Convert .Java file to .Smali file

You can compile the java classes using a normal java compiler, and then use Android's 'dx' utility to convert the compiled .class files to a dex file. And then run baksmali on the dex file to produce the smali files.

For example, let's say you have the following code in a java file named "HelloWorld.java":

public class HelloWorld {
    public static void main(String[] args) {
         System.out.println("Hello World!");
    }
}

To convert it to smali:

javac HelloWorld.java
dx --dex --output=classes.dex HelloWorld.class
baksmali d classes.dex

Try java2smali: https://github.com/ollide/intellij-java2smali

It is an application used to convert Java to Smali.