMessage()), e);
}
}
static #Nullable String readFile(#Nonnull File file)
{
try
{
try (BufferedReader fileReader = new BufferedReader(new FileReader(file)))
{
StringBuilder result = new StringBuilder();
String line;
while ((line = fileReader.readLine()) != null)
{
result.append(line);
if (fileReader.ready())
result.append("\n");
}
return result.toString();
}
}
catch (IOException e)
{
return null;
}
}
}
To use it, simply invoke it like this:
if (!SingleAppInstance.isOnlyInstanceOf("my-component"))
{
// quit
}
I hope you find this helpful.
Finally I found really simple library to achieve this. You can you use JUniqe.
The JUnique library can be used to prevent a user to run at the same
time more instances of the same Java application.
This is an example how to use it from the documentation
public static void main(String[] args) {
String appId = "myapplicationid";
boolean alreadyRunning;
try {
JUnique.acquireLock(appId);
alreadyRunning = false;
} catch (AlreadyLockedException e) {
alreadyRunning = true;
}
if (!alreadyRunning) {
// Start sequence here
}
}
here is a pretty rudimental approach.
If your application is launched from a script, check the running java/javaw processes and their command line before launch
In windows
REM check if there is a javaw process running your.main.class
REM if found, go to the end of the script and skip the launch of a new instance
WMIC path win32_process WHERE "Name='javaw.exe'" get CommandLine 2>nul | findstr your.main.class >nul 2>&1
if %ERRORLEVEL% EQU 0 goto:eof
javaw your.main.class
How can i verify if a user is root in a java application?
Thanks
Process p = Runtime.getRuntime().exec("id -u")
Keep in mind that the "root" user on a system may not be called root (although it's rare to change it), and it's also possible to alias it to another username. If the current user is root-like, the output will be 0.
Easy. Just use
System.getProperty("user.name")
run a native command?
like whoami
You can call
Process p = Runtime.getRuntime.exec("whoami")
method. Then you can process p's stdout to read output of command.
Check this: get login username in java.
The best way is to run
Process p = Runtime.getRuntime.exec("groups `whoaim`");
and try to parse string to get group call root. Your JVM process could be run by user not call root but i.e. moderator but this user could be in root group and you have root privileges.
String userName = System.getProperty("user.name");
Process p = Runtime.getRuntime().exec("groups " + userName);
String output = read(p.getInputStream());
String error = read(p.getErrorStream());
And here is a read function:
public static String read(InputStream input) throws IOException {
try (BufferedReader buffer = new BufferedReader(new InputStreamReader(input))) {
return buffer.lines().collect(Collectors.joining("\n"));
}
}
Just "another" modified solution.
Here is a complete Utility class with a working method
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StringWriter;
public interface U {
public static final Logger l = LogManager.getLogger(U.class.getName());
public static boolean isRoot() {
try {
Process p = Runtime.getRuntime().exec("id -u");
StringWriter sw = new StringWriter();
InputStreamReader isw = new InputStreamReader(p.getInputStream());
isw.transferTo(sw);
String output = sw.toString();
l.trace("id -u output = [{}]", output);
return output.startsWith("0");
} catch (IOException e) {
l.error("", e);
}
return false;
}
}
I'm running an application from inside another one for testing purposes. I want to redirect the output for the tested app to a file, so I can have a log after each test.
Is there a way to redirect the output of an app to a file from the command line in java?
You can use the output stream redirector that is supported by the Windows command line, *nix shells , e.g.
java -jar myjar.jar > output.txt
Alternatively, as you are running the app from inside the vm, you could redirect System.out from within java itself. You can use the method
System.setOut(PrintStream ps)
Which replaces the standard output stream, so all subsequent calls to System.out go to the stream you specify. You could do this before running your wrapped application, e.g. calling System.setOut(new PrintStream(new BufferedOutputStream(new FileOutputStream("output.txt"))));
If you are using a wrapper that you can't modify, then create your own wrapper. So you have FEST wrapper -> stream redirector wrapper -> tested app.
For example, you can implement a simple wrapper like this:
public class OutputRedirector
{
/* args[0] - class to launch, args[1]/args[2] file to direct System.out/System.err to */
public static void main(String[] args) throws Exception
{ // error checking omitted for brevity
System.setOut(outputFile(args(1));
System.setErr(outputFile(args(2));
Class app = Class.forName(args[0]);
Method main = app.getDeclaredMethod("main", new Class[] { (new String[1]).getClass()});
String[] appArgs = new String[args.length-3];
System.arraycopy(args, 3, appArgs, 0, appArgs.length);
main.invoke(null, appArgs);
}
protected PrintStream outputFile(String name) {
return new PrintStream(new BufferedOutputStream(new FileOutputStream(name)), true);
}
}
You invoke it with 3 additional params - the Main class to run, and the output/error directs.
When using this constructor:
new PrintStream(new BufferedOutputStream(new FileOutputStream("file.txt")));
remember to set autoflushing to true, i.e.:
new PrintStream(new BufferedOutputStream(new FileOutputStream("file.txt")), true);
otherwise you may get empty files even after your program finishes.
Yes you can set your desired file like this.
try {
System.setOut(new PrintStream(new File("output-file.txt")));
} catch (Exception e) {
e.printStackTrace();
}
System.out.println() is used to print messages on the console.
System is a class defined in the java.lang package. out is an instance of PrintStream, which is a public and static member of the class System. As all instances of PrintStream class have a public method println().
System.out is a static PrintStream that writes to the console. We can redirect the output to a different PrintStream using the System.setOut() method which takes a PrintStream as a parameter.
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;
public class SetPrintStream {
public static void main(String[] args) throws FileNotFoundException{
System.out.println("Print on console");
// Store console print stream.
PrintStream ps_console = System.out;
File file = new File("file.txt");
FileOutputStream fos = new FileOutputStream(file);
// Create new print stream for file.
PrintStream ps = new PrintStream(fos);
// Set file print stream.
System.setOut(ps);
System.out.println("Print in the file !!");
// Set console print stream.
System.setOut(ps_console);
System.out.println("Console again !!");
}
}
Output:
Print on console
Console again !!
new file.txt will be created.
For more information see my blog:
http://javaexplorer03.blogspot.in/2016/02/how-do-i-redirect-standard-output-to.html
In order to improve "vijay.shad" response I used the code bellow to direct the file to the Home Directory in Linux or MyDocuments in Windows.
try {
System.setOut(new PrintStream(new File(FileSystemView.getFileSystemView()
.getDefaultDirectory().toString()
+ File.separator + "output-file.txt")));
} catch (Exception e) {
e.printStackTrace();
}
File file = new File("xyz.txt");
PrintStream printStreamToFile = new PrintStream(file);
System.setOut(printStreamToFile);
System.out.println("Hello I am writing to File xyz.txt");
Or you can use Class FileWriter.