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Java getting absolute path from directory count list

Expected:
find the number files in the folder, and collect the absolute path for each file in the directory.
File certificatePath = new File("resources/NPL");
String absolutePath = certificatePath.getAbsolutePath();
File directory = new File(absolutePath);
int fileCount=directory.list().length;
From the above code getting the no of files in folder (resources/NPL), now i'm struggle to get the absolute path for the files.

You should use listFiles instead fo list() (provided you have the security rights to do so), otherwise you are stuck with the file names.

Well first of all what does it mean to collect it? If you need the file names it is already there for you in an array of String[] which you get from directory.list() method. If you want the full names you can use listFiles() method which returns a File[] and each file has getAbsolutePath() method. Something like:
for (File file : directory.listFiles()) {
System.out.println(file.getAbsolutePath());
}

Jump one folder up in a URL in Java

I have a URL that I get as below:
String jarFilePath = getClass().getProtectionDomain().getCodeSource().getLocation()
This would get me the complete path to the jar file. Now how do I jump one folder up and append some other path to it? For example., if the jarFilePath is something like:
c:/path/to/jar/file.jar
I want to jump one folder up and append another relative path like below:
c:/path/to/resources/path/to/resources/
Where the folders resources and jar are at the same directory level in the file system.

File f = new File("C:/path/to/jar/file.jar");
File dest = new File(f.getParentFile().getParentFile(), "resources/path/to/resources");

Just use the File-Object, that makes a lot of things easier:
import java.io.File;
String pathname = "c:/path/to/jar/file.jar";
File f = new File(pathname);
String p = f.getParent();

Try and use a File object:
File jarFile = new File(jarFilePath);
File newFolder = new File( jarFile.getParentFile().getParentFile(), "resources/path/to/resources");
If you want to use the path as a string, try using Apache Commons IO's FilenameUtils:
String resourcesPath = FilenameUtils.normalize( FilenameUtils.getPath(jarFilePath) + "/../resources/path/to/resources");

You have several ways.
You can split the path into it's elements and rebuild it until array.length -3 (-1 would be filename, -2 the last folder)
You could simple remove the file and append another ../ (which just means: "Go one directory back") (that would be something like this then: c:/path/to/jar/../resources/path/to/resources/)
You gould use a regex to get rid of the last folder and file. something like /[^/]+/[^/]+$

Get the filePath from Filename using Java

Is there a easy way to get the filePath provided I know the Filename?

You can use the Path api:
Path p = Paths.get(yourFileNameUri);
Path folder = p.getParent();

Look at the methods in the java.io.File class:
File file = new File("yourfileName");
String path = file.getAbsolutePath();

I'm not sure I understand you completely, but if you wish to get the absolute file path provided that you know the relative file name, you can always do this:
System.out.println("File path: " + new File("Your file name").getAbsolutePath());
The File class has several more methods you might find useful.

Correct solution with "File" class to get the directory - the "path" of the file:
String path = new File("C:\\Temp\\your directory\\yourfile.txt").getParent();
which will return:
path = "C:\\Temp\\your directory"

You may use:
FileSystems.getDefault().getPath(new String()).toAbsolutePath();
or
FileSystems.getDefault().getPath(new String("./")).toAbsolutePath().getParent()
This will give you the root folder path without using the name of the file. You can then drill down to where you want to go.
Example: /src/main/java...

How to check whether the path is relative or absolute in java?

I am developing a tool, which takes a path of an xml file. Now that path can be either relative or absolute. Inside the code, when I have only a string, is there a way to identify that the path is absolute or relative?

How about File.isAbsolute():
File file = new File(path);
if (file.isAbsolute()) {
...
}

There is another very similar way using Paths operations:
Path p = Paths.get(pathName);
if (p.isAbsolute()) {
...
}

How to get absolute path of directory of a file?

How can I get an absolute path of a directory containing a file specified:
// current dir is "/home/me/dev"
File file = new File("./target/test.txt");
assert absolute(file).equals("/home/me/dev/target");
It's Java 6.

You mean the methods in the documentation?
File file = new File("./target/test.txt");
String dirPath = file.getAbsoluteFile().getParentFile().getAbsolutePath()
assert dirPath.equals("/home/me/dev/target");

assert file.getParentFile().getAbsolutePath().equals("/home/me/dev/target");