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Groovy script reloading on runtime

I want to be a able to execute a groovy script from my Java application.
I want to reload the groovy script on runtime if needed. According to their tutorials, I can do something like that :
long now = System.currentTimeMillis();
for(int i = 0; i < 100000; i++) {
try {
GroovyScriptEngine groovyScriptEngine = new GroovyScriptEngine("");
System.out.println(groovyScriptEngine.run("myScript.groovy", new Binding()););
} catch (Exception e) {
e.printStackTrace();
}
}
long end = System.currentTimeMillis();
System.out.println("time " + (end - now));//24 secs
myScript.groovy
"Hello-World"
This works fine and the script is reloaded everytime i change a line in myScript.groovy.
The problem is that this is not time efficient, what it does is parsing the script from the file every time.
Is there any other alternative ? E.g something smarter that checks if the script is already parsed and if it did not change since the last parse do not parse it again.

<< edited due to comments >>
Like mentioned in one of the comments, separating parsing (which is slow) from execution (which is fast) is mandatory if you need performance.
For reactive reloading of the script source we can for example use the java nio watch service:
import groovy.lang.*
import java.nio.file.*
def source = new File('script.groovy')
def shell = new GroovyShell()
def script = shell.parse(source.text)
def watchService = FileSystems.default.newWatchService()
source.canonicalFile.parentFile.toPath().register(watchService, StandardWatchEventKinds.ENTRY_MODIFY)
boolean keepWatching = true
Thread.start {
while (keepWatching) {
def key = watchService.take()
if (key.pollEvents()?.any { it.context() == source.toPath() }) {
script = shell.parse(source.text)
println "source reloaded..."
}
key.reset()
}
}
def binding = new Binding()
def start = System.currentTimeMillis()
for (i=0; i<100; i++) {
script.setBinding(binding)
def result = script.run()
println "script ran: $result"
Thread.sleep(500)
}
def delta = System.currentTimeMillis() - start
println "took ${delta}ms"
keepWatching = false
The above starts a separate watcher thread which uses the java watch service to monitor the parent directory for file modifications and reloads the script source when a modification is detected. This assumes java version 7 or later. The sleep is just there to make it easier to play around with the code and should naturally be removed if measuring performance.
Storing the string System.currentTimeMillis() in script.groovy and running the above code will leave it looping twice a second. Making modifications to script.groovy during the loop results in:
~> groovy solution.groovy
script ran: 1557302307784
script ran: 1557302308316
script ran: 1557302308816
script ran: 1557302309317
script ran: 1557302309817
source reloaded...
script ran: 1557302310318
script ran: 1557302310819
script ran: 1557302310819
source reloaded...
where the source reloaded... lines are printed whenever a change was made to the source file.
I'm not sure about windows but I believe at least on linux that java uses the fsnotify system under the covers which should make the file monitoring part performant.
Should be noted that if we are really unlucky, the script variable will be reset by the watcher thread between the two lines:
script.setBinding(binding)
def result = script.run()
which would break the code as the reloaded script instance would not have the binding set. To fix this, we can for example use a lock:
import groovy.lang.*
import java.nio.file.*
import java.util.concurrent.locks.ReentrantLock
def source = new File('script.groovy')
def shell = new GroovyShell()
def script = shell.parse(source.text)
def watchService = FileSystems.default.newWatchService()
source.canonicalFile.parentFile.toPath().register(watchService, StandardWatchEventKinds.ENTRY_MODIFY)
lock = new ReentrantLock()
boolean keepWatching = true
Thread.start {
while (keepWatching) {
def key = watchService.take()
if (key.pollEvents()?.any { it.context() == source.toPath() }) {
withLock {
script = shell.parse(source.text)
}
println "source reloaded..."
}
key.reset()
}
}
def binding = new Binding()
def start = System.currentTimeMillis()
for (i=0; i<100; i++) {
withLock {
script.setBinding(binding)
def result = script.run()
println "script ran: $result"
}
Thread.sleep(500)
}
def delta = System.currentTimeMillis() - start
println "took ${delta}ms"
keepWatching = false
def withLock(Closure c) {
def result
lock.lock()
try {
result = c()
} finally {
lock.unlock()
}
result
}
which convolutes the code somewhat but keeps us safe against concurrency issues which tend to be hard to track down.

Java: populating Scanner with default value on Scanner.nextLine();

I am writing a java program that runs a loop and keeps asking the user for input. The program then does a bunch of things with the string, and asks for another string and repeats.
The issue is that many strings are very similar, so i would like to populate the prompt with the input from the last time in the loop. For instance: If the user enters a value as follows:
Enter the SKU Number: APE-6603/A
... Then the next time it asks for an SKU, it will wait till the user presses enter as normal, but be ready with the last value before the user even types anything:
Enter the SKU Number: APE-6603/A
... And the user can make simple changes very fast like replace the /A with /B and press enter! If the string that holds the user input is called "lookFor", is there a way to populate the prompt with this value in Java? It would be VERY useful!
Thanks!

After discussing this idea with a few people, it seems that what i want is not possible. The way of input is too simple to allow something like this.
My only possible solutions involve not running this from my IDE. I can either elect to use my application, or change the application into a GUI based applet. Running from the console will open up the "Press up" option, as suggested by rchirino, and using a GUI would let the value entered sit there for editing later.
If anyone is looking to do what i posted above, the answer is "Java cant do it!". Sorry. :)

You might want to try something like this:
public String promptandgetWithShowDefault(String prompt, String supplied) {
String prmpt = prompt + " (press Enter for \"" + supplied + "\"):";
String tmpch = null;
System.out.print(prmpt);
tmpch = scanner.nextLine().trim();
if (tmpch == null || tmpch.equals("")) {
return supplied;
} else {
return tmpch;
}
}

If the goal is to get a simple binar answer from the user like:
Would you like to do that? ( y / n ) y
then the empty string returned by the user, in the answer from Dmv, will do the trick, except that when the user types "n" or attempts to delete the trailing "y", it won't disappear, so it would then be clearer to write the prompt like:
Would you like to do that? ( [ y ] / n )
But when the goal is to get a long string, like the original question or a file path for instance, that the user can edit to correct a typo or not to overwrite previous file .... then you definitely need something else which doesn't seem to be available in Java.
Well do it in C then!!! with the help of libreadline...
it's probably possible, easier and more portable to do the same trick in Python, but I have no idea how to code in Python.
Here is a simple Java MRE to illustrate it:
import java.io.BufferedReader;
import java.io.File;
import java.io.InputStreamReader;
public class Main
{
public static void main(String[] args)
{
String path = System.getProperty("user.home") + File.separatorChar + "Documents";
File file = null;
do {
path = askForString("Enter the filepath to open:", path );
if ( ( path == null) || ( path.isBlank())) break;
file = new File( path );
} while ( ! file.exists() );
System.out.println("Openning " + path + "....");
// ......
}
public static String askForString( String message, String defaultString)
{
String response = null;
System.out.println( message);
// any extra String in cmd[] will be added in readline history
String[] cmd = { "/path/to/executable/ask4stringWdefault", defaultString};
try
{
ProcessBuilder pb = new ProcessBuilder(cmd);
// Make sure the subprocess can print on console and capture keyboard events
pb.redirectInput(ProcessBuilder.Redirect.INHERIT);
pb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
Process p = pb.start();
BufferedReader stderrBuffer = new BufferedReader(new InputStreamReader(p.getErrorStream()));
int retcode= p.waitFor();
if ( retcode != 0)
{
System.err.println("The process terminated with error code: " + retcode + "\n" + stderrBuffer.readLine());
return null;
}
response = stderrBuffer.readLine();
} catch( Exception e) {
e.printStackTrace();
}
return response;
}
}
To build the executable "ask4stringWdefault" you need first to get the GNU Readline Library utility and compile it, ideally cross-compile for any platform Java supports, to get a static library that you will link while compiling ( or cross-compiling ) the following C script:
#include <stdio.h>
#include <stdlib.h>
#include <readline/readline.h>
#include <readline/history.h>
const char *defstr;
int prefill(const char *txt, int i);
int main(int argc, const char * argv[])
{
if ( argc < 2)
{
fprintf(stderr, "You must provide a default value\n");
return -1;
} else if ( argc > 2) {
// * optional extra values can be passed to populate history * //
if ( argc > 255) argc = 255;
for ( unsigned char i=0; i < argc; i++)
{
add_history(argv[i]);
}
}
defstr = argv[1];
char *cbuffer;
rl_startup_hook = prefill;
if ((cbuffer = readline(NULL)) == NULL) /* if the user sends EOF, readline will return NULL */
return 1;
fprintf( stderr, "%s\n", cbuffer);
free(cbuffer);
return 0;
}
int prefill(const char *t, int i)
{
rl_insert_text(defstr);
return 0;
}
The result is printed on stderr as it is the only stream that Java can keep track of, stdout and stdin being under the control of the executable subprocess itself.
It works fine on a Mac with arm64 architecture, using Eclipse you can't actually edit the default provided, any character typed at the prompt will be append to default string, but just hitting return will send unchanged default value back, which can be enough for basic testing.

I think I understand what you want to do, but it's rather simple. If your program is a console application (command-line), which I'll assume, then you just need to press the UP key to populate the prompt with the last typed characters.
If you're working with GUI elements then you can check the API documentation for the particular class of object you're using and check out it's fields.
Hope this helps!

Batch file renaming – inserting text from a list (in Python or Java)

I'm finishing a business card production flow (excel > xml > indesign > single page pdfs) and I would like to insert the employees' names in the filenames.
What I have now:
BusinessCard_01_Blue.pdf
BusinessCard_02_Blue.pdf
BusinessCard_03_Blue.pdf (they are gonna go up to the hundreds)
What I need (I can manipulate the name list with regex easily):
BusinessCard_01_CarlosJorgeSantos_Blue.pdf
BusinessCard_02_TaniaMartins_Blue.pdf
BusinessCard_03_MarciaLima_Blue.pdf
I'm a Java and Python toddler. I've read the related questions, tried this in Automator (Mac) and Name Mangler, but couldn't get it to work.
Thanks in advance,
Gus

Granted you have a map where to look at the right name you could do something like this in Java:
List<Files> originalFiles = ...
for( File f : originalFiles ) {
f.renameTo( new File( getNameFor( f ) ) );
}
And define the getNameFor to something like:
public String getNameFor( File f ) {
Map<String,String> namesMap = ...
return namesMap.get( f.getName() );
}
In the map you'll have the associations:
BusinessCard_01_Blue.pdf => BusinessCard_01_CarlosJorgeSantos_Blue.pdf
Does it make sense?

In Python (tested):
#!/usr/bin/python
import sys, os, shutil, re
try:
pdfpath = sys.argv[1]
except IndexError:
pdfpath = os.curdir
employees = {1:'Bob', 2:'Joe', 3:'Sara'} # emp_id:'name'
files = [f for f in os.listdir(pdfpath) if re.match("BusinessCard_[0-9]+_Blue.pdf", f)]
idnumbers = [int(re.search("[0-9]+", f).group(0)) for f in files]
filenamemap = zip(files, [employees[i] for i in idnumbers])
newfiles = [re.sub('Blue.pdf', e + '_Blue.pdf', f) for f, e in filenamemap]
for old, new in zip(files, newfiles):
shutil.move(os.path.join(pdfpath, old), os.path.join(pdfpath, new))
EDIT: This now alters only those files that have not yet been altered.
Let me know if you want something that will build the the employees dictionary automatically.

If you have a list of names in the same order the files are produced, in Python it goes like this untested fragment:
#!/usr/bin/python
import os
f = open('list.txt', 'r')
for n, name in enumerate(f):
original_name = 'BusinessCard_%02d_Blue.pdf' % (n + 1)
new_name = 'BusinessCard_%02d_%s_Blue.pdf' % (
n, ''.join(name.title().split()))
if os.path.isfile(original_name):
print "Renaming %s to %s" % (original_name, new_name),
os.rename(original_name, new_name)
print "OK!"
else:
print "File %s not found." % original_name

Python:
Assuming you have implemented the naming logic already:
for f in os.listdir(<directory>):
try:
os.rename(f, new_name(f.name))
except OSError:
# fail
You will, of course, need to write a function new_name which takes the string "BusinessCard_01_Blue.pdf" and returns the string "BusinessCard_01_CarlosJorgeSantos_Blue.pdf".

Parse a task list

A file contains the following:
HPWAMain.exe 3876 Console 1 8,112 K
hpqwmiex.exe 3900 Services 0 6,256 K
WmiPrvSE.exe 3924 Services 0 8,576 K
jusched.exe 3960 Console 1 5,128 K
DivXUpdate.exe 3044 Console 1 16,160 K
WiFiMsg.exe 3984 Console 1 6,404 K
HpqToaster.exe 2236 Console 1 7,188 K
wmpnscfg.exe 3784 Console 1 6,536 K
wmpnetwk.exe 3732 Services 0 11,196 K
skypePM.exe 2040 Console 1 25,960 K
I want to get the process ID of the skypePM.exe. How is this possible in Java?
Any help is appreciated.

Algorithm
Open the file.
In a loop, read a line of text.
If the line of text starts with skypePM.exe then extract the number.
Repeat looping until all lines have been read from the file.
Close the file.
Implementation
import java.io.*;
public class T {
public static void main( String args[] ) throws Exception {
BufferedReader br = new BufferedReader(
new InputStreamReader(
new FileInputStream( "tasklist.txt" ) ) );
String line;
while( (line = br.readLine()) != null ) {
if( line.startsWith( "skypePM.exe" ) ) {
line = line.substring( "skypePM.exe".length() );
int taskId = Integer.parseInt( (line.trim().split( " " ))[0] );
System.out.println( "Task Id: " + taskId );
}
}
br.close();
}
}
Alternate Implementation
If you have Cygwin and related tools installed, you could use:
cat tasklist.txt | grep skypePM.exe | awk '{ print $2; }'

To find the Process Id of the application SlypePM..
Open the file
now read lines one by one
find the line which contains SkypePM.exe in the beginning
In the line containing SkypePM.exe parse the line to read the numbers after the process name leaving the spaces.
You get process id of the process
It is all string operations.
Remember the format of the file should not change after you write the code.

If you really want to parse the output, you may need a different strategy. If your output file really is the result of a tasklist execution, then it should have some column headers at the top of it like:
Image Name PID Session Name Session# Mem Usage
========================= ======== ================ =========== ============
I would use these, in particular the set of equal signs with spaces, to break any subsequent strings using a fixed-width column strategy. This way, you could have more flexibility in parsing the output if needed (i.e. maybe someone is looking for java.exe or wjava.exe). Do keep in mind the last column may not be padded with spaces all the way to the end.
I will say, in the strictest sense, the existing answers should work for just getting the PID.

Implementation in Java is not a good way. Shell or other script languages may help you a lot. Anyway, JAWK is a implementation of awk in Java, I think it may help you.

How can I pipe input to a Java app with Perl?

I need to write a Perl script that pipes input into a Java program. This is related to this, but that didn't help me. My issue is that the Java app doesn't get the print statements until I close the handle. What I found online was that $| needs to be set to something greater than 0, in which case newline characters will flush the buffer. This still doesn't work.
This is the script:
#! /usr/bin/perl -w
use strict;
use File::Basename;
$|=1;
open(TP, "| java -jar test.jar") or die "fail";
sleep(2);
print TP "this is test 1\n";
print TP "this is test 2\n";
print "tests printed, waiting 5s\n";
sleep(5);
print "wait over. closing handle...\n";
close TP;
print "closed.\n";
print "sleeping for 5s...\n";
sleep(5);
print "script finished!\n";
exit
And here is a sample Java app:
import java.util.Scanner;
public class test{
public static void main( String[] args ){
Scanner sc = new Scanner( System.in );
int crashcount = 0;
while( true ){
try{
String input = sc.nextLine();
System.out.println( ":: INPUT: " + input );
if( "bananas".equals(input) ){
break;
}
} catch( Exception e ){
System.out.println( ":: EXCEPTION: " + e.toString() );
crashcount++;
if( crashcount == 5 ){
System.out.println( ":: Looks like stdin is broke" );
break;
}
}
}
System.out.println( ":: IT'S OVER!" );
return;
}
}
The Java app should respond to receiving the test prints immediately, but it doesn't until the close statement in the Perl script. What am I doing wrong?
Note: the fix can only be in the Perl script. The Java app can't be changed. Also, File::Basename is there because I'm using it in the real script.

I've grown rather fond of the IO::Handle derived modules. They make it easy to control flushing, reading data, binary mode, and many other aspects of a handle.
In this case we use IO::File.
use IO::File;
my $tp = IO::File->new( "| java -jar test.jar" )
or die "fail - $!";
# Manual print and flush
$tp->print( 'I am fond of cake' );
$tp->flush;
# print and flush in one method
$tp->printflush( 'I like pie' );
# Set autoflush ON
$tp->autoflush(1);
$tp->print( 'I still like pie' );
Also, since the file handle is lexically scoped, you don't have to close it manually. It will automatically close when it goes out of scope.
BTW, unless you are targeting a perl older than 5.6, you can use the warnings pragma instead of -w. See perllexwarn for more info.

$|=1 only works on the currently selected file handle (by default, STDOUT). To make your TP file handle hot you need to do this after opening it:
select(TP);
$| = 1;
select(STDOUT);