Builder设计模式结合lombok减少过多传参

  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<
4000
/span> 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();