无法从抽象类读取文件

Question

I am trying to make a base file plugin which other threads will inherit. But I am stuck at a point where the file exists and can be read from a normal thread but when I try to read that file from an abstract Base file, it says File not found. Here's my base class :-

    package com.evol.fp;

    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.io.PrintWriter;

    public abstract class BaseFilePlugin extends Thread implements BaseFileReader{

        String filename = "";
        File file = null;
        boolean fileStarted = false;
        boolean fileEnded = false;

        public BaseFilePlugin() {
            file = new File(filename);
        }

        public void readFile() {
            BufferedReader br = null;
            System.out.println("Base call: " + filename);
            try {

                System.out.println("inbside ");
                br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
                if(br.readLine().trim().isEmpty()) {
                    endFile();
                    return;
                } else {
                    startFile(filename);
                    String record;
                    while((record = br.readLine().trim()) != null) {
                        parseRecord(record);
                    }
                    endFile();
                }
            } catch(Exception ioe) {
                ioe.printStackTrace();
            } finally {
                try {
                    br.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        public abstract void parseRecord(String record);

        public void startFile(String filename) {
            this.fileStarted = true;
            this.fileEnded = false;
        }

        public void endFile() {
            file.delete();
            this.fileEnded = true;
            this.fileStarted = false;
        }

        public void run() {
            while(true) {
                System.out.println("Inside run, fileName: " + filename);
                System.out.println("Filestarted: " + fileStarted + ", file exists: " + file.exists());
                if(!fileStarted) {
                    readFile();
                }
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        /**
         * @return the filename
         */
        public String getFilename() {
            return filename;
        }

        /**
         * @param filename the filename to set
         */
        public void setFilename(String filename) {
            this.filename = filename;
        }

    }

I am aware of multithreading but never implemented with base class to parse records from a file, if someone tells me what's the problem that will be great. I know that the file exists for sure. Here's my child class: -

    package com.evol.fp;

    public class FileReaderThread extends BaseFilePlugin {

        public FileReaderThread() {
            super.setFilename("E:\\soham\\soham.txt");
        }
        @Override
        public void parseRecord(String record) {
            System.out.println(record);
        }
    }

But its not calling the child's parseRecord method, using a simple main method:-

package com.evol.fp;

public class StartProcess {

public static void main(String[] args) {
    FileReaderThread thd = new FileReaderThread();
    thd.start();
}

}

Answer 1

I think it's because the parent constructor (BaseFilePlugin.class) is called first before you set your filename in super.setFile("E:\\\\soham\\\\soham.txt");

If you can remove the parent constructor instead and replace your setFileName into setFile where file is iniatilize .eg

//    public BaseFilePlugin() {
//        file = new File(filename);
//    }
....
....
/**
     * @return the file
     */
    public String getFile() {
        return file
    }

    /**
     * @param file the file to set
     */
    public void setFile(String file) {
        file = new File(file);
    }

and in your subclass

public FileReaderThread() {
  super.setFile("E:\\soham\\soham.txt");
}

Answer 2

BaseFilePlugin 's constructor creates its file with an empty string since initially String filename = ""; .

The client calls setFilename(...) which updates filename . However, file is still the same instance when the object was first created (which is using an empty string as the file name).

I would suggest to pass the file name as part of the constructor so file is properly initialized:

    public BaseFilePlugin(String filename) {
        this.filename = filename;
        file = new File(filename);
    }

Optionally, if it makes sense that an instance can read only 1 file, then make those class attributes final, and remove the setFilename() method.