020 使用@Conditional注解完成条件注入

一 .概述

在spring之中提供@Conditional注解完成条件注入.

我们可以实现特定的接口,完成配置类可以根据条件进行Bean的创建.

---

 二 .测试

public abstract class OS {
    protected String name;
    
    public String getName() {
        return this.name;
    }
}

class Windows extends OS {
    public Windows() { super.name = "windows"; } } class Linux extends OS { public Linux() { super.name = "linux"; } }

配置类:

@Configuration
public class ConditionalConfig {
    
    @Bean//只用条件成立才会创建对象
    @Conditional(WindowsConditonal.class)
    public OS windows() {
        return new Windows();
    }
    
    @Bean
    @Conditional(LinuxConditional.class) public OS linux() { return new Linux(); } }

两个条件类:

public class AbstractConditional {
    
    public String getOSName(ConditionContext context) {
        Environment environment = context.getEnvironment();
        String osName = environment.getProperty("os.name");
        return osName;
    }
}

public class WindowsConditonal extends AbstractConditional implements Condition{

    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        if(super.getOSName(context).toUpperCase().contains("WINDOWS")) {
            return true;
        }
        return false;
    }

}

public class LinuxConditional  extends AbstractConditional implements Condition{

    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        if(super.getOSName(context).toUpperCase().contains("LINUX")) {
            return true;
        }
        return false;
    }

}

只有当当前的操作系统为windows时,才会注入该bean.

测试:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes= {ConditionalConfig.class})
public class ConditionalTest {
    
    @Autowired
    private ApplicationContext context;
    
    @Test
    public void test() {
        System.out.println(context.getBean(OS.class).getName()); } }

结果返回为window,说明在当前的操作系统中只能创建一个Bean,另外一个Bean的声明并不会执行,否则getBean()方法会出现问题.