如何在Java中从类路径中真正读取文本文件 [英] How to really read text file from classpath in Java

问题描述

我正在尝试读取在CLASSPATH系统变量中设置的文本文件。不是用户变量。

I am trying to read a text file which is set in CLASSPATH system variable. Not a user variable.

我正在尝试获取文件的输入流，如下所示：

I am trying to get input stream to the file as below:

放置在CLASSPATH中的文件目录（ D：\ myDir ）并尝试以下内容：

Place the directory of file (D:\myDir)in CLASSPATH and try below:

InputStream in = this.getClass().getClassLoader().getResourceAsStream("SomeTextFile.txt");
InputStream in = this.getClass().getClassLoader().getResourceAsStream("/SomeTextFile.txt");
InputStream in = this.getClass().getClassLoader().getResourceAsStream("//SomeTextFile.txt");

放置文件的完整路径（ D：\ myDir \ SomeTextFile。 CLASSPATH中的txt ）并尝试上面3行代码。

Place full path of file (D:\myDir\SomeTextFile.txt)in CLASSPATH and try the same above 3 lines of code.

但不幸的是，他们中的任何一个都在工作，我总是得到 null 进入我的InputStream 。

But unfortunately NONE of them are working and I am always getting null into my InputStream in.

推荐答案

使用类路径上的目录，从同一个类加载器加载的类中，你应该能够使用以下任何一个：

With the directory on the classpath, from a class loaded by the same classloader, you should be able to use either of:

// From ClassLoader, all paths are "absolute" already - there's no context
// from which they could be relative. Therefore you don't need a leading slash.
InputStream in = this.getClass().getClassLoader()
                                .getResourceAsStream("SomeTextFile.txt");
// From Class, the path is relative to the package of the class unless
// you include a leading slash, so if you don't want to use the current
// package, include a slash like this:
InputStream in = this.getClass().getResourceAsStream("/SomeTextFile.txt");

如果这些不起作用，则表明还有其他问题。

If those aren't working, that suggests something else is wrong.

例如，请使用以下代码：

So for example, take this code:

package dummy;

import java.io.*;

public class Test
{
    public static void main(String[] args)
    {
        InputStream stream = Test.class.getResourceAsStream("/SomeTextFile.txt");
        System.out.println(stream != null);
        stream = Test.class.getClassLoader().getResourceAsStream("SomeTextFile.txt");
        System.out.println(stream != null);
    }
}

此目录结构：

code
    dummy
          Test.class
txt
    SomeTextFile.txt

然后（使用Unix路径分隔符，因为我在Linux机器上）：

And then (using the Unix path separator as I'm on a Linux box):

java -classpath code:txt dummy.Test

结果：

true
true

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