Rxjava: Exception in thread “main” java.lang.NoClassDefFoundError: org/reactivestreams/Publisher ?

[VeneetReddyK]

While creating a hello world program I got this exception. Here is the code:

import io.reactivex.Observable;
import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;
import io.reactivex.schedulers.Schedulers;

/**
 * Created by veneet on 30/04/17.
 */
public class MainApp {
    public static void main(String[] args) {
        // This is where the exception occurs.
        Observable<String> observable = Observable.create(e -> {
            e.onNext("Hello World!");
            e.onNext("Hello World!");
            e.onNext("Hello World!");
            e.onNext("Hello World!");
            e.onNext("Hello World!");
            e.onNext("Hello World!");

            e.onComplete();
        });
        Observer<String> observer = new Observer<String>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(String s) {
                System.out.println(s);
            }

            @Override
            public void onError(Throwable e) {
                System.err.println(e.getMessage());
            }

            @Override
            public void onComplete() {

            }
        };
        observable.subscribeOn(Schedulers.io());
        observable.subscribe(observer);

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

The build.gradle dependencies are like this:

dependencies {
    compile "io.reactivex.rxjava2:rxjava:2.1.0"
    // https://mvnrepository.com/artifact/org.reactivestreams/reactive-streams
    compile group: 'org.reactivestreams', name: 'reactive-streams', version: '1.0.0.final'
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

The complete stacktrace is like this(I think the first line is totally unrelated, but putting it to ensure):

objc[3423]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/bin/java (0x10b6dc4c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x10d0194e0). One of the two will be used. Which one is undefined.
Exception in thread "main" java.lang.NoClassDefFoundError: org/reactivestreams/Publisher
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at MainApp.main(MainApp.java:11)
Caused by: java.lang.ClassNotFoundException: org.reactivestreams.Publisher
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 13 more

[akarnokd]

Closing as repost of StackOverflow.

Please be patient on Stackoverflow.

[ghost]

@akarnokd I'm totally new java developer, and tried in eclipse Neon.3 Release (4.6.3). With the same exception. I have imported the rxjava-2.1.5.jar file of rxJava. My code is as below:

package rxjavaSample;

import java.util.Arrays;
import java.util.List;

import org.junit.Test;

import io.reactivex.Observable;

public class Rxjava1Junit {

    //@Test
    public void test() {
        Observable> t = createMyOb();
        doSubscribe(t);
    }

    // create Observable
    private Observable> createMyOb() {
        return Observable.just(Arrays.asList(new Integer(2), new Integer(5)));
    }

    // subscribe
    private void doSubscribe(Observable> objObservabled) {
        objObservabled.subscribe(i -> i.stream().mapToInt(t -> t.intValue()).forEach(s -> System.out.println(s)));
    }
}

So, what should I to do to fix this exception? Thanks for your help

[akarnokd]

Download and link the reactivestreams-1.0.1.jar from here for example.

[ghost]

@akarnokd Thanks for your quick response, In one word, the two .jar(

rxjava-2.1.5.jar,reactivestreams-1.0.1.jar

) files should be referenced. Am I right?

[akarnokd]

Yes. RxJava 2 has that single dependency which would be resolved by a build system such as Gradle, or when you ask IntelliJ to add a Maven-based library dependency. With manual projects, you have to discover and download the dependencies yourself.

[ghost]

OK, I see. Thank you so much for your help.

[wqycsu]

@akarnokd Why RxJava build the reactivestreams as a separated library?

[akarnokd]

Reactive Streams is a separate industry standard library. It is maintained by different people in a different repository.