Method to find string inside of the text file. Then getting the following lines up to a certain limit

Question

So this is what I have so far :

public String[] findStudentInfo(String studentNumber) {
                Student student = new Student();
                Scanner scanner = new Scanner("Student.txt");
                // Find the line that contains student Id
                // If not found keep on going through the file
                // If it finds it stop
                // Call parseStudentInfoFromLine get the number of courses
                // Create an array (lines) of size of the number of courses plus one
                // assign the line that the student Id was found to the first index value of the array
                //assign each next line to the following index of the array up to the amount of classes - 1
                // return string array
}

I know how to find if a file contains the string I am trying to find but I don't know how to retrieve the whole line that its in.

This is my first time posting so If I have done anything wrong please let me know.

If this is homework, it should be tagged as such. – Apr 08 '11 at 20:27 — , Apr 08 '11 at 20:27
Can you add a sample of the input file? – RonK Apr 08 '11 at 20:28 — RonK, Apr 08 '11 at 20:28

score 65 · Accepted Answer · edited Jan 02 '14 at 12:32

65

You can do something like this:

File file = new File("Student.txt");

try {
    Scanner scanner = new Scanner(file);

    //now read the file line by line...
    int lineNum = 0;
    while (scanner.hasNextLine()) {
        String line = scanner.nextLine();
        lineNum++;
        if(<some condition is met for the line>) { 
            System.out.println("ho hum, i found it on line " +lineNum);
        }
    }
} catch(FileNotFoundException e) { 
    //handle this
}

edited Jan 02 '14 at 12:32

Diego Faria

8,805
3
26
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answered Apr 08 '11 at 20:28

Amir Afghani

37,814
16
84
124

This won't give me the line that contains the string studentNumber. – Joel Sanchez Apr 08 '11 at 20:34
This was helpful. Didn't really expect to get such a fast response from everyone. – Joel Sanchez Apr 08 '11 at 20:37
1

Typically on StackOverflow, we thank people with a vote, or by accepting their answer. – Amir Afghani Apr 08 '11 at 20:37
3

@Joel On the left of each answer is a number surrounded by up/down characters. Those up/down characters represent 'votes' for & against an answer. An answer with many votes 'bubbles to the top of the list' making it easier to find later. If you asked the question, there should also be the outline of a 'tick' character near the number. Click that once to indicate a 'correct' answer. – Andrew Thompson Apr 08 '11 at 21:07
2

Shouldn't you close the Scanner? – Parth Mehrotra May 20 '15 at 20:32
I suppose - I wasn't meaning to write a complete example here. – Amir Afghani May 20 '15 at 20:43
What if I want to do that for a file on the internet? – It's Willem Nov 01 '16 at 21:18
Even better with `try (Scanner scanner = new Scanner(file)) {` and specifying the file encoding. – Emmanuel Bourg Dec 14 '16 at 11:40
You might want to close the Scanner again, if you're doing something else with the file, like "creating/destroying" it in some "before/after" method, as part of unit-tests. – DrLime2k10 Dec 14 '17 at 14:56
Would this solution fail if the phrase being searched for spanned multiple lines, though? – KirstieBallance Jan 05 '18 at 00:04

score 19 · Answer 2 · edited May 23 '16 at 15:46

19

Using the Apache Commons IO API https://commons.apache.org/proper/commons-io/ I was able to establish this using FileUtils.readFileToString(file).contains(stringToFind)

The documentation for this function is at https://commons.apache.org/proper/commons-io/javadocs/api-2.4/org/apache/commons/io/FileUtils.html#readFileToString(java.io.File)

edited May 23 '16 at 15:46

LapinoLapidus

13
5

answered Aug 15 '13 at 07:33

MGPJ

1,062
1
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I guess this will read the complete file in memory, whereas the solution of @Amir will not do this? – mvermand Jul 05 '18 at 05:43

score 7 · Answer 3 · edited Jan 14 '20 at 13:06

7

Here is a java 8 method to find a string in a text file:

for (String toFindUrl : urlsToTest) {
        streamService(toFindUrl);
    }

private void streamService(String item) {
        try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
           stream.filter(lines -> lines.contains(item))
                       .forEach(System.out::println);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

edited Jan 14 '20 at 13:06

virender

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answered Jul 18 '17 at 13:27

Amir Amiri

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1
8
14

I'm getting this error `The method foreach(System.out::println) is undefined for the type Stream` – Nasser Jul 16 '19 at 10:54
@Nasser Have you set your jdk to 1.8? I think it's the matter of java version because this feature works on java 1.8 and above. – Amir Amiri Jul 16 '19 at 11:12
This require the pattern to found on the same line. This might not be the case depending on a lot of factors. – patrik Mar 06 '20 at 12:25

Rion Williams · Answer 4 · 2011-04-08T20:38:53.947

When you are reading the file, have you considered reading it line by line? This would allow you to check if your line contains the file as your are reading, and you could then perform whatever logic you needed based on that?

Scanner scanner = new Scanner("Student.txt");
String currentLine;

while((currentLine = scanner.readLine()) != null)
{
    if(currentLine.indexOf("Your String"))
    {
         //Perform logic
    }
}

You could use a variable to hold the line number, or you could also have a boolean indicating if you have passed the line that contains your string:

Scanner scanner = new Scanner("Student.txt");
String currentLine;
int lineNumber = 0;
Boolean passedLine = false;
while((currentLine = scanner.readLine()) != null)
{
    if(currentLine.indexOf("Your String"))
    {
         //Do task
         passedLine = true;
    }
    if(passedLine)
    {
       //Do other task after passing the line.
    }
    lineNumber++;
}

Let me try that. I'll get back to you. – Joel Sanchez Apr 08 '11 at 20:33 — Joel Sanchez, Apr 08 '11 at 20:33

score 0 · Answer 5 · answered Jun 06 '18 at 12:19

This will find "Mark Sagal" in Student.txt. Assuming Student.txt contains

Student.txt

Amir Amiri
Mark Sagal
Juan Delacruz

Main.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        final String file = "Student.txt";
        String line = null;
        ArrayList<String> fileContents = new ArrayList<>();

        try {
            FileReader fReader = new FileReader(file);
            BufferedReader fileBuff = new BufferedReader(fReader);
            while ((line = fileBuff.readLine()) != null) {
                fileContents.add(line);
            }
            fileBuff.close();
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        System.out.println(fileContents.contains("Mark Sagal"));
    }
}

score -1 · Answer 6 · edited Jul 25 '17 at 07:37

Here is the code of TextScanner

public class TextScanner {

        private static void readFile(String fileName) {
            try {
              File file = new File("/opt/pol/data22/ds_data118/0001/0025090290/2014/12/12/0029057983.ds");
              Scanner scanner = new Scanner(file);
              while (scanner.hasNext()) {
                System.out.println(scanner.next());
              }
              scanner.close();
            } catch (FileNotFoundException e) {
              e.printStackTrace();
            }
          }

          public static void main(String[] args) {
            if (args.length != 1) {
              System.err.println("usage: java TextScanner1"
                + "file location");
              System.exit(0);
            }
            readFile(args[0]);
      }
}

It will print text with delimeters

score -1 · Answer 7 · answered Apr 08 '11 at 20:29

I am doing something similar but in C++. What you need to do is read the lines in one at a time and parse them (go over the words one by one). I have an outter loop that goes over all the lines and inside that is another loop that goes over all the words. Once the word you need is found, just exit the loop and return a counter or whatever you want.

This is my code. It basically parses out all the words and adds them to the "index". The line that word was in is then added to a vector and used to reference the line (contains the name of the file, the entire line and the line number) from the indexed words.

ifstream txtFile;
txtFile.open(path, ifstream::in);
char line[200];
//if path is valid AND is not already in the list then add it
if(txtFile.is_open() && (find(textFilePaths.begin(), textFilePaths.end(), path) == textFilePaths.end())) //the path is valid
{
    //Add the path to the list of file paths
    textFilePaths.push_back(path);
    int lineNumber = 1;
    while(!txtFile.eof())
    {
        txtFile.getline(line, 200);
        Line * ln = new Line(line, path, lineNumber);
        lineNumber++;
        myList.push_back(ln);
        vector<string> words = lineParser(ln);
        for(unsigned int i = 0; i < words.size(); i++)
        {
            index->addWord(words[i], ln);
        }
    }
    result = true;
}

While helpful, the OP was asking for a solution based in Java. C++ file operations are considerably different than file operations in Java, so your answer isn't entirely helpful in this context. — , Jan 09 '15 at 05:10

Method to find string inside of the text file. Then getting the following lines up to a certain limit

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