CS1103 Programming Assignment Unit 1 - Fetch the information stored at a given URL on the web, save that data to a file, and handle the exceptions

Questions

This program will fetch the information stored at a given URL on the web and save that data to a file. Besides, this will also include networking and file operations and partly an exercise in using exceptions.

1. Codes

import java.io.*;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Scanner;

/**
 * ExceptionHandling fetches the information stored at a given URL on the web and saves that data to a file.
 * This will also include networking and file operations and partly an exercise in using exceptions
 *
 * @author Zhiyao He
 */
public class ExceptionHandling {

    /**
     * copy the data from the web into the file
     *
     * @param in  a formal parameter of type InputStream
     * @param out a formal parameter of type OutputStream
     * @throws IOException
     */
    private static void copyStream(InputStream in, OutputStream out) throws IOException {
        int oneByte = in.read();
        while (oneByte >= 0) { // negative value indicates end-of-stream
            out.write(oneByte);
            oneByte = in.read();
        }
    }

    /**
     * Read the URL and the file name as strings from the user.
     * Get the input stream and the output stream.
     * Copy the data from the web into the file.
     * Handle the exceptions with try ... catch... blocks.
     *
     * @param args
     */
    public static void main(String[] args) throws IOException {
        InputStream inputStream = null;
        OutputStream outputStream = null;

        String urlString;
        String fileName;

        // Read the URL and the file name as strings from the user.
        // Surrounded by a try-with-resources block,
        // the in.close() method is automatically called when an exception occurs.
        try (Scanner in = new Scanner(System.in)) {
            System.out.print("Please input the URL: ");
            urlString = in.nextLine();

            System.out.print("Please input the fileName: ");
            fileName = in.nextLine();
            System.out.print("Writing...");
        }

        try {
            // create the URL object
            URL url = new URL(urlString);

            // get the input stream
            inputStream = url.openStream();

            // get the output stream
            outputStream = new FileOutputStream(fileName);

            // copy the data from the web into the file
            copyStream(inputStream, outputStream);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) inputStream.close();
            if (outputStream != null) outputStream.close();
        }
    }
}

2. Outputs:

Console output:

Please input the URL: https://math.hws.edu/eck/cs124/javanotes8/source/chapter11/ReverseFileWithResources.java
Please input the fileName: file
Writing...
Process finished with exit code 0

Output file (The information stored on the web at the above URL):

import java.io.*;
import java.util.ArrayList;
import java.util.Scanner;

/**
 * Reads numbers from a file named data.dat and writes them to a file
 * named result.dat in reverse order.  The input file should contain
 * exactly one real number per line.
 *    This version of the ReverseFile program uses try-with-resource
 * statements to safely open and close the Scanner that is used to
 * read the data and the PrintWriter that is used to
 * write the data.
 */
public class ReverseFileWithResources {

    public static void main(String[] args) {

        ArrayList<Double> numbers;  // An ArrayList for holding the data.

        numbers = new ArrayList<Double>();
        
        // Read the data from the input file.

        try( Scanner data = new Scanner(new File("data.dat")) ) {
            // Read numbers, adding them to the ArrayList.
            while ( data.hasNextDouble() ) {  // Read until end-of-file.
                double inputNumber = data.nextDouble();
                numbers.add( inputNumber );
            }
        }
        catch (FileNotFoundException e) {
                // Can be caused if file does not exist or can't be read.
            System.out.println("Can't open input file data.dat!");
            System.out.println("Error: " + e);
            return;  // Return from main(), since an error has occurred.
        }
        
        // Write the data to the output file.
        
        try( PrintWriter result = new PrintWriter("result.dat") ) {
            // Output the numbers in reverse order.
            for (int i = numbers.size()-1; i >= 0; i--)
                result.println(numbers.get(i));
            result.flush();  // Make sure data is actually sent to the file.
            if (result.checkError())
                System.out.println("Some error occurred while writing the file.");
            else
                System.out.println("Done!");
        }
        catch (FileNotFoundException e) {
                // Can only be caused by the PrintWriter constructor
            System.out.println("Can't open file result.dat!");
            System.out.println("Error: " + e);
        }

    }  // end of main()

} // end class ReverseFileWithTextReader

​

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This is the ending, thanks for reading.

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