在文件中找到一行並將其刪除

Question

我正在尋找一個小代碼片段，它將在文件中找到一行並刪除該行（不是內容但行），但無法找到。因此，例如我有一個文件如下：

MYFILE.TXT：

aaa 
bbb 
ccc 
ddd 

需要有這樣的功能：public void removeLine(String lineContent)，如果我通過 removeLine("bbb")，我得到的文件是這樣的：

MYFILE.TXT：

aaa 
ccc 
ddd 

Answer 1

此解決方案可能不是最佳或漂亮的，但它的工作原理。它逐行讀入輸入文件，將每行寫入臨時輸出文件。每當它遇到一條與你正在尋找的線相匹配的線時，它就會跳過寫出一條線。然後重命名輸出文件。我從示例中省略了錯誤處理，關閉了讀者/作者等。我也假設你正在尋找的行中沒有前導空白或尾隨空白。根據需要更改trim（）的代碼，以便找到匹配項。

File inputFile = new File("myFile.txt"); 
File tempFile = new File("myTempFile.txt"); 

BufferedReader reader = new BufferedReader(new FileReader(inputFile)); 
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile)); 

String lineToRemove = "bbb"; 
String currentLine; 

while((currentLine = reader.readLine()) != null) { 
    // trim newline when comparing with lineToRemove 
    String trimmedLine = currentLine.trim(); 
    if(trimmedLine.equals(lineToRemove)) continue; 
    writer.write(currentLine + System.getProperty("line.separator")); 
} 
writer.close(); 
reader.close(); 
boolean successful = tempFile.renameTo(inputFile); 

Answer 2

你想這樣做了以下內容：閱讀

打開一個新的（臨時）

• 打開舊文件的文件在舊跨越的行書寫
• 迭代文件（可能使用的是BufferedReader）
  • 對於每一行，檢查它是否與你應該刪除的內容相匹配
  • 如果匹配，什麼都不做
  • 如果不匹配，將其寫入臨時文件
• 完成後，關閉這兩個文件
• 刪除舊文件
• 重命名臨時文件到原始文件的名稱

（我不會寫實際的代碼，因爲這看起來像家庭作業，但隨時可以發佈其他問題在您遇到麻煩的特定位上）

Answer 3

public void removeLineFromFile(String file, String lineToRemove) { 

    try { 

     File inFile = new File(file); 

     if (!inFile.isFile()) { 
     System.out.println("Parameter is not an existing file"); 
     return; 
     } 

     //Construct the new file that will later be renamed to the original filename. 
     File tempFile = new File(inFile.getAbsolutePath() + ".tmp"); 

     BufferedReader br = new BufferedReader(new FileReader(file)); 
     PrintWriter pw = new PrintWriter(new FileWriter(tempFile)); 

     String line = null; 

     //Read from the original file and write to the new 
     //unless content matches data to be removed. 
     while ((line = br.readLine()) != null) { 

     if (!line.trim().equals(lineToRemove)) { 

      pw.println(line); 
      pw.flush(); 
     } 
     } 
     pw.close(); 
     br.close(); 

     //Delete the original file 
     if (!inFile.delete()) { 
     System.out.println("Could not delete file"); 
     return; 
     } 

     //Rename the new file to the filename the original file had. 
     if (!tempFile.renameTo(inFile)) 
     System.out.println("Could not rename file"); 

    } 
    catch (FileNotFoundException ex) { 
     ex.printStackTrace(); 
    } 
    catch (IOException ex) { 
     ex.printStackTrace(); 
    } 
    } 

這是我在網上找到的。

Answer 4

public static void deleteLine(String line, String filePath) { 

    File file = new File(filePath); 

    File file2 = new File(file.getParent() + "\\temp" + file.getName()); 
    PrintWriter pw = null; 
    Scanner read = null; 

    FileInputStream fis = null; 
    FileOutputStream fos = null; 
    FileChannel src = null; 
    FileChannel dest = null; 

    try { 


     pw = new PrintWriter(file2); 
     read = new Scanner(file); 

     while (read.hasNextLine()) { 

      String currline = read.nextLine(); 

      if (line.equalsIgnoreCase(currline)) { 
       continue; 
      } else { 
       pw.println(currline); 
      } 
     } 

     pw.flush(); 

     fis = new FileInputStream(file2); 
     src = fis.getChannel(); 
     fos = new FileOutputStream(file); 
     dest = fos.getChannel(); 

     dest.transferFrom(src, 0, src.size()); 


    } catch (IOException e) { 
     e.printStackTrace(); 
    } finally {  
     pw.close(); 
     read.close(); 

     try { 
      fis.close(); 
      fos.close(); 
      src.close(); 
      dest.close(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 

     if (file2.delete()) { 
      System.out.println("File is deleted"); 
     } else { 
      System.out.println("Error occured! File: " + file2.getName() + " is not deleted!"); 
     } 
    } 

} 

Answer 5

這裏是完整的類。在下面的文件中，「somelocation」指的是文件的實際路徑。

import java.io.BufferedReader; 
import java.io.BufferedWriter; 
import java.io.File; 
import java.io.FileReader; 
import java.io.FileWriter; 
import java.io.IOException; 



public class FileProcess 
{ 


    public static void main(String[] args) throws IOException 
    { 
     File inputFile = new File("C://somelocation//Demographics.txt"); 
     File tempFile = new File("C://somelocation//Demographics_report.txt"); 

     BufferedReader reader = new BufferedReader(new FileReader(inputFile)); 
     BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile)); 

     String currentLine; 

     while((currentLine = reader.readLine()) != null) { 
      if(null!=currentLine && !currentLine.equalsIgnoreCase("BBB")){ 
       writer.write(currentLine + System.getProperty("line.separator")); 
      } 
     } 
     writer.close(); 
     reader.close(); 
     boolean successful = tempFile.renameTo(inputFile); 
     System.out.println(successful); 
    } 

} 

Answer 6

使用Apache的commons-IO和Java 8，你可以使用

List<String> lines = FileUtils.readLines(file); 
List<String> updatedLines = lines.stream().filter(s -> !s.contains(searchString)).collect(Collectors.toList()); 
FileUtils.writeLines(file, updatedLines, false); 

Answer 7

package com.ncs.cache; 

import java.io.BufferedReader; 
import java.io.FileReader; 
import java.io.File; 
import java.io.FileWriter; 
import java.io.FileNotFoundException; 
import java.io.IOException; 
import java.io.PrintWriter; 

public class FileUtil { 

    public void removeLineFromFile(String file, String lineToRemove) { 

     try { 

      File inFile = new File(file); 

      if (!inFile.isFile()) { 
       System.out.println("Parameter is not an existing file"); 
       return; 
      } 

      // Construct the new file that will later be renamed to the original 
      // filename. 
      File tempFile = new File(inFile.getAbsolutePath() + ".tmp"); 

      BufferedReader br = new BufferedReader(new FileReader(file)); 
      PrintWriter pw = new PrintWriter(new FileWriter(tempFile)); 

      String line = null; 

      // Read from the original file and write to the new 
      // unless content matches data to be removed. 
      while ((line = br.readLine()) != null) { 

       if (!line.trim().equals(lineToRemove)) { 

        pw.println(line); 
        pw.flush(); 
       } 
      } 
      pw.close(); 
      br.close(); 

      // Delete the original file 
      if (!inFile.delete()) { 
       System.out.println("Could not delete file"); 
       return; 
      } 

      // Rename the new file to the filename the original file had. 
      if (!tempFile.renameTo(inFile)) 
       System.out.println("Could not rename file"); 

     } catch (FileNotFoundException ex) { 
      ex.printStackTrace(); 
     } catch (IOException ex) { 
      ex.printStackTrace(); 
     } 
    } 

    public static void main(String[] args) { 
     FileUtil util = new FileUtil(); 
     util.removeLineFromFile("test.txt", "bbbbb"); 
    } 
} 

源：http://www.javadb.com/remove-a-line-from-a-text-file/

Answer 8

這種解決方案需要被添加到構建路徑的Apache Commons IO library。它通過讀取整個文件並將每行寫回，但只有在不包含搜索項時才起作用。

public static void removeLineFromFile(File targetFile, String searchTerm) 
     throws IOException 
{ 
    StringBuffer fileContents = new StringBuffer(
      FileUtils.readFileToString(targetFile)); 
    String[] fileContentLines = fileContents.toString().split(
      System.lineSeparator()); 

    emptyFile(targetFile); 
    fileContents = new StringBuffer(); 

    for (int fileContentLinesIndex = 0; fileContentLinesIndex < fileContentLines.length; fileContentLinesIndex++) 
    { 
     if (fileContentLines[fileContentLinesIndex].contains(searchTerm)) 
     { 
      continue; 
     } 

     fileContents.append(fileContentLines[fileContentLinesIndex] + System.lineSeparator()); 
    } 

    FileUtils.writeStringToFile(targetFile, fileContents.toString().trim()); 
} 

private static void emptyFile(File targetFile) throws FileNotFoundException, 
     IOException 
{ 
    RandomAccessFile randomAccessFile = new RandomAccessFile(targetFile, "rw"); 

    randomAccessFile.setLength(0); 
    randomAccessFile.close(); 
} 

Answer 9

我重構是Narek必須創建（據我）一個稍微更有效，更容易理解的代碼的解決方案。我使用了嵌入式自動資源管理，它是Java中的一項新功能，並使用了一個Scanner類，根據我的理解和使用，該類更容易理解。

下面是編輯點評代碼：

public class RemoveLineInFile { 

    private static File file; 

    public static void main(String[] args) { 
     //create a new File 
     file = new File("hello.txt"); 
     //takes in String that you want to get rid off 
     removeLineFromFile("Hello"); 
    } 


    public static void removeLineFromFile(String lineToRemove) { 


     //if file does not exist, a file is created 

      if (!file.exists()) { 
       try { 
        file.createNewFile(); 
       } catch (IOException e) { 
        System.out.println("File "+file.getName()+" not created successfully"); 
       } 
      } 

      // Construct the new temporary file that will later be renamed to the original 
      // filename. 
      File tempFile = new File(file.getAbsolutePath() + ".tmp"); 

      //Two Embedded Automatic Resource Managers used 
      // to effectivey handle IO Responses 
      try(Scanner scanner = new Scanner(file)) { 
       try (PrintWriter pw = new PrintWriter(new FileWriter(tempFile))) { 

        //a declaration of a String Line Which Will Be assigned Later 
        String line; 

        // Read from the original file and write to the new 
        // unless content matches data to be removed. 
        while (scanner.hasNextLine()) { 
         line = scanner.nextLine(); 
         if (!line.trim().equals(lineToRemove)) { 

          pw.println(line); 
          pw.flush(); 
         } 
        } 
        // Delete the original file 
        if (!file.delete()) { 
         System.out.println("Could not delete file"); 
         return; 
        } 

        // Rename the new file to the filename the original file had. 
        if (!tempFile.renameTo(file)) 
         System.out.println("Could not rename file"); 
       } 
      } 
     catch (IOException e) 
     { 
      System.out.println("IO Exception Occurred"); 
     } 

    } 



} 

Answer 10

試試這個：

public static void main(String[] args) throws IOException { 

    File file = new File("file.csv"); 

    CSVReader csvFileReader = new CSVReader(new FileReader(file)); 

    List<String[]> list = csvFileReader.readAll(); 

    for (int i = 0; i < list.size(); i++) { 
     String[] filter = list.get(i); 
     if (filter[0].equalsIgnoreCase("bbb")) { 
      list.remove(i); 
     } 
    } 
    csvFileReader.close(); 
    CSVWriter csvOutput = new CSVWriter(new FileWriter(file)); 

    csvOutput.writeAll(list); 
    csvOutput.flush(); 

    csvOutput.close(); 
} 

Answer 11

public static void deleteLine() throws IOException { 
     RandomAccessFile file = new RandomAccessFile("me.txt", "rw"); 
     String delete; 
     String task=""; 
     byte []tasking; 
     while ((delete = file.readLine()) != null) { 
      if (delete.startsWith("BAD")) { 
       continue; 
      } 
      task+=delete+"\n"; 
     } 
     System.out.println(task); 
     BufferedWriter writer = new BufferedWriter(new FileWriter("me.txt")); 
     writer.write(task); 
     file.close(); 
     writer.close(); 
    } 

Answer 12

所以，每當我聽到有人提到，他們希望過濾掉的文字，我立刻想到去Streams（主要是因爲有一種方法稱爲filter，它按照您的需要進行過濾）。另一個答案提及使用Stream s的Apache的公地IO庫，但我認爲這將是值得的，以顯示如何在標準Java 8.這是最簡單的形式來完成：

public void removeLine(String lineContent) throws IOException 
{ 
    File file = new File("myFile.txt"); 
    List<String> out = Files.lines(file.toPath()) 
         .filter(line -> !line.contains(lineContent)) 
         .collect(Collectors.toList()); 
    Files.write(file.toPath(), out, StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING); 
} 

我認爲有ISN這裏沒有太多的解釋，基本上Files.lines得到Stream<String>的文件行，filter拿出我們不想要的行，然後collect把新文件的所有行放入List。然後，我們使用附加選項TRUNCATE在現有文件頂部的Files.write上編寫列表，以替換文件的舊內容。

當然，這種方法將每一行加載到內存中都是不利的，因爲它們在被寫回前都被存儲到List中。如果我們想幹脆不保存修改，我們就需要通過流使用某種形式的OutputStream每一個新的行寫入一個文件，因爲它傳遞，就像這樣：

public void removeLine(String lineContent) throws IOException 
{ 
    File file = new File("myFile.txt"); 
    File temp = new File("_temp_"); 
    PrintWriter out = new PrintWriter(new FileWriter(temp)); 
    Files.lines(file.toPath()) 
     .filter(line -> !line.contains(lineContent)) 
     .forEach(out::println); 
    out.flush(); 
    out.close(); 
    temp.renameTo(file); 
} 

沒有太多在這被改變例。基本上，我們不使用collect來將文件內容收集到內存中，而是使用forEach，以使通過filter的每一行都被髮送到PrintWriter，以便立即寫入到文件中而不存儲。我們必須將它保存到一個臨時文件中，因爲我們無法同時覆蓋現有文件，因爲我們仍然在讀取它，所以最後我們重命名臨時文件以替換現有文件。