Memo: [Java] If a file is in the monitored directory, process it.

background

Last time, I wrote Process and output CSV file. I want to process the CSV file when it comes into the target directory. I thought, so I will write down the code.

** First, monitor the directory **

-** WatchService usage memo ** -** Wait for the file to be created in Java, detect the creation and then perform the next process ) ** : grinning: I referred to this page. Thank you very much.

test.java

import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.Watchable;

import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.WatchEvent.*;

public class test {

    public static void main(String[] args) throws Exception {
        Path dir = Paths.get("C://develop//BOX");
        WatchService watcher = FileSystems.getDefault().newWatchService();
        dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);

        for (;;) {
            WatchKey watchKey = watcher.take();
            for (WatchEvent<?> event: watchKey.pollEvents()) {
                if (event.kind() == OVERFLOW) continue;

                WatchEvent<Path> ev = cast(event);
                Path name = ev.context();
                Path child = dir.resolve(name);
                System.out.format("%s: %s\n", event.kind().name(), child);
            }
            watchKey.reset();
        }
    }

    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>)event;
    }
}

Now, create a directory called ** BOX ** in ** C: \ develop ** and

Try compiling test.java anywhere and running the class. (* This time I am running with D: )

Wow! If you get an error when compiling:: beginner: ** here ** It will be helpful.

Now let's run the class file. Try putting a suitable file in the BOX directory.

Oops! The sample .txt that I put in the directory It says ENTRY_CREATE and ENTRY_MODIFY.

When I delete the file from the directory, I see ENTRY_DELETE.

I think that you can understand it after actually moving it, so I pasted the image when I moved it first This is written in test.java. (The comment is written in my interpretation, so I may have made a mistake ...) The second line ** WatchService watcher = FileSystems.getDefault (). newWatchService (); ** It seems to be a fixed phrase, so I will use it as it is without thinking deeply.

Path dir = Paths.get("C://develop//BOX");                            //"dir"Specify the directory to be monitored in
WatchService watcher = FileSystems.getDefault().newWatchService();   //WatchService"watcher"Created with the name
dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);     //"dir"Specify the event to be monitored in(Create,Delete,Change)

for (;;) {                                                           //Implement an infinite loop to wait for an event
   WatchKey watchKey = watcher.take();                               //Watcher key from watcher"watchKey"To get
   for (WatchEvent<?> event: watchKey.pollEvents()) {                //You can get the List where WatchEvent is stored by pollEvents method.
       if (event.kind() == OVERFLOW) continue;                       //"OVERFLOW"Is a special monitoring event that indicates that the event has disappeared or was destroyed

        WatchEvent<Path> ev = cast(event);
        Path name = ev.context();                                    //"name"Get in event context and set the file name
        Path child = dir.resolve(name);                              //Full path with resolve method("dir"In the path of"name"Added)The set
        System.out.format("%s: %s\n", event.kind().name(), child);   //At the time of output, [event name:Instructions to output with [Full path of file]
   }
   watchKey.reset();                                                 //Reset the watch key(To return the WatchKey state to READY)

** Combine the processing to process csv **

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class test{

    public static void main(String[] args) {
        process("20180712.csv",  ":00,","output.csv");
    }

    public static void process(String read_file, String searchString, String output_file){

        try(FileReader fr = new FileReader(read_file);BufferedReader br = new BufferedReader(fr);
            FileWriter fw = new FileWriter(output_file);BufferedWriter bw = new BufferedWriter(fw)){

            String line;
            while ((line = br.readLine()) != null) {
                Pattern p = Pattern.compile(searchString);
                Matcher m = p.matcher(line);
                if (m.find()){
                    String[] csvArray;
                    csvArray = line.split(",");
                    String time  = csvArray[0];
                    float press = Float.parseFloat(csvArray[1])%10000;
                    String pressure = String.format("%.2f", press);
                    String temperature  = csvArray[2];
                    String outputLine = String.join(",",time,pressure,temperature);
                    bw.write(outputLine);
                    bw.newLine();
                }else{ 
                }
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

The previous code and the code I wrote above haven't changed much. It's almost just combined.

test.java

import java.nio.file.FileSystems;      //Required for directory monitoring
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.Watchable;
import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.WatchEvent.*;

import java.io.BufferedReader;        //Required to process and output csv
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class test {

    public static void main(String[] args) throws Exception {
        
        Path dir = Paths.get(System.getenv("CSV_DIR"));       //This time, the directory to be monitored is an environment variable"CSV_DIR"Set to
        WatchService watcher = FileSystems.getDefault().newWatchService();
        dir.register(watcher, ENTRY_CREATE);                  //This time ENTRY_OK if only CREATE is detected
   
        for (;;) {
            WatchKey watchKey = watcher.take();
            for (WatchEvent<?> event: watchKey.pollEvents()) {
                if (event.kind() == OVERFLOW) continue;              
                WatchEvent<Path> ev = cast(event);
                Path name = ev.context();
                Path child = dir.resolve(name);
                String newfile =String.format("%s", child);

                process(newfile, ":00,","D://tedkuma//★"+name); //Pass the full path of the detected file to the file read by process
                System.out.println("Output success:"+name);
            }
            watchKey.reset();
        }  
    }

    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>)event;
    }

    public static void process(String read_file, String searchString, String output_file){ //The following is the same as the previous one

        try(FileReader fr = new FileReader(read_file);BufferedReader br = new BufferedReader(fr);
            FileWriter fw = new FileWriter(output_file);BufferedWriter bw = new BufferedWriter(fw)){

            String line;
            while ((line = br.readLine()) != null) {
                Pattern p = Pattern.compile(searchString);
                Matcher m = p.matcher(line);
                if (m.find()){
                    String[] csvArray;
                    csvArray = line.split(",");
                    String time  = csvArray[0];
                    float press = Float.parseFloat(csvArray[1])%10000;
                    String pressure = String.format("%.2f", press);
                    String temperature  = csvArray[2];
                    String outputLine = String.join(",",time,pressure,temperature);
                    bw.write(outputLine);
                    bw.newLine();
                }else{ 
                }
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

Since Japanese comments and ★ marks are included in the java file javac alone will result in a compile error: sweat: : skull: Error: This character cannot be mapped to encoding MS932, so it will appear. This time I'm compiling with ** javac -encodhing utf-8 test.java **. Let's run it.

I set the environment variable "CSV_DIR" to the location C: \ develop \ monitored. (This monitored directory) Put the CSV file you want to process in this.

The file name put in the directory is displayed after Output success :.

Check the tedkuma directory of the D drive specified as the output destination. A file with a star at the beginning of the file name is output, and the csv inside is also processed.

This time is over.