java - 仅过滤大型 txt 文件中的可读字符

Question

我有一个很大的 .txt 文件，其中充满了可读和不可读的字符。我正在尝试创建一个 Java 程序，该程序可以创建一个新的 .txt 文件，其中仅包含先前 .txt 文件中的可读字符。请帮助我做到这一点。任何代码将不胜感激。我是 Java 新手。

Answer 1

如果“可读”表示从“a”到“z”以及从“1”到“9”的所有字符然后你可以使用正则表达式过滤掉它们，如下所示:

public static String removeSpecialCharacters(String sentence) {
    //StringBuilder container to store all the data in
    StringBuilder stringB = new StringBuilder();
    //loop trough all the characters from the sentence
    for (char c : sentence.toCharArray()) {
        //only store characters that are equal to the below values
        if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == ' ' ) {
            stringB.append(c);
        }
    }
    return stringB.toString().toLowerCase();
}

您可以使用返回类型(字符串)追加到新的 .txt 容器中。比方说，对于您从旧文件中读取的每一行，通过removeSpecialCharacters() 方法循环并使用返回值并将其附加到新的 .txt 文件中。

如果我们读 standard java doc在读/写文件时，我们可以编译以下代码:

import static java.nio.file.StandardOpenOption.*;
import java.nio.file.*;
import java.io.*;


public class Main {

    public static void main(String[] args) {

        readFromFile();

    }

    private static void writeToFile(String line) {
        // Convert the string to a
        // byte array.
        byte data[] = removeSpecialCharacters(line).getBytes();
        Path p = Paths.get("/home/user/Desktop/outFile.txt");

        try (OutputStream out = new BufferedOutputStream(Files.newOutputStream(p, CREATE, APPEND))) {
            out.write(data, 0, data.length);
        } catch (IOException x) {
            System.err.println(x);
        }    
    }

    private static void readFromFile() {
        Path file = Paths.get("/home/user/Desktop/inFile.txt");
        try (InputStream in = Files.newInputStream(file);
            BufferedReader reader =
              new BufferedReader(new InputStreamReader(in))) {
            String line = null;
            while ((line = reader.readLine()) != null) {
                writeToFile(line +"\n");
            }
        } catch (IOException x) {
            System.err.println(x);
        }
    }

    public static String removeSpecialCharacters(String sentence) {
        //StringBuilder container to store all the data in
        StringBuilder stringB = new StringBuilder();
        //loop trough all the characters from the sentence
        for (char c : sentence.toCharArray()) {
            //only store characters that are equal to the below values
            if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == ' ' ) {
                stringB.append(c);
            }
        }
        return stringB.toString().toLowerCase();
    }
}