Develop Reference

GWT: reading from a CSV file on the Server

I try to convert an old Applet to a GWT Application but I encountered a problem with the following function:
private String[] readBrandList() {
try {
File file = new File("Brands.csv");
String ToAdd = "Default";
BufferedReader read = new BufferedReader(new FileReader(file));
ArrayList<String> BrandName = new ArrayList<String>();
while (ToAdd != null) {
ToAdd = (read.readLine());
BrandName.add(ToAdd);
}
read.close();
String[] BrandList = new String[BrandName.size()];
for (int Counter = 0; Counter < BrandName.size(); Counter++) {
BrandList[Counter] = BrandName.get(Counter);
}
return BrandList;
} catch (Exception e) {
}
return null;
}
Now apparently The BufferedReader isn't supported by GWT and I find no way to replace it other than writing all entries into the code which would result in a maintenance nightmare.
Is there any function I'm not aware of or is it just impossible?

You need to read this file on the server side of your app, and then pass the results to the client using your preferred server-client communication method. You can read and pass the entire file, if it's small, or read/transfer in chunks if the file is big.

i want to change the text in a file, my code is searching the word but not replacing the word

I am trying to replace a string from a js file which have content like this
........
minimumSupportedVersion: '1.1.0',
........
now 'm trying to replace the 1.1.0 with 1.1.1. My code is searching the text but not replacing. Can anyone help me with this. Thanks in advance.
public class replacestring {
public static void main(String[] args)throws Exception
{
try{
FileReader fr = new FileReader("G:/backup/default0/default.js");
BufferedReader br = new BufferedReader(fr);
String line;
while((line=br.readLine()) != null) {
if(line.contains("1.1.0"))
{
System.out.println("searched");
line.replace("1.1.0","1.1.1");
System.out.println("String replaced");
}
}
}
catch(Exception e){
e.printStackTrace();
}
}
}

First, make sure you are assigning the result of the replace to something, otherwise it's lost, remember, String is immutable, it can't be changed...
line = line.replace("1.1.0","1.1.1");
Second, you will need to write the changes back to some file. I'd recommend that you create a temporary file, to which you can write each `line and when finished, delete the original file and rename the temporary file back into its place
Something like...
File original = new File("G:/backup/default0/default.js");
File tmp = new File("G:/backup/default0/tmpdefault.js");
boolean replace = false;
try (FileReader fr = new FileReader(original);
BufferedReader br = new BufferedReader(fr);
FileWriter fw = new FileWriter(tmp);
BufferedWriter bw = new BufferedWriter(fw)) {
String line = null;
while ((line = br.readLine()) != null) {
if (line.contains("1.1.0")) {
System.out.println("searched");
line = line.replace("1.1.0", "1.1.1");
bw.write(line);
bw.newLine();
System.out.println("String replaced");
}
}
replace = true;
} catch (Exception e) {
e.printStackTrace();
}
// Doing this here because I want the files to be closed!
if (replace) {
if (original.delete()) {
if (tmp.renameTo(original)) {
System.out.println("File was updated successfully");
} else {
System.err.println("Failed to rename " + tmp + " to " + original);
}
} else {
System.err.println("Failed to delete " + original);
}
}
for example.
You may also like to take a look at The try-with-resources Statement and make sure you are managing your resources properly

If you're working with Java 7 or above, use the new File I/O API (aka NIO) as
// Get the file path
Path jsFile = Paths.get("C:\\Users\\UserName\\Desktop\\file.js");
// Read all the contents
byte[] content = Files.readAllBytes(jsFile);
// Create a buffer
StringBuilder buffer = new StringBuilder(
new String(content, StandardCharsets.UTF_8)
);
// Search for version code
int pos = buffer.indexOf("1.1.0");
if (pos != -1) {
// Replace if found
buffer.replace(pos, pos + 5, "1.1.1");
// Overwrite with new contents
Files.write(jsFile,
buffer.toString().getBytes(StandardCharsets.UTF_8),
StandardOpenOption.TRUNCATE_EXISTING);
}
I'm assuming your script file size doesn't cross into MBs; use buffered I/O classes otherwise.

Error in reading file java.io

So i'm trying to read the following string from the text file addToLibrary.txt
file:/Users/JEAcomputer/Music/iTunes/iTunes%20Media/Music/Flight%20Of%20The%20Conchords/Flight%20Of%20The%20Conchords/06%20Mutha'uckas.mp3
But when I do i get the following error:
java.io.FileNotFoundException: file:/Users/JEAcomputer/Music/iTunes/iTunes%20Media/Music/Flight%20Of%20The%20Conchords/Flight%20Of%20The%20Conchords/06%20Mutha'uckas.mp3 (No such file or directory)
Whats odd is that I got that string from a fileChooser using this method:
public static void addToLibrary(File f) {
String fileName = "addToLibrary.txt";
try {
FileWriter filewriter = new FileWriter(fileName, true);
BufferedWriter bufferedWriter = new BufferedWriter(filewriter);
bufferedWriter.newLine();
bufferedWriter.write(f.toURI().toString());
System.out.println("Your file has been written");
bufferedWriter.close();
} catch (IOException ex) {
System.out.println(
"Error writing to file '"
+ fileName + "'");
} finally {
}
}
An even stranger error is that my file reader can read things in another folder but not anything in iTunes Media.
I attempt to read all the files in the different folders with the following method:
public void getMusicDirectory() {
int index = 0;
try {
File[] contents = musicDir.listFiles();
//System.out.println(contents[3].toString());
for (int i = 0; i < contents.length; i++) {
//System.out.println("----------------------------------------"+contents.length);
String name = contents[i].getName();
//System.out.println(name);
if (name.indexOf(".mp3") == -1) {
continue;
}
FileInputStream file = new FileInputStream(contents[i]);
file.read();
System.out.println(contents[i].toURI().toString());
songsDir.add(new Song((new MediaPlayer(new Media(contents[i].toURI().toString()))), contents[i]));
file.close();
}
} catch (Exception e) {
System.out.println("Error -- " + e.toString());
}
try(BufferedReader br = new BufferedReader(new FileReader("addToLibrary.txt"))) {
//System.out.println("In check login try");
for (String line; (line = br.readLine()) != null; ) {
FileInputStream file = new FileInputStream(new File(line));
file.read();
songsDir.add(new Song(new MediaPlayer(new Media(line)), new File(line)));
file.close();
}
// line is not visible here.
} catch (Exception e) {
System.out.println("Error reading add to library-- " + e.toString());
}
}
So how can i make this work? why does the first part of the method work but not the second?

You are not having a problem reading the string
file:/Users/JEAcomputer/Music/iTunes/iTunes%20Media/Music/Flight%20Of%20The%20Conchords/Flight%20Of%20The%20Conchords/06%20Mutha'uckas.mp3
from a file. That part works fine. Your problem is after that, when you try to open the file with the path:
file:/Users/JEAcomputer/Music/iTunes/iTunes%20Media/Music/Flight%20Of%20The%20Conchords/Flight%20Of%20The%20Conchords/06%20Mutha'uckas.mp3
because that's not actually a path; it's a URI (although it can be converted to a path).
You could convert this to a path, in order to open it, but you have no reason to - your code doesn't actually read from the file (apart from the first byte, which it does nothing with) so there's no point in opening it. Delete the following lines:
FileInputStream file = new FileInputStream(contents[i]); // THIS ONE
file.read(); // THIS ONE
System.out.println(contents[i].toURI().toString());
songsDir.add(new Song((new MediaPlayer(new Media(contents[i].toURI().toString()))), contents[i]));
file.close(); // THIS ONE
and
FileInputStream file = new FileInputStream(new File(line)); // THIS ONE
file.read(); // THIS ONE
songsDir.add(new Song(new MediaPlayer(new Media(line)), new File(line)));
file.close(); // THIS ONE

file:/Users/JEAcomputer/Music/iTunes/iTunes%20Media/Music/Flight%20Of%20The%20Conchords/Flight%20Of%20The%20Conchords/06%20Mutha'uckas.mp3 is not a valid File reference, especially under Windows.
Since you've idendtified the String as a URI, you should treat it as such...
URI uri = URI.create("file:/Users/JEAcomputer/Music/iTunes/iTunes%20Media/Music/Flight%20Of%20The%20Conchords/Flight%20Of%20The%20Conchords/06%20Mutha'uckas.mp3");
Okay, but, there's no real way to read URI, but you can read a URL, so we need to convert the URI to URL, luckily, this is quite simple...
URL url = uri.toURL();
From there you can use URL#openStream to open an InputStream (which you can wrap in a InputStreamReader) and read the contents of the file, for example...
String imageFile = "file:/...";
URI uri = URI.create(imageFile);
try {
URL url = uri.toURL();
try (InputStream is = url.openStream()) {
byte[] bytes = new byte[1024 * 4];
int bytesRead = -1;
int totalBytesRead = 0;
while ((bytesRead = is.read(bytes)) != -1) {
// Somthing, something, something, bytes
totalBytesRead += bytesRead;
}
System.out.println("Read a total of " + totalBytesRead);
} catch (IOException ex) {
ex.printStackTrace();
}
} catch (MalformedURLException ex) {
ex.printStackTrace();
}
You could, however, save your self a lot of issues and stop using things like f.toURI().toString()); (File#toURI#toString) and simply use File#getPath instead...This would allow you to simply create a new File reference from the String...
Also, your resource management needs some work, basically, if you open it, you should close it. See The try-with-resources Statement for some more ideas

Java rename not working

Here is my code
private void edit(String search_bookname) {
String current_bookname ="", current_ISBN = "", current_author = "", current_rating = "", record = "", comma = ",", current_status = "";
int flag1 = 0, flag2 = 0;
File file = new File("Book_data.txt");
try {
BufferedReader reader = new BufferedReader (new FileReader (file));
File f = new File("Book_data_copy.txt");
FileWriter create = new FileWriter(f);
PrintWriter y = new PrintWriter(create);
while(reader.ready())
{
record = reader.readLine();
StringTokenizer st = new StringTokenizer(record, ",");
while(st.hasMoreTokens()) {
current_bookname = st.nextToken();
current_author = st.nextToken();
current_ISBN = st.nextToken();
current_rating = st.nextToken();
current_status = st.nextToken();
flag2 = 0;
if (search_bookname.equals(current_bookname)) {
flag1 = 1;
flag2 = 1;
try {
y.print(current_bookname); y.print(comma);
y.print(current_author); y.print(comma);
y.print(current_ISBN); y.print(comma);
y.print(current_rating); y.print(comma);
y.println("Borrowed");
} catch(Exception e) {}
Thread.sleep(1000);
}
}
if(flag2==0) // All non-matching records shall only be written to file. Record to be deleted will not be written to new file
{
y.print(current_bookname); y.print(comma); //One record per line..... Each field in a record is seperated by COMMA (" , " )
y.print(current_author); y.print(comma);
y.print(current_ISBN); y.print(comma);
y.print(current_rating);y.print(comma);
y.println(current_status);
}
}
reader.close();
y.close();
create.close();
} catch (Exception e) {}
if(flag1==1) //Rename File ONLY when record has been found for Edit
{
File oldFileName = new File("Book_data_copy.txt");
File newFileName = new File("Book_data.txt");
System.out.println("File renamed .....................");
try
{
newFileName.delete(); oldFileName.renameTo(newFileName);
if (oldFileName.renameTo(newFileName))
System.out.println("File renamed successfull !");
else
System.out.println("File rename operation failed !");
Thread.sleep(1000);
} catch (Exception e) {}
}
}
The project is for a library system. I am relatively new to java and I use netbeans on windows 8.1. The code outputs rename operation failed. Almost exactly the same code for edit has been used before in the program and it worked.
Any suggestions or code corrections would be helpfu.
Thanks!

Your issue is with the below code section
oldFileName.renameTo(newFileName);
if (oldFileName.renameTo(newFileName))
you are trying to rename twice. The first might pass but the 2nd will definitely fail. Check if the original file was renamed. If any error is thrown pring the stack trace and add the trace to your post.

You are trying to rename oldFileName twice:
newFileName.delete(); oldFileName.renameTo(newFileName); // rename
if (oldFileName.renameTo(newFileName)) // rename again ?!
System.out.println("File renamed successfull !");
else
System.out.println("File rename operation failed !");
The second rename in the if() fails, because the file was renamed already in the line before.

There are any number of problems here, starting with ignoring exceptions; not closing the file in a finally block; and using Reader.ready() incorrectly.

This is 2015. Use java.nio.file!
final Path srcFile = Paths.get("Book_data.txt").toAbsolutePath();
final Path dstFile = srcFile.resolveSibling("Book_data_copy.txt");
try (
final BufferedReader reader = Files.newBufferedReader(srcFile, StandardCharsets.UTF_8);
final BufferedWriter writer = Files.newBufferedWriter(dstFile, StandardCharsets.UTF_8,
StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
final PrintWriter pw = new PrintWriter(writer);
) {
// work with reader and pw
}
if (flag1 == 1)
Files.move(dstFile, srcFile, StandardCopyOption.REPLACE_EXISTING,
StandardCopyOption.ATOMIC_MOVE);
If you did that from the start, not only would your resources have been closed safely (your code doesn't do that) but you would have gotten a meaningful exception as well (you are trying to rename twice; you would have had a NoSuchFileException on the second rename).
Relying on File is an error, and it has always been.

Trouble getting file path in Netbeans project

I'm making a program that uses text files. I need to make it so that the program can be run from a different computer using its jar file. The problem is that I can't get it to find the right file path to the text files. I've tried using getResource(), but it's still not working right. Here's the code:
public class Params {
public static void init() {
hsChartSuited = new int[13][13];
file = new File(Params.class.getResource("HandStrengthDataSuited.txt").getFile());
try {
Scanner input = new Scanner(file);
for (int i = 0; i < hsChartSuited.length; i++) {
for (int j = 0; j < hsChartSuited[i].length; j++) {
hsChartSuited[i][j] = Integer.parseInt(input.next()) - 20;
}
}
} catch (FileNotFoundException e) {
System.out.println("File not found");
}
}
HandStrengthDataSuited.txt is a file that is in the src folder for my project. It's also located outside of the folder, in the project's main directory as well. I've tried printing the absolute file path, and this is what I get:
/Users/MyUsername/file:/Users/MyUsername/Documents/Homework_Soph_2012/Computer%20Science/HoldEm/dist/HoldEm.jar!/holdem/HandStrengthDataSuited.txt
The file path that I need to get is
/Users/MyUsername/Documents/Homework_Soph_2012/Computer%20Science/HoldEm/holdem/HandStrengthDataSuited.txt
Does anyone know what the problem is here?

If your files is in src folder,
class Tools {
public static InputStream getResourceAsStream(String resource)
throws FileNotFoundException
{
String stripped = resource.startsWith("/") ? resource.substring(1) : resource;
InputStream stream = null;
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
if (classLoader != null) {
stream = classLoader.getResourceAsStream(stripped);
}
if (stream == null) {
stream = Tools.class.getResourceAsStream(resource);
}
if (stream == null) {
stream = Tools.class.getClassLoader().getResourceAsStream(stripped);
}
if (stream == null) {
throw new FileNotFoundException("Resource not found: " + resource);
}
return stream;
}
}
Use:
reader = new BufferedReader(new InputStreamReader(getResourceAsStream("org/paulvargas/resources/file.txt"), "UTF-8"));