Builder设计模式--改善构造器多个参数时可显著改善可读性

　　作为一名程序开发者，设计模式其实一直有在接触，只是没有专门的去学过，所以可能对设计模式没有一个系统的理解。在一次项目中，需要使用到第三方服务商提供的功能，为了尽快的熟悉其功能代码，在官网下了demo来研究其功能实现，发现一个用来封装消息通知的类是这样写的：

  1 package cn.jpush.api.push.model.notification;
  2 
  3 import cn.jpush.api.push.model.PushModel;
  4 import cn.jpush.api.utils.Preconditions;
  5 import com.google.gson.JsonElement;
  6 import com.google.gson.JsonObject;
  7 import com.google.gson.JsonPrimitive;
  8 
  9 import java.util.HashSet;
 10 import java.util.Map;
 11 import java.util.Set;
 12 
 13 public class Notification implements PushModel {    
 14     private final Object alert;
 15     private final Set<PlatformNotification> notifications;
 16     
 17     private Notification(Object alert, Set<PlatformNotification> notifications) {
 18         this.alert = alert;
 19         this.notifications = notifications;
 20     }
 21     
 22     public static Builder newBuilder() {
 23         return new Builder();
 24     }
 25     
 26     /**
 27      * Quick set all platform alert. 
 28      * Platform notification can override this alert. 
 29      * 
 30      * @param alert Notification alert
 31      * @return first level notification object
 32      */
 33     public static Notification alert(Object alert) {
 34         return newBuilder().setAlert(alert).build();
 35     }
 36 
 37     public static Notification android(String alert, String title, Map<String, String> extras) {
 38         return newBuilder()
 39                 .addPlatformNotification(AndroidNotification.newBuilder()
 40                     .setAlert(alert)
 41                     .setTitle(title)
 42                     .addExtras(extras)
 43                     .build())
 44                 .build();
 45     }
 46 
 47     public static Notification ios(Object alert, Map<String, String> extras) {
 48         return newBuilder()
 49                 .addPlatformNotification(IosNotification.newBuilder()
 50                     .setAlert(alert)
 51                     .addExtras(extras)
 52                     .build())
 53                 .build();
 54     }
 55 
 56     public static Notification ios_auto_badge() {
 57         return newBuilder()
 58                 .addPlatformNotification(IosNotification.newBuilder()
 59                     .setAlert("")
 60                     .autoBadge()
 61                     .build())
 62                 .build();
 63     }
 64 
 65     public static Notification ios_set_badge(int badge) {
 66         return newBuilder()
 67                 .addPlatformNotification(IosNotification.newBuilder()
 68                     .setAlert("")
 69                     .setBadge(badge)
 70                     .build())
 71                 .build();
 72     }
 73 
 74     public static Notification ios_incr_badge(int badge) {
 75         return newBuilder()
 76                 .addPlatformNotification(IosNotification.newBuilder()
 77                     .setAlert("")
 78                     .incrBadge(badge)
 79                     .build())
 80                 .build();
 81     }
 82 
 83     public static Notification winphone(String alert, Map<String, String> extras) {
 84         return newBuilder()
 85                 .addPlatformNotification(WinphoneNotification.newBuilder()
 86                     .setAlert(alert)
 87                     .addExtras(extras)
 88                     .build())
 89                 .build();
 90     }
 91     
 92     public JsonElement toJSON() {
 93         JsonObject json = new JsonObject();
 94         if (null != alert) {
 95             if(alert instanceof JsonObject) {
 96                 json.add(PlatformNotification.ALERT, (JsonObject) alert);
 97             } else if (alert instanceof IosAlert) {
 98                 json.add(PlatformNotification.ALERT, ((IosAlert) alert).toJSON());
 99             } else {
100                 json.add(PlatformNotification.ALERT, new JsonPrimitive(alert.toString()));
101             }
102         }
103         if (null != notifications) {
104             for (PlatformNotification pn : notifications) {
105                 if (this.alert != null && pn.getAlert() == null) {
106                     pn.setAlert(this.alert);
107                 }
108                 
109                 Preconditions.checkArgument(! (null == pn.getAlert()), 
110                         "For any platform notification, alert field is needed. It can be empty string.");
111 
112                 json.add(pn.getPlatform(), pn.toJSON());
113             }
114         }
115         return json;
116     }
117     
118     public static class Builder {
119         private Object alert;
120         private Set<PlatformNotification> builder;
121         
122         public Builder setAlert(Object alert) {
123             this.alert = alert;
124             return this;
125         }
126         
127         public Builder addPlatformNotification(PlatformNotification notification) {
128             if (null == builder) {
129                 builder = new HashSet<PlatformNotification>();
130             }
131             builder.add(notification);
132             return this;
133         }
134         
135         public Notification build() {
136             Preconditions.checkArgument(! (null == builder && null == alert), 
137                     "No notification payload is set.");
138             return new Notification(alert, builder);
139         }
140     }
141 }

当时使用时，感觉这种设计在使用时挺方便的，尤其是对参数的注入，可能构造一个Natification类所使用的代码有点长，但是对参数的使用十分明了。后来才知道这是Builder设计模式，当构造器需多个参数时，可显著改善可读性。根据此代码，自己也仿照写了相应的代码实现。

 1 package com.startup.code.designmode.builder;
 2 
 3 public class Person {
 4     
 5     private Name name;
 6     
 7     private Address address;
 8     
 9     private Person(Builder builder) {
10         this.name = builder.name;
11         this.address = builder.address;
12     }
13     
14     @Override
15     public String toString() {
16         return this.name + "--" + this.address;
17     }
18     
19     static class Builder{
20         
21         private Name name;
22         
23         private Address address;
24         
25         public Builder name(Name name) {
26             this.name = name;
27             return this;
28         }
29         
30         public Builder address(Address address) {
31             this.address = address;
32             return this;
33         }
34         
35         public Person build() {
36             return new Person(this);
37         }
38     }
39 }

person类