asyncapi/java-template - Githubissues

Overview
Technical requirements
Supported protocols
How to use the template
- CLI
- Template Tutorial
Template configuration
Environment variables
Development
Key Files
- Generator Code
- Generated Code
Container Information
Future Enhancements
Contributors ✨

Overview

This template generates Java application code based from an AsyncAPI document.

Implementations are provided for the following protocols:

ibmmq - generating Java JMS code (utilising features from the IBM MQ AsyncAPI bindings)
kafka - generating Java code (utilising features from the Apache Kafka AsyncAPI bindings)

Technical requirements

0.50.0 =< Generator < 2.0.0,
Generator specific requirements

Supported protocols

ibmmq
- This is implemented using the JMS API with the correct jars, in this case ibmmq was chosen. The use of JMS allows allows the template to be extensible to other providers by providing the correct jars at the Maven stage.
kafka
- This is implemented using the official client library from the Apache Kafka project.

How to use the template

This template must be used with the AsyncAPI Generator. You can find all available options here.

CLI

# Install the AsyncAPI Generator
npm install -g @asyncapi/generator

# Run generation
ag https://ibm.biz/mq-asyncapi-yml-sample @asyncapi/java-template -o output -p server=production

Template Tutorial

For complete instructions on generating the Java and subsequently using it to send messages, please see the relevant tutorial:

Template configuration

You can configure this template by passing different parameters in the Generator CLI: -p PARAM1_NAME=PARAM1_VALUE -p PARAM2_NAME=PARAM2_VALUE

Name	Description	Required	Default
`server`	Server must be defined in yaml and selected when using the generator	Yes	-
`user`	User for the server to generate code for. This can also be provided as an environment variable (see below)	No	app
`password`	Password for the server to generate code for. This can also be provided as an environment variable (see below)	No	passw0rd
`package`	Java package name for generated code	No	com.asyncapi
`mqTopicPrefix`	MQ topic prefix. Used for ibmmq protocols. Default will work with dev MQ instance	No	dev//
`asyncapiFileDir`	Custom output location of the AsyncAPI file that you provided as an input	No	The root of the output directory

Environment variables

Credentials can be provided as environment variables if preferred. If set, these credentials will override those set with the template parameters.

Name	Description
`APP_USER`	Overrides `user` template parameter
`APP_PASSWORD`	Overrides `password` template parameter

All credentials are stored in env.json in the output directory, so they can be updated at any time without needing to run the generator or recompile the Java.

Development

The most straightforward command to use this template is:

ag https://ibm.biz/mq-asyncapi-yml-sample @asyncapi/java-template -o output -p server=production

For local development, you need different variations of this command. First of all, you need to know about three important CLI flags:

--debug enables the debug mode in Nunjucks engine what makes filters debugging simpler.
--watch-template enables a watcher of changes that you make in the template. It regenerates your template whenever it detects a change.
--install enforces reinstallation of the template.

There are two ways you can work on template development:

Use global Generator and template from your local sources:

# assumption is that you run this command from the root of your template
ag https://ibm.biz/mq-asyncapi-yml-sample @asyncapi/java-template -o output -p server=production

Use Generator from sources and template also from local sources. This approach enables more debugging options with awesome console.log in the Generator sources or even the Parser located in node_modules of the Generator:

# assumption is that you run this command from the root of your template
# assumption is that generator sources are cloned on the same level as the template
../generator/cli.js https://ibm.biz/mq-asyncapi-yml-sample @asyncapi/java-template -o output -p server=production

Key Files

As a developer, you may want to make changes to how the generator operates. This non-exhaustive list aims to show the files you will likely need to change most.

Generator Code

Path	Description
template/index.js	Entry point for the application
components/Common.js	Common/helper functions used across the generator
utils/*	Contains all filters
components/*	Contains reusable components

Generated Code

Note: Files in the output directory are generated using the ag command, detailed in the above section.

Path	Description
output/env.json	Used for setting environmental variables such as username and password
output/com/asyncapi/PubSubBase.java	The base used for generated publishers and subscribers

Container Information

To run the generated Java project in a Docker container, use the commands as below:

Build the image

docker build -t [PACKAGE_NAME]:[VERSION] .

Run the image in detached mode
```
docker run -d [PACKAGE_NAME]:[VERSION]
```

For further information including network setup, please see the tutorial.

Future Enhancements

General enhancements
- Add support for multiple messages per channel (ofMany)
- Support for MQTT
- Support for other protocols
ibmmq protocol enhancements
- Add support for TLS connections
- Add support for more JMS Types alongside JMS Text
- Offer Java event listener support for consumers