利用@Conditional注解實現條件裝配（小馬哥springBoot）

@Profile方式

首先介紹@Profile是因為@Profile是依靠@Conditional實現的

兩種求和的方式（for循環(huán)方式和lambda方式竿刁，通過@Profile區(qū)別）

Calculate.java

public interface Calculate {
    Integer sum(Integer... num);
}

Java7Calculate.java

@Profile("java7")
@Component
public class Java7Calculate implements Calculate {
    @Override
    public Integer sum(Integer... nums) {
        System.out.println("java7 calculating");

        Integer result = 0;
        for (Integer num : nums) {
            result += num;
        }
        return result;
    }
}

Java8Calculate.java

@Profile("java8")
@Component
public class Java8Calculate implements Calculate {
    @Override
    public Integer sum(Integer... num) {
        System.out.println("java8 calculating");
        return Stream.of(num).reduce(0, Integer::sum);
    }
}

Learn02AnnotationconfigApplication.java

@SpringBootApplication(scanBasePackages = "com.xmg.learn02annotationconfig.calculate")
public class Learn02AnnotationconfigApplication {

    public static void main(String[] args) {
//  對springApplication進行自定義祷安，其實SpringApplication.run()方法中，也是利用配置文件等先初始化SpringApplication對象缘回，這部分小馬哥后面有講
        SpringApplication springApplication = new SpringApplicationBuilder(Learn02AnnotationconfigApplication.class)
                .web(WebApplicationType.NONE)
                .profiles("java8")
                .build(args);
        ConfigurableApplicationContext context = springApplication.run(args);

        Calculate ca = context.getBean(Calculate.class);
        System.out.println(ca.sum(1, 2, 3, 4, 5));
    }

}

啟動時控制臺輸出如下：

...
The following profiles are active: java8
...
java8 calculating
15

實際上，@Profile從Spring3.1之后警绩，其實現方式時依靠@Conditional注解實現的

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(ProfileCondition.class)
public @interface Profile {

ProfileCondition.java

class ProfileCondition implements Condition {

    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        MultiValueMap<String, Object> attrs = metadata.getAllAnnotationAttributes(Profile.class.getName());
        if (attrs != null) {
            for (Object value : attrs.get("value")) {
                if (context.getEnvironment().acceptsProfiles(Profiles.of((String[]) value))) {
                    return true;
                }
            }
            return false;
        }
        return true;
    }

}

@Conditional方式

@CalConditional （仿照@Profile注解）

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(CalculateCondition.class)
public @interface CalConditional {
    String value();
}

CalculateCondition.java

public class CalculateCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        //得到java的系統(tǒng)屬性 myProfile,判斷與注解中的value值是否相等往扔，返回true代表將該類交由spirng容器管理，false則不管理
        String myProfile = System.getProperty("myProfile");

        Map<String, Object> map = metadata.getAnnotationAttributes(CalConditional.class.getName());
        String value = (String)map.get("value");

        return myProfile != null && myProfile.equals(value);
    }
}

Java7CalculateCondition.java

@CalConditional("java7")
@Component
public class Java7CalculateCondition implements Calculate {
    @Override
    public Integer sum(Integer... nums) {
        System.out.println("java7 calculating condition");//與@

        Integer result = 0;
        for (Integer num : nums) {
            result += num;
        }
        return result;
    }
}

Java8CalculateCondition.java

@CalConditional("java8")
@Component
public class Java8CalculateCondition implements Calculate {
    @Override
    public Integer sum(Integer... num) {
        System.out.println("java8 calculating condition");
        return Stream.of(num).reduce(0, Integer::sum);
    }
}

Learn02AnnotationconfigApplication.class

@SpringBootApplication(scanBasePackages = "com.xmg.learn02annotationconfig.calculate")
public class Learn02AnnotationconfigApplication {

    public static void main(String[] args) {

        System.setProperty("myProfile","java7");
        SpringApplication springApplication = new SpringApplicationBuilder(Learn02AnnotationconfigApplication.class)
                .web(WebApplicationType.NONE)
//              .profiles("java8")
                .build(args);
        ConfigurableApplicationContext context = springApplication.run(args);

        Calculate ca = context.getBean(Calculate.class);
        System.out.println(ca.sum(1, 2, 3, 4, 5));
    }

}

控制臺輸出：

...
No active profile set, falling back to default profiles: default
...
java7 calculating condition
15