How can I get constant variable from a class inside a jar using java

Question

I need to constant value from a java class but that class in a jar file. How to get that..

java class:

package com.user;
public final class Constants {
private Constants(){}
public static String NAME="name";
}

This class is present under "test.jar". i need to use this name from another repository. I don't want to use the dependency for this jar. I need to use directly.

How do I get this?

Put the Jar in the class path for the project, reference it like any other class `Constants.NAME` — MadProgrammer, Jun 01 '17 at 06:10
I can load the class using URLClassLoader. So like the same way can I get the constants — SST, Jun 01 '17 at 06:21

score 1 · Answer 1 · answered Jun 01 '17 at 07:00

Actually it is really bad practice to do what you want to do. Why define a class but dont want to reference it on a classpath? Then maybe it shouldnt be a class. Also if you have constants like that it should be an enum in 99% of the time. If you REALLY want to do it your way, you still have to load the class manually using a Classloader (see the other comments for this).

But my guess is, you want to do some configuration or something? Then you propably want to use properties. Here is a simple example:

/* You should do real exceptionhandling here */
public static void main(String[] args) throws Exception {

    final Properties config = new Properties();
    try (final FileReader reader = new FileReader("config.properties")) {
        config.load(reader);
    }

    System.out.println(config.getProperty("NAME"));
    System.out.println(config.getProperty("com.stackoverflow.version"));
}

my file "config.propertes" is just a plaintextfile with the content:

# This is a comment
NAME=name
key2=somevalue
com.stackoverflow.version=9.87.6

You can also write a Properties object back into a file. You can use properties for a lot of stuff. Look at the Properties Javadoc for more information.

SST · Accepted Answer · 2017-06-01T07:36:35.497

1

I have fixed this using the following code.

Class.getField("NAME").get(null)

Refer: Accessing Java static final ivar value through reflection

edited Jun 01 '17 at 07:36

answered Jun 01 '17 at 07:23

SST

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How can I get constant variable from a class inside a jar using java

2 Answers2