優化if...else...語句
2023-01-16 18:00:20
寫程式碼的時候經常遇到這樣的場景：根據某個欄位值來進行不同的邏輯處理。例如，不同的會員等級在購物時有不同的折扣力度。如果會員的等級很多，那麼程式碼中與之相關的if...elseif...else...會特別長，而且每新增一種等級時需要修改原先的程式碼。可以用策略模式來優化，消除這種場景下的if...elseif...else...，使程式碼看起來更優雅。
首先，定義一個介面
/**
* 會員服務
*/
public interface VipService {
void handle();
}然後，定義實現類
/**
* 白銀會員
*/
public class SilverVipService implements VipService {
@Override
public void handle() {
System.out.println("白銀");
}
}
/**
* 黃金會員
*/
public class GoldVipService implements VipService {
@Override
public void handle() {
System.out.println("黃金");
}
}最後，定義一個工廠類，目的是當傳入一個會員等級後，返回其對應的處理類
public class VipServiceFactory {
private static Map<String, VipService> vipMap = new ConcurrentHashMap<>();
public static void register(String type, VipService service) {
vipMap.put(type, service);
}
public static VipService getService(String type) {
return vipMap.get(type);
}
}為了建立會員等級和與之對應的處理類之間的對映關係，這裡通常可以有這麼幾種處理方式：
方式一：實現類手動註冊
可以實現InitializingBean介面，或者在某個方法上加@PostConstruct註解
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;
/**
* 白銀會員
*/
@Component
public class SilverVipService implements VipService, InitializingBean {
@Override
public void handle() {
System.out.println("白銀");
}
@Override
public void afterPropertiesSet() throws Exception {
VipServiceFactory.register("silver", this);
}
}
/**
* 黃金會員
*/
@Component
public class GoldVipService implements VipService, InitializingBean {
@Override
public void handle() {
System.out.println("黃金");
}
@Override
public void afterPropertiesSet() throws Exception {
VipServiceFactory.register("gold", this);
}
}方式二：從Spring容器中直接獲取Bean
public interface VipService {
void handle();
String getType();
}
/**
* 白銀會員
*/
@Component
public class SilverVipService implements VipService {
@Override
public void handle() {
System.out.println("白銀");
}
@Override
public String getType() {
return "silver";
}
}
/**
* 黃金會員
*/
@Component
public class GoldVipService implements VipService {
@Override
public void handle() {
System.out.println("黃金");
}
@Override
public String getType() {
return "gold";
}
}
/**
* 上下文
*/
@Component
public class VipServiceFactory implements ApplicationContextAware {
private static Map<String, VipService> vipMap = new ConcurrentHashMap<>();
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
Map<String, VipService> map = applicationContext.getBeansOfType(VipService.class);
map.values().forEach(service -> vipMap.put(service.getType(), service));
}
public static VipService getService(String type) {
return vipMap.get(type);
}
}
/**
* 測試
*/
@SpringBootTest
class DemoApplicationTests {
@Test
void contextLoads() {
VipServiceFactory.getService("silver").handle();
}
}方式三：反射+自定義註解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MemberLevel {
String value();
}
@MemberLevel("silver")
@Component
public class SilverVipService implements VipService {
@Override
public void handle() {
System.out.println("白銀");
}
}
@MemberLevel("gold")
@Component
public class GoldVipService implements VipService {
@Override
public void handle() {
System.out.println("黃金");
}
}
/**
* 上下文
*/
@Component
public class VipServiceFactory implements ApplicationContextAware {
private static Map<String, VipService> vipMap = new ConcurrentHashMap<>();
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
// Map<String, VipService> map = applicationContext.getBeansOfType(VipService.class);
Map<String, Object> map = applicationContext.getBeansWithAnnotation(MemberLevel.class);
for (Object bean : map.values()) {
if (bean instanceof VipService) {
String type = bean.getClass().getAnnotation(MemberLevel.class).value();
vipMap.put(type, (VipService) bean);
}
}
}
public static VipService getService(String type) {
return vipMap.get(type);
}
}完整範例程式碼
/**
* 結算業務種類
* @Author: ChengJianSheng
* @Date: 2023/1/16
*/
@Getter
public enum SettlementBusiType {
RE1011("RE1011", "轉貼現"),
RE4011("RE4011", "買斷式貼現"),
RE4021("RE4021", "回購式貼現"),
RE4022("RE4022", "回購式貼現贖回");
// ......
private String code;
private String name;
SettlementBusiType(String code, String name) {
this.code = code;
this.name = name;
}
}
/**
* 結算處理器
* @Author: ChengJianSheng
* @Date: 2023/1/16
*/
public interface SettlementHandler {
/**
* 清算
*/
void handle();
/**
* 獲取業務種類
*/
SettlementBusiType getBusiType();
}
/**
* 轉貼現結算處理
*/
@Component
public class RediscountSettlementHandler implements SettlementHandler {
@Override
public void handle() {
System.out.println("轉貼現");
}
@Override
public SettlementBusiType getBusiType() {
return SettlementBusiType.RE1011;
}
}
/**
* 買斷式貼現結算處理
*/
@Component
public class BuyoutDiscountSettlementHandler implements SettlementHandler {
@Override
public void handle() {
System.out.println("買斷式貼現");
}
@Override
public SettlementBusiType getBusiType() {
return SettlementBusiType.RE4011;
}
}
/**
* 預設處理器
* @Author: ChengJianSheng
* @Date: 2023/1/16
*/
@Component
public class DefaultSettlementHandler implements /*SettlementHandler,*/ ApplicationContextAware {
private static Map<SettlementBusiType, SettlementHandler> allHandlerMap = new ConcurrentHashMap<>();
public static SettlementHandler getHandler(SettlementBusiType busiType) {
return allHandlerMap.get(busiType);
}
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
Map<String, SettlementHandler> map = applicationContext.getBeansOfType(SettlementHandler.class);
map.values().forEach(e -> allHandlerMap.put(e.getBusiType(), e));
}
}
@SpringBootTest
class Demo2023ApplicationTests {
@Test
void contextLoads() {
// 收到結算結果通知，根據業務種類進行結算處理
SettlementHandler handler = DefaultSettlementHandler.getHandler(SettlementBusiType.RE1011);
if (null != handler) {
handler.handle();
}
}
}