Develop Reference

Java - write string to file line by line vs one-liner / cannot convert String to String[]

Relatively new to programming. I want to read a URL, modify the text string, then write it to a line-separated csv textfile.
The read & modify parts run. Also, outputting the string to terminal (using Eclipse) looks fine (csv, line by line), like this;
data_a,data_b,data_c,...
data_a1,data_b1,datac1...
data_a2,data_b2,datac2...
.
.
.
But I'm unable to write the same string to file - it just becomes a one-liner (see my below for-loops, attempts no. 1 & 2);
data_a,data_b,data_c,data_a1,data_b1,datac1,data_a2,data_b2,datac2...
I guess I'm looking for a way to, in the FileWriter or BufferedWriter loops, convert the string finalDataA to array string (i.e. include the string suffix "[0]") but I have not yet found such an approach that would not give errors of the type "Cannot convert String to String[]". Any suggestions?
String data = "";
String dataHelper = "";
try {
URL myURL = new URL(url);
HttpURLConnection myConnection = (HttpURLConnection) myURL.openConnection();
if (myConnection.getResponseCode() == URLStatus.HTTP_OK.getStatusCode()) {
BufferedReader in = new BufferedReader(new InputStreamReader(myConnection.getInputStream()));
while ((data = in.readLine()) != null) {
dataHelper = dataHelper + "\n" + data;
}
in.close();
String trimmedData = dataHelper.trim().replaceAll(" +", ",");
String parts[] = trimmedData.split(Pattern.quote(")"));// ,1.,");
String dataA = parts[1];
String finalDataA[] = dataA.split("</PRE>");
// parts 2&3 removed in this example
// Console output for testing purpose - This prints out many many lines of csv-data
System.out.println(finalDataA[0]);
//This returns the value 1
System.out.println(finalDataA.length);
// Attempt no. 1 to write to file - writes a oneliner
for(int i = 0; i < finalDataA.length; i++) {
try (BufferedWriter bw = new BufferedWriter(new FileWriter(pathA, true))) {
String s;
s = finalDataA[i];
bw.write(s);
bw.newLine();
bw.flush();
}
}
// Attempt no. 2 to write to file - writes a oneliner
FileWriter fw = new FileWriter(pathA);
for (int i = 0; i < finalDataA.length; i++) {
fw.write(finalDataA[i] + "\n");
}
fw.close();
}
} catch (Exception e) {
System.out.println("Exception" +e);
}

Create the BufferedWriter and the FileWriter ahead of the for loop, not every time around it.

From your code comments, finalDataA has one element, so the for-loop will be executed only once. Try splitting finalDataA[0] into rows.
Something like this:
String endOfLineToken = "..."; //your variant
String[] lines = finalDataA[0].split(endOfLineToken)
BufferdWriter bw = new BufferedWriter(new FileWriter(pathA, true));
try
{
for (String line: lines)
{
bw.write(line);
bw.write(endOfLineToken);//to put back line endings
bw.newLine();
bw.flush();
}
}
catch (Exception e) {}

read from file and write some parts in another file

I have to read from a text file and format the input. I'm new to java reading from files, and I don't know how to work with just some parts of what I read
Here is the initial file: http://pastebin.com/D0paWtAd
And I have to write in another file the following output:
Average,Joe,44,31,18,12,9,10
I've managed just to take everything from the file and print it to output. I would need help just in taking the output I need and print it to the screen. Any help is appreciated.
This is what I wrote up to now:
public class FileParsing {
public static String
read(String filename) throws IOException {
BufferedReader in = new BufferedReader(new FileReader("C:\\Users\\Bogdi\\Desktop\\example.txt"));
String s;
StringBuilder sb = new StringBuilder();
while((s = in.readLine())!= null) sb.append(s + "\n");
in.close();
return sb.toString();
}

If your goal is to do the specified output in another file you don't need to first get the content of your file in a StringBuilder before processing it, you can append the processed datas directly in a StringBuilder then you can write the result in a file. Here is an example that would work for the given file but you may have to modify it if the keys change in the future:
The following method will correctly process the datas from your file
public static String read(String filename) throws IOException {
BufferedReader in = new BufferedReader(new FileReader(filename));
String s;
StringBuilder sb = new StringBuilder();
while((s = in.readLine())!= null) {
String[] split1 = s.split("=");
if (split1[0].equals("name")) {
StringTokenizer tokenizer = new StringTokenizer(split1[1]);
sb.append(tokenizer.nextToken());
sb.append(",");
sb.append(tokenizer.nextToken());
sb.append(",");
} else if (split1[0].equals("index")) {
sb.append(split1[1] + ",");
} else if (split1[0].equals("FBid")) {
sb.append(split1[1]);
} else {
StringTokenizer tokenizer = new StringTokenizer(split1[1]);
String wasted = tokenizer.nextToken();
sb.append(tokenizer.nextToken() + ",");
}
}
in.close();
return sb.toString();
}
The next method will read any string to a file
public static void writeStringToFile(String string, String filePath) throws IOException {
BufferedWriter writer = new BufferedWriter(
new FileWriter(
new File(filePath)
)
);
writer.write(string);
writer.newLine();
writer.flush();
writer.close();
}
And here is a simple tests (File1.txt contains the datas from the file you shared on paste bin and I write them in another file)
public static void main(String[] args) throws Exception {
String datas = read("C:\\Tests\\File1.txt");
System.out.println(datas);
writeStringToFile(datas, "C:\\Tests\\FileOuput.txt" );
}
It will produce the exact output that you are expecting
[EDIT] #idk, apparently you have an exception executing my example, while it is working fine for me. That could only mean there is an error at data level. Here is the data sample that I used (and I believe I exactly copy the datas you shared)
And here is the result:

Good to know you are using "StringBuilder" component instead being concatenating your String values, way to go :).
More than knowledge on the Java.IO API to work with files, you will need some logic to get the results you expect. Here I came with an approach that could help you, not perfect, but can point you on how to face this problem.
//Reference to your file
String myFilePath = "c:/dev/myFile.txt";
File myFile = new File(myFilePath);
//Create a buffered reader, which is a good start
BufferedReader breader = new BufferedReader(new FileReader(myFile));
//Define this variable called line that will evaluate each line of our file
String line = null;
//I will use a StringBuilder to append the information I need
StringBuilder appender = new StringBuilder();
while ((line = breader.readLine()) != null) {
//First, I will obtain the characters after "equals" sign
String afterEquals = line.substring(line.indexOf("=") + 1, line.length());
//Then, if it contains digits...
if (afterEquals.matches(".*\\d+.*")) {
//I will just get the digits from the line
afterEquals = afterEquals.replaceAll("\\D+","");
}
//Finally, append the contents
appender.append(afterEquals);
appender.append(",");//This is the comma you want to include
}
//I will delete the last comma
appender.deleteCharAt(appender.length() - 1);
//Close the reader...
breader.close();
//Then create a process to write the content
BufferedWriter myWriter = new BufferedWriter(new FileWriter(new File("myResultFile.txt")));
//Write the full contents I get from my appender :)
myWriter.write(appender.toString());
//Close the writer
myWriter.close();
}
Hope this can help you. Happy coding!

Modifying a file at a specific line in Java

I'm writing a method that will allow me to input a line at a specific point in a file, such as a .txt or .vbs script. The problem I'm having is the writing back part, the output file is blank- not containing the entries of my ArrayList scriptCollection. Here is my test method code;
public void testMethod()throws Exception
{
BufferedReader br = new BufferedReader(new FileReader("C:/Users/jchild/Desktop/PrintScript.vbs"));
int indexNo = 1;
int appendAt=0;
String line;
while((line = br.readLine()) != null)
{
scriptCollection.add(line);
if(line.contains("Add at this point"))
{
System.out.println("Successfully read and compared"); //this is just for test output
appendAt = appendAt + indexNo;
}
indexNo++;
}
br.close();
scriptCollection.add(appendAt++,"Appended here");
System.out.println(scriptCollection.toString()); //this is just for test output
//here's what's causing the problem
FileOutputStream fos = new FileOutputStream("C:/Users/jchild/Desktop/PrintScript.txt");
PrintWriter is = new PrintWriter(fos);
for(String temp : scriptCollection)
{
is.println(temp);
}
scriptCollection.clear();
}

You have to close the streams.

Writing multiple queries from a test file

public static void main(String[] args) {
ArrayList<String> studentTokens = new ArrayList<String>();
ArrayList<String> studentIds = new ArrayList<String>();
try {
// Open the file that is the first
// command line parameter
FileInputStream fstream = new FileInputStream(new File("file1.txt"));
BufferedReader br = new BufferedReader(new InputStreamReader(fstream, "UTF8"));
String strLine;
// Read File Line By Line
while ((strLine = br.readLine()) != null) {
strLine = strLine.trim();
if ((strLine.length()!=0) && (!strLine.contains("#"))) {
String[] students = strLine.split("\\s+");
studentTokens.add(students[TOKEN_COLUMN]);
studentIds.add(students[STUDENT_ID_COLUMN]);
}
}
for (int i=0; i<studentIds.size();i++) {
File file = new File("query.txt"); // The path of the textfile that will be converted to csv for upload
BufferedReader reader = new BufferedReader(new FileReader(file));
String line = "", oldtext = "";
while ((line = reader.readLine()) != null) {
oldtext += line + "\r\n";
}
reader.close();
String newtext = oldtext.replace("sanid", studentIds.get(i)).replace("salabel",studentTokens.get(i)); // Here the name "sanket" will be replaced by the current time stamp
FileWriter writer = new FileWriter("final.txt",true);
writer.write(newtext);
writer.close();
}
fstream.close();
br.close();
System.out.println("Done!!");
} catch (Exception e) {
e.printStackTrace();
System.err.println("Error: " + e.getMessage());
}
}
The above code of mine reads data from a text file and query is a file that has a query in which 2 places "sanid" and "salabel" are replaced by the content of string array and writes another file final . But when i run the code the the final does not have the queries. but while debugging it shows that all the values are replaced properly.

but while debugging it shows that all the values are replaced properly
If the values are found to be replaced when you debugged the code, but they are missing in the file, I would suggest that you flush the output stream. You are closing the FileWriter without calling flush(). The close() method delegates its call to the underlying StreamEncoder which does not flush the stream either.
public void close() throws IOException {
se.close();
}
Try this
writer.flush();
writer.close();
That should do it.

Modify the content of a file using Java

I want to delete some content of file using java program as below. Is this the write method to replace in the same file or it should be copied to the another file.
But its deleting the all content of the file.
class FileReplace
{
ArrayList<String> lines = new ArrayList<String>();
String line = null;
public void doIt()
{
try
{
File f1 = new File("d:/new folder/t1.htm");
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader(fr);
while (line = br.readLine() != null)
{
if (line.contains("java"))
line = line.replace("java", " ");
lines.add(line);
}
FileWriter fw = new FileWriter(f1);
BufferedWriter out = new BufferedWriter(fw);
out.write(lines.toString());
}
catch (Exception ex)
{
ex.printStackTrace();
}
}
public statc void main(String args[])
{
FileReplace fr = new FileReplace();
fr.doIt();
}
}

I would start with closing reader, and flushing writer:
public class FileReplace {
List<String> lines = new ArrayList<String>();
String line = null;
public void doIt() {
try {
File f1 = new File("d:/new folder/t1.htm");
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader(fr);
while ((line = br.readLine()) != null) {
if (line.contains("java"))
line = line.replace("java", " ");
lines.add(line);
}
fr.close();
br.close();
FileWriter fw = new FileWriter(f1);
BufferedWriter out = new BufferedWriter(fw);
for(String s : lines)
out.write(s);
out.flush();
out.close();
} catch (Exception ex) {
ex.printStackTrace();
}
}
public static void main(String args[]) {
FileReplace fr = new FileReplace();
fr.doIt();
}
}

The accepted answer is great. However, there is an easier way to replace content in a file using Apache's commons-io library (commons-io-2.4.jar - you can use any latest versions)
private void update() throws IOException{
File file = new File("myPath/myFile.txt");
String fileContext = FileUtils.readFileToString(file);
fileContext = fileContext.replaceAll("_PLACEHOLDER_", "VALUE-TO-BE-REPLACED");
FileUtils.write(file, fileContext);
}
Note: Thrown IOException needs to be caught and handled by the application accordingly.

Read + write to the same file simulatenously is not ok.
EDIT: to rephrase and be more correct and specific - reading and writing to the same file, in the same thread, without properly closing the reader (and flusing the writer) is not ok.

Make sure to:
close any stream when you no longer need them
In particular before reopening it for writing.
truncate the file, to make sure it shrinks if you write less than it had.
then write the output
write individual lines, don't rely on toString.
flush and close when you are finished writing!
If you use buffered IO, you always have to ensure that the buffer is flushed at the end, or you might lose data!

I can see three problems.
First you are writing to out which I assume is System.out, not an output stream to the file.
Second, if you do write to an output stream to the file, you need to close it.
Third, the toString() method on an ArrayList isn't going to write the file like you are expecting. Loop over the list and write each String one at a time. Ask yourself whether you need to write newline characters as well.

The accepted answer is slightly wrong. Here's the correct code.
public class FileReplace {
List<String> lines = new ArrayList<String>();
String line = null;
public void doIt() {
try {
File f1 = new File("d:/new folder/t1.htm");
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader(fr);
while ((line = br.readLine()) != null) {
if (line.contains("java"))
line = line.replace("java", " ");
lines.add(line);
}
fr.close();
br.close();
FileWriter fw = new FileWriter(f1);
BufferedWriter out = new BufferedWriter(fw);
for(String s : lines)
out.write(s);
out.flush();
}
out.close();
catch (Exception ex) {
ex.printStackTrace();
}
}