Question

因此，以下程序应将输入和输出文件作为命令行参数。

class FileCopy
{
public static void main(String[] args) throws IOException
{
    String infile = null;
    String outfile = null;
    BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));    

    if (args.length >= 2) //both files given via command line
    {
        infile = args[0];
        if (fileExists(infile) == false)
        {
            infile = getInputFile();
        }
        outfile = args[1];
    }
    else if (args.length == 1) //input file given via command line
    {
        infile = args[0];
        outfile = getOutputFile(infile);
    }
    else //no files given on command line
    {
        infile = getInputFile();
        outfile = getOutputFile(infile);
    }

    //create file objects to use
    File in = new File(infile);
    File out = new File(outfile);

    /*
     *rest of code
     */
}

//get the input file from the user if given file does not exist
public static String getInputFile() //throws IOException
{
    BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
    String fileName = null;
    boolean haveFile = false;

    while(haveFile == false)
    {
        System.out.println("Enter a valid filename for input:");
        System.out.print(">> ");
        try
        {
            fileName = stdin.readLine();
        }
        catch (IOException e)
        {
            System.out.println("Caught exception: " + e);
        }
        haveFile = fileExists(fileName);
    }

    return fileName;    
}

//get the output file and test things
public static String getOutputFile(String infile)
{
    BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
    File input = new File(infile);
    String filename = null;
    boolean more = true;
    while(more)
    {
        System.out.println("Enter a valid filename for output:");
        System.out.print(">> ");
        try
        {
            filename = stdin.readLine();
        }
        catch (IOException e)
        {
            System.out.println("Caught exception: " + e);
        }
        File output = new File(filename);
        if (output.exists())
        {
            more = false;
        }
        if (filename == infile)
        {
            int selection;
            String inputString = null;

            System.out.println("The output file given matches the input file. Please choose an option:");
            System.out.println("1) Enter new filename");
            System.out.println("2) Overwrite existing file");
            System.out.println("3) Backup existing file");
            System.out.print(">> ");
            try
            {
                inputString = stdin.readLine();
            }
            catch (IOException e)
            {
                System.out.println("Caught exception: " + e);
            }
            selection = Integer.valueOf(inputString);
            switch (selection)
            {
                case 1: //new filename
                case 2: //overwrite
                case 3: //backup
                default: System.exit(0);
            }
        }
    }
    return null;
}

//check the given file to see if it exists in the current working directory
public static boolean fileExists(String n)
{
    return (new File(n)).exists();
}
}

Answer 1

我相信你错过了一个细节：

当你的程序只有一个参数（args.length == 1）时，即只定义输入文件时，根本不会调用fileExists(); infile设置为args[0]，根本没有验证。您应该像对两参数案例一样添加特定的检查。

Answer 2

我也遇到过类似的问题。我在eclipse下工作，不得不在我的当前目录中指定“src / file.txt”，在src目录中有一个名为“file”的文件。

注意：它没有命名为“file.txt”（这会导致字符串被解释为“file.txt.txt”！）。

假设您的“src”目录中有一个名为“file”的文件，请尝试对此程序进行测试：

import java.io.File;

public class FileChecker {

public static boolean Exists( String file ) 
{ 
    System.out.println("File being checked: " + file);
    return( (file.length()) > 0 && (new File(file).exists()) );
}

public static void main( String[] args ) 
{
    File dir = new File("src");

    System.out.println("List of files in source directory: ");
    if( dir.isDirectory()){
        File[] filenames = dir.listFiles();
        for( Object file : filenames ) {
            System.out.println(file.toString());
        }

    }
    else
        System.out.println("Directory does not exist.");

    if(FileChecker.Exists("src/file.txt"))
        System.out.println("File exists");
    else
        System.out.println("File does not exist");
}

}

它将打印出源目录中的当前文件，以便您可以查看文件是否确实存在，然后您可以测试它是否确实存在。适用于我。

检查java中是否存在文件

2 个答案: