自定义注解实现责任链

自定义注解 ChainComponent

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface ChainComponent {

    /**
     * bean的名称
     */
    @AliasFor(annotation = Component.class)
    String value() default "";

    /**
     * 分类
     */
    String category() default "default";

    /**
     * 描述
     */
    String desc() default "";

}

上下文数据对象 Context

public class Context<T> {
    private T data;

    public Context(T data) {
        this.data = data;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }
}

策略容器 ChainContext

public class ChainContext<T> {
    private List<ChainProcessor<T>> elements = new ArrayList<>();
    private int pos = 0;
    private int n = 0;

    public ChainContext(List<ChainProcessor<T>> elements) {
        this.elements = elements;
        this.n = elements.size();
    }

    public T handler(Context<T> context) {
        if (pos < n) {
            ChainProcessor<T> processor = elements.get(pos++);
            System.err.printf("%s, 执行...%n", processor.getDesc());
            processor.doHandler(context, this);
        }
        return context.getData();
    }
}

策略接口 ChainProcessor

public interface ChainProcessor<T> {

    // 执行具体的动作，及调用下一个策略
    void doHandler(Context<T> context, ChainContext<T> chain);

    // 用来描述当前的策略
    default String getDesc() {
        return "";
    }

}

折扣策略

CouponDiscount

@ChainComponent(value = "coupon", category = "product", desc = "优惠券折扣实现")
public class CouponDiscount implements ChainProcessor<Double> {
    private final double discountAmount;

    public CouponDiscount() {
        this.discountAmount = 10;
    }

    @Override
    public void doHandler(Context<Double> context, ChainContext<Double>
            chain) {
        double price = context.getData();
        double result = Math.max(price - discountAmount, 0);
        context.setData(result);
        chain.handler(context);
    }

    @Override
    public String getDesc() {
        return "优惠券折扣实现";
    }
}

FixedDiscount

@ChainComponent(value = "fixed", category = "product", desc = "固定折扣实现")
public class FixedDiscount implements ChainProcessor<Double> {
    private final double discountAmount;

    public FixedDiscount() {
        this.discountAmount = 5;
    }

    @Override
    public void doHandler(Context<Double> context, ChainContext<Double>
            chain) {
        double price = context.getData();
        double result = Math.max(price - this.discountAmount, 0);
        context.setData(result);
        chain.handler(context);
    }

    @Override
    public String getDesc() {
        return "固定折扣实现";
    }
}

VipExtraDiscount

@ChainComponent(value = "vip", category = "product", desc = "VIP会员额外折扣实现")
public class VipExtraDiscount implements ChainProcessor<Double> {
    private final double discountAmount;

    public VipExtraDiscount() {
        this.discountAmount = 8;
    }

    @Override
    public void doHandler(Context<Double> context, ChainContext<Double>
            chain) {
        double price = context.getData();
        double result = Math.max(price - this.discountAmount, 0);
        context.setData(result);
        chain.handler(context);
    }

    @Override
    public String getDesc() {
        return "VIP会员额外折扣实现";
    }
}

数据处理策略

@ChainComponent(value = "html", category = "data", desc = "HTML标签过滤")
public class HtmlFilter implements ChainProcessor<String> {
    public void doHandler(Context<String> context, ChainContext<String>
            chain) {
        String html = context.getData();
        html = html.replace("<", "").replace(">", "");
        context.setData(html);
        chain.handler(context);
    }

    public String getDesc() {
        return "HTML标签过滤";
    }
}

@ChainComponent(value = "sensitive", category = "data", desc = "敏感词过滤")
public class SensitiveFilter implements ChainProcessor<String> {
    public void doHandler(Context<String> context, ChainContext<String>
            chain) {
        String data = context.getData();
        data = data.replaceAll("sb", "**");
        context.setData(data);
        chain.handler(context);
    }

    public String getDesc() {
        return "敏感词过滤";
    }
}

容器后置初始化组件

@Component
public class ChainComponentInitialization implements SmartInitializingSingleton, ApplicationContextAware {

    private ApplicationContext context;

    @Override
    public void afterSingletonsInstantiated() {
        // 外层Map根据category进行分组，value则是根据bean的名称进行
        final Map<String, Map<String, ChainMetadata>> CHAINS = new ConcurrentHashMap<>();
        // 通过自定义的注解获取所有的beanName
        String[] names = this.context.getBeanNamesForAnnotation(ChainComponent.class);
        for (String name : names) {
            // 通过beanName和类型获取bean对象
            ChainProcessor<?> bean = this.context.getBean(name, ChainProcessor.class);
            // 因为要获取注解元信息，所以这里要判断是否是代理对象，如果是代理对象则要获取父类
            Class<?> targetClass = AopUtils.getTargetClass(bean);
            ChainComponent cc = targetClass.getAnnotation(ChainComponent.class);
            if (cc != null) {
                String category = cc.category();
                // 普通的javabean对象
                ChainMetadata metadata = new ChainMetadata(name, category, cc.desc(), bean);
                Map<String, ChainMetadata> ret = CHAINS.computeIfAbsent(category, key -> new HashMap<>());
                ret.put(name, metadata);
            }
        }
        // 都处理完成以后发布事件
        this.context.publishEvent(new ChainEvent(Collections.unmodifiableMap(CHAINS)));
    }

    public void setApplicationContext(ApplicationContext context) throws BeansException {
        this.context = context;
    }
}

ChainMetadata

public class ChainMetadata<T> {
    private String name;
    private String category;
    private String desc;
    private ChainProcessor<T> bean;

    public ChainMetadata() {
    }

    public ChainMetadata(String name, String category, String desc, ChainProcessor<T> bean) {
        this.name = name;
        this.category = category;
        this.desc = desc;
        this.bean = bean;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getCategory() {
        return category;
    }

    public void setCategory(String category) {
        this.category = category;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public ChainProcessor<T> getBean() {
        return bean;
    }

    public void setBean(ChainProcessor<T> bean) {
        this.bean = bean;
    }
}

ChainEvent

public class ChainEvent extends ApplicationEvent {
    public ChainEvent(Object source) {
        super(source);
    }
}

自定义事件监听器

@Component
public class ChainService implements ApplicationListener<ChainEvent> {
    private Map<String, Map<String, ChainMetadata>> chains;

    private <T> List<ChainProcessor<T>> getChains(String category,
                                                  List<String> rules, Class<T> clazz) {
        Map<String, ChainMetadata> chainMap = this.chains.get(category);
        if (chainMap != null) {
            List<ChainProcessor<T>> processors = new ArrayList<>();
            for (String rule : rules) {
                ChainMetadata metadata = chainMap.get(rule);
                if (metadata != null) {
                    processors.add(metadata.getBean());
                }
            }
            return processors;
        }
        return List.of();
    }

    // 根据分类获取该分离下指定的策略
    public <T> ChainContext<T> getChainContext(String category, List<String>
            rules, Class<T> clazz) {
        return new ChainContext<>(getChains(category, rules, clazz));
    }

    @Override
    public void onApplicationEvent(ChainEvent event) {
        // 监听到事件后，将数据赋值给当前的成员变量
        this.chains = (Map<String, Map<String, ChainMetadata>>) event.getSource();
    }
}

类图

更新: 2025-07-18 16:06:24
原文: https://www.yuque.com/lsxxyg/sz/ewtu12hg17b0a0y4