基本概念

简单描述

建造者模式是一种用来创建具有复杂类型的对象（比如汽车，需要各种零件组装构成—复杂）所使用的设计模式。可以设置不同的可选参数，定制化地创建不同的对象（比如：有天窗的汽车，能容纳7个人的汽车，双排气筒，马力够的汽车等）。

应用场景

1、一个对象有多个成员变量，且部分成员变量存在默认值（可选），使用构造函数和set方法造成可读性差的问题；
2、对象初始参数过多，直接用构造函数new出来，代码不够简洁，容易出错；
3、直接使用默认构造函数new出对象，再采用set方法为成员赋值，可能会产生一种情况：在所有的成员变量都没有赋值成功之前，对象属于无效状态（例如对象长方形，需要等待长和宽的值都set成功）；
4、需要一次性创建具有相互依赖关系的多个对象时，需要在对象创建完成前验证成员变量的约束条件时；希望最终创建的对象是不可变对象的情况下，不能在类中暴露set方法。

以上几种情况下，就可以使用到建造者模式。

具体实现示例

以下代码参照 极客时间：设计模式之美

  1. public class ResourcePoolConfig {
  3.     private String name;
  5.     private int maxTotal;
  7.     private int maxIdle;
  9.     private int minIdle;
  11.     public ResourcePoolConfig(Builder builder) {
  12.         this.name = builder.name;
  13.         this.maxTotal = builder.maxTotal;
  14.         this.maxIdle = builder.maxIdle;
  15.         this.minIdle = builder.minIdle;
  16.     }
  18.     public static ResourcePoolConfig.Builder newBuilder() {
  19.         return new ResourcePoolConfig.Builder();
  20.     }
  22.     public static class Builder {
  24.         private static final int DEFAULT_MAX_TOTAL = 8;
  26.         private static final int DEFAULT_MAX_IDLE = 8;
  28.         private static final int DEFAULT_MIN_IDLE = 0;
  31.         private String name;
  33.         private int maxTotal = DEFAULT_MAX_TOTAL;
  35.         private int maxIdle = DEFAULT_MAX_IDLE;
  37.         private int minIdle = DEFAULT_MIN_IDLE;
  39.         public ResourcePoolConfig build() {
  40.             // 校验逻辑：包括必填项校验、依赖关系校验、约束条件校验等
  41.             if (StringUtils.isBlank(name)) {
  42.                 throw new IllegalArgumentException("...");
  43.             }
  44.             if(maxIdle > maxTotal) {
  45.                 throw new IllegalArgumentException("...");
  46.             }
  47.             ...
  48.             return new ResourcePoolConfig(this);    
  49.         }
  51.         public Builder setName(String name) {
  52.             if(StringUtils.isBlank(name)) {
  53.                 throw new IllegalArgumentException("...");
  54.             }
  55.             this.name = name;
  56.             return this;
  57.         }
  59.         public Builder setMaxTotal(int maxTotal) {
  60.             if(maxTotal <= 0) {
  61.                 throw new IllegalArgumentException("...");
  62.             }
  63.             this.maxTotal = maxTotal;
  64.             return this;
  65.         }
  67.         public Builder setMaxIdle(int maxIdle) {
  68.             if(maxIdle <= 0) {
  69.                 throw new IllegalArgumentException("...");
  70.             }
  71.             this.maxIdle = maxIdle;
  72.             return this;
  73.         }
  75.         public Builder setMinIdle(int minIdle) {
  76.             if(minIdle <= 0) {
  77.                 throw new IllegalArgumentException("...");
  78.             }
  79.             this.minIdle = minIdle;
  80.             return this;
  81.         }
  82.     }
  83. }
  88. public static void main(String[] args) {
  90.     ResourcePoolConfig config = new ResourcePoolConfig.Builder()
  91.                         .setName("name")
  92.                         .setMaxTotal(16)
  93.                         .setMaxIdle(10)
  94.                         .setMinIdle(8)
  95.                         .build();
  96. }

业务场景

微信支付请求参数封装

基于微信JSAPI支付请求参数的封装

实现构造者模式步骤

  1. ## 外部类
  2. 1、构造方法， public WxJsApiRequest(builder)
  3. 2、调用静态内部类构造方法的静态方法：WxJsApiRequest.newBuilder
  6. 1、静态内部类 Builder
  7. 2、构造方法  public Builder()
  8. 3、静态内部类 Builder细节
  9.  - 以成员变量为方法名称，形参为成员变量，返回值为Builder实例,方法代码块内部可添加约束条件
  10.  - 内部非静态方法（普通方法）build，内部构造WxJsAPiRequest实例对象new WxJsApiRequest(builder)

Request对象封装

  1. package com.cmic.model;
  3. import com.alibaba.fastjson.JSONObject;
  4. import com.alibaba.fastjson.annotation.JSONField;
  5. import lombok.Getter;
  7. import java.io.Serializable;
  8. import java.util.List;
  11. /**
  12.  * 建造者模式
  13.  * 1、静态内部类 Builder
  14.  * 2、调用静态内部类构造方法的静态方法：WxJsApiRequest.newBuilder
  15.  * 3、静态内部类 Builder细节
  16.  * - 以成员变量为方法名称，形参为成员变量，返回值为Builder实例
  17.  * - 内部非静态方法（普通方法）build，内部 构造WxJsAPiRequest实例对象，new WxJsApiRequest(build)
  18.  */
  21. @Getter
  22. public class WxJsApiRequest implements Serializable {
  24.     private static final long serialVersionUID = 1L;
  26.     private String appId;
  28.     private String mchId;
  30.     private String description;
  32.     private String outTradeNo;
  34.     private String timeExpire;
  36.     private String attach;
  38.     private String notifyUrl;
  40.     private String goodsTag;
  42.     private WxAmount amount;
  44.     private JSONObject payer;
  46.     private WxDetail detail;
  48.     private JSONObject sceneInfo;
  50.     private JSONObject settleInfo;
  52.     WxJsApiRequest() {
  54.     }
  56.     WxJsApiRequest(Builder builder) {
  57.         this.appId = builder.appId;
  58.         this.mchId = builder.mchId;
  59.         this.description = builder.description;
  60.         this.outTradeNo = builder.outTradeNo;
  61.         this.timeExpire = builder.timeExpire;
  62.         this.attach = builder.attach;
  63.         this.notifyUrl = builder.notifyUrl;
  64.         this.goodsTag = builder.goodsTag;
  65.         this.amount = new WxAmount(builder);
  66.         this.payer = builder.payer;
  67.         this.detail = new WxDetail(builder);
  68.         this.sceneInfo = builder.sceneInfo;
  69.         this.settleInfo = builder.settleInfo;
  70.     }
  73.     @Override
  74.     public String toString() {
  75.         return "WxJsApiRequest{" +
  76.                 "appId='" + appId + '\'' +
  77.                 ", mchId='" + mchId + '\'' +
  78.                 ", description='" + description + '\'' +
  79.                 ", outTradeNo='" + outTradeNo + '\'' +
  80.                 ", timeExpire='" + timeExpire + '\'' +
  81.                 ", attach='" + attach + '\'' +
  82.                 ", notifyUrl='" + notifyUrl + '\'' +
  83.                 ", goodsTag='" + goodsTag + '\'' +
  84.                 ", amount=" + amount +
  85.                 ", payer=" + payer +
  86.                 ", detail=" + detail +
  87.                 ", sceneInfo=" + sceneInfo +
  88.                 ", settleInfo=" + settleInfo +
  89.                 '}';
  90.     }
  92.     public static WxJsApiRequest.Builder newBuilder() {
  93.         return new WxJsApiRequest.Builder();
  94.     }
  96.     public static class Builder {
  98.         private String appId;
  100.         private String mchId;
  102.         private String description;
  104.         private String outTradeNo;
  106.         private String timeExpire;
  108.         private String attach;
  110.         private String notifyUrl;
  112.         private String goodsTag;
  114.         private Integer total;
  116.         private String currency;
  118.         private JSONObject payer;
  120.         private Integer costPrice;
  122.         private List<String> goodsDetail;
  124.         private JSONObject sceneInfo;
  126.         private JSONObject settleInfo;
  129.         private Builder() {
  131.         }
  133.         public WxJsApiRequest.Builder appId(String appId) {
  134.             this.appId = appId;
  135.             return this;
  136.         }
  138.         public WxJsApiRequest.Builder mchId(String mchId) {
  139.             this.mchId = mchId;
  140.             return this;
  141.         }
  143.         public WxJsApiRequest.Builder description(String description) {
  144.             this.description = description;
  145.             return this;
  146.         }
  148.         public WxJsApiRequest.Builder outTradeNo(String outTradeNo) {
  149.             this.outTradeNo = outTradeNo;
  150.             return this;
  151.         }
  153.         public WxJsApiRequest.Builder timeExpire(String timeExpire) {
  154.             this.timeExpire = timeExpire;
  155.             return this;
  156.         }
  158.         public WxJsApiRequest.Builder attach(String attach) {
  159.             this.attach = attach;
  160.             return this;
  161.         }
  163.         public WxJsApiRequest.Builder notifyUrl(String notifyUrl) {
  164.             this.notifyUrl = notifyUrl;
  165.             return this;
  166.         }
  168.         public WxJsApiRequest.Builder goodsTag(String goodsTag) {
  169.             this.goodsTag = goodsTag;
  170.             return this;
  171.         }
  173.         public WxJsApiRequest.Builder total(Integer total) {
  174.             this.total = total;
  175.             return this;
  176.         }
  178.         public WxJsApiRequest.Builder currency(String currency) {
  179.             this.currency = currency;
  180.             return this;
  181.         }
  183.         public WxJsApiRequest.Builder payer(JSONObject payer) {
  184.             this.payer = payer;
  185.             return this;
  186.         }
  188.         public WxJsApiRequest.Builder costPrice(Integer costPrice) {
  189.             // todo: 成员变量的约束，比如 costPrice>0
  190.             this.costPrice = costPrice;
  191.             return this;
  192.         }
  194.         public WxJsApiRequest.Builder goodsDetail(List<String> goodsDetail) {
  195.             this.goodsDetail = goodsDetail;
  196.             return this;
  197.         }
  199.         public WxJsApiRequest.Builder sceneInfo(JSONObject sceneInfo) {
  200.             this.sceneInfo = sceneInfo;
  201.             return this;
  202.         }
  204.         public WxJsApiRequest.Builder settleInfo(JSONObject settleInfo) {
  205.             this.settleInfo = settleInfo;
  206.             return this;
  207.         }
  209.         public WxJsApiRequest build() {
  210.             // todo: 成员变量之间的约束条件， 比如 total > costPrice
  211.             return new WxJsApiRequest(this);
  212.         }
  214.     }
  216.     @Getter
  217.     private static class WxAmount {
  219.         private Integer total;
  221.         private String currency;
  223.         private WxAmount(Builder builder) {
  224.             this.total = builder.total;
  225.             this.currency = builder.currency;
  226.         }
  227.     }
  229.     @Getter
  230.     private class WxDetail {
  232.         private Integer costPrice;
  234.         private List<String> goodsDetail;
  236.         private WxDetail(Builder builder) {
  237.             this.costPrice = builder.costPrice;
  238.             this.goodsDetail = builder.goodsDetail;
  239.         }
  240.     }
  241. }

具体调用处理

  1. @RequestMapping(value = "test", method = RequestMethod.GET)
  2. public WxJsApiRequest test() {
  3.     WxPayConfig instance = WxPayConfig.getInstance();
  4.     WxPayParamConf wxPayParamConf = instance.getWxPayParamConf();
  5.     System.out.println(JSON.toJSONString(wxPayParamConf));
  7.     List<String> goodsDetail = new ArrayList<>();
  9.     goodsDetail.add("test1");
  10.     goodsDetail.add("test2");
  12.     JSONObject payer = new JSONObject();
  13.     payer.put("openid", "oa6sh5Q_tRltHkl11CJE-MF4GZ64");
  15.     WxJsApiRequest wxJsApiRequest = WxJsApiRequest.newBuilder()
  16.         .appId("wxe97be9fe6f5b66cb")
  17.         .mchId("1421036202")
  18.         .description("测试商品")
  19.         .outTradeNo("P1234546")
  20.         .timeExpire("2021-06-16 16:55:00")
  21.         .notifyUrl("http://qa.weimi24.com/wxReceiver")
  22.         .total(2) // amout相关-总金额
  23.         .currency("CNY") // amount相关-货币类型
  24.         .payer(payer)
  25.         .costPrice(1)
  26.         .goodsDetail(goodsDetail)
  27.         .build();
  30.     System.out.println(JSON.toJSONString(wxJsApiRequest));
  31.     System.out.println(wxJsApiRequest.toString());
  32.     return wxJsApiRequest;
  33. }