在对象属性上添加注解，实现属性加工（如：对属性进行排序+价签）

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前言

如何给属性使用注解？

一、创建注解

//创建类使用的注解
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Inherited
public @interface BankAPI {
    
    
    String desc() default "";
    String url() default "";
}

//创建属性使用的注解
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Documented
@Inherited
public @interface BankAPIField {
    
    
    int order() default -1;
    int length() default -1;
    String type() default "";
}

二、使用注解

//抽象类
public abstract class AbstractAPI {
    
    
}

//使用两个注解
import lombok.Data;

@BankAPI(url = "/bank/createUser", desc = "创建用户接口")
@Data
public class CreateUserAPI extends AbstractAPI {
    
    
    @BankAPIField(order = 0, type = "S", length = 10)
    private String address;
    @BankAPIField(order = 1, type = "S", length = 10)
    private String name;
    @BankAPIField(order = 2, type = "S", length = 18)
    private String identity;
    @BankAPIField(order = 4, type = "S", length = 11)
    private String mobile;
    @BankAPIField(order = 3, type = "N", length = 5)
    private int age;
}

import lombok.Data;

import java.math.BigDecimal;

@BankAPI(url = "/bank/pay", desc = "支付接口")
@Data
public class PayAPI extends AbstractAPI {
    
    
    @BankAPIField(order = 1, type = "N", length = 20)
    private long userId;
    @BankAPIField(order = 2, type = "M", length = 10)
    private BigDecimal amount;
}

三、controller 和service进行测试

//controller

import lombok.RequiredArgsConstructor;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.io.IOException;
import java.math.BigDecimal;

@RestController
@RequestMapping("bank/demo")
@RequiredArgsConstructor
public class BankApiController {
    
    
    private final BankService bankService;

    @GetMapping(value = "pay")
    public ResultStr pay() throws Exception {
    
    
        return new ResultStr(bankService.pay(1111L, new BigDecimal(1234)));
    }

    @GetMapping(value = "createUser")
    public ResultStr createUser() throws IOException {
    
    
        return new ResultStr(bankService.createUser("上海市","张三", "9999", "15196637832", 30));
    }

}

//service

import org.springframework.stereotype.Service;

import java.io.IOException;
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Arrays;
import java.util.Comparator;

@Service
public class BankService {
    
    

    //创建用户方法
    public String createUser(String address,String name, String identity, String mobile, int age) throws IOException {
    
    
        CreateUserAPI createUserAPI = new CreateUserAPI();
        createUserAPI.setAddress(address);
        createUserAPI.setName(name);
        createUserAPI.setIdentity(identity);
        createUserAPI.setAge(age);
        createUserAPI.setMobile(mobile);
        return remoteCall(createUserAPI);
    }

    //支付方法
    public String pay(long userId, BigDecimal amount) throws IOException {
    
    
        PayAPI payAPI = new PayAPI();
        payAPI.setUserId(userId);
        payAPI.setAmount(amount);
        return remoteCall(payAPI);
    }

    private String remoteCall(AbstractAPI api) throws IOException {
    
    
        //从BankAPI注解获取请求地址
        BankAPI bankAPI = api.getClass().getAnnotation(BankAPI.class);
        bankAPI.url();
        StringBuilder stringBuilder = new StringBuilder();
        Arrays.stream(api.getClass().getDeclaredFields()) //获得所有字段
                .filter(field -> field.isAnnotationPresent(BankAPIField.class)) //查找标记了注解的字段
                .sorted(Comparator.comparingInt(a -> a.getAnnotation(BankAPIField.class).order())) //根据注解中的order对字段排序
                .peek(field -> field.setAccessible(true)) //设置可以访问私有字段
                .forEach(field -> {
    
    
                    //获得注解
                    BankAPIField bankAPIField = field.getAnnotation(BankAPIField.class);
                    Object value = "";
                    try {
    
    
                        //反射获取字段值
                        value = field.get(api);
                    } catch (IllegalAccessException e) {
    
    
                        e.printStackTrace();
                    }
                    //根据字段类型以正确的填充方式格式化字符串
                    switch (bankAPIField.type()) {
    
    
                        case "S": {
    
    
                            stringBuilder.append(String.format("%-" + bankAPIField.length() + "s", value.toString()).replace(' ', '_'));
                            break;
                        }
                        case "N": {
    
    
                            stringBuilder.append(String.format("%" + bankAPIField.length() + "s", value.toString()).replace(' ', '0'));
                            break;
                        }
                        case "M": {
    
    
                            if (!(value instanceof BigDecimal))
                                throw new RuntimeException(String.format("{} 的 {} 必须是BigDecimal", api, field));
                            stringBuilder.append(String.format("%0" + bankAPIField.length() + "d", ((BigDecimal) value).setScale(2, RoundingMode.DOWN).multiply(new BigDecimal("100")).longValue()));
                            break;
                        }
                        default:
                            break;
                    }
                });
        //签名逻辑
        return stringBuilder.toString();
    }
}

四、测试结果

主要看看remoteCall()方法