面试时总被问，spring 中应用了哪些设计模式，你在理论开发中又应用哪些设计模式。给他手指一个方向跟他说，这就是一个模式：go out!。
这就是一种模式：策略模式，一个接口的多个实现形式 (算法)。本文梳理了应用 springboot 实现的三种实现策略模式的利用
咱们晓得，springboot 利用初始化的过程是通过事件机制进行的。次要是通过 EventPublishingRunListener 在不同的初始化阶段发送不同的 SpringApplicationEvent (不同的子)事件，触发相应逻辑 (这里的逻辑指 class 的加载) 的加载和初始化。
当 ApplicationPreparedEvent 事件发送后，对于利用来讲，阐明整个初始化过程已实现，也意味着所有的类已放入 spring ioc 中。
这时咱们就能够联合本人的业务逻辑实现策略模式的利用，咱们通过以下三种形式实现策略的利用
形式一：应用 ApplicationListener 和 ContextRefreshedEvent
外围应用的是 ApplicationContext.getBeanNamesForAnnotation(Class annotationType)办法，基于注解类，获取标有指定注解类的所有实例
咱们的业务逻辑是这样的：利用 Api 接管规定参数(authType)，Api 依据 authType 值的不同，应用不同的 auth service，执行相应的规定业务逻辑。
public interface UserValidator<D, R> {
String check(D data, R rule);œ}
@Service
@Validator(authType = AuthType.B_USER)
public class BUserValidator implements UserValidator<String, String> {
@Override
public String check(String data, String rule) {System.out.println("客官，这里 B 端用户逻辑");
return "";
}}
@Service
@Validator(authType = AuthType.C_USER)
public class CUserValidator implements UserValidator<String, String> {
@Override
public String check(String data, String rule) {System.out.println("客官，这里 C 端用户逻辑");
return "";
}}
public enum AuthType {
B_USER(1, "b 端用户"),
C_USER(2, "c 端用户");
public final int type;
public final String code;
AuthType(int type, String code) {
this.type = type;
this.code = code;
}}
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
@Inherited
public @interface Validator {
AuthType authType();}
@Component
public class AuthContainer implements ApplicationListener<ContextRefreshedEvent> {
private ConcurrentHashMap<Integer, UserValidator> validatorMap = new ConcurrentHashMap<>();
@Override
public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {String[] names = context.getBeanNamesForAnnotation(Validator.class);
if (names.length > 0) {for (String name : names) {System.out.println("UserValidator:" + name);
UserValidator userValidator = context.getBean(name, UserValidator.class);
Validator validator = userValidator.getClass().getAnnotation(Validator.class);
validatorMap.put(validator.authType().type, userValidator);
}
}
}
public ConcurrentHashMap<Integer, UserValidator> getValidatorMap() {return validatorMap;}}
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Api 接口定义如下，依据不同的 authType 值，执行不同的 auth service
@RequestMapping(“/client_auth”)
@RestController
public class Client3 {
@Autowired
private AuthContainer authContainer;
@RequestMapping("getAuth")
public String getRule(@RequestParam("authType") Integer authType) {
// if authType=1，B_USER; if authType=2，C_USER;
ConcurrentHashMap<Integer, UserValidator> map = authContainer.getValidatorMap();
UserValidator userValidator = map.get(authType);
String res = userValidator.check("hi", "看看什么规定");
return res;
}}
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形式二：应用 ApplicationContextAware 和 @PostConstruct
咱们的业务逻辑是这样的：利用 Api 接管规定参数 (ruleType)，Api 依据 ruleType 值的不同，应用不同的 rule service，执行相应的规定业务逻辑。
外围应用的是 ApplicationContext.getBeanNamesForAnnotation(Class annotationType)办法，基于注解类，获取标有指定注解类的所有实例
代码构造：
外围代码如下：
public abstract class RuleValidator<D, R> {
public abstract String check(D data, R rule);}
@RuleMapping(ruleCodeEnum = RuleCodeEnum.COUNT)
@Service
public class CountRuleValidator extends RuleValidator<String, String> {
@Override
public String check(String data, String rule) {System.out.println("客官，这里是数量规定区域");
return "";
}}
@RuleMapping(ruleCodeEnum = RuleCodeEnum.PRICE)
@Service
public class PriceRuleValidator extends RuleValidator<String, String> {
@Override
public String check(String data, String rule) {System.out.println("客官，这里是价格规定区域");
return "";
}}
public enum RuleCodeEnum {
/** 价格规定 */
PRICE(1, "price"),
/** 数量规定 */
COUNT(2, "count");
public final int type;
public final String code;
RuleCodeEnum(int type, String code) {
this.type = type;
this.code = code;
}}
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
@Inherited
public @interface RuleMapping {
String ruleCode() default "";
String ruleDesc() default "";
RuleCodeEnum ruleCodeEnum();}
@Component
public class RuleValidatorInit implements ApplicationContextAware {
private static ApplicationContext context;
private Map<Integer, RuleValidator> validatorMap = new HashMap<>();
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {this.context = applicationContext;}
public Map<Integer, RuleValidator> getValidatorMap() {return validatorMap;}
@PostConstruct
public void afterPropertiesSet() {String[] names = context.getBeanNamesForAnnotation(RuleMapping.class);
if (names.length > 0) {for (String name : names) {RuleValidator ruleValidator = context.getBean(name, RuleValidator.class);
RuleMapping ruleMapping = ruleValidator.getClass().getAnnotation(RuleMapping.class);
validatorMap.put(ruleMapping.ruleCodeEnum().type, ruleValidator);
}
}
}}
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Api 接口定义如下，依据不同的 ruleType 值，执行不同的 rule service
@RequestMapping(“/client”)
@RestController
public class Client {
@Autowired
private RuleValidatorInit ruleValidatorInit;
@RequestMapping("getRule")
public String getRule(@RequestParam("ruleType") Integer ruleType) {Map<Integer, RuleValidator> map = ruleValidatorInit.getValidatorMap();
System.out.println(map);
RuleValidator<String, String> ruleValidator = map.get(ruleType);
String res = ruleValidator.check("hi", "看看什么规定");
return res;
}}
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形式三：应用 ApplicationContextAware
比照形式一，这里不须要定义指定注解了
外围应用的是 ApplicationContext.getBeansOfType(classType)办法，获取接口 classType 的所有子类实例
代码构造：
外围代码如下：
public interface RoleValidator<D, R> {
String check(D data, R rule);
RoleCodeEnum source();}
@Service
public class BRoleValidator implements RoleValidator<String, String> {
@Override
public String check(String data, String rule) {System.out.println("客官，这里 B 端用户逻辑");
return "";
}
@Override
public RoleCodeEnum source() {return RoleCodeEnum.B_USER;}}
@Service
public class CRoleValidator implements RoleValidator<String, String> {
@Override
public String check(String data, String rule) {System.out.println("客官，这里 C 端用户逻辑");
return "";
}
@Override
public RoleCodeEnum source() {return RoleCodeEnum.C_USER;}}
public enum RoleCodeEnum {
B_USER(1, "b 端用户"),
C_USER(2, "c 端用户");
public final int type;
public final String code;
RoleCodeEnum(int type, String code) {
this.type = type;
this.code = code;
}}
@Component
public class RoleValidatorInit implements ApplicationContextAware {
private static Map<RoleCodeEnum, RoleValidator> builderMap = new HashMap<>();
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {for (RoleValidator roleValidator : applicationContext.getBeansOfType(RoleValidator.class).values()) {builderMap.put(roleValidator.source(), roleValidator);
}
}
public static RoleValidator getRoleValidator(RoleCodeEnum role) {return builderMap.get(role);
}}
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Api 接口定义如下，依据不同的 roleType 值，执行不同的 role service
@RequestMapping(“/client_role”)
@RestController
public class Client2 {
@Autowired
private RoleValidatorInit roleValidatorInit;
@RequestMapping("getRole")
public String getRule(@RequestParam("roleType") Integer roleType) {
// if roleType=1，B_USER; if roleType=2，C_USER;
RoleValidator roleValidator = roleValidatorInit.getRoleValidator(RoleCodeEnum.B_USER);
String res = roleValidator.check("hi", "看看什么规定");
return res;
}}
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总结
通过三种形式的比照，对于外围局部，其实就是几行代码的不同。无论是利用 Event 事件还是通过 Aware，实质都是拿到或利用 ApplicationContext 去解析接口，拿到实现类的实例，放入汇合，而后在客户端 (或其余) 获取汇合，依据枚举标识拿到对应的子类，执行对应的业务逻辑。