如何在 grails 中运行 Java 程序

Question

I am so confused on this .... I have a Java application that I have written and want to run it in grails.

I found this article ( How to run java programs in grails? ) and I am confused about the solution that was approved.

1. Do i need to make a controller first?
2. Do i have to import my java class files from my java application in the controller?
3. do i create ANOTHER controller inside src/java and then call the second controller (inside src/java) from the controller in the /project_name/Controllers folder??

I just need some clarity.

Thanks!

UPDATE:

Okay -- I made my project and then put in a contraller and put my java files in src/jave. I have one controller file and this is what it is (and this is the code in my controller):

//package mttestbox
import mttestbox.MTBoxController
//import MTInit

class MTBoxController {

    def index() 
    { 
        MTInit.main(RunMT_GUI)
    }
}

I am getting the following error (and it is not a surprise because I am so confused):

URI:/MTTestBox/MTBox/index
Class: groovy.lang.MissingPropertyException
Message: No such property: MTInit for class: mttestbox.MTBoxController

What did I do wrong???

Thanks!!

Answer 1

Agree with everything said so far but want to mention, without being certain what the OP's true intent is, that grails jobs might be what you want. They're processes that are run on a timer using Quartz, so if you're just looking to run something on the server periodically, without any web interaction, you could go that route.

Answer 2

First, Grails is used to create web based applications, so you will need a controller that will respond to your browser request.

Secondly, if your controller is in a different package than the class of your Java program that has your public static void main(String[] args) method then you will need to import that class into your controller.

Finally, you do not need to create another controller inside src/java . Controllers exist within the grails-app/controllers directory structure.

Following the instructions provided in the linked post in your question should give you all you need to accomplish calling your Java program from a Grails controller.

Answer 3

I found the answer. I found out that you have to put the groovy controller package declaration in the java class files(s).

package <groovy controller name>;

once that is done, the import can then be used in the controller. Once i did this, i was able to fire up grails and goto the default page and then, my app ran on my machine as an executable from a web call in grails (i did a /WEB-INF/grails-app/views/XXX/index.gsp not found error, but I think that because I have not made any GSPs yet (???).

Here is neat trick (found this using NetBeans): if you have more than one Java class file: 1. edit one of them by adding the groovy controller package name. 2. Save jave file. 3. Highlight all java class files needed (including the one that was edited in step 1). 4. move them to Java Source Packages folder in grails project. 5. when promted tell the IDE to move them. 6. When promted tell the IDE to Refactor.

Makes all the edits in all the needed files for you. Then - run and see what happens!!!

Thanks everyone!!!

ironmantis7x

Answer 4

In grails 3 you have to put your java program in src/main/groovy

create a package "hello" inside src/main/groovy

package hello;

class HelloWorld {
      public static void main(String arg[]){ 

      System.out.println("running java program in grails 3");

      }
}

Now you just have to import hello.* in the controller and call the method inside index() method

def index(){
HelloWorld.main()
}

This should work.