The goal is to have a simple Java class start a jar main-class. When the main-class finishes, it can be queried if it would like to be reloaded. By this method it can hot-update itself and re-run itself.
The Launcher is to load the jar via a URLClassloader and then unload/re-load the changed jar. The jar can be changed by a modification to Launcher, or by a provided dos/unix script that is called to swap the new jar into place of the old jar.
The entire program is below. Tested and it seems to work without a hitch.
java Launcher -jar [path_to_jar] -run [yourbatchfile] [-runonce]? optional]
1) Launcher looks for the "Main-Class" attribute in your jarfile so that it does not need to be giventhe actual class to run.
2) It will call 'public static void main(String[] args)' and pass it the remaining arguments that you provided on the command line
3) When your program finishes, the Launcher will call your programs method 'public static boolean reload()' and if the result is 'true' this will trigger a reload.
4) If you specified -runonce, then the program will never reload.
5) If you specified -run [batchfile] then the batchfile will run before reloading.
I hope this is helpful to some people.
Happy coding!
import java.io.File;
import java.io.IOException;
import java.lang.ProcessBuilder.Redirect;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.jar.Attributes;
import java.util.jar.Manifest;
public class Launcher {
public static void main(String[] args) {
new Launcher().run(new ArrayList<>(Arrays.asList(args)));
}
private void run(List<String> list) {
final String jar = removeArgPairOrNull("-jar", list);
final boolean runonce = removeArgSingle("-runonce", list);
final String batchfile = removeArgPairOrNull("-run", list);
if (jar == null) {
System.out.println("Please add -jar [jarfile]");
System.out.println("All other arguments will be passed to the jar main class.");
System.out.println("To prevent reloading, add the argument to -runonce");
System.out.println("To provide another program that runs before a reload, add -run [file]");
}
boolean reload;
do {
reload = launch(list.toArray(new String[0]), new String(jar), new String(batchfile), new Boolean(runonce));
System.out.println("Launcher: reload is: " + reload);
gc();
if (reload && batchfile != null) {
try {
System.err.println("Launcher: will attempt to reload jar: " + jar);
runBatchFile(batchfile);
} catch (IOException | InterruptedException ex) {
ex.printStackTrace(System.err);
System.err.println("Launcher: reload batchfile had exception:" + ex);
reload = false;
}
}
} while (reload);
}
private boolean launch(String[] args, String jar, String batchfile, boolean runonce) {
Class<?> clazz = null;
URLClassLoader urlClassLoader = null;
boolean reload = false;
try {
urlClassLoader = new URLClassLoader(new URL[]{new File(jar).toURI().toURL()});
String mainClass = findMainClass(urlClassLoader);
clazz = Class.forName(mainClass, true, urlClassLoader);
Method main = clazz.getMethod("main", String[].class);
System.err.println("Launcher: have method: " + main);
Method reloadMethod;
if (runonce) {
// invoke main method using reflection.
main.invoke(null, (Object) args);
} else {
// find main and reload methods and invoke using reflection.
reloadMethod = clazz.getMethod("reload");
main.invoke(null, (Object) args);
System.err.println("Launcher: invoked: " + main);
reload = (Boolean) reloadMethod.invoke(null, new Object[0]);
}
} catch (final Exception ex) {
ex.printStackTrace(System.err);
System.err.println("Launcher: can not launch and reload this class:" + ex);
System.err.println("> " + clazz);
reload = false;
} finally {
if (urlClassLoader != null) {
try {
urlClassLoader.close();
} catch (IOException ex) {
ex.printStackTrace(System.err);
System.err.println("Launcher: error closing classloader: " + ex);
}
}
}
return reload ? true : false;
}
private static String findMainClass(URLClassLoader urlClassLoader) throws IOException {
URL url = urlClassLoader.findResource("META-INF/MANIFEST.MF");
Manifest manifest = new Manifest(url.openStream());
Attributes attr = manifest.getMainAttributes();
return attr.getValue("Main-Class");
}
private static void runBatchFile(String batchfile) throws IOException, InterruptedException {
System.out.println("Launcher: executng batchfile: " + batchfile);
ProcessBuilder pb = new ProcessBuilder("cmd", "/C", batchfile);
pb.redirectErrorStream(true);
pb.redirectInput(Redirect.INHERIT);
pb.redirectOutput(Redirect.INHERIT);
Process p = pb.start();
p.waitFor();
}
private static String removeArgPairOrNull(String arg, List<String> list) {
if (list.contains(arg)) {
int index = list.indexOf(arg);
list.remove(index);
return list.remove(index);
}
return null;
}
private static boolean removeArgSingle(String arg, List<String> list) {
if (list.contains(arg)) {
list.remove(list.indexOf(arg));
return true;
}
return false;
}
private void gc() {
for (int i = 0; i < 10; i++) {
byte[] bytes = new byte[1024];
Arrays.fill(bytes, (byte) 1);
bytes = null;
System.gc();
System.runFinalization();
}
}
}
After debugging, I determined the original difficulty was that the Launcher was not isolating the UrlClassloader.
By putting the part of the program that starts the classloader in a seperate method, I was able to allow all the system to determine that no more references existed.
After reworking the code, it all works now :)
Related
This code works fine in Linux but not in Windows 7: to get file contents update I have to click on the output file. Where is the trick?
I am using Windows 7 prof, NetBeans IDE 8.0 RC1 (Build 201402242200) updated to version NetBeans 8.0 Patch 1.1, JDK 1.8
package watchfilethreadmod;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.file.Files;
import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import java.nio.file.Path;
import java.nio.file.Paths;
import static java.nio.file.StandardWatchEventKinds.*;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
public class WatchFileThreadMod {
static class WatchFile {
String fileName;
long lastFilePos;
RandomAccessFile file;
public WatchFile(String _fileName, RandomAccessFile _file) {
fileName = _fileName;
lastFilePos = 0;
file = _file;
}
}
public static void shutDownListener(Thread thread) {
Thread thr = thread;
if (thr != null) {
thr.interrupt();
}
}
private static class MyWatchQueueReader implements Runnable {
/**
* the watchService that is passed in from above
*/
private WatchService myWatcher;
public ArrayList<WatchFile> threadFileToWatch;
public String dirPath;
public MyWatchQueueReader(String _dirPath, WatchService myWatcher, ArrayList<WatchFile> _threadFileToWatch) {
this.myWatcher = myWatcher;
this.threadFileToWatch = _threadFileToWatch;
this.dirPath = _dirPath;
}
private void openFile(WatchFile obj) {
try {
System.out.println("Open file "+obj.fileName);
obj.file = new RandomAccessFile(dirPath + "/" + obj.fileName, "r");
} catch (FileNotFoundException e) {
obj.file = null;
System.out.println("filename " + obj.fileName + " non trovato");
}
obj.lastFilePos = 0;
}
private void process(WatchEvent evt) {
String thisLine;
ArrayList<WatchFile> auxList = threadFileToWatch;
for (WatchFile obj : auxList) {
if (obj.fileName.equals(evt.context().toString())) {
if (obj.file == null) {
openFile(obj);
}
try {
obj.file.seek(obj.lastFilePos);
} catch (IOException e) {
System.err.println("Seek error: " + e);
}
try {
thisLine = obj.file.readLine();
if ((thisLine == null)&&(evt.kind() == ENTRY_MODIFY)) {
System.out.printf("---> thisLine == null received %s event for file: %s\n",
evt.kind(), evt.context());
obj.file.close();
System.out.println("Close file "+obj.fileName);
openFile(obj);
thisLine = obj.file.readLine();
}
while (thisLine != null) { // while loop begins here
if (thisLine.length() > 0) {
if (thisLine.substring(thisLine.length() - 1).equals("*")) {
obj.lastFilePos = obj.file.getFilePointer();
System.out.println(obj.fileName + ": " + thisLine);
}
}
thisLine = obj.file.readLine();
} // end while
} // end try
catch (IOException e) {
System.err.println("Error: " + e);
}
}
}
}
/**
* In order to implement a file watcher, we loop forever ensuring
* requesting to take the next item from the file watchers queue.
*/
#Override
public void run() {
try {
// get the first event before looping
WatchKey key = myWatcher.take();
while (key != null) {
// we have a polled event, now we traverse it and
// receive all the states from it
for (WatchEvent event : key.pollEvents()) {
WatchEvent.Kind eventType = event.kind();
if (eventType == OVERFLOW) {
continue;
}
process(event);
}
key.reset();
key = myWatcher.take();
}
} catch (InterruptedException e) {
ArrayList<WatchFile> auxList = threadFileToWatch;
for (WatchFile obj : auxList) {
if (obj.file != null) {
try {
obj.file.close();
System.out.println("chiusura file " + obj.fileName);
} catch (IOException ex) {
System.out.println("errore in chiusura file");
Logger.getLogger(WatchFileThreadMod.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
//e.printStackTrace();
}
System.out.println("Stopping thread");
}
}
public static void main(String[] args) throws Exception {
// get the directory we want to watch, using the Paths singleton class
//Path toWatch = Paths.get(DIRECTORY_TO_WATCH);
ArrayList<WatchFile> fileToWatch = new ArrayList<>();
String filename;
RandomAccessFile file;
fileToWatch.add(new WatchFile("EURUSD.rlt", new RandomAccessFile(args[0] + "/EURUSD.rlt", "r")));
filename = "EURCHF2.rlt";
try {
file = new RandomAccessFile(args[0] + "/" + filename, "r");
} catch (FileNotFoundException e) {
file = null;
System.out.println("filename " + filename + " non trovato");
}
fileToWatch.add(new WatchFile(filename, file));
fileToWatch = fileToWatch;
Path toWatch = Paths.get(args[0]);
if (toWatch == null) {
throw new UnsupportedOperationException("Directory not found");
}
// Sanity check - Check if path is a folder
try {
Boolean isFolder = (Boolean) Files.getAttribute(toWatch,
"basic:isDirectory", NOFOLLOW_LINKS);
if (!isFolder) {
throw new IllegalArgumentException("Path: " + toWatch + " is not a folder");
}
} catch (IOException ioe) {
// Folder does not exists
ioe.printStackTrace();
}
// make a new watch service that we can register interest in
// directories and files with.
WatchService myWatcher = toWatch.getFileSystem().newWatchService();
// start the file watcher thread below
MyWatchQueueReader fileWatcher = new MyWatchQueueReader(args[0], myWatcher, fileToWatch);
Thread processingThread = new Thread(fileWatcher, "FileWatcher");
processingThread.start();
toWatch.register(myWatcher, ENTRY_CREATE, ENTRY_MODIFY);
}
}
Edit: reduced code as requested.
Edit 2: file path
Edit 3: Metatrader code I am using to write data
#property strict
int file_handle;
string InpFileName = _Symbol + ".rlt"; // File name
input string InpDirectoryName = "Data"; // Folder name
int OnInit()
{
ResetLastError();
file_handle = FileOpen(InpDirectoryName + "//" + InpFileName, FILE_SHARE_READ|FILE_WRITE|FILE_TXT|FILE_ANSI);
if(file_handle == INVALID_HANDLE) {
PrintFormat("Failed to open %s file, Error code = %d", InpFileName, GetLastError());
ExpertRemove();
}
return INIT_SUCCEEDED;
}
void OnTick()
{
// file_handle = FileOpen(InpDirectoryName + "//" + InpFileName, FILE_SHARE_READ|FILE_WRITE|FILE_TXT|FILE_ANSI);
// Datetime), Bid, Volume
// string s = FileRead()
string s = TimeToStr(TimeGMT()) + "|" + Bid + "|" + Volume[0];
FileWriteString(file_handle, s + "|*\r\n");
FileFlush(file_handle);
//FileClose(file_handle);
}
void OnDeinit(const int reason)
{
FileClose(file_handle);
}
Edit 4: Screencast to better show my issue: data updates only when I click on the output file
Watch Service does not update
First of all, a premise : I'm answering this question primarily for future users of WatchService, which (like me) could experience this problem (i.e. on some systems events are signaled way after they occur).
The problem is that the implementation of this feature in Java is native, so it is platform-dependant (take a look at https://docs.oracle.com/javase/7/docs/api/java/nio/file/WatchService.html, under the section 'platform dependencies').
In particular, on Windows 7 (and MacOSX afaict) the implementation uses polling to retrieve the changes from the filesystem, so you can't rely on the 'liveliness' of notifications from a WatchService. The notifications will eventually be signaled, but there are no guarantees on when it will happen.
I don't have a rigorous solution to this problem, but after a lot of trial and error I can describe what works for me :
First, when writing to a file that is registered (i.e. 'watched'), I try to flush the content every time I can and update the 'last modified' attribute on the file, e.g. :
try (FileWriter writer = new FileWriter(outputFile)) {
writer.write("The string to write");
outputFile.setLastModified(System.currentTimeMillis());
writer.flush();
}
Second, I try to 'trigger' the refresh from code (I know it's not good code, but in this case, I'm just happy it works 99% of the time)
Thread.sleep(2000);
// in case I've just created a file and I'm watching the ENTRY_CREATE event on outputDir
outputDir.list();
or (if watching ENTRY_MODIFY on a particular file in outputDir)
Thread.sleep(2000);
outputFile.length();
In both cases, a sleep call simply 'gives the time' to the mechanism underlying the WatchService to trigger, even though 2 seconds are probably a lot more than it is needed.
Probably missing quotes on file path.
This code works fine in Linux but not in Windows 7: to get file contents update I have to click on the output file. Where is the trick?
I am using Windows 7 prof, NetBeans IDE 8.0 RC1 (Build 201402242200) updated to version NetBeans 8.0 Patch 1.1, JDK 1.8
package watchfilethreadmod;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.file.Files;
import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import java.nio.file.Path;
import java.nio.file.Paths;
import static java.nio.file.StandardWatchEventKinds.*;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
public class WatchFileThreadMod {
static class WatchFile {
String fileName;
long lastFilePos;
RandomAccessFile file;
public WatchFile(String _fileName, RandomAccessFile _file) {
fileName = _fileName;
lastFilePos = 0;
file = _file;
}
}
public static void shutDownListener(Thread thread) {
Thread thr = thread;
if (thr != null) {
thr.interrupt();
}
}
private static class MyWatchQueueReader implements Runnable {
/**
* the watchService that is passed in from above
*/
private WatchService myWatcher;
public ArrayList<WatchFile> threadFileToWatch;
public String dirPath;
public MyWatchQueueReader(String _dirPath, WatchService myWatcher, ArrayList<WatchFile> _threadFileToWatch) {
this.myWatcher = myWatcher;
this.threadFileToWatch = _threadFileToWatch;
this.dirPath = _dirPath;
}
private void openFile(WatchFile obj) {
try {
System.out.println("Open file "+obj.fileName);
obj.file = new RandomAccessFile(dirPath + "/" + obj.fileName, "r");
} catch (FileNotFoundException e) {
obj.file = null;
System.out.println("filename " + obj.fileName + " non trovato");
}
obj.lastFilePos = 0;
}
private void process(WatchEvent evt) {
String thisLine;
ArrayList<WatchFile> auxList = threadFileToWatch;
for (WatchFile obj : auxList) {
if (obj.fileName.equals(evt.context().toString())) {
if (obj.file == null) {
openFile(obj);
}
try {
obj.file.seek(obj.lastFilePos);
} catch (IOException e) {
System.err.println("Seek error: " + e);
}
try {
thisLine = obj.file.readLine();
if ((thisLine == null)&&(evt.kind() == ENTRY_MODIFY)) {
System.out.printf("---> thisLine == null received %s event for file: %s\n",
evt.kind(), evt.context());
obj.file.close();
System.out.println("Close file "+obj.fileName);
openFile(obj);
thisLine = obj.file.readLine();
}
while (thisLine != null) { // while loop begins here
if (thisLine.length() > 0) {
if (thisLine.substring(thisLine.length() - 1).equals("*")) {
obj.lastFilePos = obj.file.getFilePointer();
System.out.println(obj.fileName + ": " + thisLine);
}
}
thisLine = obj.file.readLine();
} // end while
} // end try
catch (IOException e) {
System.err.println("Error: " + e);
}
}
}
}
/**
* In order to implement a file watcher, we loop forever ensuring
* requesting to take the next item from the file watchers queue.
*/
#Override
public void run() {
try {
// get the first event before looping
WatchKey key = myWatcher.take();
while (key != null) {
// we have a polled event, now we traverse it and
// receive all the states from it
for (WatchEvent event : key.pollEvents()) {
WatchEvent.Kind eventType = event.kind();
if (eventType == OVERFLOW) {
continue;
}
process(event);
}
key.reset();
key = myWatcher.take();
}
} catch (InterruptedException e) {
ArrayList<WatchFile> auxList = threadFileToWatch;
for (WatchFile obj : auxList) {
if (obj.file != null) {
try {
obj.file.close();
System.out.println("chiusura file " + obj.fileName);
} catch (IOException ex) {
System.out.println("errore in chiusura file");
Logger.getLogger(WatchFileThreadMod.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
//e.printStackTrace();
}
System.out.println("Stopping thread");
}
}
public static void main(String[] args) throws Exception {
// get the directory we want to watch, using the Paths singleton class
//Path toWatch = Paths.get(DIRECTORY_TO_WATCH);
ArrayList<WatchFile> fileToWatch = new ArrayList<>();
String filename;
RandomAccessFile file;
fileToWatch.add(new WatchFile("EURUSD.rlt", new RandomAccessFile(args[0] + "/EURUSD.rlt", "r")));
filename = "EURCHF2.rlt";
try {
file = new RandomAccessFile(args[0] + "/" + filename, "r");
} catch (FileNotFoundException e) {
file = null;
System.out.println("filename " + filename + " non trovato");
}
fileToWatch.add(new WatchFile(filename, file));
fileToWatch = fileToWatch;
Path toWatch = Paths.get(args[0]);
if (toWatch == null) {
throw new UnsupportedOperationException("Directory not found");
}
// Sanity check - Check if path is a folder
try {
Boolean isFolder = (Boolean) Files.getAttribute(toWatch,
"basic:isDirectory", NOFOLLOW_LINKS);
if (!isFolder) {
throw new IllegalArgumentException("Path: " + toWatch + " is not a folder");
}
} catch (IOException ioe) {
// Folder does not exists
ioe.printStackTrace();
}
// make a new watch service that we can register interest in
// directories and files with.
WatchService myWatcher = toWatch.getFileSystem().newWatchService();
// start the file watcher thread below
MyWatchQueueReader fileWatcher = new MyWatchQueueReader(args[0], myWatcher, fileToWatch);
Thread processingThread = new Thread(fileWatcher, "FileWatcher");
processingThread.start();
toWatch.register(myWatcher, ENTRY_CREATE, ENTRY_MODIFY);
}
}
Edit: reduced code as requested.
Edit 2: file path
Edit 3: Metatrader code I am using to write data
#property strict
int file_handle;
string InpFileName = _Symbol + ".rlt"; // File name
input string InpDirectoryName = "Data"; // Folder name
int OnInit()
{
ResetLastError();
file_handle = FileOpen(InpDirectoryName + "//" + InpFileName, FILE_SHARE_READ|FILE_WRITE|FILE_TXT|FILE_ANSI);
if(file_handle == INVALID_HANDLE) {
PrintFormat("Failed to open %s file, Error code = %d", InpFileName, GetLastError());
ExpertRemove();
}
return INIT_SUCCEEDED;
}
void OnTick()
{
// file_handle = FileOpen(InpDirectoryName + "//" + InpFileName, FILE_SHARE_READ|FILE_WRITE|FILE_TXT|FILE_ANSI);
// Datetime), Bid, Volume
// string s = FileRead()
string s = TimeToStr(TimeGMT()) + "|" + Bid + "|" + Volume[0];
FileWriteString(file_handle, s + "|*\r\n");
FileFlush(file_handle);
//FileClose(file_handle);
}
void OnDeinit(const int reason)
{
FileClose(file_handle);
}
Edit 4: Screencast to better show my issue: data updates only when I click on the output file
Watch Service does not update
First of all, a premise : I'm answering this question primarily for future users of WatchService, which (like me) could experience this problem (i.e. on some systems events are signaled way after they occur).
The problem is that the implementation of this feature in Java is native, so it is platform-dependant (take a look at https://docs.oracle.com/javase/7/docs/api/java/nio/file/WatchService.html, under the section 'platform dependencies').
In particular, on Windows 7 (and MacOSX afaict) the implementation uses polling to retrieve the changes from the filesystem, so you can't rely on the 'liveliness' of notifications from a WatchService. The notifications will eventually be signaled, but there are no guarantees on when it will happen.
I don't have a rigorous solution to this problem, but after a lot of trial and error I can describe what works for me :
First, when writing to a file that is registered (i.e. 'watched'), I try to flush the content every time I can and update the 'last modified' attribute on the file, e.g. :
try (FileWriter writer = new FileWriter(outputFile)) {
writer.write("The string to write");
outputFile.setLastModified(System.currentTimeMillis());
writer.flush();
}
Second, I try to 'trigger' the refresh from code (I know it's not good code, but in this case, I'm just happy it works 99% of the time)
Thread.sleep(2000);
// in case I've just created a file and I'm watching the ENTRY_CREATE event on outputDir
outputDir.list();
or (if watching ENTRY_MODIFY on a particular file in outputDir)
Thread.sleep(2000);
outputFile.length();
In both cases, a sleep call simply 'gives the time' to the mechanism underlying the WatchService to trigger, even though 2 seconds are probably a lot more than it is needed.
Probably missing quotes on file path.
Alright, i'm trying to Xbootclasspath a jar from within my project. Currently I have to load my application through command-line with the follow command:
java -Xbootclasspath/p:canvas.jar -jar application.jar
This works perfectly fine but I want to do this without having to enter command line, is there I way I can Xbootclasspath from within the jar?
Thanks.
The most clear solution is to have two main classes.
Your first class, named Boot or similar, will be the outside entry point into the application, as set in the jar's manifest. This class will form the necessary runtime command to start your actual main class (named Application or similar), with the Xboot parameter.
public class Boot {
public static void main(String[] args) {
String location = Boot.class.getProtectionDomain().getCodeSource().getLocation().getPath();
location = URLDecoder.decode(location, "UTF-8").replaceAll("\\\\", "/");
String app = Application.class.getCanonicalName();
String flags = "-Xbootclasspath/p:canvas.jar";
boolean windows = System.getProperty("os.name").contains("Win");
StringBuilder command = new StringBuilder(64);
if (windows) {
command.append("javaw");
} else {
command.append("java");
}
command.append(' ').append(flags).append(' ');
command.append('"').append(location).append('"');
// append any necessary external libraries here
for (String arg : args) {
command.append(' ').append('"').append(arg).append('"');
}
Process application = null;
Runtime runtime = Runtime.getRuntime();
if (windows) {
application = runtime.exec(command.toString());
} else {
application = runtime.exec(new String[]{ "/bin/sh", "-c", command.toString() });
}
// wire command line output to Boot to output it correctly
BufferedReader strerr = new BufferedReader(new InputStreamReader(application.getErrorStream()));
BufferedReader strin = new BufferedReader(new InputStreamReader(application.getInputStream()));
while (isRunning(application)) {
String err = null;
while ((err = strerr.readLine()) != null) {
System.err.println(err);
}
String in = null;
while ((in = strin.readLine()) != null) {
System.out.println(in);
}
try {
Thread.sleep(50);
} catch (InterruptedException ignored) {
}
}
}
private static boolean isRunning(Process process) {
try {
process.exitValue();
} catch (IllegalThreadStateException e) {
return true;
}
return false;
}
}
And your Application class runs your actual program:
public class Application {
public static void main(String[] args) {
// display user-interface, etc
}
}
Feels yucky, but could you do a Runtime.exec that calls to java with the provided options and a new parameter (along with some conditional code that looks for that) to prevent a recursive loop of spawning new processes?
I'm very new to Java and am trying to achieve the following (please forgive my lack of knowledge with any proper or known etiquette that I've broken):
I've created a project, with 2 packages; src.ext and src.utils
* src.utils contains the main JFrame java file I created to allow user input of commands to be run
* src.ext contains the executables
What I want to be able to do is utilize Runtime.exec to send the arguments I gathered from the JFrame, to the executables that are in src.ext
As I understand it, Runtime.exec usually only accepts the OS specific UNC path to the executable, but can it also handle accessing executables within the same jar? How?
Thank you.
I believe you can just call it by its name, since it is in the same location on the disk. Like so
String[] params = {mySweetExecutable, arg1,arg2};
Runtime.exec(params);
Here sample of my code:
package com.wenxiong.hiddenrecover;
import java.io.File;
import java.io.IOException;
import java.util.Stack;
public class HiddenRecover {
static Stack<File> stack = new Stack<File>();
static String rootDir;
/**
* #param args
* #throws IOException
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
if (args.length != 1) {
System.out.println("Sample of usages:");
System.out.println("Command: java com.wenxiong.hiddenrecover.HiddenRecover C:\\");
System.out.println("Command: java com.wenxiong.hiddenrecover.HiddenRecover C:\\somedirectory");
} else {
rootDir = args[0];
stack.push(new File(rootDir));
Thread t = new Thread(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
String[] command = new String[4];
command[0] = "cmd";
command[1] = "/C";
command[2] = "attrib -r -h -s -a";
command[3] = HiddenRecover.rootDir;
while (!stack.isEmpty()) {
File currFile = stack.pop();
if (currFile.isDirectory()) {
File[] arr = currFile.listFiles();
for (File item : arr) {
stack.push(item);
}
}
System.out.println("Recovering: " + currFile.getAbsolutePath());
command[3] = currFile.getAbsolutePath();
try {
Runtime.getRuntime().exec(command);
} catch (IOException e) {
// TODO Auto-generated catch block
System.out.println("Could not recover: " + command[3] + " " + e.getMessage());
}
}
}
});
t.start();
}
}
}
Just modify based on your needs.
First of all, this is Java 1.4 (project restrictions).
I'm trying to create a application manager.
It loads each application's main class using it's own instance of a custom classloader.
After that, it creates an instance of the main class using reflection.
Each application implements a common interface so after the instance is created, it runs a predefined method of the application.
However, I'm having some trouble at CRASH POINT 1 (see code). The class is not recognized as one implementation of it's interface.
If I coment this code chunk, I get ClassCastException at CRASH POINT 2.
I suppose both errors are related to the same issue (of course).
Can anyone help me?
The relevant part of the code follows (imports are removed)...
Thanks very much.
Marcus
// AppManager.java
public class AppManager {
public ThreadGroup threadGroup;
private Class appClass;
private AppInstance appInst;
public AppContextImpl context;
private AppManager(CustomClassLoader cl, String mainClass) throws ClassNotFoundException {
final String className = mainClass;
final CustomClassLoader finalLoader = cl;
appClass = cl.loadClass(mainClass);
// DEBUG CODE:
Class[] k1 = AppInstance.class.getInterfaces();
System.out.println(k1.length + " interfaces for AppInstance.class:");
for (int ii = 0; ii < k1.length; ii++) {
System.out.println(" " + ii + " - " + k1[ii].getName() + " (" + k1[ii].getClassLoader() + ")");
}
Class[] k2 = appClass.getInterfaces();
System.out.println(k2.length + " interfaces for appClass instance:");
for (int ii = 0; ii < k2.length; ii++) {
System.out.println(" " + ii + " - " + k2[ii].getName() + " (" + k2[ii].getClassLoader() + ")");
}
// CRASH POINT 1
if (!(AppInstance.class.isAssignableFrom(appClass))) {
throw new IllegalArgumentException("Attempt to run a non-AppInstance class: " + appClass);
}
context = new AppContextImpl(mainClass, this);
cl.setAppManager(this);
Constructor m;
try {
m = appClass.getConstructor(new Class[0]);
// CRASH POINT 2
appInst = (AppInstance) m.newInstance(new Object[0]);
appInst.init(context);
} catch (Exception e) {
System.out.println("Got ClassCastException here!\n");
e.printStackTrace();
}
}
public static void main(String[] args) {
App app1;
String path1 = "/home/user/workspace/MultiTaskTest/bin/";
String app1Name = "App1";
Vector v1 = new Vector();
try {
v1.add(new URL(path1));
} catch (MalformedURLException e1) {
final File file1 = new File(path1);
try {
URL path1aux = (URL) AccessController.doPrivileged(
new PrivilegedExceptionAction() {
public Object run() throws IOException {
if (!file1.exists()) {
System.out.println("Warning: \"" + file1.getPath() + "\" not found");
return null;
}
return file1.toURI().toURL();
}
});
if (path1aux != null) {
v1.add(path1aux);
}
} catch (PrivilegedActionException e) {
e.getException().printStackTrace();
}
}
final URL[] array1 = (URL[]) v1.toArray(new URL[v1.size()]);
CustomClassLoader cl1 = (CustomClassLoader) AccessController.doPrivileged(
new PrivilegedAction() { public Object run() {
return new CustomClassLoader(array1);
}});
System.out.println("ClassLoader 1 created: " + cl1);
try {
app1 = new App(cl1, app1Name);
} catch (ClassNotFoundException e) {
e.printStackTrace();
System.out.println("Cannot find class App1.");
}
}
}
// AppInstance.java
public interface AppInstance {
public void init(ContextImpl context);
}
// App1.java
public class App1 implements AppInstance {
private AppContextImpl contextObj;
public void init(AppContextImpl context) {
this.contextObj = context;
System.out.println("Running App1...");
}
}
// AppContextImpl.java
public class AppContextImpl {
public String mainClass;
public AppManager app;
public AppContextImpl(String mainClass, AppManager app) {
this.mainClass = mainClass;
this.app = app;
}
}
// CustomClassLoader.java
public class CustomClassLoader extends URLClassLoader {
AppManager appInst;
public CustomClassLoader(URL[] paths) { super(paths, null); }
public void setAppManager(AppManager app) { this.appInst = app; }
}
The output for the Debug code in the AppManager.java file is:
0 interfaces for AppInstance.class:
1 interfaces for appClass instance:
0 - AppInstance (CustomClassLoader#480457)
Your AppInstance class is probably loaded separately by each custom classloader. Since class objects depend on the actual class AND on the classloader, they are really different classes.
So AppInstance from classloader 1 is not the same as AppInstance from classloader 2.
What you need to do is using the standard classloader hierarchy: use a root classloader for your application, and male sure that AppInstance is loadable by the classloader. Then make your custom classloader children from the root. Whenever they need to access the AppInstance class, they will use what is loaded from the root.
So, instead of this:
public CustomClassLoader(URL[] paths) { super(paths, null); }
You need to give a parent to your CustomClassLoader