SpringBoot之@ConditionalOnProperty注解使用方法

#配置是否加载类
is_load_bean: true

/**
 * @author: jiangjs
 * @description: 使用@ConditionalOnProperty
 * @date: 2023/4/24 10:20
 **/
@Component
@Slf4j
public class UseConditionalOnProperty {

    @Value("${is_load_bean}")
    private String isLoadBean;

    @Bean
    @ConditionalOnProperty(value = "is_load_bean",havingValue = "true",matchIfMissing = true)
    public void loadBean(){
        log.info("是否加载当前类");
    }

    @Bean
    public void compareLoadBean(){
        log.info("加载bean属性：" + isLoadBean);
    }
}

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

	/**
	 * name别名，数组类型，获取对应property名称的值，与name不能同时使用
	 */
	String[] value() default {};

	/**
	 * 属性前缀，未指定时，自动以点"."结束，有效前缀由一个或多个词用点"."连接。
     * 如：spring.datasource
	 */
	String prefix() default "";

	/**
	 * 属性名称，配置属性完整名称或部分名称，可与prefix组合使用，不能与value同时使用
	 */
	String[] name() default {};

	/**
	 * 可与name组合使用，比较获取到的属性值与havingValue的值是否相同，相同才加载配置
	 */
	String havingValue() default "";

	/**
	 * 缺少该配置属性时是否加载，默认为false。如果为true，没有该配置属性时也会正常加载；反之则不会生效
	 */
	boolean matchIfMissing() default false;

}

@Override
	public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
		//获取所有注解ConditionalOnProperty下的所有属性match，message
        List<AnnotationAttributes> allAnnotationAttributes = annotationAttributesFromMultiValueMap(
				metadata.getAllAnnotationAttributes(ConditionalOnProperty.class.getName()));
		List<ConditionMessage> noMatch = new ArrayList<>();
		List<ConditionMessage> match = new ArrayList<>();
        //遍历注解中的属性
		for (AnnotationAttributes annotationAttributes : allAnnotationAttributes) {
            //创建判定的结果，ConditionOutcome只有两个属性，
			ConditionOutcome outcome = determineOutcome(annotationAttributes, context.getEnvironment());
			(outcome.isMatch() ? match : noMatch).add(outcome.getConditionMessage());
		}
		if (!noMatch.isEmpty()) {
            //如果有属性没有匹配，则返回
			return ConditionOutcome.noMatch(ConditionMessage.of(noMatch));
		}
		return ConditionOutcome.match(ConditionMessage.of(match));
	}

private ConditionOutcome determineOutcome(AnnotationAttributes annotationAttributes, PropertyResolver resolver) {
	//初始化
    Spec spec = new Spec(annotationAttributes);
    List<String> missingProperties = new ArrayList<>();
    List<String> nonMatchingProperties = new ArrayList<>();
    //收集属性，将结果赋值给missingProperties，nonMatchingProperties
    spec.collectProperties(resolver, missingProperties, nonMatchingProperties);
    if (!missingProperties.isEmpty()) {
        //missingProperties属性不为空，说明设置matchIfMissing的是false，则不加载类
        return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnProperty.class, spec)
                .didNotFind("property", "properties").items(Style.QUOTE, missingProperties));
    }
    if (!nonMatchingProperties.isEmpty()) {
        //nonMatchingProperties属性不为空，则设置的属性值与havingValue值不匹配，则不加载类
        return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnProperty.class, spec)
                .found("different value in property", "different value in properties")
                .items(Style.QUOTE, nonMatchingProperties));
    }
    return ConditionOutcome
            .match(ConditionMessage.forCondition(ConditionalOnProperty.class, spec).because("matched"));
}

private static class Spec {

		private final String prefix;

		private final String havingValue;

		private final String[] names;

		private final boolean matchIfMissing;
        //初始化，给各属性赋值
		Spec(AnnotationAttributes annotationAttributes) {
			String prefix = annotationAttributes.getString("prefix").trim();
			if (StringUtils.hasText(prefix) && !prefix.endsWith(".")) {
				prefix = prefix + ".";
			}
			this.prefix = prefix;
			this.havingValue = annotationAttributes.getString("havingValue");
			this.names = getNames(annotationAttributes);
			this.matchIfMissing = annotationAttributes.getBoolean("matchIfMissing");
		}

        //处理name与value
		private String[] getNames(Map<String, Object> annotationAttributes) {
			String[] value = (String[]) annotationAttributes.get("value");
			String[] name = (String[]) annotationAttributes.get("name");
            //限制了value或name必须指定
			Assert.state(value.length > 0 || name.length > 0,
					"The name or value attribute of @ConditionalOnProperty must be specified");
			//value和name只能有一个存在，不能同时使用
            Assert.state(value.length == 0 || name.length == 0,
					"The name and value attributes of @ConditionalOnProperty are exclusive");
            return (value.length > 0) ? value : name;
		}

		private void collectProperties(PropertyResolver resolver, List<String> missing, List<String> nonMatching) {
			//遍历names,即value或name的值
            for (String name : this.names) {
                //前缀 + name，获取配置文件中key
				String key = this.prefix + name;
                //验证配置属性中包含key
				if (resolver.containsProperty(key)) {
                    //如包含，则获取key对应的值，与havingValue的值进行匹配
					if (!isMatch(resolver.getProperty(key), this.havingValue)) {
                        //不匹配则添加到nonMatching
						nonMatching.add(name);
					}
				}
				else {
                    //验证配置属性中没有包含key，判断是否配置了matchIfMissing属性
					if (!this.matchIfMissing) {
                        //该属性不为true则添加到missing中
						missing.add(name);
					}
				}
			}
		}

		private boolean isMatch(String value, String requiredValue) {
            //验证requiredValue是否有值
			if (StringUtils.hasLength(requiredValue)) {
                //有值，则进行比较，不区分大小写
				return requiredValue.equalsIgnoreCase(value);
			}
            //没有值，则验证value是否等于false
            //这也是为什么name, value不配置值的情况下, 类依然会被加载的原因
			return !"false".equalsIgnoreCase(value);
		}

		@Override
		public String toString() {
			StringBuilder result = new StringBuilder();
			result.append("(");
			result.append(this.prefix);
			if (this.names.length == 1) {
				result.append(this.names[0]);
			}
			else {
				result.append("[");
				result.append(StringUtils.arrayToCommaDelimitedString(this.names));
				result.append("]");
			}
			if (StringUtils.hasLength(this.havingValue)) {
				result.append("=").append(this.havingValue);
			}
			result.append(")");
			return result.toString();
		}

	}