I am learning multithread in Java. To practice, I want do multithread to read three txt files in paralel, adding each line of three files into one List. This is my code:
ArrayList<String> allLinesFromFiles= new ArrayList<String>();
Lock blockThread=new ReentrantLock();
Thread t = null;
for (String file : files) {
t= new Thread(new Runnable() {
#Override
public void run() {
try {
FileReader fichero;
fichero = new FileReader(file);
BufferedReader bufferFichero = new BufferedReader(fichero);
String line = bufferFichero.readLine();
while (line != null) {
writeList(line.toLowerCase());
line = bufferFichero.readLine();
}
bufferFichero.close();
}catch (IOException e) {
System.out.println("Error IO");
}
}
private void writeList(String line) {
blockThread.lock();
allLinesFromFiles.add(line);
blockThread.unlock();
}
});
t.start();
}
try {
t.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
Collections.sort(allLinesFromFiles);
I used lock/unlocks (ReentrantLock) in the method "writeList" to synchronize because three threads writting in the ArrayList I thought maybe is needed. Is correct? Have I to use CopyOnWriteArrayList instead of ArrayList?
I used join() to wait the finish of three threads but my code dont work correctly.
A simple way base on your code is to add an AtomicInteger count to know if the read Thread is ended or not，and the Main Thread wait for the end:
List<String> files = Arrays.asList("a.txt", "b.txt", "c.txt");
ArrayList<String> allLinesFromFiles= new ArrayList<String>();
Lock blockThread=new ReentrantLock();
AtomicInteger count = new AtomicInteger(0); // counter
Thread t = null;
for (String file : files) {
t= new Thread(new Runnable() {
#Override
public void run() {
try {
FileReader fichero;
fichero = new FileReader(getClass().getClassLoader().getResource(file).getFile());
BufferedReader bufferFichero = new BufferedReader(fichero);
String line = bufferFichero.readLine();
while (line != null) {
writeList(line.toLowerCase());
line = bufferFichero.readLine();
}
bufferFichero.close();
}catch (IOException e) {
e.printStackTrace();
System.out.println("Error IO");
}finally {
count.getAndIncrement(); // counter ++
}
}
private void writeList(String line) {
blockThread.lock();
allLinesFromFiles.add(line);
blockThread.unlock();
}
});
t.start();
}
while (count.intValue() < 3) {
TimeUnit.MILLISECONDS.sleep(500);
}
Collections.sort(allLinesFromFiles);
System.out.println(allLinesFromFiles);
But, a better way is:
List<String> filePaths = Arrays.asList("a.txt", "b.txt", "c.txt");
List<String> result = new ArrayList<>();
filePaths.parallelStream().forEach(filePath -> {
try {
List<String> strings = Files.readAllLines(
Paths.get(ReadTest.class.getClassLoader().getResource(filePath).toURI()));
result.addAll(strings);
} catch (IOException | URISyntaxException e) {
e.printStackTrace();
}
});
Collections.sort(result);
System.out.println(result);
This question already has answers here:
run interactive command line application from java
(2 answers)
Closed 6 years ago.
Basically, I have a process which runs when I press a button on my java application.
And this process executes a command to the terminal of the OS.
But sometimes this command needs to have an interaction with the user.
And I would like to know if this was possible to have the interaction from the process to the user when needed?
My code:
File marsSimulator = new File("resources/mars_simulator/Mars4_5.jar");
if(marsSimulator.exists() && temp.exists()){
String res="";
try {
Process p = Runtime.getRuntime().exec(new String[]{"java","-jar",marsSimulator.getAbsolutePath(),tempAssembly.getAbsolutePath()});
p.waitFor();
InputStream is = p.getInputStream();
byte b[] = new byte[is.available()];
is.read(b, 0, b.length); // probably try b.length-1 or -2 to remove "new-line(s)"
res = new String(b);
} catch (Exception ex) {
ex.printStackTrace();
}
}
Also, I forgot to say that the application is made with SWING and that the output of the process is shown onto a TextArea... Should I change anything ?
Notice that the process blocks when there is an interaction with the user. If there isn't, the process doesn't block !
What do I need to do in this case (which I don't know how to do it ) ?
When the process needs the interaction. I need to know when the process wants some interaction.
I need to get the output generated of the process interactively (line by line).
P.S.: For people who wanna understand the process line, I am using the Mars Simulator (http://courses.missouristate.edu/KenVollmar/MARS/) and I am sending the jar application into a process with a mips assembly code associated.
This next pieces of code is working with my project
Hope it will help for the next adventurers!
And thank you to Nicolas Filotto for helping me.
My class ObservableStream:
class ObservableStream extends Observable {
private final Queue<String> lines = new ConcurrentLinkedQueue<>();
public void addLine(String line) {
lines.add(line);
setChanged();
notifyObservers();
}
public String nextLine() {
return lines.poll();
}
public String getLine(){return lines.peek();}
}
And the other part of the code:
Process p = Runtime.getRuntime().exec(new String[]{"java","-jar",marsSimulator.getAbsolutePath(),tempAssembly.getAbsolutePath()});
//This code does the interaction from the process with the GUI ! Implied, input interaction+output interaction from the process
ObservableStream out = new ObservableStream();
// Observer that simply sends to my external process line by line what we put in
// the variable output
PrintWriter writer = new PrintWriter(p.getOutputStream(), true);
out.addObserver(
(o, arg) -> {
ObservableStream stream = (ObservableStream) o;
String line;
while ((line = stream.nextLine()) != null) {
writer.println(line);
}
}
);
ObservableStream input = new ObservableStream();
input.addObserver(
(o, arg) -> {
ObservableStream stream = (ObservableStream) o;
String line;
while ((line = stream.nextLine()) != null) {
outputTextArea.appendText(line+"\n");
}
}
);
// The thread that reads the standard output stream of the external process
// and put the lines into my variable input
new Thread(
() -> {
try (BufferedReader reader = new BufferedReader(
new InputStreamReader(p.getInputStream()))
) {
String line;
while ((line = reader.readLine()) != null) {
input.addLine(line);
}
} catch (IOException e1) {
e1.printStackTrace();
}
}
).start();
new Thread(
()->{
while(p.isAlive()){
String res = input.getLine();
if(res!=null && res.equals("Enter integer value:")) {
boolean integerIsRequested=true;
Thread t=null;
while(integerIsRequested){
if(t==null) {
t = new Thread(new Runnable() {
public void run() {
String test1 = JOptionPane.showInputDialog("Enter Integer value:");
while(!test1.matches("^\\d+$")){
test1 = JOptionPane.showInputDialog("Error: Not a valid Integer.\nEnter a correct Integer value:");
}
Integer i = Integer.valueOf(test1);
if (i != null) {
out.addLine(test1);
}
}
});
t.start();
}
if(!t.isAlive()){
integerIsRequested=false;
}
}
}
}
outputTextArea.appendText("Program executed\n");
}
).start();
By the way, this post is unique Jarrod ;)
To implement such use case I would personally use:
An Observable object to notify my UI when a new line has been provided by the external process
An Observable object to which I add new lines provided by my UI
An Observer of #1 that will refresh the data of my UI
An Observer of #2 that will send the lines provided by my UI to my external process
A Thread that will check if a new line has been provided by my external process and if so it will provide those lines to #1
So as I don't have your full env, I will show you how it will work with mock objects:
First my fake external application that only does an Echo of what he receives:
public class Echo {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while (true) {
String line = scanner.nextLine();
System.out.printf("echo > %s%n", line);
}
}
}
If this class receives foo, it will print into the standard output stream echo > foo
Then my Observable class
public class ObservableStream extends Observable {
private final Queue<String> lines = new ConcurrentLinkedQueue<>();
public void addLine(String line) {
lines.add(line);
setChanged();
notifyObservers();
}
public String nextLine() {
return lines.poll();
}
}
NB: The class ObservableStream (as it is implemented so far) is meant to have only one Observer no more which is enough according to your needs. Indeed is only used to decouple your UI from how the data is retrieved or published
Then finally the main code:
Process p = Runtime.getRuntime().exec(
new String[]{"java", "-cp", "/my/path/to/my/classes", "Echo"}
);
// The Observable object allowing to get the input lines from my external process
ObservableStream input = new ObservableStream();
// A mock observer that simply prints the lines provided by the external process
// but in your case you will update your text area instead
input.addObserver(
(o, arg) -> {
ObservableStream stream = (ObservableStream) o;
String line;
while ((line = stream.nextLine()) != null) {
System.out.printf("Line Received from the external process: %s%n", line);
}
}
);
// The thread that reads the standard output stream of the external process
// and put the lines into my variable input
new Thread(
() -> {
try (BufferedReader reader = new BufferedReader(
new InputStreamReader(p.getInputStream()))
) {
String line;
while ((line = reader.readLine()) != null) {
input.addLine(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
).start();
// The Observable object allowing to send the input lines to my external process
ObservableStream output = new ObservableStream();
// Observer that simply sends to my external process line by line what we put in
// the variable output
PrintWriter writer = new PrintWriter(p.getOutputStream(), true);
output.addObserver(
(o, arg) -> {
ObservableStream stream = (ObservableStream) o;
String line;
while ((line = stream.nextLine()) != null) {
writer.println(line);
}
}
);
// A simple scanner used to send new messages to my external process
Scanner scanner = new Scanner(System.in);
while (true) {
output.addLine(scanner.nextLine());
}
If this code receives foo, it will print into the standard output stream Line Received from the external process: echo > foo
I hope it answers your question... subProcessStuff "emulates" that sub process. It can be anything - but this way we have all in place. It requires 2 params passed into console. String and Integer. Gobbler got Callback which is an interface, with anonymous implementation - and there are checks for params. To answer if subprocess waits we simply track what is says - just like if a user would operate with it.
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.Scanner;
class Test1 {
public static void main(String[] args) {
for (String arg : args)
System.out.println("arg: " + arg);
for (String arg : args)
if (arg.equals("-test")) {
subProcessStuff();
return;
}
mainProcess();
}
public static void subProcessStuff() {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
try {
System.out.println("Enter String");
String s = br.readLine();
System.out.println("Enered String: " + s);
System.out.println("Enter Integer:");
int i = Integer.parseInt(br.readLine());
System.out.println("Entered Integer: " + i);
} catch (IOException e) {
System.err.println("io error - " + e.getMessage());
} catch (NumberFormatException nfe) {
System.err.println("Invalid Format!");
}
}
private static PrintStream out;
public static void mainProcess() {
String[] commands = { "ls", "-alt" };
ProcessBuilder builder = new ProcessBuilder("java", "Test1", "-test");
// builder.inheritIO(); // I avoid this. It was messing me up.
try {
Process proc = builder.start();
InputStream errStream = proc.getErrorStream();
InputStream inStream = proc.getInputStream();
OutputStream outStream = proc.getOutputStream();
new Thread(new StreamGobbler("err", out, errStream)).start();
out = new PrintStream(new BufferedOutputStream(outStream));
Callback cb = new Callback() {
#Override
public void onNextLine(String line) {
if (line.equals("Enter String")) {
out.println("aaaaa");
out.flush();
}
if (line.equals("Enter Integer:")) {
out.println("123");
out.flush();
}
}
};
new Thread(new StreamGobbler("in", out, inStream, cb)).start();
int errorCode = proc.waitFor();
System.out.println("error code: " + errorCode);
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
if (out != null) {
out.close();
}
}
}
}
interface Callback {
void onNextLine(String line);
}
class StreamGobbler implements Runnable {
private PrintStream out;
private Scanner inScanner;
private String name;
private Callback cb;
public StreamGobbler(String name, PrintStream out, InputStream inStream) {
this.name = name;
this.out = out;
inScanner = new Scanner(new BufferedInputStream(inStream));
}
public StreamGobbler(String name, PrintStream out, InputStream inStream, Callback cb) {
this.name = name;
this.out = out;
inScanner = new Scanner(new BufferedInputStream(inStream));
this.cb = cb;
}
#Override
public void run() {
while (inScanner.hasNextLine()) {
String line = inScanner.nextLine();
if (cb != null)
cb.onNextLine(line);
System.out.printf("%s: %s%n", name, line);
}
}
}
I don't think you can check the state of the process from the Java. However you can do it by using some Linux command. (Of course if you're using Linux)
If your Java process has access to the /proc directory then you can read the status file for the process.
For example for a process with process id 12280
/proc/12280/status
Here's the relevant output of the status file
Name: java
State: S (sleeping)
Tgid: 12280
Pid: 12280
PPid: 12279
...
Second line gives the state of the process. You'll need to run a thread to continuously poll this file to read the status.
Line by Line The Code i use to interract with a different jar which is a speechRecognizer.I think you want to achieve something like this.
Example:
The jar i am interracting(speechRecognizer) is executing different commands and run some other Threads.Every time it has to interract with the main jar it prints something that i need.For example (user said:How are you),so you can have a same logic and when external jar need interraction with user it prints something and you read it into the main app.So:
// About Process
private Process process;
private BufferedReader bufferedReader;
private boolean stopped = true;
Thread processChecker;
//Running it in a Thread so the app don't lags
new Thread(() -> {
try {
stopped = false;
//Starting the external jar..
ProcessBuilder builder = new ProcessBuilder("java", "-jar", System.getProperty("user.home")
+ File.separator + "Desktop" + File.separator + "speechRecognizer.jar", "BITCH_PLEASE");
//Redirecting the ErrorStream
builder.redirectErrorStream(true);
process = builder.start();
bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line;
//Check continusly if the process is still alive
//i case of crash i should do something..
processChecker = new Thread(() -> {
while (process.isAlive()) {
try {
Thread.sleep(1200);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
stopSpeechReader(false);
});
processChecker.start();
// Continuesly Read Output of external process
while (!stopped) {
while ((line = bufferedReader.readLine()) != null && !line.isEmpty()) {
System.out.println(line);
checkSpeechResult(line);
}
}
// Interrupt the mf Thread if is Alive
if (processChecker.isAlive())
processChecker.interrupt();
System.out.println("SpeechReader Stopped! Process is alive:" + process.isAlive() + " >Exit Value:"
+ process.exitValue());
} catch (Exception e) {
e.printStackTrace();
}
}).start();
I am reading a csv file from a location.
Could you please tell me how can I stop the Producer Thread and Consumer Thread incase file is not found in this case ?
Below is my program which creates two threads, Producer and Consumer Threads to read the data from the file
package com.util;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.PipedReader;
import java.io.PipedWriter;
import au.com.bytecode.opencsv.CSVReader;
public class TestProgram {
public static void main(String args[]) {
final String startToken = ",Nifty 50 Gainers";
final String endToken = "50 Losers";
final PipedWriter pipedWriter = new PipedWriter();
PipedReader pipedReaderTmp = null;
try {
pipedReaderTmp = new PipedReader(pipedWriter);
} catch (IOException e) {
}
final PipedReader pipedReader = pipedReaderTmp;
// Consumer
new Thread(new Runnable() {
#Override
public void run() {
try {
CSVReader csvReader = new CSVReader(pipedReader);
while (true) {
String[] line = csvReader.readNext(); // blocks until the next line is available
if (line == null)
break; // end of stream has been reached
if (line != null && line.length > 3) {
String indices_name = line[1];
if (indices_name != null) {
System.out.println(indices_name);
}
}
}
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
// Producer
new Thread(new Runnable() {
#Override
public void run() {
try {
BufferedReader br = new BufferedReader(new FileReader(
"C:\\Users\\ravikiranv\\Downloads\\MA050116.csv"));
String line = null;
while ((line = br.readLine()) != null) {
if (startToken.equals(line))
break;
}
while ((line = br.readLine()) != null) {
if (line.contains((endToken))) {
break;
} else {
pipedWriter.write(line + '\n');
}
}
pipedWriter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
}
}
See the Javadoc for PipedReader.read().
Throws:
IOException - if the pipe is broken, unconnected, closed, or an I/O error occurs.
So just close it and the other end wwil get an IOException.
Note: The PipedReader has some issues - you may find it safer/better to use something like a `BlockingQueue.
You can and should instantiate and start the Threads only if you know the file exists. This keeps you safe from the concerns to stop threads from within.
File file = new File("C:\\Users\\ravikiranv\\Downloads\\MA050116.csv");
if (file.exists()) {
new Thread(new Runnable() { ... }).start();
...
}
If you don't want that for a reason, you could keep a reference to the consumer thread and stop it from within the producer. For an example how to do that, see this answer
For my application, I need to continuously read from a file and the application will proceed on reading 100 from that file. I'm writing to the same line of the file i.e I'm overwriting the file contents. But my program reads the next line in after each iteration of the loop. My code:
public class h{
private int flag=0;
public void scan()
{
String filename="file1.txt";
try{
int i,j;
int nooflines=1;
String textData = new String();
try{
FileReader fr = new FileReader(filename);
BufferedReader textReader = new BufferedReader(fr);
while(flag==0){
textData=textReader.readLine();
if(textData==null){
Thread.sleep(3000);
continue;
}
process(textData);
}
textReader.close();
}catch(InterruptedException e){
System.out.println(e.getMessage());
}
}catch (IOException e){
System.out.println(e.getMessage());
}
}
public void process(String data){
if(data.equals("100")){
System.out.println(data);
flag=1;
}
}
}
So after one iteration my code will be scanning the second line, but the file1.txt is opened using write mode(-w) which erase its contents and writes at the beginning of the file. So how can I edit my program to keep scanning the first line of the file only?
I think this'll do it.
BufferedReader textReader;
while(flag==0){
textReader = new BufferedReader(new FileReader(filename));
textData=textReader.readLine();
if(textData==null){
Thread.sleep(3000);
continue;
}
process(textData);
}
To read your file from the beginning every 3s:
ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();
ses.scheduleAtFixedRate(new Runnable() {
#Override
public void run() {
try(BufferedReader br = new BufferedReader(new FileReader(filename))) {
while(keepReading) {
keepReading = process(br.readLine());
}
}
}
}, 0, 3, TimeUnit.SECONDS); // every 3s
public boolean process(String data) {
// do something
return data != null && !data.equals("100");
}
I am trying to call a simple program test.exe which is as simple as-
int main()
{
int a;
cout<<"Welcome\n";
while(cin>>a&&a!=0)
cout<<"you entered "<<a<<endl;
}
I want to run it from a java program as a process, and send+recieve i/o from it. I am using the process with 2 threads as follows-
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Processproblem {
public static void main(String[] args)throws IOException, InterruptedException {
final Process process;
try {
process = Runtime.getRuntime().exec("test.exe");
} catch (IOException e1) {
e1.printStackTrace();
return;
}
new Thread(new Runnable() {
public void run() {
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
try {
while ((line = br.readLine()) != null) {
System.out.println("[OUT] " + line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
byte[] buffer = new byte[1024];
int reading=0;
System.out.println(reading);
BufferedWriter bw= new BufferedWriter(new OutputStreamWriter(process.getOutputStream()));
while(reading!=-1)
{
reading= System.in.read(buffer);
for(int i = 0; i < buffer.length; i++) {
int intValue = new Byte(buffer[i]).intValue();
if (intValue == 0) {
reading = i;
break;
}
else
{
bw.append((char)intValue);
}
}
bw.newLine();
bw.flush();
}
} catch (Exception e) {
}
}
}
).start();
}
}
But they are not working as expected. When i run the program it just shows the "Welcome\n" message and then stops for input. When i give a integer and press enter in the java console it does nothing.
What am I doing wrong? They are two separate threads so why are they blocking each other? Is there any problem in my concept?
The program waits for your input. Grab the process output stream (using getOutputStream) and write to it.