kleash/java-di-framework

This project aims to make a light-weight dependency injection framework using Java

Custom Java Dependency Injection Framework

This project aims to make a light-weight dependency injection framework using Java.

Getting started

• Declare as dependency in pom.xml

<dependency>
   <groupId>com.github.kleash</groupId>
   <artifactId>java-di-framework</artifactId>
   <version>1.0</version>
</dependency>

• Annotate all classes you want to auto instantiate and auto injected with @Component.
  • By default, all classes are singleton, to declare a class scope to prototype use @Component(type = ClassScope.PROTOTYPE)
• Annotate all fields in your @Component annotated classes with @Autowired to automatically inject dependencies into your classes.
• Invoke ApplicationContextCreator.getInstance().scan("<<base package name here>>") from main method for starting dependency injection.

Design consideration

• Using reflection for auto-discovering and instantiating classes.
• Keeping only one instance of ApplicationContextCreator by using singleton pattern to make sure only one application context is available throughout the lifecycle. It helps in maintaining all instantiated beans at one place.
• Custom exception handling for various scenarios for ease of understanding.
• Annotation based markers to give user flexibility of manual or automatic handling of dependencies.
• Hashmap based data structure is used for easy retrieval of instantiated classes and their object.

Limitations

• Cannot handle inner classes for auto bean creation.
• Doesn't handle interfaces and their implementations.
• It will not scan classes in internal Jars.
• Most of the items of Pending features

Changelog

1.0

• Scans all classes in a given package and auto instantiate and wire them together.
• Multiple class scopes such as singleton, prototype.
• Custom exceptions. Few of them are:
  • BeanCreationException, if unable to create instance of a class with @Component annotation. For example, when constructor is not visible.
  • ContextCreateException, if unable to initiate classloader and scan passed package.
  • UnsatisfiedDependencyException, when class is autowired but not declared as @Component.

Pending features

• Dependency injection of classes with parameterized constructors.
• More robust classpath scanning.
• Add scanning by class. As of now, it scans all classes in given package.
• Detecting and handling cyclic dependencies.
• Add a way to allow user to inject dependency manually instead to creating automatically using reflection, for example @Bean.
• Provide annotations for Post bean creation hook and shutdown hook, for example @PostConstruct, @PreDestroy.
• Add support for constructor based injection for @Autowired annotation.
• Better logging.