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);
        }
    }
}

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);
        }
    }
}

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);
        }
    }
}

 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：