Create a read-only file

问题

I was wondering wether it is possible to create or simulate a file with a content set at creation and the assurance that nobody can ever change the file. If possible, can I do it in java?

回答1:

Setting a file to read only is not going to make it so no one can ever change it. It takes about 3 seconds to unset the read only flag. The file can then be opened in a hex editor or other program that can handle the file type and changes can be made.

回答2:

yes we can make read only file in java using setReadOnly() method.

After using this method, you will not be able to write or edit into the file.

import java.io.File;

public class FileReadOnly {
  public static void main(String[] args) {
    File file = new File("c:/file.txt");
    file.setReadOnly();
    System.out.println("File is in read only mode");
    }
}

or in this way also.

import java.io.File;
import java.io.IOException;

public class FileAttributesDemo {

  public static void main(String[] args) throws IOException {
    // Create a new file, by default canWrite=true, readonly=false
    File file = new File("test.txt");
    if (file.exists()) {
      file.delete();
    }
    file.createNewFile();
    System.out.println("Before. canWrite?" + file.canWrite());

    // set to read-only, atau canWrite = false */
    file.setWritable(false);
    System.out.println("After. canWrite?" + file.canWrite());
  }
}

回答3:

If you simply just need to create a Read-Only file, then won't the code below be sufficient? Unless I am missing something from your question:

import java.io.File;
import java.io.IOException;

public class FileAttributesDemo {

  public static void main(String[] args) throws IOException {
    // Create a new file, by default canWrite=true, readonly=false
    File file = new File("test.txt");
    if (file.exists()) {
      file.delete();
    }
    file.createNewFile();
    System.out.println("Before. canWrite?" + file.canWrite());

    // set to read-only, atau canWrite = false */
    file.setWritable(false);
    System.out.println("After. canWrite?" + file.canWrite());
  }
}

回答4:

Try:

• file.setReadOnly()
• Runtime.getRuntime().exec("attrib " + "" + file.getAbsolutePath() + "" + " +R"); //(works on Windows)

回答5:

To make it so setWritable(true) does not enable writing again you could extend File and override the setWritable() methods.

import java.io.File;
import java.io.IOException;
import java.lang.Override;

public class FileAttributeDemo2 {
    private static class ReadOnlyFile extends File {
        public ReadOnlyFile(String pathname) {
            super(pathname);
        }

        @Override
        public boolean setWritable(boolean writeable) {
            return setWritable(writeable, true);
        }

        @Override
        public boolean setWritable(boolean writeable, boolean ownerOnly) {
            if (!writeable) {
                return super.setWritable(false, ownerOnly);
            }
            return false;
        }
    }

    public static void main (String[] args) throws IOException {
        File file = new ReadOnlyFile("test.txt");
        if (file.exists()) {
            file.delete();
        }
        file.createNewFile();
        System.out.println("Before. canWrite? " + file.canWrite());

        file.setWritable(false);
        System.out.println("Set writable false. canWrite? " + file.canWrite());

        file.setWritable(true);
        System.out.println("Set writable true. canWrite? " + file.canWrite());

    }
}

which produces the output:

Before. canWrite? true 
Set Writable False. canWrite? false 
Set Writable True. canWrite? false

回答6:

Read-only way can be useful altough it is not impossible to change or crack.So if you can not create an unreachable file then you can convert its contents to not understandable thanks to some kind of Encryption algorithms.For example AES may be so usefull.

回答7:

In this case simply you have to create a file using File class after that by reference you have to call setReadOnly() method.

    File f=new File("abc.txt");
    f.setReadOnly();

来源：https://stackoverflow.com/questions/9477257/create-a-read-only-file