参数绑定与校验：别让错误输入走进业务

import java.math.BigDecimal;
import java.util.*;
public class Main {
  record Part(Long skuId,Integer quantity) {}
  record Input(String name,BigDecimal price,List<Part> parts) {}
  static List<String> validate(Input input) {
    List<String> errors=new ArrayList<>();
    if(input==null) return List.of("$"); // 根对象缺失，不能继续解引用
    String name=input.name();
    if(name==null || name.isBlank() || name.codePointCount(0,name.length())>80) errors.add("name");
    BigDecimal price=input.price();
    if(price==null || price.compareTo(new BigDecimal("0.01"))<0
        || price.compareTo(new BigDecimal("1000000"))>0 || price.scale()>2) errors.add("price");
    List<Part> parts=input.parts();
    if(parts==null) { errors.add("parts"); return errors; }
    if(parts.isEmpty() || parts.size()>100) { errors.add("parts.size"); return errors; }
    Set<Long> seen=new HashSet<>(); long total=0;
    for(int i=0;i<parts.size();i++) {
      Part part=parts.get(i); String path="parts["+i+"]";
      if(part==null) { errors.add(path); continue; } // 空元素有独立错误路径
      if(part.skuId()==null || part.skuId()<=0 || !seen.add(part.skuId())) errors.add(path+".skuId");
      Integer q=part.quantity();
      if(q==null || q<1 || q>99) errors.add(path+".quantity");
      else total+=q; // 只累计合法数量，非法负数不能抵消总量
    }
    if(total>1000) errors.add("parts.totalQuantity");
    return errors;
  }
  static Input good(List<Part> parts) { return new Input("汤",new BigDecimal("12.50"),parts); }
  static void check(boolean ok) { if(!ok) throw new AssertionError(); }
  public static void main(String[] args) {
    check(validate(good(List.of(new Part(7L,2)))).isEmpty());
    check(validate(null).equals(List.of("$")));
    check(validate(new Input(" ",null,List.of(new Part(7L,1)))).equals(List.of("name","price")));
    check(validate(good(List.of(new Part(7L,1),new Part(7L,2)))).contains("parts[1].skuId"));
    check(validate(new Input("汤",new BigDecimal("0.001"),List.of(new Part(7L,1)))).contains("price"));
    check(validate(good(List.of(new Part(7L,0)))).contains("parts[0].quantity"));
    check(validate(good(List.of())).equals(List.of("parts.size")));
    check(validate(good(Collections.nCopies(101,new Part(7L,1)))).equals(List.of("parts.size")));
    List<Part> many=new ArrayList<>(); for(long id=1;id<=11;id++) many.add(new Part(id,99));
    check(validate(good(many)).contains("parts.totalQuantity"));
    System.out.println("PASS 9 validation tests");
  }
}