如何检查 java 中目录的写权限？

Question

I would like a code snippet that checks whether a directory has read/write permissions and do something if it does, and does something else if it doesnt. I tried an example shown here:

try {
    AccessController.checkPermission(new FilePermission("/tmp/*", "read,write"));
System.out.println("Good");
    // Has permission
} catch (SecurityException e) {
    // Does not have permission
System.out.println("Bad");
}

The problem is the exception is always triggered, so it always ends up printing "Bad" regardless of whether the directory has write permissions or not. (I chmod the directories to 777 or 000 to test).

Is there an alternative or some way to accomplish what I need?

Answer 1

if you just want to check if you can write:

File f = new File("path");
if(f.canWrite()) {
  // write access
} else {
  // no write access
}

for checking read access, there is a function canRead()

Answer 2

In Java 7 i do it like this:

if(Files.isWritable(path)){
  //ok, write
}

Docs

Answer 3

You should use the path of the directory alone ( "/tmp" ) to query the permissions of a directory:

AccessController.checkPermission(new FilePermission("/tmp", "read,write"));

With "/tmp/*" you query the permissions of all files inside the /tmp directory.

Answer 4

Java has its own permission model revolving around the use of an AccessController and Permission classes. The permissions are granted to a code source (the location from where the classes are loaded), and in some/most cases these permissions are different from any underlying permissions required to access the desired resource.

For instance, although you may have granted all users to read and write to the /tmp directory, this isn't sufficient for the AccessController to grant your code the necessary permission. You'll also need to add a rule in the policy file used (by the AccessController) to read and write files from the /tmp directory. The rule to be created will be equivalent to the following:

grant codeBase "<location of the codebase>" {
    permission java.io.FilePermission "/tmp/-", "read, write";
};

Answer 5

This seems to work fine:

assertFalse(Files.isWritable(new File("/etc/").toPath()));
assertTrue(Files.isWritable(new File("/tmp/").toPath()));

Answer 6

Do you want to check permissions for folder or for files in folder ?

"/*" in path name means a directory and all the files contained in that directory.

see javadoc

Answer 7

java.io.File has two methods canRead and canWrite that should suffice.

Answer 8

if(DocumentFile.fromFile(file).canWrite()){
   //allowed
   ...
}else{
   ...
}

Answer 9

On Windows, File.canWrite() does not always provide an accurate result. I would recommand using the following:

import java.nio.file.Files;
import java.nio.file.Paths;
...

if(Files.isWritable(Paths.get("path"))){
  //ok, write
}

Answer 10

Oops, one more thing. The directory also has to be executable, at least on linux:

  /** Make sure output dir exists and is writeable. */
  public boolean validateOutputDir(Path publishDirectory, Formatter error) {
    if (!Files.exists(publishDirectory)) {
      error.format(" Output directory '%s' does not exist%n", publishDirectory);
      return false;
    }
    if (!Files.isDirectory(publishDirectory)) {
      error.format(" Output directory '%s' is not a directory%n", publishDirectory);
      return false;
    }
    if (!Files.isWritable(publishDirectory)) {
      error.format(" Output directory '%s' is not writeable%n", publishDirectory);
      return false;
    }
    if (!Files.isExecutable(publishDirectory)) {
      error.format(" Output directory '%s' is not executable%n", publishDirectory);
      return false;
    }
    return true;
  }