Why is my program denying access to create a file?

问题:

In the book I'm reading on Java, it demonstrates serialization by using a program that writes to a file and stores it away. I'm getting a strange error that I don't know how to read and it denies me access to creating a .txt file. Here's the error:

Exception in thread "main" java.io.FileNotFoundException: C:\testFile.txt (Access is denied)
    at java.io.FileOutputStream.open(Native Method)
    at java.io.FileOutputStream.<init>(Unknown Source)
    at java.io.FileOutputStream.<init>(Unknown Source)
    at serializableTests.MyProgram.main(MyProgram.java:18)

Here's the two classes for the program:

User class:

public class User implements Serializable {

    private static final long serialVersionUID = 4415605180317327265L;

    private String username;
    private String password;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

And here's the main class:

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.OutputStream;


public class MyProgram {
    public static void main(String[] args) throws IOException {
        User user = new User();
        user.setUsername("tpage");
        user.setPassword("password123");

        File file = new File("C:\\testFile.txt");
        OutputStream fileOutputStream = new FileOutputStream(file);
        ObjectOutputStream outputStream = new ObjectOutputStream(fileOutputStream);
        outputStream.writeObject(user);
        System.out.println("I've store the user object in a file called " + file.getName());
    }
}

output

2019-04-22 08:40:28,895 [main] INFO  g.t.service.impl.CsvServiceImpl - Directory structure created data/test/tnx-log/tnc.log false 
2019-04-22 08:40:28,895 [main] INFO  g.t.service.impl.CsvServiceImpl - file.getAbsoluteFile() : C:\Users\jigar\apps\workspace\trade-publisher\data\test\tnx-log\tnc.log canWrite() : false
2019-04-22 08:40:28,895 [main] INFO  g.t.service.impl.CsvServiceImpl - txn log file created data/test/tnx-log/tnc.log true 

2019-04-22 08:40:28,957 [main] INFO  g.t.service.impl.CsvServiceImpl - Directory structure created data/test/tnx-log/tnc.log false 
2019-04-22 08:40:28,957 [main] INFO  g.t.service.impl.CsvServiceImpl - file.getAbsoluteFile() : C:\Users\jigar\apps\workspace\trade-publisher\data\test\tnx-log\tnc.log canWrite() : false


@Override
    public void createTxnInfoFile() throws IOException {
        File file = new File(txnLogFile);
        if (!file.exists()) {
            boolean directoryStructureCreated = file.getParentFile().mkdirs();
            logger.info("Directory structure created {} {} ", txnLogFile, directoryStructureCreated);
            logger.info("file.getAbsoluteFile() : " + file.getAbsoluteFile() + " canWrite() : " + file.canWrite());
            boolean fileCreated = file.createNewFile();
            logger.info("txn log file created {} {} ", txnLogFile, fileCreated);
        }
        file = null;
    }

回答1:

On recent versions of Windows, you cannot write to the root folder of the system drive without elevated privileges.

To make it work, change the location to another drive or change to a subfolder in C, such as your profile directory, e.g. c:\users\yourname\testfile.txt

(Note that you're using a .txt ending but the file produced will not be readable in an editor. Serialization is a binary format.)

EDIT:

To implement this in code change

File file = new File("C:\\testFile.txt");

to something like

File file = new File("C:\\users\\bane\\testFile.txt");

I've used your SO name "bane" - replace with whatever your login name is on your pc.

回答2:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class CopyFiles {
    private File targetFolder;
    private int noOfFiles;
    public void copyDirectory(File sourceLocation, String destLocation)
            throws IOException {
        targetFolder = new File(destLocation);
        if (sourceLocation.isDirectory()) {
            if (!targetFolder.exists()) {
                targetFolder.mkdir();
            }

            String[] children = sourceLocation.list();
            for (int i = 0; i < children.length; i++) {
                copyDirectory(new File(sourceLocation, children[i]),
                        destLocation);

            }
        } else {

            InputStream in = new FileInputStream(sourceLocation);
            OutputStream out = new FileOutputStream(targetFolder + "\\"+ sourceLocation.getName(), true);
            System.out.println("Destination Path ::"+targetFolder + "\\"+ sourceLocation.getName());            
            // Copy the bits from instream to outstream
            byte[] buf = new byte[1024];
            int len;
            while ((len = in.read(buf)) > 0) {
                out.write(buf, 0, len);
            }
            in.close();
            out.close();
            noOfFiles++;
        }
    }

    public static void main(String[] args) throws IOException {

        File srcFolder = new File("C:\\sourcefolder\\");
        String destFolder = new String("C:\\destination\\");
        CopyFiles cf = new CopyFiles();
        cf.copyDirectory(srcFolder, destFolder);
        System.out.println("No Of Files got Retrieved from Source ::"+cf.noOfFiles);
        System.out.println("Successfully Retrieved");
    }
}