Can you tell on runtime if you're running java from within a jar?

Question

I have an application that some of my users run from Eclipse, and others run it by using a jar file.

I want some actions to be done when running from within the jar,

Answer 1

I have two better solutions. first:

URL url = this.getClass().getClassLoader().getResource("input.txt");
URLConnection urlConnection = url.openConnection();
if (urlConnection instanceof JarURLConnection) {
    // run in jar
} else {
    // run in ide
}

second:

String protocol = this.getClass().getResource("").getProtocol();
if(Objects.equals(protocol, "jar")){
    // run in jar
} else if(Objects.equals(protocol, "file")) {
    // run in ide
}

Answer 2

Here is some code you can run from a normally or as a jar.

import java.applet.Applet;
import java.net.URL;
import java.security.CodeSource;

public class TestApplet extends Applet {

    public TestApplet(){    
        URL path = TestApplet.class.getResource("TestApplet.class");

        if(path.toString().startsWith("jar:"))
            System.out.println("I'm in a jar");
        else
            System.out.println("I'm not in a jar");
    }

    public static void main(String args[]) throws Exception{
        new TestApplet();
    }
}

To put it in a jar and run it use the following:

jar cf test.jar TestApplet.class
java -cp test.jar TestApplet

Answer 3

You could check the system class path property for the Equinox launcher:

if (System.getProperty("java.class.path").contains("org.eclipse.equinox.launcher")) {
    System.out.println("You're running inside Eclipse");
}

There are some other potential properties that you may check for, which you can find in Eclipse through Help -> About -> Configuration Details.

Jon's answer is good if you want to know whether you'r running from a JAR versus running from a bunch of class files. But if you use a JAR in both cases then it won't tell you what you need.

Answer 4

Well, you can tell whether or not a class has been loaded from a JAR file - use Foo.class.getResource("Foo.class") and see whether the returned URL begins with "jar:"

For example, take this program:

public class Foo {

    public static void main(String[] args) {
        System.out.println(Foo.class.getResource("Foo.class"));
    }
}

Running it loading the file from the file system:

file:/C:/Users/Jon/Test/com/whatever/Foo.class

Running it from a jar file:

jar:file:/C:/Users/Jon/Test/foo.jar!/com/whatever/Foo.class

Answer 5

Another approach is putting information in the manifest file, and testing for if that information is available at runtime.

If it is, then the code was started with "-jar". Otherwise it was started in another way, e.g. directly from Eclipse.

Answer 6

You could try:

boolean inJar = false;

try
{
  CodeSource cs = DataResolver.class.getProtectionDomain().getCodeSource();
  inJar = cs.getLocation().toURI().getPath().endsWith(".jar");
}
catch (URISyntaxException e)
{
e.printStackTrace();
}

If you're running from a jar file then cs.getLocation().toURI() will give you the URI of that file; if you're running from inside Eclipse then it'll probably be the path to directory containing your class files.