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
@Component
public 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
@Component
public 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<String, AOrderTypeHandler> 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> T getBeansWithAnnotation(ConfigurableListableBeanFactory beanFactory, Class<T> manager, Class<? extends OrderTypeHandlerAnno> annotation, String code) throws BeansException {        if (ObjectUtils.isEmpty(code)) {            throw new RuntimeException("code is null ");        }        Collection<T> 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
@Inherited
public @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
 */
@RestController
public 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


<?xml version="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>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.kayak</groupId>
    <artifactId>study-design</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>study-design</name>
    <description>Demo project for Spring Boot</description>


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


    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>


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


</project>