Develop Reference

Pick a particular file from directory using java

I need some help in picking the exact file from directory on Windows using Java. Below is the code which I have written for this. But when I pass my input as "XYZ" file it always picks the "ABC" file only.
My input to pick the file was 'XYZ', but output always returns 'ABC' file
directoryPath = new File(System.getProperty("user.dir") + "\\TestFilesDirectory\\");
String contents[] = directoryPath.list();
System.out.println("List of files and directories in the specified directory : " + directoryPath);
for (int i = 0; i < contents.length; i++) {
// System.out.println(contents[i]);
ArrayList<String> fileNameList = new ArrayList<String>();
String[] fileNameSplit = contents[i].split("_");
for (int k = 0; k < fileNameSplit.length; k++) {
// System.out.println(fileNameSplit[k].toUpperCase());
fileNameList.add(fileNameSplit[k].toUpperCase());
}
if (fileNameList.contains("ABC") {
System.out.println("Pick ABC file from directory ");
source = new File(directoryPath + "\\" + contents[i] + "");
}
System.out.println("Base File: " + source);
else if (fileNameList.contains("DEF") {
System.out.println("Pick DEF file from directory ");
source = new File(directoryPath + "\\" + contents[i] + "");
}
else if (fileNameList.contains("XYZ") {
System.out.println("Pick XYZ file from directory ");
source = new File(directoryPath + "\\" + contents[i] + "");
}
Below are my files in Test directory:

I think that your code can be improved. As far as I can tell you need to retrieve the path of a given file matching either the first or second part of its filename. So for example:
DEF_GHI.txt
can be matched by either inputting def or ghi into your search method. The easiest and most concise way to do so would be:
public Optional<File> findByName(String name, String directoryPath) {
try (var fileStream = Files.list(Path.of(directoryPath))) {
return fileStream
.filter(path -> Arrays.stream(path.getFileName().toString().split("_"))
.map(part -> part.replaceAll("\\.[^.]*$", ""))
.anyMatch(part -> part.equalsIgnoreCase(name)))
.findAny()
.map(Path::toFile);
} catch (IOException e) {
System.err.println("Unable to open directory stream for path:: " + directoryPath);
e.printStackTrace();
}
return Optional.empty();
}
What this does is the following:
Accepts a filename and a path representing a directory to search at
Creates a stream of paths representing the files under the given directory
Gets the filename for each given path and performs the following:
Splits the string using _ in order to retrieve both parts (if present)
Replaces everything after the . character (including it) in order to get rid of the file extension.
Attempts to match each part against the provided name parameter
Map the found path value to a File (if present)
Lastly returns either the optionally wrapped File or an empty Optional.
I hope this is what you are looking for.

File. ListFiles with FileNameFilter returning null instead of list of files with matching file name

I have written a find function which is like this :
public static List<File> find ( String path, String fName) {
List<File> list = new ArrayList<>() ;
File dir = new File(path) ;
if( dir. isDirectory() ) {
for( String aChild : dir. list()) {
list = find(path + File.separator + aChild, fName) ;
}
}
else {
File[] files = dir. listFiles ( (d, name) -> name. startsWith(fName) && name. endsWith(".txt")) ;
for(File fl : files)
list. add(fl) ;
}
return list;
}
The Directory structure on my Local machine is like C:\Salary with sub directories like January, February etc. Each of the sub directory contains files like 601246_jan_sal.txt or 601246_ feb_sal.txt.
I am calling the find function like
List<File> filePath = Utils. find("C:\\Salary\\", "601246") ;
And then performing operation on each individual file.
The problem is that in the find method dir.listFiles(FileNameFilter) is returning null value.
What am I doing wrong?

Below is basically the same method with the exception that is uses regex along with the String#matches() method to determine a file name match. I used regex so that the ? and * wildcard characters can be used within your file name search criteria, for example:
"601246*.txt"
You may find this useful for other searches you might like to carry out.
There is no returned object with this method, you just need to pass the List to it. Here is an example of how you might use it:
List<File> fileList = new ArrayList<>();
String searchCriteria = "601246*.txt";
searchFolder(new File("C:\\Salary"), searchCriteria, fileList);
// Display found files within the Console Window:
if (!fileList.isEmpty()) {
for (File file : fileList) {
System.out.println(file.getAbsolutePath());
}
}
else {
System.out.println("File name (" + searchCriteria + ") can not be found!");
}
This will search the directory (and all its sub-directories) located at C:\Salary within the local file system for all files that start with 601246 and ends with .txt. Since your files are in the following format:
601246_jan_sal.txt or 601246_ feb_sal.txt
and you happen to want all the files for February Sales, your search criteria might be: *feb?sal.txt.
Here is the searchFolder() method:
/**
* This method navigates through the supplied directory and any
* sub-directories contained within it for the supplied file name search
* criteria. Anything found is placed within the supplied List object.<br>
*
* #param file (File) The starting point directory (folder) in
* the local file system where the file(s) search
* should begin.<br>
*
* #param searchCriteria (String) The name of the file to search for. The
* wildcard characters '?' and '*' can also be used
* within the search criteria. Using an asterisk (*)
* allows you to replace a string of text. This is
* often useful if you know what kind of file you’re
* looking for but don’t know where it is or what
* certain name parts might be. <br><br>
*
* The wildcard '?' lets you use it to replace any character in a search.
* This means that if you’re looking for a file and you’re not sure how it
* is spelled, you can simply substitute '?' for the characters you don’t
* know. In the following example, we search for files that start with
* “img_2” and ends with “.jpg”:<pre>
*
* img_2???.jpg</pre><br>
*
* #param list (List Interface of type File: {#code List<File>})
* This would be the List of File you pass to this
* method. It will be this list that is filled with
* found files objects.<br>
*
* #param ignoreLetterCase (Optional - Boolean) Default is true. The search
* is not letter case sensitive. If false is
* supplied then the search is letter case
* sensitive.
*/
public static void searchFolder(File file, String searchCriteria, List<File> list, boolean... ignoreLetterCase) {
boolean ignoreCase = true;
if (ignoreLetterCase.length > 0) {
ignoreCase = ignoreLetterCase[0];
}
// Convert the supplied criteria string to a Regular Expression
// for the String#matches() method
String regEx = searchCriteria.replace("?", ".").replace("-", ".").replace("*", ".*?");
if (ignoreCase) {
regEx = "(?i)" + regEx;
}
if (file.isDirectory()) {
//System.out.println("Searching directory ... " + file.getAbsoluteFile());
//do you have permission to read this directory?
if (file.canRead()) {
for (File temp : file.listFiles()) {
if (temp.isDirectory()) {
searchFolder(temp, searchCriteria, list, ignoreCase);
}
else {
if (temp.getName().matches(regEx)) {
list.add(temp);
}
}
}
}
else {
System.err.println(file.getAbsoluteFile() + " - PERMISSION DENIED!");
}
}
}

Since you are using recursion, you should pass the list (of files) as a parameter to method find and not create a new list on each invocation. Hence the method find does not need to return a value.
public static void find(String path, String fName, List<File> fileList) {
File dir = new File(path);
if (dir.isDirectory()) {
for (File aChild : dir.listFiles()) {
if (aChild.isDirectory()) {
find(aChild.getAbsolutePath(), fName, fileList);
}
else {
String name = aChild.getName();
if (name.startsWith(fName) && name.endsWith(".txt")) {
fileList.add(aChild);
}
}
}
}
else {
String name = aChild.getName();
if (name.startsWith(fName) && name.endsWith(".txt")) {
fileList.add(aChild);
}
}
}
If method parameter path indicates a directory, then list the files in that directory. For each file in the directory, check whether the name of the file matches your search criteria and if it does then add it to the list. If it doesn't then check if it is itself a directory and if it is then recursively call method find with the new directory.
Initially call method find like so
List<File> list = new ArrayList<File>();
find("C:\\Salary\\", "601246", list);
Now list should contain the list of relevant files. So the following line will print the contents of list
System.out.println(list);

I see a fundamental problem in your logic that answers your question. Here are the key lines along with an explanation:
if( dir.isDirectory() ) {
....
}
else {
File[] files = dir.listFiles(...); // <- "dir" is a file, not a directory
for(File fl : files)
list.add(fl) ;
}
You check if File object dir represents a directory. If that test fails (ie: it's not a directory), then you call dir.listFiles on it and assign the result to files. But if it's not a directory, then by the definition of that function, it will return null. It seems that if the check for a directory fails, you should just add the object to list instead of performing another operation on it.
I think you want this:
if( dir.isDirectory() ) {
....
}
else {
list.add(dir) ;
}
I guess dir isn't really the right name for the variable here, as it isn't always a directory.

Note that the Files.walk() method already does what you're trying to do.
public static List<File> find ( String path, String fName) {
List<File> result = new ArrayList<>();
FileVisitor<Path> visitor = new SimpleFileVisitor() {
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {
if (attrs.isRegularFile()) {
String name = file.getFileName();
if (name.startsWith(fName) && name.endsWith(".txt")) {
result.add(file.toFile());
}
}
return FileVisitResult.CONTINUE;
}
};
Files.walk(Paths.get(path), visitor);
return result;
}

How do I conditionally get code to loop back to specific point in code in java?

I am creating an application that automatically sorts and organizes files into a database​. I have written my code to read files within the imported folder one at a time, and process them into the DB. However, I am having trouble looping this process, so that I can process files that are nested in any amount of folders within the original folder that the user wants to input.
I simply need to instruct my program to go back to a specific part of my code and start running from there again.
Another possible way to solve this issue would be to create a way to list out all of the individual files within folder (including all the files within subfolders), and I could easily fit that into my program too.
I tried using labeled continue, return, and break keywords based off of an answer I got online, but I never expected those to succeed in looping my code back to a specific spot.
JFileChooser chooser = new JFileChooser();
chooser.setSelectedFiles(null);
chooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
chooser.showOpenDialog(null);
//Getting file paths from within folder
File f = chooser.getSelectedFile();
String file = f.getAbsolutePath();
if (f.isDirectory()) {
//Need to loop back to here
File folder = new File(file);
File[] listOfFiles = folder.listFiles();
for (int i = 0; i < listOfFiles.length; i++) {
if (listOfFiles[i].isDirectory()) {
//Code here is run if there is a folder within a folder. I tested it too
//I want the code here to loop back above where it says "Need to loop back to here"
}
if (listOfFiles[i].isFile()) { //Once I list the files from within the folder, their information gets assigned variable here, and the rest of my program sorts it and saves it to DB accordingly.
//Everything below here is not important, but it might be helpful to see what happens each file with the folders.
System.out.println(listOfFiles[i]);
String filename = (listOfFiles[i].getName()); //For Files
Long filemodified = (listOfFiles[i].lastModified());
String filepath = (listOfFiles[i].getAbsolutePath());
Long filesizeraw = (listOfFiles[i].length());
long filehashcode = (listOfFiles[i].hashCode());
String fileparent = (listOfFiles[i].getParent());
Currently, there is no error message. It would process any individual files directly in the imported file (not nested in any folder within the folder), but wouldn't get to any of the files that are in folders within folders.

Another possible way to solve this issue would be to create a way to list out all of the individual files within folder (including all the files within subfolders), and I could easily fit that into my program too
Although this doesn't do the SQLite inserts, the following class extracts a list (of File objects) the files (thus file name and path are available via the File object).
public class FTS {
private ArrayList<File> mFileList; //Resultant list of Files extracted
private String mBaseDirectory; // The Directory to search
private long mSubDirectoryCount; // The count of the subdirectories
//Constructor
public FTS(String directory) {
this.mBaseDirectory = directory;
this.mSubDirectoryCount = 0;
buildFileListing(this.mBaseDirectory);
}
//
private void buildFileListing(String directory) {
// Initialise the ArrayList for the result
if (mFileList == null) {
mFileList = new ArrayList(){};
}
//Get the File (directory to process)
File dir = new File(directory);
// Get the List of the Directories contents
String[] filelist = dir.list();
// If empty (null) then return
if (filelist == null) {
return;
}
// Loop through the directory list
for (String s: filelist) {
//get the current list item as a file
File f = new File(dir.getAbsolutePath() + File.separator + s);
// is it a file or directory?
if (f.isFile() && !f.isDirectory()) {
this.mFileList.add(f); // If a file then add the file to the extracted list
} else {
// If a directory then increment the count of the subdirectories processed
mSubDirectoryCount++;
// and then recursively call this method to process the directory
buildFileListing(f.getAbsolutePath());
}
}
}
// return the list of extracted files
public ArrayList<File> getFileList() {
return this.mFileList;
}
// return the number of sub-directories processed
public long getSubDirectoryCount() {
return this.mSubDirectoryCount;
}
}
An example usage of the above is :-
public class Main {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
FTS fileTreeSearch;
String BaseDirectory = "E:" + File.separator;
List<File> files = (fileTreeSearch = new FTS(BaseDirectory)).getFileList();
System.out.println("Extracted " + String.valueOf(files.size()) + " files, from " + String.valueOf(fileTreeSearch.getSubDirectoryCount()) + " sub-directories of " + BaseDirectory);
/* this commented out code would process all the extracted files
for (File f: files) {
System.out.println("File is " + f.getName() + "\t\t path " + f.getAbsolutePath());
}
*/
}
}
Example output from running the above :-
Extracted 186893 files, from 54006 sub-directories of E:\

Rename file in JFileChooser if file exists and user inputs extension

The code works as it has to until user inputs a filename with extension (.txt) and it already exists. So if the file "test.txt" exists and the user decides to name the new file as "test", it will be named as "test(1).txt", but if the user adds extension like "test.txt", the file will be named as "test.txt" and the next file user names "test.txt" will be saved as "test.txt(1).txt".
Is it possible to get the name of file from JFileChooser, remove it's extension if user input it and use it as name of the new file after adding number in the middle of original file name and it's extension? I can get name without extension as String type, but I need it as File type.
File ft = fc.getSelectedFile();
String ext = ".txt";
File tmp = new File(ft.getPath());
if (!fc.getSelectedFile().getAbsolutePath().endsWith(ext)){
ft = new File (ft + ext);
}
File test = new File(ft.getPath());
File temp = new File(ft.getPath());
File temp1 = new File(ft.getPath());
int count = 1;
while (temp.exists()) {
if(tmp.getAbsolutePath().endsWith(ext)){
}
File ft1 = new File (tmp + "(" + count + ")");
ft = new File (tmp + "(" + count + ")" + ext);
count++;
temp = new File(ft.getPath());
temp1 = new File(ft1.getPath());
}
if (!temp1.getAbsolutePath().endsWith(ext)){
ft = new File (temp1 + ext);
}
int cnt = count - 1;
if (!test.equals(temp)){
JOptionPane.showMessageDialog(null, "File already exists. So it's saved with (" + cnt + ") at the end.");
}

OK so I've tried to make this work without changing your code too much. Try this:
String filePath = fc.getSelectedFile().getAbsolutePath();
final String ext = ".txt";
String filePathWithoutExt;
if (filePath.endsWith(ext)) {
filePathWithoutExt = filePath.substring(0, filePath.length() - ext.length());
} else {
filePathWithoutExt = filePath;
}
File test = new File(filePathWithoutExt + ext);
File temp = new File(filePathWithoutExt + ext);
int count = 0;
while (temp.exists()) {
count++;
temp = new File(filePathWithoutExt + "(" + count + ")" + ext);
}
if (!test.equals(temp)) {
JOptionPane.showMessageDialog(null,
"File already exists. So it's saved with (" + count + ") at the end.");
}
EDIT:
By the recommendation of Marco N. it could be better to determine whether or not an extension exists by finding the last position of the . since this would also work with extensions other than ".txt". This value would then be used to split the string. The replacement code would look like this:
final int lastPeriodPos = filePath.lastIndexOf(".");
if (lastPeriodPos >= 0) {
filePathWithoutExt = filePath.substring(0, lastPeriodPos);
} else {
filePathWithoutExt = filePath;
However this would also have some issues if the user entered a file name that contained the . anywhere other than just before the file extension.

Hmm, I think this entry might be useful as well:
Remove filename extension in Java
I currently lack the time to properly test it (or better test it at all) but shouldn't it work this way:
public static String removeExtention(File f) {
String name = f.getName();
// Now we know it's a file - don't need to do any special hidden
// checking or contains() checking because of:
final int lastPeriodPos = name.lastIndexOf('.');
if (lastPeriodPos <= 0)
{
// No period after first character - return name as it was passed in
return f;
}
else
{
// Remove the last period and everything after it
File renamed = new File(f.getParent(), name.substring(0, lastPeriodPos));
return renamed;
}
}
I briefly tried to adjust the code from the posting mentioned above and it may very well contain some errors or flaws. (If you find some, do not hesitate to comment on them. Some of them might be due to my current lack of time, but I am always willing to learn and improve.) However I hope this may help you to find a proper solution to your problem.

Determine which JAR file a class is from

I am not in front of an IDE right now, just looking at the API specs.
CodeSource src = MyClass.class.getProtectionDomain().getCodeSource();
if (src != null) {
URL jar = src.getLocation();
}
I want to determine which JAR file a class is from. Is this the way to do it?

Yes. It works for all classes except classes loaded by bootstrap classloader. The other way to determine is:
Class klass = String.class;
URL location = klass.getResource('/' + klass.getName().replace('.', '/') + ".class");
As notnoop pointed out klass.getResource() method returns the location of the class file itself. For example:
jar:file:/jdk/jre/lib/rt.jar!/java/lang/String.class
file:/projects/classes/pkg/MyClass$1.class
The getProtectionDomain().getCodeSource().getLocation() method returns the location of the jar file or CLASSPATH
file:/Users/home/java/libs/ejb3-persistence-1.0.2.GA.jar
file:/projects/classes

Checkout the LiveInjector.findPathJar() from Lombok Patcher LiveInjector.java. Note that it special cases where the file doesn't actually live in a jar, and you might want to change that.
/**
* If the provided class has been loaded from a jar file that is on the local file system, will find the absolute path to that jar file.
*
* #param context The jar file that contained the class file that represents this class will be found. Specify {#code null} to let {#code LiveInjector}
* find its own jar.
* #throws IllegalStateException If the specified class was loaded from a directory or in some other way (such as via HTTP, from a database, or some
* other custom classloading device).
*/
public static String findPathJar(Class<?> context) throws IllegalStateException {
if (context == null) context = LiveInjector.class;
String rawName = context.getName();
String classFileName;
/* rawName is something like package.name.ContainingClass$ClassName. We need to turn this into ContainingClass$ClassName.class. */ {
int idx = rawName.lastIndexOf('.');
classFileName = (idx == -1 ? rawName : rawName.substring(idx+1)) + ".class";
}
String uri = context.getResource(classFileName).toString();
if (uri.startsWith("file:")) throw new IllegalStateException("This class has been loaded from a directory and not from a jar file.");
if (!uri.startsWith("jar:file:")) {
int idx = uri.indexOf(':');
String protocol = idx == -1 ? "(unknown)" : uri.substring(0, idx);
throw new IllegalStateException("This class has been loaded remotely via the " + protocol +
" protocol. Only loading from a jar on the local file system is supported.");
}
int idx = uri.indexOf('!');
//As far as I know, the if statement below can't ever trigger, so it's more of a sanity check thing.
if (idx == -1) throw new IllegalStateException("You appear to have loaded this class from a local jar file, but I can't make sense of the URL!");
try {
String fileName = URLDecoder.decode(uri.substring("jar:file:".length(), idx), Charset.defaultCharset().name());
return new File(fileName).getAbsolutePath();
} catch (UnsupportedEncodingException e) {
throw new InternalError("default charset doesn't exist. Your VM is borked.");
}
}

Use
String path = <Any of your class within the jar>.class.getProtectionDomain().getCodeSource().getLocation().getPath();
If this contains multiple entries then do some substring operation.

private String resourceLookup(String lookupResourceName) {
try {
if (lookupResourceName == null || lookupResourceName.length()==0) {
return "";
}
// "/java/lang/String.class"
// Check if entered data was in java class name format
if (lookupResourceName.indexOf("/")==-1) {
lookupResourceName = lookupResourceName.replaceAll("[.]", "/");
lookupResourceName = "/" + lookupResourceName + ".class";
}
URL url = this.getClass().getResource(lookupResourceName);
if (url == null) {
return("Unable to locate resource "+ lookupResourceName);
}
String resourceUrl = url.toExternalForm();
Pattern pattern =
Pattern.compile("(zip:|jar:file:/)(.*)!/(.*)", Pattern.CASE_INSENSITIVE);
String jarFilename = null;
String resourceFilename = null;
Matcher m = pattern.matcher(resourceUrl);
if (m.find()) {
jarFilename = m.group(2);
resourceFilename = m.group(3);
} else {
return "Unable to parse URL: "+ resourceUrl;
}
if (!jarFilename.startsWith("C:") ){
jarFilename = "/"+jarFilename; // make absolute path on Linux
}
File file = new File(jarFilename);
Long jarSize=null;
Date jarDate=null;
Long resourceSize=null;
Date resourceDate=null;
if (file.exists() && file.isFile()) {
jarSize = file.length();
jarDate = new Date(file.lastModified());
try {
JarFile jarFile = new JarFile(file, false);
ZipEntry entry = jarFile.getEntry(resourceFilename);
resourceSize = entry.getSize();
resourceDate = new Date(entry.getTime());
} catch (Throwable e) {
return ("Unable to open JAR" + jarFilename + " "+resourceUrl +"\n"+e.getMessage());
}
return "\nresource: "+resourceFilename+"\njar: "+jarFilename + " \nJarSize: " +jarSize+" \nJarDate: " +jarDate.toString()+" \nresourceSize: " +resourceSize+" \nresourceDate: " +resourceDate.toString()+"\n";
} else {
return("Unable to load jar:" + jarFilename+ " \nUrl: " +resourceUrl);
}
} catch (Exception e){
return e.getMessage();
}
}

With Linux, I'm using a small script to help me find in which jar a class lies that can be used in a find -exec:
findclass.sh:
unzip -l "$1" 2>/dev/null | grep $2 >/dev/null 2>&1 && echo "$1"
Basically, as jars are zip, unzip -l will print the list of class resources, so you'll have to convert . to /. You could perform the replacement in the script with a tr, but it's not too much trouble to do it yourself when calling the script.
The, the idea is to use find on the root of your classpath to locate all jars, then runs findclass.sh on all found jars to look for a match.
It doesn't handle multi-directories, but if you carefully choose the root you can get it to work.
Now, find which jar contains class org.apache.commons.lang3.RandomUtils to you un-mavenize your project (...):
$ find ~/.m2/repository/ -type f -name '*.jar' -exec findclass.sh {} org/apache/commons/lang3/RandomUtils \;
.m2/repository/org/apache/commons/commons-lang3/3.7/commons-lang3-3.7.jar
.m2/repository/org/apache/commons/commons-lang3/3.6/commons-lang3-3.6.jar
.m2/repository/org/apache/commons/commons-lang3/3.6/commons-lang3-3.6-sources.jar
$