Java 在文件中查找一行并将其删除

Find a line in a file and remove it

提问by Narek

I'm looking for a small code snippet that will find a line in file and remove that line (not content but line) but could not find. So for example I have in a file following:

我正在寻找一个小的代码片段，它将在文件中找到一行并删除该行（不是内容而是行）但找不到。因此，例如我在以下文件中：

myFile.txt:

我的文件.txt:

aaa
bbb
ccc
ddd

Need to have a function like this: public void removeLine(String lineContent), and if I pass removeLine("bbb"), I get file like this:

需要有这样的函数：public void removeLine(String lineContent)，如果我通过 removeLine("bbb")，我会得到这样的文件：

myFile.txt:

我的文件.txt：

aaa
ccc
ddd

采纳答案by SingleShot

This solution may not be optimal or pretty, but it works. It reads in an input file line by line, writing each line out to a temporary output file. Whenever it encounters a line that matches what you are looking for, it skips writing that one out. It then renames the output file. I have omitted error handling, closing of readers/writers, etc. from the example. I also assume there is no leading or trailing whitespace in the line you are looking for. Change the code around trim() as needed so you can find a match.

这个解决方案可能不是最佳的或漂亮的，但它有效。它逐行读入输入文件，将每一行写入临时输出文件。每当遇到与您要查找的内容相匹配的行时，它就会跳过写出该行。然后重命名输出文件。我在示例中省略了错误处理、关闭读取器/写入器等。我还假设您要查找的行中没有前导或尾随空格。根据需要更改 trim() 周围的代码，以便您可以找到匹配项。

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);

回答by Adam Batkin

You want to do something like the following:

您想要执行以下操作：

• Open the old file for reading
• Open a new (temporary) file for writing
• Iterate over the lines in the old file (probably using a BufferedReader)
  • For each line, check if it matches what you are supposed to remove
  • If it matches, do nothing
  • If it doesn't match, write it to the temporary file
• When done, close both files
• Delete the old file
• Rename the temporary file to the name of the original file

• 打开旧文件进行阅读
• 打开一个新的（临时）文件进行写入
• 迭代旧文件中的行（可能使用BufferedReader）
  • 对于每一行，检查它是否与您应该删除的内容匹配
  • 如果匹配，则不执行任何操作
  • 如果不匹配，则将其写入临时文件
• 完成后，关闭这两个文件
• 删除旧文件
• 将临时文件重命名为原始文件的名称

(I won't write the actual code, since this looks like homework, but feel free to post other questions on specific bits that you have trouble with)

（我不会写实际的代码，因为这看起来像家庭作业，但可以随意发布有关您遇到问题的特定位的其他问题）

回答by Narek

    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();
    }
  }

This I have found on the internet.

这是我在网上找到的。

回答by Altair

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!");
        }
    }

}

回答by Sireesh Yarlagadda

Here is the complete Class. In the below file "somelocation" refers to the actual path of the file.

这是完整的类。在下面的文件中，“某个位置”是指文件的实际路径。

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);
    }

}

回答by Zeze

Using apache commons-io and Java 8 you can use

使用 apache commons-io 和 Java 8，您可以使用

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

回答by iCrazybest

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");
    }
}

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

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

回答by BullyWiiPlaza

This solution requires the Apache Commons IO libraryto be added to the build path. It works by reading the entire file and writing each line back but only if the search term is not contained.

此解决方案需要将Apache Commons IO 库添加到构建路径中。它的工作原理是读取整个文件并将每一行写回，但前提是不包含搜索词。

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();
}

回答by Siddhartha Gupta

I refactored the solution that Narek had to create (according to me) a slightly more efficient and easy to understand code. I used embedded Automatic Resource Management, a recent feature in Java and used a Scanner class which according to me is more easier to understand and use.

我重构了 Narek 必须创建的解决方案（根据我的说法）一个稍微更高效且易于理解的代码。我使用了嵌入式自动资源管理，这是 Java 中的一项最新特性，并使用了一个 Scanner 类，据我说它更容易理解和使用。

Here is the code with edited Comments:

这是带有编辑注释的代码：

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");
        }

    }



}

回答by AMA

Try this:

尝试这个：

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();
}