如何真正从 Java 中的类路径读取文本文件 [英] How to really read text file from classpath in Java

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本文介绍了如何真正从 Java 中的类路径读取文本文件的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

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:

将文件目录(D:myDir)放在CLASSPATH中,然后尝试以下操作:

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");

将文件的完整路径 (D:myDirSomeTextFile.txt) 放在 CLASSPATH 中并尝试以上 3 行代码.

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

但不幸的是,它们都没有工作,我总是将 null 输入到我的 InputStream in 中.

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

推荐答案

有了类路径上的目录,从同一个类加载器加载的类,你应该能够使用:

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");

如果这些都不起作用,则表明有其他问题.

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

例如,以下面的代码为例:

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);
    }
}

还有这个目录结构:

code
    dummy
          Test.class
txt
    SomeTextFile.txt

然后(在 Linux 机器上使用 Unix 路径分隔符):

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

java -classpath code:txt dummy.Test

结果:

true
true

这篇关于如何真正从 Java 中的类路径读取文本文件的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!

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