I know that Mojarra is Eclipse EE4J implementation of the Jakarta Faces specification.
But what about this dependency:
<!-- https://mvnrepository.com/artifact/jakarta.faces/jakarta.faces-api -->
<dependency>
<groupId>jakarta.faces</groupId>
<artifactId>jakarta.faces-api</artifactId>
<version>4.0.0</version>
</dependency>
Obviously it is also an implementation of Jakarta Faces specification implemented by Eclipse EE4J as well:
https://github.com/jakartaee/faces
So, are they same project or not? and what is the difference between them?
Obviously it is also an implementation of Jakarta Faces specification implemented by Eclipse EE4J as well
No, it is not.
Follow the https://mvnrepository.com/artifact/jakarta.faces/jakarta.faces-api link and download the JAR file and inspect its contents using any zip tool. You'll see that it contains only jakarta.* classes. It does not contain classes from the implementation package such as com.sun.faces.* (Mojarra) or org.apache.myfaces.* (MyFaces). In other words, it only contains the API classes not the impl classes.
This JAR file is essentially the "Jakarta Faces specification" part of your first statement:
I know that Mojarra is Eclipse EE4J implementation of the Jakarta Faces specification.
As to,
So, are they same project or not
no, the Mojarra project is here https://github.com/eclipse-ee4j/mojarra and the Mojarra dependency is here:
<!-- https://mvnrepository.com/artifact/org.glassfish/jakarta.faces -->
<dependency>
<groupId>org.glassfish</groupId>
<artifactId>jakarta.faces</artifactId>
<version>4.0.0-M1</version>
</dependency>
Download the JAR file and inspect its contents. You'll see that it contains jakarta.* classes and com.sun.faces.* classes.
what is the difference between them?
The API can be included as <scope>provided</scope> in projects targeting a full fledged Jakarta EE server which already ships with API+impl out the box. You'll then be able to import jakarta.faces.* classes in your code. For those servers, you only need to include the impl (Mojarra or MyFaces) as <scope>provided</scope> if you wish to be able to step through the source code in IDE's debugger and/or if you wish to monkeypatch some implementation classes.
But in barebones servletcontainers such as Tomcat, the API dependency as <scope>compile</scope> won't work because the implementation is missing. You'll need the impl dependency instead.