基于编程方式实现条件装配

爱被打了一巴掌 2021-11-15 13:52 254阅读 0赞

> 本文主要讲通过编程方式来实现条件装配 —— `@Condition`

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#### 首先我们添加判断类 ####

`OnSystemPropertyCondition.java`

package xyz.suiwo.diveinspringboot.condition;
    
    import org.springframework.context.annotation.Condition;
    import org.springframework.context.annotation.ConditionContext;
    import org.springframework.core.type.AnnotatedTypeMetadata;
    
    import java.lang.annotation.Annotation;
    import java.util.Map;
    
    /** * @author suiwo * @title: OnSystemPropertyCondition * @date 2019-06-06 15:04 * * 系统属性条件判断 */
    public class OnSystemPropertyCondition implements Condition { 
    
        @Override
        public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { 
            Map<String, Object> attributes = metadata.getAnnotationAttributes(ConditionalOnSystemProperty.class.getName());
            String  propertyName = String.valueOf(attributes.get("name"));
            String  propertyValue = String.valueOf(attributes.get("value"));
            String  javaPropertyValue = System.getProperty(propertyName);
            System.out.println(javaPropertyValue);
    
            return propertyValue.equals(javaPropertyValue);
        }
    }

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#### 然后添加注解类 ####

`ConditionalOnSystemProperty.java`

package xyz.suiwo.diveinspringboot.condition;
    
    import org.springframework.context.annotation.Conditional;
    
    import java.lang.annotation.*;
    
    /** * @author suiwo * @title: ConditionalOnSystemProperty * @date 2019-06-06 15:02 * * Java系统属性条件判断 */
    @Retention(RetentionPolicy.RUNTIME)
    @Target({  ElementType.TYPE, ElementType.METHOD })
    @Documented
    @Conditional(OnSystemPropertyCondition.class)
    public @interface ConditionalOnSystemProperty { 
    
        /** * Java系统属性名称 * @return */
        String name();
    
        /** * Java系统属性值 * @return */
        String value();
    
    }

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#### 最后我们添加引导启动类 ####

`ConditionalSystemPropertyBootstrap.java`

package xyz.suiwo.diveinspringboot.bootstrap;
    
    import org.springframework.boot.WebApplicationType;
    import org.springframework.boot.builder.SpringApplicationBuilder;
    import org.springframework.context.ConfigurableApplicationContext;
    import org.springframework.context.annotation.Bean;
    import xyz.suiwo.diveinspringboot.condition.ConditionalOnSystemProperty;
    
    /** * @author suiwo * @title: ConditionalSystemPropertyBootstrap * @date 2019-06-06 15:10 * * 系统属性条件引导类 */
    public class ConditionalSystemPropertyBootstrap { 
    
        @Bean
        @ConditionalOnSystemProperty(name = "user.name",value = "zhangsan")
        public String helloWorld(){ 
             return "Hello world zhangsan";
        }
    
        @Bean
        @ConditionalOnSystemProperty(name = "user.name",value = "suiwo")
        public String helloW(){ 
            return "Hello world suiwo";
        }
    
        public static void main(String[] args) { 
            ConfigurableApplicationContext context =
                    new SpringApplicationBuilder(ConditionalSystemPropertyBootstrap.class)
                            .web(WebApplicationType.NONE)
                            .run(args);
            System.out.println(context.getBean("helloW",String.class));
            System.out.println(context.getBean("helloWorld",String.class));
    
            //关闭上下文
            context.close();
        }
    }

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#### 当我们运行后会发现终端运行结果 ####

.   ____          _            __ _ _
     /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
    ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
     \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
      '  |____| .__|_| |_|_| |_\__, | / / / /
     =========|_|==============|___/=/_/_/_/
     :: Spring Boot ::        (v2.1.5.RELEASE)
    
    2019-06-14 11:28:50.783  INFO 30704 --- [           main] s.d.b.ConditionalSystemPropertyBootstrap : Starting ConditionalSystemPropertyBootstrap on suiwoMBP with PID 30704 (/Users/dive-in-spring-boot/target/classes started by suiwo in /Users/dive-in-spring-boot)
    2019-06-14 11:28:50.790  INFO 30704 --- [           main] s.d.b.ConditionalSystemPropertyBootstrap : No active profile set, falling back to default profiles: default
    suiwo
    suiwo
    2019-06-14 11:28:51.251  INFO 30704 --- [           main] s.d.b.ConditionalSystemPropertyBootstrap : Started ConditionalSystemPropertyBootstrap in 1.218 seconds (JVM running for 1.945)
    Hello world suiwo
    Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'helloWorld' available
    	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:769)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1221)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:294)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:204)
    	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1111)
    	at xyz.suiwo.diveinspringboot.bootstrap.ConditionalSystemPropertyBootstrap.main(ConditionalSystemPropertyBootstrap.java:36)
    
    Process finished with exit code 1

#### 由此可见当不满足条件时，此时bean无法装配 ####