Java設計模式-Builder構造者模式

介紹:
構造者模式,又稱之為建造者模式,建造者模式,單例模式以及工廠模式都屬於創建型模式
1
應用場景

今天學mybatis的時候，知道了SQLSessionFactory使用的是builder模式來生成的。再次整理一下什么是builder模式以及應用場景。
當一個bean類重載了多個構造方法時,並且參數隨機使用時,考慮使用構造者模式,

builder模式也叫建造者模式，builder模式的作用將一個復雜對象的構建與他的表示分離，使用者可以一步一步的構建一個比較復雜的對象。

2.3 builder模式

package com.wangjun.designPattern.builder;

public class Product3 {
    
    private final int id;
    private final String name;
    private final int type;
    private final float price;
    
    private Product3(Builder builder) {
        this.id = builder.id;
        this.name = builder.name;
        this.type = builder.type;
        this.price = builder.price;
    }
    
    public static class Builder {
        private int id;
        private String name;
        private int type;
        private float price;
        
        public Builder id(int id) {
            this.id = id;
            return this;
        }
        public Builder name(String name) {
            this.name = name;
            return this;
        }
        public Builder type(int type) {
            this.type = type;
            return this;
        }
        public Builder price(float price) {
            this.price = price;
            return this;
        }
        
        public Product3 build() {
            return new Product3(this);
        }
    }

}

 

可以看到builder模式將屬性定義為不可變的，然后定義一個內部靜態類Builder來構建屬性，再通過一個只有Builder參數的構造器來生成Product對象。Builder的setter方法返回builder本身，以便可以將屬性連接起來。我們就可以像下面這樣使用了。

Product3 p3 = new Product3.Builder()
                            .id(10)
                            .name("phone")
                            .price(100)
                            .type(1)
                            .build();

 

當然具體使用builder的情況肯定沒有這么簡單，但是思路大致一樣：先通過某種方式取得構造對象需要的所有參數，再通過這些參數一次性構建這個對象。比如MyBatis中SqlSessionFactoryBuilder就是通過讀取MyBatis的xml配置文件來獲取構造SqlSessionFactory所需要的參數的。

 

 

 

1
Demo

package com.yunsuibi;

public class User {
private final String firstName; // required
private final String lastName; // required
private final int age; // optional
private final String phone; // optional
private final String address; // optional

private User(UserBuilder builder) {
this.firstName = builder.firstName;
this.lastName = builder.lastName;
this.age = builder.age;
this.phone = builder.phone;
this.address = builder.address;
}

public String getFirstName() {
return firstName;
}

public String getLastName() {
return lastName;
}

public int getAge() {
return age;
}

public String getPhone() {
return phone;
}

public String getAddress() {
return address;
}

@Override
public String toString() {
return "User [firstName=" + firstName + ", lastName=" + lastName + ", age=" + age + ", phone=" + phone
+ ", address=" + address + "]";
}

public static class UserBuilder {
private final String firstName;
private final String lastName;
private int age;
private String phone;
private String address;

public UserBuilder(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}

public UserBuilder age(int age) {
this.age = age;
return this;
}

public UserBuilder phone(String phone) {
this.phone = phone;
return this;
}

public UserBuilder address(String address) {
this.address = address;
return this;
}

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

}
}

運行

public static void main(String[] args) {
User build = new User.UserBuilder("Jhon", "Doe").address("北京").build();
System.out.println(build);
User build2 = new User.UserBuilder("李四", "哈哈").address("12").build();
System.out.println(build2);
}

 

參考：java之構造者模式

參考：Java設計模式之builder模式