CODEWITHSUNDEEP
javajava-native-interface
user256717
user256717

Reputation:

Java.library.path setting programmatically

Can I set java.library.path programmatically from java code itself?

The following doesn't work.

    System.setProperty("java.library.path", "/blah");

Upvotes: 17

Views: 15580

Answers (5)

secmask
secmask

Reputation: 8107

Maybe this will help: Setting "java.library.path" programmatically

When messing around with JNI, one has to set the java.library.path accordingly. Unfortunately the only way is to add a system property before the application is started:

java -Djava.library.path=/path/to/libs

Changing the system property later doesn’t have any effect, since the property is evaluated very early and cached. But the guys over at jdic discovered a way how to work around it. It is a little bit dirty – but hey, those hacks are the reason we all love Java…

System.setProperty( "java.library.path", "/path/to/libs" );  
Field fieldSysPath = ClassLoader.class.getDeclaredField( "sys_paths" );  
fieldSysPath.setAccessible( true );  
fieldSysPath.set( null, null );

Explanation

At first the system property is updated with the new value. This might be a relative path – or maybe you want to create that path dynamically.

The Classloader has a static field (sys_paths) that contains the paths. If that field is set to null, it is initialized automatically. Therefore forcing that field to null will result into the reevaluation of the library path as soon as loadLibrary() is called…

Upvotes: 23

MNos
MNos

Reputation: 520

I'm just quoting from the link provided by secmask (https://cedarsoft.com/blog.html), in case the link goes dead:

Changing the system property java.library.path later doesn’t have any effect, since the property is evaluated very early and cached. But the guys over at jdic discovered a way how to work around it. It is a little bit dirty – but hey, those hacks are the reason we all love Java. 

System.setProperty("java.library.path", "/path/to/libs");
Field fieldSysPath = ClassLoader.class.getDeclaredField("sys_paths");
fieldSysPath.setAccessible(true);
fieldSysPath.set(null, null);

Explanation:

At first the system property is updated with the new value. This might be a relative path – or maybe you want to create that path dynamically. The Classloader has a static field (sys_paths) that contains the paths. If that field is set to null, it is initialized automatically.Therefore forcing that field to null will result into the reevaluation of the library path as soon as loadLibrary() is called.

Upvotes: 0

Sunil Gulabani
Sunil Gulabani

Reputation: 29

Yes it will read the Environment Variables. Following is the code for setting the Environment variable using the ini4j.

import java.io.IOException;
import org.ini4j.Reg;


public class SettingWinEnvironmentUsing_ini4j {

    public static void main(String args[])
    {
        System.out.println("Setting System Environment Variables");

        Reg reg = new Reg();
        Reg.Key env = reg.add("HKEY_CURRENT_USER\\Environment");
        env.put("RR_PROPERTY_PATH", "c:\\path");
        try {
            reg.write();
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println(env.get("RR_PROPERTY_PATH"));
    }
}

You can find the ini4j jar at

http://cropforge.org/plugins/scmsvn/viewcvs.php/IAPlugin/lib/ini4j-0.5.2-SNAPSHOT.jar?rev=656&root=icisjavatools&view=log

Upvotes: -1

Sunil Gulabani
Sunil Gulabani

Reputation: 29

import java.util.Map;

public class ReadingEnvironment {

    public static void main(String[] args) {
        System.out.println("Reading System Environment Variables:\n");
        // System.out.println(System.getenv());
        Map<String, String> env = System.getenv();
        for (String envName : env.keySet()) {
            System.out.format("%s=%s%n", envName, env.get(envName));
        }
    }
}

Upvotes: -6

Manuel Selva
Manuel Selva

Reputation: 19050

No you can't. This property is a read only value. You can change it at JVM launchin time with:

-Djava.library.path=your_path

If you want to load a library from a specific location, you can use System.load(libraryPath) instead with the full path to the library.

Upvotes: 19

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