使用注解干掉大量if else和switch-白红宇

最近正在做工单系统，每种类型工单的操作是相似的但是又有不同，比如工单审批是相同的，但是工单启动是不同的，因此自然而然想到把工单的操作放到一个抽象类中，每种工单实现不同的操作。

工单服务抽象类ProcessInstanceService

@Servicepublic abstract class ProcessInstanceService{    public abstract String start(BaseParamDTO baseParamDTO);        public void approval(BaseParamDTO baseParamDTO, String user) {        System.out.println("审批通过");    }}复制代码

现在有一种扩容工单和一种权限申请工单

@Servicepublic class ExpansionService extends ProcessInstanceService{    @Override    public String start(BaseParamDTO baseParamDTO) {        System.out.println("扩容");    }}@Servicepublic class PrivilegeService extends ProcessInstanceService{    @Override    public String start(BaseParamDTO baseParamDTO) {        System.out.println("权限申请");    }} 复制代码

前端启动工单，这个时候需要根据工单类型获取对应的服务进行操作，因此使用了工厂模式

public enum  WorksheetTypeEnum {    EXPANSION("扩容", "machine_expansion"),    PRIVILEGE("登录权限","privilege_login");        private String cnName;    private String activitiDefineName;    WorksheetTypeEnum(String cnName, String activitiDefineName){        this.cnName = cnName;        this.activitiDefineName = activitiDefineName;    }}@Componentpublic class ProcessInstanceFactory {    @Autowired    private ExpansionService expansionService;        @Autowired    private PrivilegeService privilegeService;        public ProcessInstanceService getProcessInstanceService(WorksheetTypeEnum worksheetTypeEnum){        switch (worksheetTypeEnum){            case EXPANSION:                return expansionService;            case PRIVILEGE:                return privilegeService;            default:                return null;        }    }}复制代码

当前的代码已经使用枚举简化了if else，但是仍然存在问题，当新增一种工单时，ProcessInstanceFactory必须注入新的工单服务，然后添加新的case。那有没有什么方法不用修改工厂类直接添加新的工单类型呢，那就是使用注解。

首先创建一个注解

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)public @interface ServiceTypeAnnotation {    /**     * 工单类型名称     * @return     */    WorksheetTypeEnum value();}复制代码

为每个工单服务加上注解

@Service@ServiceTypeAnnotation(value = WorksheetTypeEnum.EXPANSION)public class ExpansionService extends ProcessInstanceService{}@Service@ServiceTypeAnnotation(value = WorksheetTypeEnum.PRIVILEGE)public class PrivilegeService extends ProcessInstanceService{}复制代码

修改工厂类ProcessInstanceFactory，在初始化的时候通过上下文拿到所有加了注解的类放到map中

@Componentpublic class ProcessInstanceFactory {    @Autowired    private DefaultService defaultService;    @Autowired    private ApplicationContext applicationContext;    private Map
    
      map = Maps.newConcurrentMap();    @PostConstruct    public void init(){        Map
     
       beansWithAnnotation = applicationContext.getBeansWithAnnotation(ServiceTypeAnnotation.class);        for (Object bean : beansWithAnnotation.values()){            ServiceTypeAnnotation annotation = bean.getClass().getAnnotation(ServiceTypeAnnotation.class);            map.put(annotation.value(), (ProcessInstanceService) bean);        }    }    public ProcessInstanceService getProcessInstanceService(WorksheetTypeEnum worksheetTypeEnum){        ProcessInstanceService processInstanceService = map.get(worksheetTypeEnum);        if (processInstanceService == null){            return defaultService;        } else {            return processInstanceService;        }    }复制代码

这样如果需要新增一个工单服务，只需要对新的类加上注解就可以了，如新增一个手工工单

public enum  WorksheetTypeEnum {    EXPANSION("扩容", "machine_expansion"),    PRIVILEGE("登录权限","privilege_login"),    ASSIGNMENT("手工工单", "assignments");    }@Service@ServiceTypeAnnotation(value = WorksheetTypeEnum.ASSIGNMENT)public class AssignmentService extends ProcessInstanceService{}复制代码