Calculator Custom Java Annotation (@Calculate, @EnableCalculatorProcessor)

This example (calculator-annotation) implements the similar annotation mechanism of Spring Data JPA Repositories. That is, a classpath-scanner searches for specific interfaces and creates a proxy for all found interfaces. Every method should need two integer parameter and integer return type. This proxy can then be @Autowired into your classes.

Usage

For enabling this annotation, you simply need to add the following annotation to your configuration class:

@Configuration 
@EnableCalculatorProcessor({"my.package"})
public class MyApplication {

  ...
} 

Remark:

This will now scan "my.package" and all subpackages for interfaces that implement com.example.calculator.processor.CalculatorProcessor and create implementations for them.

package my.package.service;

import com.example.calculator.processor.CalculatorProcessor;
import ...

public interface CalculatorService extends CalculatorProcessor {

   @Calculate(method = ADD)
   int addNumbers(int firstNumber, int secondNumber);

   @Calculate(method = SUB)
   int subtractNumbers(int firstNumber, int secondNumber);

   @Calculate(method = DIV)
   int divideNumbers(int firstNumber, int secondNumber);

   @Calculate(method = MUL)
   int multiplyNumbers(int firstNumber, int secondNumber);
}

A java.lang.reflect.Proxy will be created for the found interface. Every method will be transformed into a calculate-processor-definition and will be compiled on startup.

• Only two integer parameters are supported
• Only integer return type is supported
• @Calculcate annotation supports only four methods: ADD (Addition), SUB (Subtraction), DIV (Division), MUL (Multiplication).

Example

CalculatorApplication.java

Add @EnableCalculatorProcessor for enabling the Calculator Annotation

@SpringBootApplication
@EnableCalculatorProcessor("com.example.services")
public class CalculatorApplication {
	public static void main(String[] args) {
		SpringApplication.run(CalculatorApplication.class, args);
	}
}

CalculatorService.java

Create an interface which extends CalculatorProcessor and add @Calculate to the an abstract method

public interface CalculatorService extends CalculatorProcessor {

   @Calculate(method = ADD)
   int addNumbers(int firstNumber, int secondNumber);
}

CalculatorController.java

Inject or Autowire the CalculatorService and call addNumbers directly passing the values

public class CalculatorController {

    @Autowired
    private CalculatorService calculatorService;

    @GetMapping("/add")
    public int addNumbers(int firstNumber, int secondNumber) {
        return calculatorService.addNumbers(firstNumber, secondNumber);
    }
}

License

See LICENSE file.