如何从 txt 文件中读取并根据 Java 中的数字和字符串分隔文本

Question

The program is reading from a text file. Each line of the text file starts with a number from -2 to 2. The number is the then followed by a sentence. Please see below for the first three lines of the txt file:

1 Campanella gets the tone just right -- funny in the middle of sad in the middle of hopeful .
-2 Nothing more than an amiable but unfocused bagatelle that plays like a loosely-connected string of acting-workshop exercises .
1 It 's a sharp movie about otherwise dull subjects .
1 ... it 's as comprehensible as any Dummies guide , something even non-techies can enjoy .
-1 -LRB- Green is -RRB- the comedy equivalent of Saddam Hussein , and I 'm just about ready to go to the U.N. and ask permission for a preemptive strike .

The only lines that should be read are the ones that have a number, one space and then text in that order. The last two lines should not be considered because they have ... and - respectively before the text. The first three sentences are fine however.

I have a class called placeholder with the following fields:

public class placeholder implements Comparable<placeholder> {
    protected int score;
    protected String text;

    public placeholder(int score, String text) {
        this.score = score;
        this.text = text;
    }
}

I would like a method called readFile to go by line by line and store every single line into a list called reviewsDB . Each object in the list will be of type placeholder and the number at the start of the line will by the score value and the following words will be the text value. What code can I put in the following area to break each line up between the number and text?

    public static List<placeholder> readFile(String filename) {

        File movieReviews = new File("reviews.txt");

        try {

            Scanner scanner = new Scanner(movieReviews);
            scanner.nextLine();

            List<placeholder> reviewsDB = new ArrayList<placeholder>();

            while (scanner.hasNextLine()) {
                int sentenceScore = 0;
                String sentenceText = null;

                //code to separate the number and text in each line here
                placeholder newSentence = new placeholder(sentenceScore, sentenceText);

                reviewsDB.add(newSentence);
            }

            return reviewsDB;
        }

        catch (Exception e) {

            System.out.println("Something went wrong");

            return null;
        }

    }

Answer 1

• Read the file into a stream using Files#lines
• Filter the lines which meet your criteria using regex "-?\\d\\s\\w+.*"
• Split each line into two parts using String#split using space as delimeter and limit the resulting array to a length of two line.split("\\s",2)
• Collect the stream to a list of Placeholder objects

Example code:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Example {

    public static void main(String[] args) {
        List<placeholder> list= readFile("path to your file");
        list.forEach(System.out::println);
    }
    public static List<placeholder> readFile(String filename) {
        List<Placeholder> reviewsDB = new ArrayList<>();
        try (Stream<String> content = Files.lines(Paths.get(filename))) {
            reviewsDB = content
                    .filter(line -> line.matches("-?\\d\\s\\w+.*"))
                    .map(line -> line.split("\\s",2))
                    .map(arr -> new placeholder(Integer.parseInt(arr[0]), arr[1]))
                    .collect(Collectors.toList());
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return reviewsDB;
    }
}

Answer 2

You can use regex. It's best to match patterns. You may have n number of characters, positive-negative also. You can add (-|+) if you have + also at the beginning.

Hope you don't have scientific notations.

while (scanner.hasNextLine()) {
    int sentenceScore = 0;
    String sentenceText = null;
    String line = scanner.nextLine();
    Matcher m = p.matcher(line);
    if (m.matches()) {
        System.out.println(m.group(1));
        System.out.println(m.group(2));
    }
    // code to separate the number and text in each line here
    placeholder newSentence = new placeholder(sentenceScore, sentenceText);

    reviewsDB.add(newSentence);
}

I used the below regex

Pattern p = Pattern.compile("^(-?\\d+)(.*)");

- is optional - -? meant this Then one or more digits - \d+

Then the second group is any character after the first group - (.*)

You can play with your inputs here I tested your input here.

Answer 3

You can use Files.readAllLines(Path, Charset) to get a List of Strings representing the content of your file. Then you can iterate through the list and use String.split(Regex, Limit) to split the string in parts. Then you can create a new Placeholder-Object from the parts.

See:

• https://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#readAllLines-java.nio.file.Path-java.nio.charset.Charset-
• https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#split-java.lang.String-int-