Develop Reference

java.io.File constructor behaviour or perhaps multithreading issue?

I have the following code:
class Abcd{
//wired by spring to give the directory filePath ="/var/tmp/"
private String filePath;
public void myMethod(String id, String date){
filePath= filePath+ id+ "_" + date;
File f = new File(filePath);
if(f.exists){//Do something}
else{
System.out.println("File not found at file path:"+filePath);
}
}
}
The above code is behaving weird , intermittently the filePath contains all the files of directory /var/tmp/ . So , if /var/tmp directory contains two files called "id1_01012017" and "id2_10102017".
This is the intermittent output
File not found at file path:/var/tmp/id1_01012017id2_10102017
Am unable to figure out whats happening

The best way to do this is to maintain that filePath remains immutable. You will find that if you change this line:
filePath = filePath + id + "_" + date;
to the following:
String tempFilePath = filePath + id + "_" + date;
and operate on tempFilePath instead of filePath, your code will become thread-safe and work as expected.

Get character from string between similar sings

I am trying to get a path of an image in my android device, such as:
/ storage/emulated/0/DCIM/Camera/NAME.jpg
and just trying to grab the image name, but i can.
I am trying with ...
String s = imagePath;
Where the route imagePath
            
s = s.substring (s.indexOf ("/") + 1);
s.substring s = (0, s.indexOf () ".");
Log.e ("image name", s);
it returns me :
storage/emulated/0/DCIM/Camera/NAME.jpg
and i only want
NAME.jpg

You need String.lastIndexOf():
String imagePath = "/path/to/file/here/file.jpg";
String path = imagePath.substring(imagePath.lastIndexOf('/') + 1);

You can do something like that:
File imgFile = new File(imagePath);
String filename = imgFile.getFilename();
This saves you a lot of hassle when you want to use your application cross-platform, because on Linux you have "/" as path delimiters and "\" on Windows

In case, if you are dealing with File object, then you can use its predefined method getName().
i.e.:
File mFile = new File("path of file");
String filename = mFile.getName();

Code cannot find my file

I have written a short program that will find a file I have made and print some of its details. It executes all right, but it cannot detect the file size or if it is hidden or not. E.G.
file path: C:\temp\filetext.txt last modified: 0 file size: 0 Is file hidden?false
The file does exist in the temp folder on C. I'm not really sure what the problem is
public void Q1()
{
String fileName = "filetext.txt";
getFileDetails(fileName);
}
public void getFileDetails(String fileName)
{
String dirName = "C:/temp/";
File productsFile = new File(dirName + fileName);
long size = productsFile.length();
System.out.println("file path: " + productsFile.getAbsolutePath() + " last modified: " + productsFile.lastModified() + " file size: " + productsFile.length() + " Is file hidden?" + productsFile.isHidden());
}

File does not need a physical file to work with. Therefore your File object can exist even if the physical file it is supposed to represent does not exist/cannot be found. Check the JavaDoc for length() and lastModified(), they both return 0L in case for example the file does not exist. So make sure your File objects is linked to an existing file on your file system by calling file.exists() before calling the other methods.

Get file size in Java from relative path to file

How can I get file size in Java if I have a relative path to a file such as:
String s = "/documents/19/21704/file2.pdf/0929c695-d023-49d7-a8ff-65ccea46bebc"
I tried with two diferent strings:
String[] separatedPath = s.split("/");
List<String> wordList = Arrays.asList(separatedPath);
String ret = "/" + wordList.get(1) + "/" + wordList.get(2) + "/" + wordList.get(3)+ "/" + wordList.get(4);
s = ret;
In this case s="/documents/19/21704/file2.pdf";
In second case s="/documents/19/21704/file2.pdf/0929c695-d023-49d7-a8ff-65ccea46bebc"
I tried with:
File file1 = new File(s);
long filesize = file1.length();
and with:
String filePath = new File(s).toURI().getPath();
File file2 = new File(filePath);
long filesize2 = file1.length();
and also with (if the problem is in not providing full path):
String absolutePath = FileUtil.getAbsolutePath(file1);
File file3 = new File(absolutePath);
long filesize3 = file3.length();
byte[] bytes1=FileUtil.getBytes(file1);
byte[] bytes2=FileUtil.getBytes(file2);
byte[] bytes3=FileUtil.getBytes(file3);
I am always getting in debug that filesizes in all cases are 0.
Maybe is worth noticing that the three attributes of file1 and file2 and file3 are always:
filePath: which is always null;
path: "/documents/19/21704/liferay-portlet-development.pdf"
prefixLength: 1
Since I am also using Liferay I also tried their utility.
long compId = article.getCompanyId();
long contentLength = DLStoreUtil.getFileSize(compId, CompanyConstants.SYSTEM, s);
I also should notice that in my .xhtml view I can access the file with:
<a target="_blank"
href="/documents/19/21704/file2.pdf/0929c695-d023-49d7-a8ff-65ccea46bebc">
file2.pdf
</a>
Pdf opens in a new window. So it is stored on my server.
What am I doing wrong here? That I cant get the file size from bean?
Any answer would be greatly appreciated.
What am I doing wrong here?

In Java, you can use the File.length() method to get the file size in bytes.
File file =new File("c:\\java_xml_logo.jpg");
if(file.exists()){
double bytes = file.length();
}
System.out.println("bytes : " + bytes);

The problem is that your "relative" path is expressed as an absolute path (begining with "/", which is read as FS root).
A relative file path should look like:
documents/19/21704/file2.pdf/0929c695-d023-49d7-a8ff-65ccea46bebc
./documents/19/21704/file2.pdf/0929c695-d023-49d7-a8ff-65ccea46bebc
Or, you could get your application root folder File and compose the absolute path:
File rootFolder =new File("path to your app root folder");
File myfile=new File(rootFolder, "/documents/19/21704/file2.pdf/0929c695-d023-49d7-a8ff-65ccea46bebc");

Create a File in a folder

In Java, I have a File object representing a folder:
String folderName = "/home/vektor/folder";
File folder = new File(folderName);
Now I want to create another File representing a file in this folder. I want to avoid doing a string concatenation like this:
String fileName = "test.txt";
File file = new File(folderName + "/" + fileName);
Because if I go deeper in creating this structure, I will come up with something like this:
File deepFile = new File(folderName + "/" + anotherFolderName + ... + "/" + fileName);
I would instead like to do something like
File betterFile = folder.createUnder(fileName);
Or even:
File otherFile = SomeFileUtils.createFileInFolder(folder, fileName);
Do you know of such solution?
Note: It's quite OK to use "/" because Java will translate it to "\" for Windows, but it is not clean - I should use something like "file.separator" from System.getProperties().

Look at the Javadoc for File and you will see that the constructor takes a File object as parent.
Use the following form:
File deepFile = new File(folder, fileName);

I would use
String folderName =
String fileName =
File under = new File(folderName, fileName);
or
File folderFile =
String fileName =
File under = new File(folderFile, fileName);
simple as that ;)