如何检查args [0]是否是普通字符串而不是不存在的文件？

I'm writing a program that expects an argument which can be both a file and a normal String argument. If it is a file, then I want to read the content of the file, if it is a String, I want to read the String.

我正在编写一个程序,它需要一个可以是文件和普通String参数的参数。如果是文件,那么我想读取文件的内容,如果是String,我想读取String。

The only idea I came up with is doing something like:

我想出的唯一想法就是:

File file = new File(args[0]);

and then checking whether if ( !file.isDirectory() || !file.isFile() ) and if that's the case, treating args[0] as a String. But if args[0] is a non existing file, like C:/Users/Name/Desktop/nonexistingFile.txt, it treats this argument like a String: "C:/Users/Name/Desktop/nonexistingFile.txt" to work with instead of saying "it's a non existing file".

然后检查是否(!file.isDirectory()||!file.isFile())以及是否是这种情况,将args [0]视为String。但是如果args [0]是一个非现有文件,比如C:/Users/Name/Desktop/nonexistingFile.txt,它会将此参数视为字符串:“C:/Users/Name/Desktop/nonexistingFile.txt”工作而不是说“这是一个不存在的文件”。

How to check if args[0] is a normal String and not a non existing file?

如何检查args [0]是普通字符串而不是非现有文件?

1 个解决方案

#1

If with args you are referring to the String array of your main method, then it is guaranteed to contains no null and every single element is a (proper) String.

如果使用args引用main方法的String数组,则保证不包含null,并且每个元素都是(正确的)String。

However you would need to check whether args length is at least 1 as there is no guarantee that the user would had provided any argument:

但是,您需要检查args长度是否至少为1,因为无法保证用户提供任何参数:

public static void main(String[] args) {
   if (args.length <= 0) {
     // complain no argument was provided?
     return;
   }
   final String myFileName = args[0];
   final File myFile = new File(myFileName);
   if (!myFile.exists()) {
     // complain is not an existing file
   } else if (myFile.isFile()) {
     // handle the case the input file is a regular file.
   } else if (myFile.isDirectory()) {
     // handle the case the input file is in fact a directory
   } else {
     // complain is neither.
     // some operating system may contain other types of devices that are neither
     // files nor directories. so you should deal with such cases gracefully.
   }
}

However, since in practice some other piece of code may call that main method, not just the VM's start-up code perhaps you wanna do the actual check that args is in fact not null nor does it contain null (at least not in args[0]):

但是,因为在实践中,其他一些代码可能会调用该main方法,而不仅仅是VM的启动代码,或许您想要进行实际检查,即args实际上不是null,也不包含null(至少不在args中[ 0]):

public static void main(String[] args) {
   if (args == null) {
     // complain about this unexpected input (return or throw NPE, IAE???)
     throw new IllegalArgumentException(); // in this case IAE.
   } else if (args.length <= 0) {
     // complain no argument was provided?
     return;
   } else if (args[0] == null) {
     // complain about this unexpected input (return or throw NPE, IAE???)
     throw new NullPointerException(); // in this case NPE.
   }
   ...

#1