Reading a Specific Line from a file

Programming Questions

tfootee

Reading a Specific Line from a file

in Programming Questions • 3 months ago

I am making a program that searches for music files, stores their locations in a .txt file, then goes and gets the MetaData from those files and stores that in a separate .txt file. The reason for storing in .txt files is that I ran out of memory. However, I need to be able to go and read a specific line of each of those files. The code does a great job at finding and storing those file locations, but then I need to read those file locations one at a time and go get the metadata. But How do you read lines in a file one at a time? Here is the code: **** Problem starts at the last while statement ***** and I inserted a line that just says "END" at the end of the file that stores the file locations.

void updateFiles() {
music = null;
music = new File(dataPath("SongList.txt"));
if(music.exists() == true) {
music.delete();
}
music = null;
music = new File(dataPath("SongMeta.txt"));
if(music.exists() == true) {
music.delete();
}
songList = createWriter(dataPath("SongList.txt"));
songMeta = createWriter(dataPath("SongMeta.txt"));
musicLocations = loadStrings(dataPath("Music Locations.txt"));
fileNames.clear();
search.clear();
search.append(musicLocations);
filesListed.clear();
music = null;
music = new File(dataPath("/musicFiles"));
foundSongs = music.list(jpgFilterwav);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFiltermp3);
addedSongs = 0;
...
solutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFiltersnd);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
if(musicLocations.length != 0) {
musicLoaded = 0;
while(musicLoaded < search.size()) {
music = null;
...
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFilterau);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFiltersnd);
...
search.append(music.getAbsolutePath() + "/" + filesListed.get(searchNumber));
}
searchNumber++;
}
musicLoaded++;
}
skip = 0;
}
searchNumber = 0;
while(searchNumber < fileNames.size()) {
if(fileNames.get(searchNumber).indexOf("[Ljava.lang.String;") > -1) {
fileNames.remove(searchNumber);
searchNumber--;
}
searchNumber++;
}
}
searchNumber = 0;
println("Number of Songs Available: " + fileNames.size());
while(searchNumber < fileNames.size()) {
songList.println(fileNames.get(searchNumber));
fileNames.remove(searchNumber);
}
songList.println("END");
fileNames.clear();
songList.flush();
songList.close();
searchNumber = 0;
songListReader = createReader(dataPath("SongList.txt"));
while(true) {
if(songListReader.readLine().equals("END")) {
break;
} else {
player = null;
player = minim.loadFile(songListReader.readLine(), 340);
meta = null;
meta = player.getMetaData();
println(meta.title() + "," + meta.album() + "," + meta.author() + "," + meta.length());
songMeta.println(meta.title() + "," + meta.album() + "," + meta.author() + "," + meta.length());
searchNumber++;
}
}
println("Got Meta Data!");
println(metaData.array());
}

Replies(11)

dimkir

Re: Reading a Specific Line from a file

3 months ago

Who are you? This code is amazing!

tfootee

Re: Reading a Specific Line from a file

3 months ago

Well, thats my hour of 16yr old troubleshooting and programming. hahaha... basically took what was in my head and on my whiteboard onto paper.

dimkir

Re: Reading a Specific Line from a file

3 months ago

Good lad!

by the way you can make your code more tidy and clear if you do some "decomposition" (wrapping parts of functionality into a method). Eg:

You can wrap this:

music = null;
music = new File(dataPath("SongList.txt"));
if(music.exists() == true) {
music.delete();
}

Into a method like this:

/**
* Deletes file from data directory.
* @param filePath should be relative path to filename
* in data directory. Eg. "myfile.txt" or "myfile.mp3" or "au_files\\music.au"
*/
void deleteFileFromDataDirIfExists(String filePath) {
File f = new File(dataPath(filePath));
if ( f.exists() ) {
f.delete();
}
}

Then this code:

music = new File(dataPath("SongList.txt"));
if(music.exists() == true) {
music.delete();
}
music = null;
music = new File(dataPath("SongMeta.txt"));
if(music.exists() == true) {
music.delete();
}

will turn into two lines:

deleteFileFromDataDirIfExists("SongList.txt");
deleteFileFromDataDirIfExists("SongMeta.txt");

not only it is shorter, but it is now clear even from the name of the method what is happening. This allows the code to be read like a book: glance at line and it's clear what's happening there.

Another benefit is that you:

if there's a bug in the code or if you want to update it (for example you want the file be deleted in all subdirectories of data) then you only have to update one place in code, namely: deleteFileFromDataDirIfExists() method.

dimkir

Re: Reading a Specific Line from a file

3 months ago

Also this code:

foundSongs = music.list(jpgFilterwav);
//
// why not use for() loop?
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}

can be wrapped into method:

/**
* Scans directory 'dir' for the files complying with 'filter' and adds
* their absolute path (ie "c:\\tmp\\blabla\\file.ext" to fileList.
* @param filter valid filter
* @param dir directory with files.
* @param fileList already instantiated stringList. Items will be appended.
*/
void addFilteredFilenamesToStringList(FilenameFilter filter, File dir, StringList fileList){
String[] foundFiles = dir.list(filter);
for(String file : foundFiles){
String fullFilepath = dir.getAbsolutePath() + File.separator + file;
fileList.append(fullFilepath);
}
}

And this will turn this code of 35 lines

foundSongs = music.list(jpgFilterwav);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFiltermp3);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFilteraiff);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFilterau);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}
foundSongs = music.list(jpgFiltersnd);
addedSongs = 0;
while(addedSongs < foundSongs.length) {
fileNames.append(music.getAbsolutePath() + "/" + foundSongs[addedSongs]);
addedSongs++;
}

into just 5 lines:

addFilteredFilenamesToStringList(jpgFilterwav, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFiltermp3, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFilteraiff, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFilterau, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFiltersnd, musicFileDir, fileNames);

again it's more clear to read like this and if you need a fix, there's only one place to look

tfootee

Re: Reading a Specific Line from a file

3 months ago

Thank you for the suggestions. The whole sole purpose of why it is so long is the fact that it works my searching every folder, file, and everything for specific file types. You can make it search any file type. And, it isn't limited to just searching 1 folder. It will search an entire computer! all with just this little piece of code. It lists all the files in a specific folder, adds folders within that folder to the search list, and then if any files meet the filter requirements, they go to the found list. then it goes and repeats this process for every folder, inside every folder, inside every everything.

dimkir

Re: Reading a Specific Line from a file

3 months ago

Thus after tidying up your beginning of void updateFiles() should look like something like this:

void updateFiles() {
deleteFileFromDataDirIfExists("SongList.txt");
deleteFileFromDataDirIfExists("SongMeta.txt");
songList = createWriter(dataPath("SongList.txt"));
songMeta = createWriter(dataPath("SongMeta.txt"));
musicLocations = loadStrings(dataPath("Music Locations.txt"));
fileNames.clear();
search.clear();
search.append(musicLocations); // why do we append our locations to it?
filesListed.clear();
File musicFileDir = new File(dataPath("/musicFiles"));
addFilteredFilenamesToStringList(jpgFilterwav, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFiltermp3, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFilteraiff, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFilterau, musicFileDir, fileNames);
addFilteredFilenamesToStringList(jpgFiltersnd, musicFileDir, fileNames);

From over 50 lines into 22 lines.

So forget copy/paste and start using decomposition :)

tfootee

Re: Reading a Specific Line from a file

3 months ago

well, funny thing you should bring up copy/paste. I typed that entire algorithm by hand. no copy or paste. This is a brief explanation of how it all works

dimkir

Re: Re: Reading a Specific Line from a file

3 months ago

This is a very good structure you have made! Your thinking is definately very good. And that saying, I believe you would agree that every time there's space for improvement:

searchNumber = 0;
while (searchNumber < filesListed.size ()) {
searchFile = null;
searchFile = new File(filesListed.get(searchNumber));
if (searchFile.isFile() == false) {
search.append(music.getAbsolutePath() + "/" + filesListed.get(searchNumber));
}
searchNumber++;
}

what do you think of using in this case a for() loop?

for(int i = 0 ; i < fileListed.size(); i++){
File sFile = new File(filesListed.get(i));
if ( sFile.isDirectory() == true ){
String absolutePath = music.getAbsolutePath() + "/" + filesListed.get(i);
search.append( absolutePath );
}
}

PhiLho

Re: Reading a Specific Line from a file

3 months ago

To reply the original question, here is a way:
http://stackoverflow.com/questions/5868369/how-to-read-a-large-text-file-line-by-line-in-java

tfootee

Re: Reading a Specific Line from a file

3 months ago

what do you think of using in this case a for() loop?"

I had some very hard times trying to get a for() loop work work. Don't ask me why, but instead i switched to a while statement.

To reply the original question, here is a way:

Thank you. However, How can I modify it so that I only read line 20 for example?

datguy

Re: Reading a Specific Line from a file

3 months ago

There's no easy way to directly access a specific line in the file, but you could do something like this:

                
                 import java.io.*;
                 

                 String readLineNumber(String fileName, int lineNumber) {
                 

                   String strLine = null;
                 

                   try {
                 

                     // Open the file
                     FileInputStream fstream = new FileInputStream(fileName);
                     BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
                 

                     int currentlineNumber = 0;
                     boolean lineFound = false;
                 

                     // Read File Line By Line
                     while ( (strLine = br.readLine ()) != null) {
                       currentlineNumber++;
                       if (currentlineNumber == lineNumber) {
                         lineFound = true;
                         break;
                       }
                     }
                     if (!lineFound) strLine = null; 
                 

                     // Close the file
                     fstream.close();
                   }  
                   catch (IOException e) {
                     e.printStackTrace();
                     strLine = null;
                   }
                   return strLine;
                 }
                
                
                 

                 Rather than reading a specific line number, I think it's more likely that you would want to return the line containing a specific string value.  You could write a similar method and change the logic within the while loop to break when that value is found.