最近对接三方门票系统，发现报文中数字签名的生成规则，是其他部分的参数值按照指定的顺序拼接在一起经过3Des加密之后经过Md5生成的。想着要对接5-6个接口，每个接口都要按照这种规则的话，会重复很多生成签名的硬编码，此刻想到了Java的反射。

import lombok.Data;

import java.util.List;

/**
 * @author jack
 */
@Data
public class CreateOrderReq {
    @BeanFieldAnnotation(order = 1)
    private String orderNo;

    @BeanFieldAnnotation(order = 2)
    private String productCode;

    private String productName;

    @BeanFieldAnnotation(order = 3)
    private Integer num;

    @BeanFieldAnnotation(order = 4)
    private String travelDate;

    @BeanFieldAnnotation(order = 5)
    private String linkMan;

    @BeanFieldAnnotation(order = 6)
    private String phone;

    @BeanFieldAnnotation(order = 7)
    private String certNo;

    private List<Tourist> tourists;

    @Data
    public static class Tourist{
        private String name;
        private String phone;
        private String certNo;
    }
}

编写注解类

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @author jack
 */
@Target({ElementType.FIELD, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface BeanFieldAnnotation {
    int order();
}

编写测试用例：

import com.google.common.base.Joiner;
import com.google.common.collect.Lists;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        CreateOrderReq req = new CreateOrderReq();

        req.setOrderNo("202403162140180001");
        req.setProductCode("3000065");
        req.setProductName("成人票");
        req.setTravelDate("2024-03-20");
        req.setNum(1);
        req.setLinkMan("张三");
        req.setPhone("18307202406");
        req.setCertNo("420621199310062934");

        List<CreateOrderReq.Tourist> tourists = Lists.newArrayList();
        CreateOrderReq.Tourist tourist = new CreateOrderReq.Tourist();
        tourist.setName("张三");
        tourist.setPhone("18307202406");
        tourists.add(tourist);
        req.setTourists(tourists);

        List<String> strs = Lists.newArrayList();
        Field[] fields = req.getClass().getDeclaredFields();
        List<Field> result = getOrderedField(fields);
        result.forEach(field -> {
            field.setAccessible(true);
            try {
                strs.add(String.valueOf(field.get(req)) );
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        });
        System.out.println("拼接后的字符串:"+ Joiner.on("").join(strs));
    }

    private static List<Field> getOrderedField(Field[] fields){
        // 用来存放所有的属性域
        List<Field> fieldList = new ArrayList<>();
        // 过滤带有注解的Field
        for(Field f:fields){
            if(f.getAnnotation(BeanFieldAnnotation.class)!=null){
                fieldList.add(f);
            }
        }
        // 这个比较排序的语法依赖于java 1.8
        fieldList.sort(Comparator.comparingInt(
                m -> m.getAnnotation(BeanFieldAnnotation.class).order()));
        return fieldList;
    }
}

运行结果