How do i call a Java command from a stand alone java program.
I understand that Runtime.getRuntime().exec("cmd c/ javac <>.java"); would work. However, this would be platform specific.
Any other APIs available that could make it work in j2sdk1.4 ?
If you can run everything in the same JVM, you could do something like this:
public class Launcher {
...
public static void main(String[] args) throws Exception {
launch(Class.forName(args[0]), programArgs(args, 1));
}
protected static void launch(Class program, String[] args) throws Exception {
Method main = program.getMethod("main", new Class[]{String[].class});
main.invoke(null, new Object[]{args});
}
protected static String[] programArgs(String[] sourceArgs, int n) {
String[] destArgs = new String[sourceArgs.length - n];
System.arraycopy(sourceArgs, n, destArgs, 0, destArgs.length);
return destArgs;
}
And run it with a command line like this:
java Launcher OtherClassWithMainMethod %CMD_LINE_ARGS%
Calling Runtime.getRuntime().exec() is not only platform specific, it is extremely inefficient. It will result in spawning a brand new shell and an entire jvm which could potentially be very expensive depending on the dependencies of this application (no pun intended).
The best way to execute "external" Java code would be to place it in your CLASSPATH. If you must call an application's main method you can simply import and call the method directly. This could be done like so:
import my.externals.SomeMain
// call as if we are running from console
SomeMain.main(new String[] {"some", "console", "arguments"})
Of course, the best case scenario would be to simply use this as an external library and access the code you need without having to call SomeMain.main(). Adhering to best practices and writing proper encapsulated modular objects allows for much greater portability and ease of use when being used by other applications.
When you leave the JVM and move to system commands, then you have to deal with the platform specific commands yourself. The JVM offers a good way for abstraction, so why move away?
If you want to execute java specific binaries, check out the ant libraries of java. You can execute ant scripts from java which execute platform depending commands.
Java programming from quercus php on GAE:
import com.newatlanta.commons.vfs.provider.gae.GaeVFS;
import org.apache.commons.io.IOUtils;
import java.lang.Long;
import java.lang.Boolean;
GaeVFS::setRootPath(quercus_servlet_request()->getSession(true)->getServletContext()->getRealPath('/'));
define('VFSM', GaeVFS::getManager());
//VFSM->resolveFile('gae://gaevfs')->createFolder();
$file=VFSM->resolveFile('gae://gaevfs/tmp1');
//$file->createFile();
$text='pp';
$method=$file->getClass()->getDeclaredMethod('updateContentSize', array(Long::TYPE, Boolean::TYPE));
$method->setAccessible(true);
$method->invoke($file, strlen($text), true);
$out=$file->getContent()->getOutputStream();
IOUtils::write($text, $out, 'UTF8');
$out->close();
$in=$file->getContent()->getInputStream();
$method=$file->getClass()->getDeclaredMethod('doGetContentSize',array());
$method->setAccessible(true);
$len=$method->invoke($file);
$whole=IOUtils::toString($in, 'UTF8').':'.$len."<br>";
$in->close();
echo $whole;
GaeVFS::clearFilesCache();
GaeVFS::close();
Related
I want to create a GUI app in java for signing j2me app which is done by JadTool.jar but it is a Command Line Interface Apps. So I just want to use it as library and pass the parameters in program. How it can be done?
Check out Runtime. It will allow you to execute a command. You can use this to start your command line interface library.
Edit:
Ah, I didn't read care carefully earlier. If you're using a Java library starting a separate process is not the best solution.
Just reference the JadTool jar from your project. If the functionality you need isn't accessible in the library, edit the source and recompile. Make sure JadTool's license allows this.
If you're against editing the source (or not allowed) try using reflection to invoke the private run method you need.
A jar is just a library of classes, the fact that it can be run from the command line is caused by the presence of a main method in a class. As jadtool's source is available it's easy to see its very simple main:
public static void main(String[] args) {
int exitStatus = -1;
try {
new JadTool().run(args);
exitStatus = 0;
} catch (Exception e) {
System.err.println("\n" + e.getMessage() + "\n");
}
System.exit(exitStatus);
}
Unfortunately, that run() method is private, so calling it directly from another class won't work, leading to a reduced set of options:
#WilliamMorrison 's solution of going via Runtime - not really a library call, but it would work.
see Any way to Invoke a private method?
I'm working on java application which perform some Runtime sub-process on files, for some files I got error cause the Send error report to Microsoft window to appear ,I need to handle this error programmatically, without showing this window to user. Please can anyone help ?
To Suppress windows error reporting the .exe that is being invoked should not terminate with an unhandled exception. This only works if you have access to the source of the application.
Based on the WER Reference - you should use the Win32 API call WerAddExcludedApplication to add the specific .exe files that you are intending to ignore to the per-user ignore list - you could create a simple stub-application that allows you to add applications by name to the ignore list. Then when you invoke the application it does not trigger the error.
Similarly you could create another application to remove them using the WerRemoveExcludedApplication.
Alternatives are to use JNI/JNA to make a class to encapsulate this functionality rather than using Runtime.exec
Here is a simple example using Java Native Access (JNA), which is a simpler version of JNI (no C++ needed for the most part). Download the jna.jar and make it part of your project.
import com.sun.jna.Native;
import com.sun.jna.WString;
import com.sun.jna.win32.StdCallLibrary;
public class JNATest {
public interface CLibrary extends StdCallLibrary {
CLibrary INSTANCE = (CLibrary) Native.loadLibrary("wer.dll",
CLibrary.class);
int WerAddExcludedApplication(WString name, boolean global);
int WerRemoveExcludedApplication(WString name, boolean global);
}
public static void main(String[] args) {
CLibrary.INSTANCE.WerAddExcludedApplication(new WString("C:\\foo.exe"), false);
CLibrary.INSTANCE.WerRemoveExcludedApplication(new WString("C:\\foo.exe"), false);
}
}
Basically, replace the new WString(...) value with the name of the application that you are intending to ignore. It should be ignored for the purposes of windows error reporting at that point.
Bear in mind that the wer.dll is only on Windows Vista and newer, so if this is a problem, then you may need to edit the registry entries manually.
You can always use try-catch-finally statement:
try
{
some code here (the code that is causing the error);
}
catch (Exception x)
{
handle exception here;
}
It works for me...
EDIT Here is the link that can help you a little bit more:
http://www.exampledepot.com/egs/Java%20Language/TryCatch.html
I am trying to grab filesystem events on OS / Kernel level on OS X.
There are 2 requirements i have to follow. The first one is to do this in java as the whole project im developing for is written in java. The second one is that i have to find out when a document is opened.
For Linux I used inotify-java, but I can't find a good equivalent on OS X. Also the JNA doesn't provide a helpful binding. Currently I'm avoiding catching events by frequently calling the lsof program. This, however, is a bad solution.
Thanks for the help.
You can use dtrace on OSX, but since it needs root privileges it's not something you'd want to put into a runtime of a system.
In any case, you won't be able to do this in pure Java (any Java API would be a wrapper around some lower level C introspection, and if you're doing it kernel-wide, would need to be done as root).
If you just want to track when your program is opening files (as opposed to other files on the same system) then you can install your own Security Manager and implement the checkRead() family of methods, which should give you an idea of when accesses are happening.
import java.io.*;
public class Demo {
public static void main(String args[]) throws Exception {
System.setSecurityManager(new Sniffer());
File f = new File("/tmp/file");
new FileInputStream(f);
}
}
class Sniffer extends SecurityManager {
public void checkRead(String name) {
System.out.println("Opening " + name);
}
}
Other than an anonymous class (new OutputStream() { ... }), can anyone suggest a moral equivalent of new FileOutputStream("/dev/null") that also works on Windows?
In case someone's wondering 'what's this for?'
I have a program that does a consistency analysis on a file. It has a 'verbose' option. When the verbose option is on, I want to see a lot of output. The program is not in a hurry, it's a tool, so instead of writing all those extra if statements to test if I want the output, I just want to write it to the bit-bucket when not desired.
You can use NullOutputStream from apache commons
https://commons.apache.org/proper/commons-io/javadocs/api-2.4/org/apache/commons/io/output/NullOutputStream.html
Or just implement your own
package mypackage;
import java.io.OutputStream;
import java.io.IOException;
public class NullOutputStream extends OutputStream {
public void write(int i) throws IOException {
//do nothing
}
}
NUL works for Windows NT, but that doesn't work in *NIX.
output = new FileOutputStream("NUL");
Better use NullOutputStream of the Commons IO instead to be platform independent.
Starting from JDK 11, you can use a new static method on OutputStream - nullOutputStream.
var out = OutputStream.nullOutputStream();
As long as you don't care about the slight performance difference (and you don't feel like you might run out of space), you can just use "/dev/null". On Windows, it will create a real file on whatever your current drive is (e.g., c:\dev\null).
Is there any way to execute perl code without having to use Runtime.getRuntime.exec("..."); (parse in java app)?
I've been looking into this myself recently. The most promising thing I've found thus far is the Inline::Java module on CPAN. It allows calling Java from Perl but also (via some included Java classes) calling Perl from Java.
this looks like what you're asking for
Inline::Java provides an embedded Perl interpreter in a class. You can use this to call Perl code from your Java code.
Graciliano M. Passos' PLJava also provides an embedded interpreter.
Don't use JPL (Java Perl Lingo)--the project is dead and has been removed from modern perls.
Inline::Perl is the accepted way. But there's also Jerl which may be run from a JAR.
Here's an example without using the VM wrapper (which is not so fun).
Here's some examples using the jerlWrapper class to make it easier to code:
import jerlWrapper.perlVM;
public final class HelloWorld {
/* keeping it simple */
private static String helloWorldPerl = "print 'Hello World '.$].\"\n\";";
public static void main(String[] args) {
perlVM helloJavaPerl = new perlVM(helloWorldPerl);
helloJavaPerl.run();
}
}
or
import jerlWrapper.perlVM;
public final class TimeTest {
/* The (ugly) way to retrieve time within perl, with all the
* extra addition to make it worth reading afterwards.
*/
private static String testProggie = new String(
"my ($sec, $min, $hr, $day, $mon, $year) = localtime;"+
"printf(\"%02d/%02d/%04d %02d:%02d:%02d\n\", "+
" $mon, $day + 1, 1900 + $year, $hr, $min, $sec);"
);
public static void main(String[] args) {
perlVM helloJavaPerl = new perlVM(testProggie);
boolean isSuccessful = helloJavaPerl.run();
if (isSuccessful) {
System.out.print(helloJavaPerl.getOutput());
}
}
}
I could have sworn it was easy as pie using the Java Scripting API.
But apparently it's not on the list of existing implementations...
So, maybe this helps instead :
java and perl
edit: i said "maybe"
No, I don't believe this exists. While there have been several languages ported to the JVM (JRuby, Jython etc) Perl is not yet one of them.
In the future, the standard way to use any scripting language is through the java Scripting Support introduced in JSR 223. See the scripting project homepage for a list of scripting languages supported at the moment. Unfortunately, Perl isn't on there yet :-(