Using a compile-time environment variable to configure RestApplicationPath

Question

As stated in the documentation of rest-dispatch, the rest application path must be configured in the GIN module via a constant, here "/api/v1":

public class DispatchModule extends AbstractGinModule {
   @Override
   protected void configure() {
       RestDispatchAsyncModule.Builder dispatchBuilder = 
               new RestDispatchAsyncModule.Builder();
       install(dispatchBuilder.build());
       bindConstant().annotatedWith(RestApplicationPath.class).to("/api/v1");   
   }
}

I would like to make the "/api/v1" constant be resolved at compile time, based on an environment variable set by the build system depending on the target environment (prod, dev, etc...), and on other criteria (the build artifact major version...).

The problem is I do not manage to rely on a compile time variable. Neither TextResource/CssResource nor GWT's deferred binding won't help here, since GWT.create() cannot be used in GIN module. Another option I considered is using a custom Generator, but this seems to be too complex for this very simple need.

How do you solve this problem ?

Answer 1

If you use Maven as your build system, you could leverage the templating-maven-plugin to generate a Java class that will contain static variables defined in your POM file. That generated class will be used by your GWT code.

For example, you would want to populate a BuildConstants class template

public class BuildConstants {
  // will be replaced by Maven
  public static final String API_VERSION  = "${myapi.version}";
}

and using a Maven property:

<myapi.version>v1</myapi.version>

that will be compiled to

public class BuildConstants {
  // will be replaced by Maven
  public static final String API_VERSION  = "v1";
}

and you could reference those constants from within your DispatchModule:

bindConstant().annotatedWith(RestApplicationPath.class).to("/api/" + BuildConstants.API_VERSION);   

Here's a sample config of the templating-maven-plugin that I use in a project:

<plugin>
  <groupId>org.codehaus.mojo</groupId>
  <artifactId>templating-maven-plugin</artifactId>
  <version>1.0-alpha-3</version>
  <executions>
    <execution>
      <id>filter-src</id>
      <goals>
        <goal>filter-sources</goal>
      </goals>
      <configuration>
        <sourceDirectory>${basedir}/src/main/java-templates</sourceDirectory>
        <outputDirectory>${project.build.directory}/generated-sources/java-templates
        </outputDirectory>
      </configuration>
    </execution>
   </executions>
</plugin>