reading input from file until specific word is read - java

i am writing a java program to read a file and print output to another string variable.which is working perfectly as intended using is code.
{
String key = "";
FileReader file = new FileReader("C:/Users/raju/Desktop/input.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while (line != null) {
key += line;
line = reader.readLine();
}
System.out.println(key); //this prints contents of .txt file
}
this prints whole text in the file.But i want to only print the lines till word END is encountered in file.
example: if input.txt file contains following text : this test file END extra in
it should print only :
this test file


Just do a simple indexOf to see where it is and if it exists in the line. If the instance is found one option would be using substring to cut off everything up until the index of the keyword. For a bit more control though try using java regular expressions.
String key = "";
FileReader file = new FileReader("C:/Users/raju/Desktop/input.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while ((line = reader.readLine()) != null && line.indexOf("Keyword to look for") == -1)
key += line;
System.out.println(key);


I am not sure why it needs to be any more complicated than this:
BufferedReader re = new BufferedReader(new InputStreamReader(System.in));
while (true) {
String str = re.readLine();
if (str.equals("exit")) break;
// whatever other code.
}


You can do it in many ways. one of them is using indexOf method to specify the start index of "END" in input and then using subString method.
for more information, read documentation of String calss. HERE


This will work for your issue.
public static void main(String[] args) throws IOException {
String key = "";
FileReader file = new FileReader("/home/halil/khalil.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while (line != null) {
key += line;
line = reader.readLine();
} String output = "";
if(key.contains("END")) {
output = key.split("END")[0];
System.out.println(output);
}
}


You have to change your logic to check if the line contains "END".
If END not found in a line, add the line to key stringin your program
If yes, split that line into word array, read the line till you encounter the word "END" and append it to your key string. Consider using Stringbuilder for key.
while (line != null) {
line = reader.readLine();
if(!line.contains("END")){
key += line;
}else{
//Note that you can use split logic like below, or use java substring
String[] words = line.split("");
for(String s : words){
if(s.equals("END")){
return key;
}
key += s;
}
}
}

Related

How to read every line of a text file including empty lines

I want to be able to read an entire text file that has empty lines between text. Every solution I try to implement seems to stop reading after it reaches an empty line. I want to be able to read an entire text file, including empty lines, and store the contents in a String. This is what I have now. I included two implementations. How can I alter either of the implementations to continue reading after an empty line? Also, I want the empty lines in the text file to be included in the String that it is being stored in.
File templateFile = new File(templatePath);
String oldContent = "";
BufferedReader reader = new BufferedReader(new FileReader(templateFile));
//Implementation 1
String line = reader.readLine();
while(line != null) {
oldContent = oldContent + line + System.lineSeparator();
line = reader.readLine();
}
/* Implementation 2
Scanner sc = new Scanner(templateFile);
while(sc.hasNext()) {
oldContent = sc.nextLine();
} */

Using java 11 java.nio.file.Files.readString()
oldContent = Files.readString(Paths.get(templatePath));

How to store multiple lines from file into String from Scanner `

Using Scanner, i'm not sure how to read a file with multiple lines and store it all into a String. I use a loop like :
while(file.hasNext())
{
string += file.nextLine();
}
I find that the file.hasNext method eats up all of the data in the file and so file.nextInt() doesn't have any values to find and so it returns and error. What can I do to "reset" the Scanner? I tried creating a new Scanner object but that didn't change anything. I have to run this string through a method and I have run into this problem many times. What should I do?

Maybe you should try StringBuilder.
StringBuilder builder = new StringBuilder();
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String line;
while ((line = br.readLine()) != null) {
builder.append(line);
// process the line.
}
}
later
String text = builder.toString();

To read the entire contents of a Scanner source into a String, set the Scanner's delimiter to the end of the file:
String contents = file.useDelimiter("\\Z").next();

BufferedReader to read lines, then assign the new formed line's tokens to variables

I have a text file that I need to modify before parsing it. 1) I need to combine lines if leading line ends with "\" and delete white spaced line. this has been done using this code
public List<String> OpenFile() throws IOException {
try (BufferedReader br = new BufferedReader(new FileReader(path))) {
String line;
StringBuilder concatenatedLine = new StringBuilder();
List<String> formattedStrings = new ArrayList<>();
while ((line = br.readLine()) != null) {
if (line.isEmpty()) {
line = line.trim();
} else if (line.charAt(line.length() - 1) == '\\') {
line = line.substring(0, line.length() - 1);
concatenatedLine.append(line);
} else {
concatenatedLine.append(line);
formattedStrings.add(concatenatedLine.toString());
concatenatedLine.setLength(0);
}
}
return formattedStrings;
}
}
}//The formattedStrings arrayList contains all of the strings formatted for use.
Now My question, how can I search those lines for pattern and assign their token[i] to variables that I can call or use later.
the New combined text will look like this:
Field-1 Field-2 Field-3 Field-4 Field-5 Field-6 Field-7
Now, if the line contains "Field-6" and "Field-2" Then set the following:
String S =token[1] token[3];
String Y =token[5-7];
Question you might have for me, how am I deciding on which token to save to a string? I will manually search for the pattern in the text file and if the "Line contain Field-6 and Field-2 or any other required pattern. Then manually count which token I need to assign to the string. However, it will be nice if there is another way to approach this, for ex assign what's in between token[4] and token[7] to string (s) if the line has token[2] and token[6]. or another way that provides more Granule Control over what to store as string and what to ignore.

How to handle ArrayIndexedBoundexception in Java

I have been trying to get a specific columns from a csv file say having 30 columns but i need only 3 columns entirely when i execute the following code only i get only one entire column data..how to get 3 column data at a time.when i run it prints only one column...when i try to print multiple column it shows error message like
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at ReadCVS.main(ReadCVS.java:19)
public static void main(String[] args) throws Exception {
String splitBy = ",";
BufferedReader br = new BufferedReader(new FileReader("txt.csv"));
String line = br.readLine();
while((line = br.readLine()) !=null){
String[] b = line.split(splitBy);
PrintWriter out = new PrintWriter(new FileWriter("new.csv",true));
out.println(b[0]);
out.close();
}
br.close();
}

The problem is probably is:
You have only one line in your, txt.csv file.
When you called br.readLine(); for the first time, that line is read from the file and stored in String line variable. But you ignored that line, and you've read again, in your while condition:
while((line = br.readLine()) !=null)
So maybe you have an empty line or empty string after that first line. Then the while condition is true, but an empty String is stored in line variable. So the b[] has no element and b[0] is out of the bound.
One solution is to change this line:
String line = br.readLine();
to
String line = null;
[EDIT]
So if you try to read a file like the one in mkyong's site (as you linked in your comment) and split the lines by "," and write them in a new file for example, you can use a code like the code below:
public static void main(String[] args) throws IOException {
BufferedWriter out = new BufferedWriter(new FileWriter("c:\\new.csv",true));
BufferedReader br = new BufferedReader(new FileReader("c:\\txt.csv"));
String splitBy = ",";
String line = null;
while((line = br.readLine()) !=null){
StringBuffer newLine = new StringBuffer();
String[] b = line.split(splitBy);
for (int i = 0; i<b.length; i++)
{
if(b[i] == null || b[i].trim().isEmpty())
continue;
newLine.append(b[i].trim() + ";");
}
out.write(newLine.toString());
out.newLine();
}
out.close();
br.close();
}
Also you should know that the following line opens the output file in appendable way(the second boolean parameter in the constructor):
BufferedWriter out = new BufferedWriter(new FileWriter("c:\\new.csv",true));
Also I assumed the contents of the source file is the same as in mkyong's site, somethimg like this:
"1.0.0.0",, , ,"1.0.0.255","16777216", , "16777471","AU" ,, "Australia"
"1.0.1.0" , ,, "1.0.3.255" ,, ,"16777472","16778239" , , "CN" , ,"China"
"1.0.4.0","1.0.7.255","16778240","16779263","AU","Australia"
"1.0.8.0","1.0.15.255","16779264","16781311","CN","China"
"1.0.16.0","1.0.31.255","16781312","16785407","JP","Japan"
"1.0.32.0","1.0.63.255","16785408","16793599","CN","China"
"1.0.64.0","1.0.127.255","16793600","16809983","JP","Japan"
"1.0.128.0","1.0.255.255","16809984","16842751","TH","Thailand"
Good Luck.

check if a value exists in an external file (java)

Is it possible (and wise) to check if a value exists in an external text file.
So if i have a file: bankcodes.txt that contains the next lines:
INGB
ABNA
...
Is it possible to check if a value is present in this file?
The reason is that these values can change and need to be easily changed whitout making a new jar file.
If there is another, wiser way of doing this i would like to hear it too.

From here:
https://stackoverflow.com/a/4716623/110933
Read contents of file line by line and check the value you get for "line" for the value you want:
BufferedReader br = new BufferedReader(new FileReader("file.txt"));
try {
StringBuilder sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
sb.append("\n");
line = br.readLine();
}
String everything = sb.toString();
} finally {
br.close();
}

Give example how i did it , while File.txt -> our text and ourValue it the one we searching
String ourValue="value"
BufferedReader br = new BufferedReader(new FileReader("File.txt"));
String line = br.readLine();
boolean exist = false;
while (line != null&&!exist) {
if (ourValue.equals(line)) {
exist = true;
} else {
line = br.readLine();
}
}
System.out.println("the value " +ourValue+" exist in the Text? "+ exist);
}

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