Develop Reference

Reading a file in a directory in java and storing its offset in the directory

I want to be able to read files from a directory in java without the worry of getting an out of memory exception because files.listfiles() and files.list() can only hold so much. I also want to know if there is a way to store the offset of the file in the directory so I can store that number and not have to iterate through the directory again to find it, is this possible?
Right now I'm using Jaime Hablutzel's answer from another question to go through the directory but wondering if I can store the file offset in the directory to go directly to it next time.
My thought was to store the filenames in a text file then store a count to record the number of characters until each new line was encountered which is another filename then use the RandomAccessFile seek() method to go directory to that line from the saved count.
How to list 2 million files in a directory in java

Okay I solved my problem on what I wanted to do. I created an offset to each file I stored in a textfile by taking the length + 1 of each filename and adding it to the offset then writing it to a file.
public static void readOffsets()
{
try {
File file = new File("indexFile.txt");
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
FileWriter fw = new FileWriter("indexFile2.txt");
PrintWriter pw = new PrintWriter(fw);
String line;
int offset = 0;
pw.write(offset + "\n");
while((line = br.readLine()) != null)
{
int length = line.length();
offset += length + 1;
pw.write(offset + "\n");
}
pw.close();
br.close();
}
catch(IOException ioe)
{
ioe.printStackTrace();
}
}
Then when seeking the offset using the randomaccessfile I would get the correct filename.
public static void seekOffset()
{
try {
RandomAccessFile file = new RandomAccessFile("IndexFile.txt", "r");
file.seek(693);
System.out.println(file.readLine());
}
catch(IOException ioe)
{
}
}

How to rename a txt file using Java after copying contents from another txt file

I have created a program where there is a file called groups.txt. This file contains a list of names. To delete a group, it has to exist within the file. I used the Scanner method to search through each line for the name. If it contains the line, it sets val as 1. Which triggers the val == 1 condition. What I wanted to do during this block, is try to delete groupName from the groups.txt file. To do this, I created a new txt file called TempFile which copies all the names from groups.txt EXCEPT groupName. This file is then renamed to groups.txt and the old groups.txt file is deleted.
Everything works as intended, except the renaming. The temp.txt file still exists and the groups.txt file is unchanged. I checked the boolean success, and it always returns as false. Any ideas how to solve this?
if (method.equals("delete group")){
int val = 0;
String groupName = myClient.readLine();
try {
Scanner file = new Scanner(new File("groups.txt"));
while (file.hasNextLine()){
String line = file.nextLine();
if (line.indexOf(groupName) != -1){
val = 1;
}
}
if (val == 1){
try {
File groupFile = new File("groups.txt");
File tempFile = new File("temp.txt");
BufferedReader reader = new BufferedReader(new FileReader(groupFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String currentLine;
System.out.println(groupName);
while ((currentLine = reader.readLine()) != null){
String trimLine = currentLine.trim();
if (trimLine.equals(groupName)){
continue;
} else {
writer.write(currentLine + System.getProperty("line.separator"));
}
}
writer.close();
reader.close();
groupFile.delete();
boolean success = tempFile.renameTo("groups.txt");
} catch (IOException f){
System.err.println("File Not Found: " + f.getMessage());
} }
} catch (FileNotFoundException f){
System.err.println("File Not Found Exception: " + f.getMessage());
}
}
CODE BEFORE THE ABOVE:
if (command.equals("group")){
String method = myClient.readLine();
if (method.equals("create group")){
String groupName = myClient.readLine();
int val = 0;
try {
Scanner file = new Scanner(new File("groups.txt"));
while (file.hasNextLine()){
String line = file.nextLine();
if (line.indexOf(groupName) != -1){
Report.error("group name already exists, please pick another");
val = 1;
}
}
} catch (FileNotFoundException f){
System.err.println("File Not Found: " + f.getMessage());
}
if (val == 0){
try {
PrintWriter out = new PrintWriter(new FileWriter("groups.txt", true));
out.println(groupName);
out.close();
} catch (IOException e){
Report.error("IOException: " + e.getMessage());
}
}
In the second part of the code, this is where I originally update the groups.txt file. So every time the user adds a group, it updates the groups.txt file by adding the new groupName to the end of the file. First, I make sure the groupName doesn't already exist using Scanner. myClient is a BufferedReader which reads from another class which stores what the user types in the command line.

Also do not forget to close Scanner. First you should make delete() work and make sure you know your current working directory, and write your filepath relative to it. Check with:
File file = new File("abc.txt");
System.out.println(file.getAbsolutePath());
One thing might be unrelated, also check your environment because
In the Unix'esque O/S's you cannot renameTo() across file systems. This behavior is different than the Unix "mv" command. When crossing file systems mv does a copy and delete which is what you'll have to do if this is the case. The same thing would happen on Windows if you tried to renameTo a different drive, i.e. C: -> D:

Android/java Not all Data written to text file is readable

Ok so i am attempting to retrieve a .txt file from a server, write it to a local file and then be able to recall it later.
I noticed that i was not able to read back the file after i copied it locally
At first i thought it was something wrong with my read back code as when i open the file in wordpad or wordpad++ the content is present and written correctly as far as i can tell to the file.
However after much testing i determined there was nothing apparently wrong with the read back code.
So i added a test, i added some static writes to the code that does the copying:
bw.write("This is the test" + "\r\n");
bw.write("My first line!" + "\r\n");
bw.write("My second line ");
bw.write("keeps going on...P" + "\r\n");
Now when i run it everything writes correctly to the file (or appears to) but during read back only the static writes above are read.
Even though i can visually see the content in the file, the stuff that was copied from the web based file is (although present) never read back.
Any help would be appreciated
This is the code i am using to read and copy the file
** This is the file i am reading from on the web
CrewAdviceMasterControlURL = http://lialpa.org/CM3/CrewAdvices/advice_master.txt
public static String GetMasterFileStream(String Operation) throws Exception {
StringBuilder sb = new StringBuilder();
BufferedWriter bw = null;
String inputLine = null;
URL AdviceMasterControl = new URL(CrewAdviceMasterControlURL);
File outfile = new File("sdcard/CM3/advices/advice_master.txt");
if(!outfile .exists()){
outfile .createNewFile();
}
FileWriter fileWriter = new FileWriter(outfile);
bw = new BufferedWriter(fileWriter);
BufferedReader in = new BufferedReader(new InputStreamReader(AdviceMasterControl.openStream()));
System.out.println("Creating the master");
bw.write("This is the test" + "\r\n");
bw.write("My first line!" + "\r\n");
bw.write("My second line ");
bw.write("keeps going on...P" + "\r\n");
while ((inputLine = in.readLine()) != null)
{
System.out.println(inputLine); //for producing test output
sb.append((inputLine + "\r\n"));
bw.write(String.valueOf(inputLine) + "\r\n");
}
in.close();
bw.close();
return sb.toString();
}
and this is the code i am using to read it back
public static String GetLocalMasterFileStream(String Operation) throws Exception {
String FullPath = "/sdcard/CM3/advices/advice_master.txt";
System.out.println("path is " + FullPath);
File file = new File(FullPath);
if (file.canRead() == true) {System.out.println("-----Determined that file is readable");}
//Read text from file
StringBuilder text = new StringBuilder();
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
line = br.readLine();
System.out.println("-----" + line);
while ((line = br.readLine()) != null) {
text.append(line);
System.out.println("-----" + line); //for producing test output
text.append('\n');
}
br.close();
return text.toString();
}

Solved this problem. The problem was with the txt file its self on the server. When the file was uploaded via FTP the ftp program was in auto. This seems to have forced the upload in binary instead of ASCII.
I re-uploaded in ASCII and it solved the problem.

Reading large numbers of text files in java

I have an application that needs to read only specific content from a text file. I have to read the text from 10,000 different text files arranged in a folder and have to populate the content from all those text files into a single CSV file.
My application runs fine, but it is reading up to file number 999 only. No error, but is not reading file after 999.
Any ideas?
public void calculate(String location) throws IOException{
String mylocation = location;
File rep = new File(mylocation);
File f2 = new File (mylocation + "\\" + "metricvalue.csv");
FileWriter fw = new FileWriter(f2);
BufferedWriter bw = new BufferedWriter (fw);
if(rep.exists() && rep.isDirectory()){
File name[] = rep.listFiles();
for(int j = 0; j < name.length; j++){
if(name[j].isFile()){
String filename = name[j].getPath();
String nameinfo = name[j].getName();
File f1= new File (filename);
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader (fr);
String line = null;
while((line = br.readLine()) != null){
if(line.contains(" | #1 #2 % Correct")){
bw.write(nameinfo + ",");
while((line=br.readLine()) != null) {
if((line.indexOf("#" ) != -1)){
String info[] = line.split("\\s+");
String str = info[2] + "," + info[3] + ",";
bw.write(str);
}
}
}
}
bw.newLine();
br.close();
}
}
}
bw.close();
}

Your platform's file system is limited to 999 open files. You may need to increase the limit or close() the FileReader explicitly:
fr.close();

How to debug:
Put a breakpoint at File name[] = rep.listFiles();
Open variables when Eclipse pauses and check that your array contains all of the file names you want. This will tell you if your problem is there or in your parsing.

You need to debug your code. Here are a couple of pointers to get you started:
File name[] = rep.listFiles();
for(int j =0;j<name.length; j++) {
if(name[j].isFile()) {
What is the size of the array? Figure it out. If there are 10000 elements in the array, that's how many iterations your loop will do, there is simply no other way. Just adding
System.out.println(name.length) will answer this question for you
If the array is shorter than 10000, that's your answer, you simply counted your files incorrectly. If it is not, then your problem must be that one of the "files" isn't really a file (and the test of the if statement fails). Add an else statement to it, and print out the name ... Or better yet, remove this if at all (in general, avoid nested conditionals encompassing the entire body of an outer structure, especially, huge ones like this, it makes your code fragile, and logic very hard to follow), and replace it with
if(!name[j].isFile()) {
System.out.println("Skipping " + name[j] + " because it is not a plain file.");
continue;
}
This will tell you which of 10000 files you are skipping. If it does not print anything, that means, that you do in fact read all 10000 files, as you expect, and the actual problem causing the symptom you are investigating, is elsewhere.

Java save multiline string to text file

I am new to Java and trying to save a multi line string to a text file.
Right now, it does work within my application. Like, if I save the file from my application and then open it from my application, it does put a space between lines. However, if I save the file from my app and then open it in Notepad, it is all on one line.
Is there a way to make it show multi line on all programs? Here's my current code:
public static void saveFile(String contents) {
// Get where the person wants to save the file
JFileChooser fc = new JFileChooser();
int rval = fc.showSaveDialog(fc);
if(rval == JFileChooser.APPROVE_OPTION) {
File file = fc.getSelectedFile();
try {
//File out_file = new File(file);
BufferedWriter out = new BufferedWriter(new FileWriter(file));
out.write(contents);
out.flush();
out.close();
} catch(IOException e) {
messageUtilities.errorMessage("There was an error saving your file. IOException was thrown.", "File Error");
}
}
else {
// Do nothing
System.out.println("The user choose not to save anything");
}
}

depending on how you are constructing your string, you may just be running into a line ending problem. Notepad does not support unix line endings (\n only) it only supports windows line endings (\n\r). try opening your saved file using a more robust editor, and/or make sure you are using the proper line endings for your platform. java's system property (System.getProperty("line.separator")) will get you the proper line ending for the platform that the code is running on.
while you're building your string to be saved to the file, rather than explicitly specifying "\n" or "\n\r" (or on the mac "\r") for your line endings, you would instead append the value of that system property.
like so:
String eol = System.getProperty("line.separator");
... somewhere else in your code ...
String texttosave = "Here is a line of text." + eol;
... more code.. optionally adding lines of text .....
// call your save file method
saveFile(texttosave);

Yea as the previous answer mentions the System.getProperty("line.seperator").
your code doesn't show how you created String contents but since you said you were new to java I thought i'd mention that in java concatenating Strings is not nice since it creates a. If you are building the String by doing this:
String contents = ""
contents = contents + "sometext" + "some more text\n"
Then consider using java.lang.StrinBuilder instead
StringBuilder strBuilder = new StringBuilder();
strBuilder.append("sometext").append("somre more text\n");
...
String contents = strBuilder.toString();
Another alternative is to stream what ever your planning to write to a file rather than building a large string and then outputting that.

You could add something like:
contents = contents.replaceAll("\\n","\\n\\r");
if notepad does not display correctly. However you might run into a different problem: at each save/load you will get multiple \r chars. Then to avoid that at load you would have to call the same code above but with reversed parameters. This is really an ugly solution just to get the text to display properly in notepad.

I had this same problem my guy friend, after much thought and research I even found a solution.
You can use the ArrayList to put all the contents of the TextArea for exemple, and send as parameter by calling the save, as the writer just wrote string lines, then we use the "for" line by line to write our ArrayList in the end we will be content TextArea in txt file.
if something does not make sense, I'm sorry is google translator and I who do not speak English.
Watch the Windows Notepad, it does not always jump lines, and shows all in one line, use Wordpad ok.
private void SaveActionPerformed(java.awt.event.ActionEvent evt) {
String NameFile = Name.getText();
ArrayList< String > Text = new ArrayList< String >();
Text.add(TextArea.getText());
SaveFile(NameFile, Text);
}
public void SaveFile(String name, ArrayList< String> message) {
path = "C:\\Users\\Paulo Brito\\Desktop\\" + name + ".txt";
File file1 = new File(path);
try {
if (!file1.exists()) {
file1.createNewFile();
}
File[] files = file1.listFiles();
FileWriter fw = new FileWriter(file1, true);
BufferedWriter bw = new BufferedWriter(fw);
for (int i = 0; i < message.size(); i++) {
bw.write(message.get(i));
bw.newLine();
}
bw.close();
fw.close();
FileReader fr = new FileReader(file1);
BufferedReader br = new BufferedReader(fr);
fw = new FileWriter(file1, true);
bw = new BufferedWriter(fw);
while (br.ready()) {
String line = br.readLine();
System.out.println(line);
bw.write(line);
bw.newLine();
}
br.close();
fr.close();
} catch (IOException ex) {
ex.printStackTrace();
JOptionPane.showMessageDialog(null, "Error in" + ex);
}