Spring framework interface cover (extensions Interface)

　　In the daily development, the existence of such a scenario, the interface framework provides one kind of A default implementation AImpl, along with the demand for change, today AImpl not meet the functional needs, then, how can we do? Of course, is to modify AImpl implementation code, but, if it is dependent on a third party it? Or, we wrote out of a function module, AImpl a default implementation provided us for this module, users can use it, it can also be covered on request (or an extension), how to do?

　　In this regard, spring offers us @Conditional notes, using it can solve such problems.

　　Here, for example. There RandomGenerator interface, the interface which has a Generator () method to generate a random string, and there are two implementation classes StringRandomGenerator NumberRandomGenerator, wherein StringRandomGenerator is the default implementation. That is, when we do not configure NumberRandomGenerator, uses StringRandomGenerator generate a random string, when we have configured NumberRandomGenerator, uses NumberRandomGenerator generate a random string.

 

/ ** 
 * top level interface generates a random string 
 * / 
public  interface randomGenerator { 
    Object Generator (); 
}

 

 

import org.apache.commons.lang.RandomStringUtils;

public class StringRandomGenerator implements RandomGenerator {
    @Override
    public Object generator() {
        char[] chars = {'a','b','c','d','e','f','g'};
        String random = RandomStringUtils.random(5, chars);
        return "StringRandomGenerator:"+random;
    }
}

 

/ ** 
 * When the NumberRandomGenerator registered as spring bean, StringRandomGenerator failure 
 * equivalent generator function generator NumberRandomGenerator a method of covering the StringRandomGenerator 
 * / 
@Component 
public  class NumberRandomGenerator the implements randomGenerator { 
    @Override 
    public Object generator () { 
        String Random = RandomStringUtils.random (. 5, to true , to true );
         return "NumberRandomGenerator:" + Random; 
    } 
}

 

/ ** 
 * configuration class 
 * / 
@SpringBootConfiguration 
public  class RandomGeneratorConfig { 

    / ** 
     * @ConditionalOnMissingBean (= RandomGenerator.class value) 
     * the annotation means: if the container is not Ioc RandomGenerator the bean type 
     * will register to StringRandomGenerator Ioc container 
     * / 
    @Bean 
    @ConditionalOnMissingBean (value . randomGenerator = class )
     public randomGenerator stringRandomGenerator () {
         return  new new stringRandomGenerator (); 
    } 
}

 

Finally, write a test controller

@RestController
public class RandomController {
    @Autowired
    private RandomGenerator randomGenerator;

    @GetMapping("/random")
    public Object random() {
        return randomGenerator.generator();
    }
}

 

In the case where the registered NumberRandomGenerator Ioc container, the test results are as follows:

 

Next, we will comment on NumberRandomGenerator class @Component kill, then test

 

 

 

perfect!