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：

 package cn.jpush.api.push.model.notification;

 import cn.jpush.api.push.model.PushModel;
 import cn.jpush.api.utils.Preconditions;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonPrimitive;

 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;

 public class Notification implements PushModel {
     private final Object alert;
     private final Set<PlatformNotification> notifications;

     private Notification(Object alert, Set<PlatformNotification> notifications) {
         this.alert = alert;
         this.notifications = notifications;
     }

     public static Builder newBuilder() {
         return new Builder();
     }

     /**
      * Quick set all platform alert.
      * Platform notification can override this alert.
      *
      * @param alert Notification alert
      * @return first level notification object
      */
     public static Notification alert(Object alert) {
         return newBuilder().setAlert(alert).build();
     }

     public static Notification android(String alert, String title, Map<String, String> extras) {
         return newBuilder()
                 .addPlatformNotification(AndroidNotification.newBuilder()
                     .setAlert(alert)
                     .setTitle(title)
                     .addExtras(extras)
                     .build())
                 .build();
     }

     public static Notification ios(Object alert, Map<String, String> extras) {
         return newBuilder()
                 .addPlatformNotification(IosNotification.newBuilder()
                     .setAlert(alert)
                     .addExtras(extras)
                     .build())
                 .build();
     }

     public static Notification ios_auto_badge() {
         return newBuilder()
                 .addPlatformNotification(IosNotification.newBuilder()
                     .setAlert("")
                     .autoBadge()
                     .build())
                 .build();
     }

     public static Notification ios_set_badge(int badge) {
         return newBuilder()
                 .addPlatformNotification(IosNotification.newBuilder()
                     .setAlert("")
                     .setBadge(badge)
                     .build())
                 .build();
     }

     public static Notification ios_incr_badge(int badge) {
         return newBuilder()
                 .addPlatformNotification(IosNotification.newBuilder()
                     .setAlert("")
                     .incrBadge(badge)
                     .build())
                 .build();
     }

     public static Notification winphone(String alert, Map<String, String> extras) {
         return newBuilder()
                 .addPlatformNotification(WinphoneNotification.newBuilder()
                     .setAlert(alert)
                     .addExtras(extras)
                     .build())
                 .build();
     }

     public JsonElement toJSON() {
         JsonObject json = new JsonObject();
         if (null != alert) {
             if(alert instanceof JsonObject) {
                 json.add(PlatformNotification.ALERT, (JsonObject) alert);
             } else if (alert instanceof IosAlert) {
                 json.add(PlatformNotification.ALERT, ((IosAlert) alert).toJSON());
             } else {
                 json.add(PlatformNotification.ALERT, new JsonPrimitive(alert.toString()));
             }
         }
         if (null != notifications) {
             for (PlatformNotification pn : notifications) {
                 if (this.alert != null && pn.getAlert() == null) {
                     pn.setAlert(this.alert);
                 }

                 Preconditions.checkArgument(! (null == pn.getAlert()),
                         "For any platform notification, alert field is needed. It can be empty string.");

                 json.add(pn.getPlatform(), pn.toJSON());
             }
         }
         return json;
     }

     public static class Builder {
         private Object alert;
         private Set<PlatformNotification> builder;

         public Builder setAlert(Object alert) {
             this.alert = alert;
             return this;
         }

         public Builder addPlatformNotification(PlatformNotification notification) {
             if (null == builder) {
                 builder = new HashSet<PlatformNotification>();
             }
             builder.add(notification);
             return this;
         }

         public Notification build() {
             Preconditions.checkArgument(! (null == builder && null == alert),
                     "No notification payload is set.");
             return new Notification(alert, builder);
         }
     }
 }

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。

 package com.startup.code.designmode.builder;

 public class Person {

     private Name name;

     private Address address;

     private Person(Builder builder) {
         this.name = builder.name;
         this.address = builder.address;
     }

     @Override
     public String toString() {
         return this.name + "--" + this.address;
     }

     static class Builder{

         private Name name;

         private Address address;

         public Builder name(Name name) {
             this.name = name;
             return this;
         }

         public Builder address(Address address) {
             this.address = address;
             return this;
         }

         public Person build() {
             return new Person(this);
         }
     }
 }

person类

 package com.startup.code.designmode.builder;

 public class Name {

     private String firstName; // 姓
     private String lastName; // 名
     private String nickName; // 昵称
     private String usedName; // 曾用名

     @Override
     public String toString() {
         return "firstName:" + this.firstName + ",lastName:" + this.lastName + ",nickName:" + this.nickName + ",userdName:" + this.usedName;
     }

     private Name(Builder builder) {
         this.firstName = builder.firstName;
         this.lastName = builder.lastName;
         this.nickName = builder.nickName;
         this.usedName = builder.usedName;
     }

     /**
      * Name的内部构造类
      * @author chenq
      *
      */
     static class Builder {
         private String firstName;
         private String lastName;
         private String nickName;
         private String usedName;

         public Builder firstName(String firstName) {
             this.firstName = firstName;
             return this;
         }

         public Builder lastName(String lastName) {
             this.lastName = lastName;
             return this;
         }

         public Builder nickName(String nickName) {
             this.nickName = nickName;
             return this;
         }

         public Builder usedName(String usedName) {
             this.usedName = usedName;
             return this;
         }

         public Name build() {
             return new Name(this);
         }
     }
 }

Name类

 package com.startup.code.designmode.builder;

 public class Address {

     private String province; // 省
     private String city; // 市
     private String district; // 区县

     private Address(Builder builder) {
         this.province = builder.province;
         this.city = builder.city;
         this.district = builder.district;
     }

     @Override
     public String toString() {
         return "province:" + this.province + ",city:" + this.city + ",district:" + this.district;
     }

     /**
      * Address的内部构造类
      * @author chenq
      *
      */
     static class Builder {
         private String province;
         private String city;
         private String district;

         public Builder province(String province) {
             this.province = province;
             return this;
         }

         public Builder city(String city) {
             this.city = city;
             return this;
         }

         public Builder district(String district) {
             this.district = district;
             return this;
         }

         public Address build() {
             return new Address(this);
         }
     }
 }

Address

测试类

package com.startup.code.designmode.builder;

public class BuilderTest {

    public static void main(String[] args) {
        Person person = new Person.Builder()
                        .address(new Address.Builder().province("江苏省").city("盐城市").district("建湖县").build())
                        .name(new Name.Builder().firstName("陈").lastName("群").nickName("rocky").usedName("陈大群").build())
                        .build();
        System.out.println(person);
    }

}

输出：

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