java - 从文本文件中删除特定行

Question

我试图从文件中删除特定行。但是我在从文本文件中删除特定行时遇到问题。比方说，我想在以下文件中删除 Blueberry 的文本文件:

旧列表文本文件:

Chocolate
Strawberry
Blueberry
Mango

新列表文本文件:

Chocolate
Strawberry
Mango

我尝试运行我的 Java 程序，当我输入删除时，它没有从文本文件中删除该行。

输出:请删除:d蓝莓删除:蓝莓

当我打开我的文本文件时，它只循环显示“Blueberry”这个词。

文本文件:

Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry

我的问题是如何从文本文件中删除特定行？

这是我的 Java 代码:

String input="Please delete: ";
System.out.println(input);

try
        {        
            BufferedReader reader = new BufferedReader
                    (new InputStreamReader (System.in));
            line = reader.readLine();

            String inFile="list.txt";
            String line = "";


            while(!line.equals("x"))
            { 
                switch(line)
                {                   

                    case "d":

                    line = reader.readLine();
                    System.out.println("Remove: " + line);
                    String lineToRemove="";

                    FileWriter removeLine=new FileWriter(inFile);
                    BufferedWriter change=new BufferedWriter(removeLine);
                    PrintWriter replace=new PrintWriter(change);

                    while (line != null) {
                       if (!line.trim().equals(lineToRemove))
                       {
                             replace.println(line);
                             replace.flush();
                       }   
                    }
                    replace.close();
                    change.close();
                    break;

                }
                System.out.println(input);
                line = reader.readLine();  


            }

        }
        catch(Exception e){
            System.out.println("Error!");
        }

Answer 1

让我们快速看一下您的代码...

line = reader.readLine();
//...
while (line != null) {
   if (!line.trim().equals(lineToRemove))
   {
         replace.println(line);
         replace.flush();
   }   
}

基本上，您读取文件的第一行，然后反复将其与 lineToRemove 进行比较，直到永远。这个循环永远不会退出

这是一个概念验证，您需要根据需要对其进行修改。

基本上，您需要确保自己正在做的是，您正在读取输入文件的每一行，直到没有更多行为止

// All the important information
String inputFileName = "...";
String outputFileName = "...";
String lineToRemove = "...";
// The traps any possible read/write exceptions which might occur
try {
    File inputFile = new File(inputFileName);
    File outputFile = new File(outputFileName);
    // Open the reader/writer, this ensure that's encapsulated
    // in a try-with-resource block, automatically closing
    // the resources regardless of how the block exists
    try (BufferedReader reader = new BufferedReader(new FileReader(inputFile));
             BufferedWriter writer = new BufferedWriter(new FileWriter(outputFile))) {
        // Read each line from the reader and compare it with
        // with the line to remove and write if required
        String line = null;
        while ((line = reader.readLine()) != null) {
            if (!line.equals(lineToRemove)) {
                writer.write(line);
                writer.newLine();
            }
        }
    }

    // This is some magic, because of the compounding try blocks
    // this section will only be called if the above try block
    // exited without throwing an exception, so we're now safe
    // to update the input file

    // If you want two files at the end of his process, don't do
    // this, this assumes you want to update and replace the 
    // original file

    // Delete the original file, you might consider renaming it
    // to some backup file
    if (inputFile.delete()) {
        // Rename the output file to the input file
        if (!outputFile.renameTo(inputFile)) {
            throw new IOException("Could not rename " + outputFileName + " to " + inputFileName);
        }
    } else {
        throw new IOException("Could not delete original input file " + inputFileName);
    }
} catch (IOException ex) {
    // Handle any exceptions
    ex.printStackTrace();
}

看看Basic I/O和 The try-with-resources Statement了解更多详情