Develop Reference

Java Changing Linux File Permission Sometimes Does not Work

I am working on a task, which is changing the file's permission to 640 after our code exports the file to our Linux server. The same code works in our Dev server, but in our Uat server, sometimes the permission is changed to 640 successfully, sometimes the permission can not be changed, is still the default 600.
I checked the SystemOut.log, no any error for this.
My related Java code is like below:
private void exportXXXFiles() {
......
//Settings for the access permissions of the exported files
Set<PosixFilePermission> filePerms = new HashSet<PosixFilePermission>();
filePerms.add(PosixFilePermission.OWNER_READ);
filePerms.add(PosixFilePermission.OWNER_WRITE);
filePerms.add(PosixFilePermission.GROUP_READ);
try {
Path localFilePath = ......;
Files.setPosixFilePermissions(localFilePath, filePerms);
......
} catch (IOException e) {
e.printStackTrace();
}
}
I am confused why the same code works in our Dev server but not stable in our Uat server, where sometimes it works sometimes it does not work. I assume that is the environment issue, but I have no idea what the exact issue is. Who can give me some suggestions?
Thanks!

There are a few reason why changing permissions might not work. These include:
The application doesn't have permission to change permissions. With classic UNIX / Linux, you need to be the file owner or root to change an file's permissions. Then there are ACLs.
The file system might be read-only, or mounted read only.
The file system type might not support the combination of permissions you are trying to use. For example, FAT did not support execute permissions, and NTFS permissions work a bit differently. Unfortunately, when you mount a "foreign" file system type on Linux, the OS doesn't provide a way to direcrly manipulate the file system's native permissions.
It is possible that what you are trying to do is blocked by SE Linux or AppArmor or similar.
Now, some of these may result in a Java exception when you attempt to change the permission. But that is up to the OS and the file system drivers. Java can only throw an exception if the OS tells Java that the permission change attempt failed, and it can only report / interpret the reason (the errno) returned by the chmod syscall.

Executing java.exe from C# in Azure Function

I'm trying to execute java to run a JAR file from an Azure function, but it seems like the java PATH variable isn't defined or something because Azure can't seem to find it. Code below:
Process proc = new Process();
try
{
proc.StartInfo.UseShellExecute = false;
proc.StartInfo.CreateNoWindow = false;
proc.StartInfo.RedirectStandardOutput = true;
proc.StartInfo.FileName = "java.exe";
proc.StartInfo.Arguments = "-jar file path and some more arguments";
proc.Start();
proc.WaitForExit();
if (proc.HasExited)
log.Info(proc.StandardOutput.ReadToEnd());
log.Info("Java Success!");
}
catch (Exception e)
{
log.Info("Java Fail");
log.Info(e.Message);
}
Even if I remove the proc.StartInfo.Arguments or tell it to use java.exe instead of java I still get the same error, below:
[Info] The system cannot find the file specified
Is calling java not supported in Azure functions?

OK figured this out. So far, the best way is to fully qualify the path to java.exe...
so I changed
proc.StartInfo.FileName = java.exe";
to
proc.StartInfo.FileName = "D:\\Program Files (x86)\\Java\\jdk1.8.0_73\\bin\\java.exe";
You can figure out the full path to Java using KUDU, which is https://[yourFunctionName].scm.azurewebsites.net/
If you click on Tools->DebugConsole, you can browse until you find where Java is located.
Note hard coding the path to Java is probably a bad idea so you should probably use application settings.
Edit Below is a link to a GitHub Repo with my final project. The project does some other stuff, but you can see where I call Java to execute the Batik JAR.
https://github.com/osuhomebase/SVG2PNG-AzureFunction

As of September 2022,
proc.StartInfo.FileName = java.exe";
Worked fine for me. It appears the Azure Function Environment has the JDK installed and the JAVA PATH variable set.

jep went wrong when interpreting python in java

the java code is
String SCRIPT_PATH = "D:\\codes\\Python\\StockDataAnalysis\\MatGraph.py";
try {
Jep jep = new Jep();
jep.runScript(SCRIPT_PATH);
} catch (Exception ex) {
ex.printStackTrace();
}
and it throws exception:
ImportError: No module named site
Python is no doubt installed correctly, for I can run python project on PyCharm. Jep is also set correctly, with lib path added to the PATH in windows System

You could try creating instance of Jep like so:
new Jep(false, path);
where as per javadoc (https://github.com/mrj0/jep/blob/master/src/jep/Jep.java#L299):
#param interactive
whether {#link #eval(String)} should support the slower
behavior of potentially waiting for multiple statements #param includePath
a path of directories separated by File.pathSeparator that
will be appended to the sub-intepreter's sys.path
This approach worked for me in similar case. In my case path was pointing to a directory
...virtualenv\projectname\Lib\site-packages
created for my virtual env where all my python libs for my project are stored.
Please notice that you need to install jep inside of that virtual env first in order to make it work.

Open a path with Desktop.open() from java on ubuntu (linux)

From my application written in java I want to open a folder, using the operating system file explorer.
I use Desktop.open(new File(path))
This works fine on windows, but on ubuntu 11.10 (linux) it doesn't work.
Using the Desktop.open to open a file does work, both on ubuntu and windows.
Using a step in between:
File fPath=new File(fPath)
and testing it with fPath.exists() and fPath.isDirectory() both gives true.
using the Desktop.open(new File(path)) gives me this exception:
java.io.IOException: Failed to show URI:file:/and/here/the/path/I/use/
at sun.awt.X11.XDesktopPeer.launch(Unknown Source)
at sun.awt.X11.XDesktopPeer.open(Unknown Source)
at java.awt.Desktop.open(Unknown Source)
I was not able to test this on an apple computer yet, but I hoped the Desktop.open(new File(path)) was system independent.....
by the way, the complete code:
Desktop desktop = null;
// Before more Desktop API is used, first check
// whether the API is supported by this particular
// virtual machine (VM) on this particular host.
if (!Desktop.isDesktopSupported()) {
// show Error
return;
}
desktop = Desktop.getDesktop();
String path = "here the path ";
// by the way: I use System.getProperty("file.separator") as file seperator
try {
File fPath=new File(path);
if(!fPath.exists()){
// show Error
return;
}
if(!fPath.isDirectory()){
// show Error
return;
}
desktop.open(new File(path));
} catch (IOException e) {
log.severe(e.getMessage());
e.printStackTrace();
// show Error
return;
}
Some extra information:
OS: Linux (3.0.0-16-generic - amd64)
Java: 1.6.0_30-b12
Java home: /opt/java/64/jre1.6.0_30

I had the same problem. But in my case it was Ubuntu 18.04 and java 1.8.0_161-b12
In Windows 10, everything is working fine. But on Ubuntu
Desktop.getDesktop().open(new file)
the program stopped responding.
I decided to wrap the call in the executor:
private ExecutorService executorService;
BasicThreadFactory factory = new BasicThreadFactory.Builder()
.namingPattern("YourPatternIndeficator")
.build();
executorService = Executors.newSingleThreadExecutor(factory);
if (Desktop.isDesktopSupported()) {
File myFile = new File(path);
executorService.execute(() -> {
try {
Desktop.getDesktop().open(myFile);
} catch (IOException e) {
e.printStackTrace();
}
});
}

I was running into what sounds like the same issue on Mint 13. From what I can tell, changes to mime handling for opening directories has broken the java Desktop api. I was able to work around the problem by editing
~/.local/share/applications/defaults.list
and adding this line
x-directory/normal=nautilus.desktop
I'm running Mint 13 Cinnamon with java version "1.7.0_05"

I can't confirm the error. I took your code and constructed a main method around it, and everything works as expected. I don't exactly know where the default applications are set (in my case PCMan was opened instead of usual Nautilus, but it should fulfil its purpose in the end).
Over at java.awt.Desktop.open doesn’t work with PDF files? I have found a link pointing to an issue in Suns (Oracles) bug tracker stating that the method for opening files using AWT isn't reliable even on Windows. Maybe you should think of alternative ways of opening such applications. Furthermore AWT is deprecating soon almost for sure.
If you are utilizing SWT in your application, you could use org.eclipse.swt.program.Program.

I was running into the same issue and decided to give Java 7 a whirl. I'm running java version "1.7.0_147-icedtea" on Ubuntu 11.10_x64 and am able to open file locations in Nautilus quite happily now.

I have the same issue on my Linux Mint (and not in Windows).
That link helped me :
Troubles with java.awt.Desktop browse() method.
This seems to work on my Linux Mint-KDE.
I changed the line
Desktop.getDesktop().desktop.open(new File("/home/user/mypath"));// this throws IOException: Failed to show URI (except in Windows)
with
Desktop.getDesktop().desktop.open(new File("///home/user/mypath"));// this launches Dolphin
or with
Desktop.getDesktop().desktop.open(new File(new URI("file:///home/user/mypath").getPath()));// this launches Dolphin
Dolphin was launched with my folder "mypath". But I found no way to open a file like a pdf or txt on my Linux while it works on Windows with the first code.
(Java 1.8.0_25, Netbeans 8.02, Linux Mint 12 KDE)

I have the issue with Kubuntu 18.04 and java 11. It was solved with
sudo apt install libgnome2-0 gvfs
see https://bugs.launchpad.net/ubuntu/+source/openjdk-8/+bug/1574879/comments/5 for details. java.awt.Desktop works with Gnome not with KDE.

how can I check the compiler and runtime in netbeans?

in one of my questions ,somebody said that I have to make sure that I'm not using compiler 1.6 and 1.5 runtime when i want to execute or debug my program,but I don't know how can i check compiler and runtime in NetBeans ,I am beginner with NetBeans.
my question was:
**I debug my project and the result was :
debug: Have no FileObject for C:\Program Files\Java\jdk1.6.0_02\jre\lib\sunrsasign.jar
Have no FileObject for C:\Program Files\Java\jdk1.6.0_02\jre\classes**
what should i do?
and he answers : you have to make sure that you are not using compiler 1.6 and 1.5 runtime when you want to execute or debug your program

Here's what I use to find out everything about my building environment (never felt too warm with Eclipse):
import static java.lang.System.out;
public class Zeug {
static String[] opts = new String[] { "java.version", "java.vendor",
"java.vendor.url", "java.home", "java.vm.specification.version",
"java.vm.specification.vendor", "java.vm.specification.name",
"java.vm.version", "java.vm.vendor", "java.vm.name",
"java.specification.version", "java.specification.vendor",
"java.specification.name", "java.class.version", "java.class.path",
"java.library.path", "java.io.tmpdir", "java.compiler",
"java.ext.dirs", "os.name", "os.arch", "os.version",
"file.separator", "path.separator", "line.separator", "user.name",
"user.home", "user.dir" };
public static void main(String[] args) {
for(String o : opts) {
out.println(o + ": " + System.getProperty(o));
}
}
}

Go to Tools-->Java Platform and you should see the JDK you are using listed. I am using java-6-sun-1.6.0.16 which does indeed have the jar file you need.
Download the latest JDK from Sun. Go to Tools-->Java Platform and click Add Platform. Navigate to where you installed the latest JDK, name it something meaningful like JDK 1.6.0.16 or whatever and click Finish. Right click on the top level of your project and click Properties. At the top of the popup window change the Java Platform to the one you just added and click ok. At that point, you should not experience your current problem when you compile.
JDK Download Link

You can set the Java version to be used in the project properties (right click on the project).
Edit: after seeing your specific error message: this seems to be a deeper problem. For some reason Netbeans is looking for a file sunrsasign.jar, which is not normally part of the JDK. Looking for the filename on Google indicates that it's part of a cryptography extension, but that seems to have been integrated into the JDK by now. So the JAR is not needed anymore.
I don't know whether it's Netbeans (are you using the most recent version?) or your application that is mistakenly looking for a JAR that has been integrated into the JDK library itselt.