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基于编程方式实现条件装配

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本文主要讲通过编程方式来实现条件装配

本文主要讲通过编程方式来实现条件装配 —— @Condition

首先我们添加判断类

OnSystemPropertyCondition.java

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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);
    }
}

然后添加注解类

ConditionalOnSystemProperty.java

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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();

}

最后我们添加引导启动类

ConditionalSystemPropertyBootstrap.java

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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();
    }
}

当我们运行后会发现终端运行结果

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  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: 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