Spring Boot 注解之 @ConditionalOnProperty

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1、使用情景

1）根据配置属性有条件地创建 Bean

2）可以用在类及方法上：标有 @Configuration 的类以及标有 @Bean 的方法

3）当属性满足时才会使标有该注解的类或方法生效

2、使用详情

序号 配置项 having 是否创建 Bean
1 config-test.property.action: true havingValue=”true” 创建
2 config-test.property.action: false havingValue=”false” 创建
3 config-test.property.action: enable havingValue=”enable” 创建
4 config-test.property.action: no havingValue=”enable” 不创建
5 config-test.property.action: true 不配置 创建
6 config-test.property.action: false 不配置 不创建
7 config-test.property.action: enable 不配置 创建
8 config-test.property.action: no 不配置 创建

3、案例

1）创建一个 Cake 类，getKind 方法返回当前蛋糕的口味：

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public abstract class Cake {

    protected String kind;

    public String getKind() {
        return kind;
    }
}

2）创建两个子类 PineappleCake、StrawberryCake，表示不同口味的蛋糕：

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public class PineappleCake extends Cake {
    public PineappleCake() {
        this.kind = "PineappleCake";
    }
}

public class StrawberryCake extends Cake {
    public StrawberryCake() {
        this.kind = "StrawberryCake";
    }
}

3）创建 Config 类，其中使用 @ConditionalOnProperty 注解根据配置文件指定的口味创建相应的 Bean

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@Configuration
public class Config {

    @Bean(name = "customCake")
    @ConditionalOnProperty(prefix = "cake.property", name = "kind", havingValue = "PineappleCake")-
    public Cake pineappleCake() {
        return new PineappleCake();
    }

    @Bean(name = "customCake")
    @ConditionalOnProperty(prefix = "cake.property", name = "kind", havingValue = "StrawberryCake")
    public Cake strawberryCake() {
        return new StrawberryCake();
    }
}

4）单元测试用例

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@SpringBootTest
class TestSpringBootApplicationTests {

    private final ApplicationContextRunner contextRunner = new ApplicationContextRunner();

    @Test
    void contextLoads() {
        this.contextRunner.withPropertyValues("cake.property.kind=PineappleCake")
                .withUserConfiguration(Config.class)
                .run(context -> {
                    assertThat(context).hasBean("customCake");
                    Cake cake = context.getBean(PineappleCake.class);
                    assertThat(cake.getKind()).isEqualTo("PineappleCake");
                    assertThat(context).doesNotHaveBean("StrawberryCake");
                });
    }
}

5）使用案例

配置文件 application.yml 添加如下属性：

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cake:
  property:
    kind: PineappleCake

按名称注入，获得的 kind 值与配置文件相同

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@SpringBootTest
class TestSpringBootApplicationTests {

    @Resource
    @Qualifier("customCake")
    private Cake cake;

    @Test
    void contextLoads2() {
        assertThat(cake.getKind()).isEqualTo("PineappleCake");
    }
}