在 Spring Boot 中，如何干掉 if else

/** * 订单实体 */public class OrderDTO {    private String code;    private BigDecimal price;

    /*     * 订单类型：     * 1：普通订单     * 2：团购订单     * 3：促销订单     */    private String type;//getter,setter自己实现}

/** * 订单处理 */public interface IOrderService {

    /**     * 根据订单的不同类型做出不同的处理     *     * @param dto 订单实体     * @return 为了简单，返回字符串     */    String orderHandler(OrderDTO dto);

}//实现类1@Componentpublic class OrderServiceImpl implements IOrderService {

    @Override    public String orderHandler(OrderDTO dto) {        if ("1".equals(dto.getType())) {            //普通订单处理        } else if ("2".equals(dto.getType())) {            //团购订单处理        } else if ("3".equals(dto.getType())) {            //促销订单处理        }        //未来订单类型增加    }

}//实现类二@Componentpublic class OrderServiceImpl implements IOrderService {    //使用策略模式实现    @Autowired    private HandlerContext handlerContext;

    @Override    public String orderHandler(OrderDTO dto) {        /*         * 1：使用if..else实现         * 2：使用策略模式实现         */        AOrderTypeHandler instance = handlerContext.getInstance(dto.getType());        return instance.handler(dto);    }

}

HandlerContext和HandlerProccessor
/** * 订单策略模式环境 * 这个类的注入由HandlerProccessor实现 */public class HandlerContext {    private Map<String, AOrderTypeHandler> handlerMap;

    /**     * 构造传参不能直接使用注解扫入     */    public HandlerContext(Map<String, AOrderTypeHandler> handlerMap) {        this.handlerMap = handlerMap;    }

    /**     * 获得实例     *     * @param type     * @return     */    public AOrderTypeHandler getInstance(String type) {        if (type == null) {            throw new IllegalArgumentException("type参数不能为空");        }        AOrderTypeHandler clazz = handlerMap.get(type);        if (clazz == null) {            throw new IllegalArgumentException("该类型没有在枚举OrderTypeHandlerAnno中定义，请定义：" + type);        }        return clazz;    }

}

/** * 策略模式，处理type与实现类的映射关系 */@Componentpublic class HandlerProccessor implements BeanFactoryPostProcessor {    /**     * 扫描@OrderTypeHandlerAnno注解，初始化HandlerContext，将其注册到spring容器     *     * @param beanFactory bean工厂     * @throws BeansException     */    @Override    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {        Map handlerMap = new HashMap<>();        for (OrderTypeEnum temp : OrderTypeEnum.values()) {            AOrderTypeHandler beanInstacle = getBeansWithAnnotation(beanFactory, AOrderTypeHandler.class, OrderTypeHandlerAnno.class, temp.getCode());            handlerMap.put(temp.getCode(), beanInstacle);        }        HandlerContext context = new HandlerContext(handlerMap);        //单例注入        beanFactory.registerSingleton(HandlerContext.class.getName(), context);    }    /*     * 通过父类+注解找到实体类     */    private  T getBeansWithAnnotation(ConfigurableListableBeanFactory beanFactory, Class manager, Class annotation, String code) throws BeansException {        if (ObjectUtils.isEmpty(code)) {            throw new RuntimeException("code is null ");        }        Collection tCollection = beanFactory.getBeansOfType(manager).values();        for (T t : tCollection) {            OrderTypeHandlerAnno orderTypeHandlerAnno = t.getClass().getAnnotation(annotation);            if (ObjectUtils.isEmpty(orderTypeHandlerAnno)) {                throw new RuntimeException("该注解没有写入值 :" + code);            }            //注解值是否与code相等            if (code.equals(orderTypeHandlerAnno.value().getCode())) {                return t;            }        }        throw new RuntimeException("通过code没有找到该注解对应的实体类 :" + code);    }}

/** * 订单类型处理定义 * 使用抽象类，那么子类就只有一个继承了 */public abstract class AOrderTypeHandler {

    /**     * 一个订单类型做一件事     *     * @param dto 订单实体     * @return 为了简单，返回字符串     */    abstract public String handler(OrderDTO dto);

}

/** * 订单类型注解 * 使用方式： * 1：普通订单 @OrderTypeHandlerAnno("1") * 2：团购订单 @OrderTypeHandlerAnno("2") * 3：促销订单 @OrderTypeHandlerAnno("3") */@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inheritedpublic @interface OrderTypeHandlerAnno {

    OrderTypeEnum value();

}

/** * 订单类型枚举 */public enum OrderTypeEnum {    Normal("1", "普通"),    Group("2", "团队"),    Promotion("3", "促销");

    private String code;    //代码    private String name;    //名称，描述

    OrderTypeEnum(String code, String name) {        this.code = code;        this.name = name;    }

    public String getCode() {        return code;    }

    public void setCode(String code) {        this.code = code;    }

    public String getName() {        return name;    }

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

    /**     * 根据code属性获取name属性     *     * @param code     * @return     */    public static String getNameByCode(String code) {        for (OrderTypeEnum temp : OrderTypeEnum.values()) {            if (temp.getCode().equals(code)) {                return temp.getName();            }        }        return null;    }

}

//业务代码/** * 普通订单处理 */@Component@OrderTypeHandlerAnno(OrderTypeEnum.Normal)public class NormalOrderHandler extends AOrderTypeHandler {

    @Override    public String handler(OrderDTO dto) {        return "处理普通订单";    }

}

/** * 团队订单处理 */@Component@OrderTypeHandlerAnno(OrderTypeEnum.Group)public class GroupOrderHandler extends AOrderTypeHandler {

    @Override    public String handler(OrderDTO dto) {        return "处理团队订单";    }

}

/** * 促销订单处理 */@Component@OrderTypeHandlerAnno(OrderTypeEnum.Promotion)public class PromotionOrderHandler extends AOrderTypeHandler {

    @Override    public String handler(OrderDTO dto) {        return "处理促销订单";    }

}

controller

/** * 策略模式 */@RestControllerpublic class StrategyController {    @Resource(name = "orderServiceImpl")    private IOrderService orderService;

    @GetMapping("/api/order")    @ResponseBody    public String orderSave(OrderDTO dto) {        String str = orderService.orderHandler(dto);        return "{\"status\":1,\"msg\":\"保存成功\",\"data\":\"" + str + "\"}";    }

}pom.xml文档

"1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0modelVersion>    <parent>        <groupId>org.springframework.bootgroupId>        <artifactId>spring-boot-starter-parentartifactId>        <version>2.2.1.RELEASEversion>        <relativePath/>     parent>    <groupId>com.kayakgroupId>    <artifactId>study-designartifactId>    <version>0.0.1-SNAPSHOTversion>    <name>study-designname>    <description>Demo project for Spring Bootdescription>

    <properties>        <java.version>1.8java.version>    properties>

    <dependencies>        <dependency>            <groupId>org.springframework.bootgroupId>            <artifactId>spring-boot-starter-webartifactId>        dependency>

        <dependency>            <groupId>org.springframework.bootgroupId>            <artifactId>spring-boot-starter-testartifactId>            <scope>testscope>            <exclusions>                <exclusion>                    <groupId>org.junit.vintagegroupId>                    <artifactId>junit-vintage-engineartifactId>                exclusion>            exclusions>        dependency>    dependencies>

    <build>        <plugins>            <plugin>                <groupId>org.springframework.bootgroupId>                <artifactId>spring-boot-maven-pluginartifactId>            plugin>        plugins>    build>

project>