javax.ws.rs.ProcessingException: RESTEASY004655: Unable to invoke request

I'm trying, as a client, to post a zip file to a "Restservice", using RestEasy 3.0.19. This is the code:

public void postFileMethod(String URL)  {       
         Response response = null;              
         ResteasyClient client = new ResteasyClientBuilder().build();
         ResteasyWebTarget target = client.target(URL); 

         MultipartEntityBuilder entityBuilder = MultipartEntityBuilder.create();

         FileBody fileBody = new FileBody(new File("C:/sample/sample.zip"), 
ContentType.MULTIPART_FORM_DATA);              

         entityBuilder.addPart("my_file", fileBody);            
         response = target.request().post(Entity.entity(entityBuilder, 
MediaType.MULTIPART_FORM_DATA));            
}   

The error I get is this one:

javax.ws.rs.ProcessingException: RESTEASY004655: Unable to invoke request
....
Caused by: javax.ws.rs.ProcessingException: RESTEASY003215: could not 
find writer for content-type multipart/form-data type: 
org.apache.http.entity.mime.MultipartEntityBuilder

How can I solve this problem? I looked into some posts, but the code is slightly different from mine.

Thank you guys.

You are mixing two different HTTP clients RESTEasy and Apache HttpClient. Here is the code which uses RESTEasy only

public void postFileMethod(String URL) throws FileNotFoundException {
    Response response = null;
    ResteasyClient client = new ResteasyClientBuilder().build();
    ResteasyWebTarget target = client.target(URL);

    MultipartFormDataOutput mdo = new MultipartFormDataOutput();
    mdo.addFormData("my_file", new FileInputStream(new File("C:/sample/sample.zip")), MediaType.APPLICATION_OCTET_STREAM_TYPE);
    GenericEntity<MultipartFormDataOutput> entity = new GenericEntity<MultipartFormDataOutput>(mdo) { };

    response = target.request().post(Entity.entity(entity,
            MediaType.MULTIPART_FORM_DATA));
}

You need to have resteasy-multipart-provider to have it working:

<dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-multipart-provider</artifactId>
    <version>${resteasy.version}</version>
</dependency>