Builder设计模式结合lombok减少过多传参

男娘i 2021-09-17 12:18 260阅读 0赞

[https://blog.csdn.net/j16421881/article/details/79368004][https_blog.csdn.net_j16421881_article_details_79368004]

建造者模式将复杂对象的创建过程简化，用来传参也很合适。lombok的主要作用是通过一些注解，消除样板式代码，更多详见 lombok官网。该框架已经内置了这种模式。

过多的传参，可读性差，尤其是参数类型一致顺序还容易写颠倒。下面以一则不友好的传参为例展示一下，如何通过lombok迅速重构。

public class Mytest {
      public static void main(String[] args) {
        pay("2018-02-25", "小明", "2", "3");
      }
      public static void pay(String date, String name, String term, String amount) {
        System.out.println(date + "日，借款人" + name + "在第" + term + "期还款" + amount);
      }
    }

首先将参数封装。   
Builder跟Date分别是两个聚合注解，省去了手写getter、setter跟builder方法。

import lombok.Builder;
    import lombok.Data;
    @Data
    @Builder
    public class BidBuilder {
      private String date;
      private String name;
      private String term;
      private String amount;
    }

加上该注解后，通过反编译发现lombok生成的实际代码如下

public class BidBuilder
    {
      private String date;
      private String name;
      private String term;
      private String amount;
    
      public void setDate(String date)
      {
        this.date = date;
      }
    
      public void setName(String name)
      {
        this.name = name;
      }
    
      public void setTerm(String term)
      {
        this.term = term;
      }
    
      public void setAmount(String amount)
      {
        this.amount = amount;
      }
    
      public boolean equals(Object o)
      {
        if (o == this) {
          return true;
        }
        if (!(o instanceof BidBuilder)) {
          return false;
        }
        BidBuilder other = (BidBuilder)o;
        if (!other.canEqual(this)) {
          return false;
        }
        Object this$date = getDate();Object other$date = other.getDate();
        if (this$date == null ? other$date != null : !this$date.equals(other$date)) {
          return false;
        }
        Object this$name = getName();Object other$name = other.getName();
        if (this$name == null ? other$name != null : !this$name.equals(other$name)) {
          return false;
        }
        Object this$term = getTerm();Object other$term = other.getTerm();
        if (this$term == null ? other$term != null : !this$term.equals(other$term)) {
          return false;
        }
        Object this$amount = getAmount();Object other$amount = other.getAmount();return this$amount == null ? other$amount == null : this$amount.equals(other$amount);
      }
    
      protected boolean canEqual(Object other)
      {
        return other instanceof BidBuilder;
      }
    
      public int hashCode()
      {
        int PRIME = 59;int result = 1;Object $date = getDate();result = result * 59 + ($date == null ? 43 : $date.hashCode());Object $name = getName();result = result * 59 + ($name == null ? 43 : $name.hashCode());Object $term = getTerm();result = result * 59 + ($term == null ? 43 : $term.hashCode());Object $amount = getAmount();result = result * 59 + ($amount == null ? 43 : $amount.hashCode());return result;
      }
    
      public String toString()
      {
        return "BidBuilder(date=" + getDate() + ", name=" + getName() + ", term=" + getTerm() + ", amount=" + getAmount() + ")";
      }
    
      public static class BidBuilderBuilder
      {
        private String date;
        private String name;
        private String term;
        private String amount;
    
        public String toString()
        {
          return "BidBuilder.BidBuilderBuilder(date=" + this.date + ", name=" + this.name + ", term=" + this.term + ", amount=" + this.amount + ")";
        }
    
        public BidBuilder build()
        {
          return new BidBuilder(this.date, this.name, this.term, this.amount);
        }
    
        public BidBuilderBuilder amount(String amount)
        {
          this.amount = amount;return this;
        }
    
        public BidBuilderBuilder term(String term)
        {
          this.term = term;return this;
        }
    
        public BidBuilderBuilder name(String name)
        {
          this.name = name;return this;
        }
    
        public BidBuilderBuilder date(String date)
        {
          this.date = date;return this;
        }
      }
    
      BidBuilder(String date, String name, String term, String amount)
      {
        this.date = date;this.name = name;this.term = term;this.amount = amount;
      }
    
      public static BidBuilder.BidBuilderBuilder builder()
      {
        return new BidBuilder.BidBuilderBuilder();
      }
    
      public String getDate()
      {
        return this.date;
      }
    
      public String getName()
      {
        return this.name;
      }
    
      public String getTerm()
      {
        return this.term;
      }
    
      public String getAmount()
      {
        return this.amount;
      }
    }

通过lombok几行代码就实现了大量需要手动完成的模版代码。重构后如下

public class Mytest2 {
      public static void main(String[] args) {
        BidBuilder bidBuilder =
            BidBuilder.builder().date("2018-02-25").name("小明").term("2").amount("3").build();
        pay(bidBuilder);
      }
    
      public static void pay(BidBuilder bidBuilder) {
        System.out.println(
            bidBuilder.getDate()
                + "日，借款人"
                + bidBuilder.getName()
                + "在第"
                + bidBuilder.getTerm()
                + "期还款"
                + bidBuilder.getAmount());
      }
    }

后续若需要添加新的参数，只需更改BidBuilder，比如添加下次还款时间，只需要添加一行.

@Data
    @Builder
    public class BidBuilder {
      // 篇幅限制，省略其他参数
      // 下次还款时间 
      private String nextDate;
    }
     // 然后动态生成新的Builder
     BidBuilder bidBuilder =
            BidBuilder.builder()
                .date("2018-02-25")
                .name("小明")
                .term("2")
                .amount("100")
                .nextDate("2018-03-25")
                .build();

[https_blog.csdn.net_j16421881_article_details_79368004]: https://blog.csdn.net/j16421881/article/details/79368004