[online] Revert GENERATOR_HOST explicit setting

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
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Description of the PR

Removing GENERATOR_HOST usage, and moving configuration to server. We may want to consider removing GENERATOR_HOST completely from GenApiServer (if possible), and just using built-in support for retrieving the host/port. I was trying to reduce confusion around this variable in the code that is removed by this PR, but upon discussion it seems the environment variable just adds confusion and is therefore not the appropriate configuration to target.

modules/openapi-generator-online/src/main/java/org/openapitools/codegen/online/configuration/OpenAPIDocumentationConfig.java

@@ -52,7 +52,6 @@ public class OpenAPIDocumentationConfig {
 
         String version = properties.getProperty("version", "unknown");
 
-
         return new ApiInfoBuilder()
             .title("OpenAPI Generator Online")
             .description("This is an online openapi generator server.  You can find out more at https://github.com/OpenAPITools/openapi-generator.")
@@ -66,18 +65,7 @@ public class OpenAPIDocumentationConfig {
 
     @Bean
     public Docket customImplementation(){
-        String host;
-        try {
-            String baseUrl = System.getenv("GENERATOR_HOST");
-            if (baseUrl == null) {
-                baseUrl = System.getProperty("generator.host", "http://localhost");
-            }
-            host = new URI(baseUrl).getHost();
-        } catch (URISyntaxException e) {
-            host = "";
-        }
         return new Docket(DocumentationType.SWAGGER_2)
-                .host(host)
                 .select()
                     .apis(RequestHandlerSelectors.basePackage("org.openapitools.codegen.online.api"))
                     .build()

modules/openapi-generator-online/Dockerfile

@@ -4,9 +4,10 @@ WORKDIR /generator
 
 COPY target/openapi-generator-online.jar /generator/openapi-generator-online.jar
 
-ENV GENERATOR_HOST=http://localhost
+# GENERATOR_HOST can be used to determine the target location of a download link.
+# The default value asumes binding to host via: docker -p 8080:8080 image_name
+ENV GENERATOR_HOST=http://localhost:8080
 
 EXPOSE 8080
 
-CMD ["java", "-jar", "/generator/openapi-generator-online.jar"]
-
+CMD ["java", "-jar", "/generator/openapi-generator-online.jar" ]

modules/openapi-generator-online/README.md

 # OpenAPI generated server
 
-Spring Boot Server 
+A Spring Boot Server application which hosts a client/server generator API.
 
 
 ## Overview  
+
 This server was generated by the [OpenAPI Generator](https://openapi-generator.tech) project.
-By using the [OpenAPI-Spec](https://openapis.org), you can easily generate a server stub.
+By using the [OpenAPI-Spec](https://openapis.org), you can easily generate a server stub or one of 100+ client packages.
+
 This is an example of building a OpenAPI-enabled server in Java using the SpringBoot framework.
 
 The underlying library integrating OpenAPI to SpringBoot is [springfox](https://github.com/springfox/springfox)
 
-Start your server as a simple java application
+## Building
+
+Refer to [root README](../../README.md) for build directions.
+
+## Running
+
+### Via command line
+
+Running is as simple as:
+
+```
+java -jar ./target/openapi-generator-online.jar
+```
+
+This exposes the API on local port 8080.
+
+Springfox supports configuration of the "host" value in the output OpenAPI document by setting the `Host` HTTP header in the request.
+To set this explicitly, pass the system property `springfox.documentation.swagger.v2.host` with the desired host. For example:
+
+```
+java -Dspringfox.documentation.swagger.v2.host=example.com:8888 -jar ./target/openapi-generator-online.jar
+```
+
+### Via Docker
+
+After building from source, change to this module directory (`cd modules/openapi-generator-online`) and build the docker image:
+
+```
+docker build -t openapitools/openapi-generator-online:latest .
+```
+
+Now, run the docker image:
+
+```
+docker run -d -p 8888:8080 \
+        -e GENERATOR_HOST=http://localhost:8888 \
+        openapitools/openapi-generator-online
+```
 
-Change default port value in application.properties
+The `GENERATOR_HOST` variable is used here to ensure download links generated by the API refer to the proper API location.