Use threading to process file chunk by chunk

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感情败类
感情败类 2021-01-22 14:56

I have a arraylist which consists of 5000 IP Addresses. For each IP Address, I want to execute a SNMPGet request and a FTPDownload command. I want to implement it in a fashion,

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  • 2021-01-22 15:07

    Herewith adding working example having 5 threads. Just put the test.txt in your CLASS_PATH of the application.

    class MyRunnable implements Runnable {
    List<List<String>> records;
    MyRunnable(List<List<String>> records){
        this.records = records;
    }
    public void run(){
        for(List list : records){
            System.out.println(Thread.currentThread().getName() + " : "+list.toString());
        }
    }}
    

    Main Class -

    public class FileProcessThreads {
    public List<List<String>> process(String fileName) throws IOException {
        List<List<String>> records = new ArrayList<>();
        BufferedReader br = new BufferedReader(new FileReader(fileName));
        String line = null;
        while((line = br.readLine()) != null){
            List<String> listValues = Arrays.asList(line.split(" "));
            records.add(listValues);
        }
        System.out.println(records.size());
        return records;
    }
    public static void main(String[] args) throws IOException {
        FileProcessThreads fp = new FileProcessThreads();
        List<List<String>> records = fp.process("test.txt");
        ExecutorService es = Executors.newFixedThreadPool(5);
        int recordsInEachThread = (int) (records.size()/5);
        System.out.println(recordsInEachThread);
    
        MyRunnable my1 = new MyRunnable(records.subList(0, recordsInEachThread));
        MyRunnable my2 = new MyRunnable(records.subList(recordsInEachThread+1, recordsInEachThread*2));
        MyRunnable my3 = new MyRunnable(records.subList(recordsInEachThread*2 + 1, recordsInEachThread*3));
        MyRunnable my4 = new MyRunnable(records.subList(recordsInEachThread*3 + 1, recordsInEachThread*4));
        MyRunnable my5 = new MyRunnable(records.subList(recordsInEachThread*4 + 1, records.size() - 1));
        es.execute(my1);
        es.execute(my2);
        es.execute(my3);
        es.execute(my4);
        es.execute(my5);
        es.shutdown();
    }}
    
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  • 2021-01-22 15:17

    Executor Framework will be best suit for your solution. I have created one example here. You can increase the number of threads as per your requirement.

    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    
    class SomeRunnable implements Runnable {
        int threadNo = -1 ;
        List<String> list = new ArrayList<String>();
        public SomeRunnable(List list, int threadNo ) {
            this.list.addAll(list);
            this.threadNo =threadNo;
        }
        @Override
        public void run() {
            for (String element : list) {
                System.out.println("By Thread:" + threadNo+", Processed Element:" +element);
            }
        }
    
    }
    
    public class ExecutorDemo {
        public static void main(String[] args) {
            List<String> list = new ArrayList<String>();
            for (int i = 0; i < 100; i++) {
                list.add("Elem:"+i);
            }
            // Divide list 
            int divideIndex = list.size()/2;
            //Create objects of Runnable
            SomeRunnable obj1 = new SomeRunnable(list.subList(0, divideIndex),1);
            SomeRunnable obj2 = new SomeRunnable(list.subList(divideIndex,list.size()),2);
    
            //Create fixed Thread pool, here pool of 2 thread will created
            ExecutorService pool = Executors.newFixedThreadPool(2);
    
            pool.execute(obj1);
            pool.execute(obj2);
    
            pool.shutdown();
        }
    
    }
    
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