在 Spring Boot 中，如何干掉 if else

/** * 訂單實體 */public class OrderDTO {    private String code;    private BigDecimal price;

    /*     * 訂單類型：     * 1：普通訂單     * 2：團購訂單     * 3：促銷訂單     */    private String type;//getter,setter自己實現(xiàn)}

/** * 訂單處理 */public interface IOrderService {

    /**     * 根據(jù)訂單的不同類型做出不同的處理     *     * @param dto 訂單實體     * @return 為了簡單，返回字符串     */    String orderHandler(OrderDTO dto);

}//實現(xiàn)類1@Componentpublic class OrderServiceImpl implements IOrderService {

    @Override    public String orderHandler(OrderDTO dto) {        if ("1".equals(dto.getType())) {            //普通訂單處理        } else if ("2".equals(dto.getType())) {            //團購訂單處理        } else if ("3".equals(dto.getType())) {            //促銷訂單處理        }        //未來訂單類型增加    }

}//實現(xiàn)類二@Componentpublic class OrderServiceImpl implements IOrderService {    //使用策略模式實現(xiàn)    @Autowired    private HandlerContext handlerContext;

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

}

HandlerContext和HandlerProccessor
/** * 訂單策略模式環(huán)境 * 這個類的注入由HandlerProccessor實現(xiàn) */public class HandlerContext {    private Map<String, AOrderTypeHandler> handlerMap;

    /**     * 構造傳參不能直接使用注解掃入     */    public HandlerContext(Map<String, AOrderTypeHandler> handlerMap) {        this.handlerMap = handlerMap;    }

    /**     * 獲得實例     *     * @param type     * @return     */    public AOrderTypeHandler getInstance(String type) {        if (type == null) {            throw new IllegalArgumentException("type參數(shù)不能為空");        }        AOrderTypeHandler clazz = handlerMap.get(type);        if (clazz == null) {            throw new IllegalArgumentException("該類型沒有在枚舉OrderTypeHandlerAnno中定義，請定義：" + type);        }        return clazz;    }

}

/** * 策略模式，處理type與實現(xiàn)類的映射關系 */@Componentpublic class HandlerProccessor implements BeanFactoryPostProcessor {

    /**     * 掃描@OrderTypeHandlerAnno注解，初始化HandlerContext，將其注冊到spring容器     *     * @param beanFactory bean工廠     * @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);        //單例注入        beanFactory.registerSingleton(HandlerContext.class.getName(), context);    }

    /*     * 通過父類+注解找到實體類     */    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("該注解沒有寫入值 :" + code);            }            //注解值是否與code相等            if (code.equals(orderTypeHandlerAnno.value().getCode())) {                return t;            }        }        throw new RuntimeException("通過code沒有找到該注解對應的實體類 :" + code);    }

}

/** * 訂單類型處理定義 * 使用抽象類，那么子類就只有一個繼承了 */public abstract class AOrderTypeHandler {

    /**     * 一個訂單類型做一件事     *     * @param dto 訂單實體     * @return 為了簡單，返回字符串     */    abstract public String handler(OrderDTO dto);

}

/** * 訂單類型注解 * 使用方式： * 1：普通訂單 @OrderTypeHandlerAnno("1") * 2：團購訂單 @OrderTypeHandlerAnno("2") * 3：促銷訂單 @OrderTypeHandlerAnno("3") */@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inheritedpublic @interface OrderTypeHandlerAnno {

    OrderTypeEnum value();

}

/** * 訂單類型枚舉 */public enum OrderTypeEnum {    Normal("1", "普通"),    Group("2", "團隊"),    Promotion("3", "促銷");

    private String code;    //代碼    private String name;    //名稱，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;    }

    /**     * 根據(jù)code屬性獲取name屬性     *     * @param code     * @return     */    public static String getNameByCode(String code) {        for (OrderTypeEnum temp : OrderTypeEnum.values()) {            if (temp.getCode().equals(code)) {                return temp.getName();            }        }        return null;    }

}

//業(yè)務代碼/** * 普通訂單處理 */@Component@OrderTypeHandlerAnno(OrderTypeEnum.Normal)public class NormalOrderHandler extends AOrderTypeHandler {

    @Override    public String handler(OrderDTO dto) {        return "處理普通訂單";    }

}

/** * 團隊訂單處理 */@Component@OrderTypeHandlerAnno(OrderTypeEnum.Group)public class GroupOrderHandler extends AOrderTypeHandler {

    @Override    public String handler(OrderDTO dto) {        return "處理團隊訂單";    }

}

/** * 促銷訂單處理 */@Component@OrderTypeHandlerAnno(OrderTypeEnum.Promotion)public class PromotionOrderHandler extends AOrderTypeHandler {

    @Override    public String handler(OrderDTO dto) {        return "處理促銷訂單";    }

}

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文檔

"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>