设计模式之建造者模式

Posted 2021-03-04 juncaif

前言

建造者模式也是常用的设计模式，Lombok的@Builder就是一个典型的应用。
google guava cache创建cache就只能通过builder方式

建造者模式

建造者模式有四个角色: 1product 2抽象builder 3实现builder 4 director
建造者模式是的创建对象算法独立，调用者可以不可见对象创建的逻辑。

Lombok @Builder

Lombok @Builder通过Builder静态内部类的方式，使用Builder创建对象。
@Builder是一个无序的创建过程

import lombok.Builder;
import lombok.Data;

@Builder
@Data
public class Person1 {
    String name;
    int age;
}
/*  编译后再反编译
public class Person1 {
    String name;
    int age;

    Person1(final String name, final int age) {
        this.name = name;
        this.age = age;
    }

    public static Person1.Person1Builder builder() {
        return new Person1.Person1Builder();
    }

    public String getName() {
        return this.name;
    }

    public int getAge() {
        return this.age;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public void setAge(final int age) {
        this.age = age;
    }

    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof Person1)) {
            return false;
        } else {
            Person1 other = (Person1)o;
            if (!other.canEqual(this)) {
                return false;
            } else {
                Object this$name = this.getName();
                Object other$name = other.getName();
                if (this$name == null) {
                    if (other$name == null) {
                        return this.getAge() == other.getAge();
                    }
                } else if (this$name.equals(other$name)) {
                    return this.getAge() == other.getAge();
                }

                return false;
            }
        }
    }

    protected boolean canEqual(final Object other) {
        return other instanceof Person1;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $name = this.getName();
        int result = result * 59 + ($name == null ? 43 : $name.hashCode());
        result = result * 59 + this.getAge();
        return result;
    }

    public String toString() {
        return "Person1(name=" + this.getName() + ", age=" + this.getAge() + ")";
    }

    public static class Person1Builder {
        private String name;
        private int age;

        Person1Builder() {
        }

        public Person1.Person1Builder name(final String name) {
            this.name = name;
            return this;
        }

        public Person1.Person1Builder age(final int age) {
            this.age = age;
            return this;
        }

        public Person1 build() {
            return new Person1(this.name, this.age);
        }

        public String toString() {
            return "Person1.Person1Builder(name=" + this.name + ", age=" + this.age + ")";
        }
    }
}



public class BuilderTest01 {
    public static void main(String[] args) {
        test01();
    }
    //测试Lombok @Builder使用静态内部类一步步建造对象
    public static void test01(){
        Person1 person1 = Person1.builder().name("jack").age(10).build();
        System.out.println(person1.toString());
    }
}

完整的建造者代码

实现四个角色：1product 2抽象builder 3实现builder 4director

product

import lombok.Data;
import lombok.ToString;

@Data
@ToString
public class House {
    private String buleprint;
    private String partA;
    private String partB;

    public House(String buleprint, String partA, String partB) {
        this.buleprint =buleprint;
        this.partA = partA;
        this.partB = partB;
    }

    public static HouseBuiler createBuilder(){
        return new HouseBuiler();
    }
/*    public String toString() {
        return "House(buleprint=" + this.getBuleprint() + ", partA=" + this.getPartA() + ", partB=" + this.getPartB() + ")";
    }*/
    //public属性
    @ToString
    public static class HouseBuiler extends Builder {
        private String buleprint;
        private String  partA;
        private String  partB;
        @Override
        public House build(){
            return new House(this.buleprint,this.partA,this.partB);
        }
        @Override
        public HouseBuiler buildPartA(String partA){
            this.partA = partA;
            return this;
        }
        @Override
        public HouseBuiler buildPartB(String partB){
            this.partB = partB;
            return this;
        }
        @Override
        public HouseBuiler buildBuleprint(String buleprint){
            this.buleprint = buleprint;
            return this;
        }
/*        public String toString() {
            return "House.HouseBuiler(buleprint=" + this.buleprint + ", partA=" + this.partA + ", partB=" + this.partB + ")";
        }*/
    }
}

抽象builder

package com.learn.java.javabase.designpattern.builder;

public abstract class Builder {
    public abstract Builder buildPartA(String partA);
    public abstract Builder buildPartB(String part);
    public abstract Builder buildBuleprint(String buleprint);
    public abstract House build();
}

builder实现类

package com.learn.java.javabase.designpattern.builder;

public class ConcreteBuilder extends Builder {
    private String buleprint;
    private String partA;
    private String partB;
    @Override
    public House build(){
        return new House(this.buleprint,this.partA,this.partB);
    }
    @Override
    public ConcreteBuilder buildPartA(String partA){
        this.partA = partA;
        return this;
    }
    @Override
    public ConcreteBuilder buildPartB(String partB){
        this.partB = partB;
        return this;
    }
    @Override
    public ConcreteBuilder buildBuleprint(String buleprint){
        this.buleprint = buleprint;
        return this;
    }
}

director

package com.learn.java.javabase.designpattern.builder;

public class Director {
    public static House build(Builder builder){
        return  builder.buildBuleprint("buluptint").buildPartA("part a").buildPartB("part b").build();
    }
}

测试类

public class BuilderTest02 {
    public static void main(String[] args) {
        test02();
    }
    public static void test01(){
        //无序调用，使用者其实拥有Director角色
        House house = House.createBuilder().buildBuleprint("蓝图").buildPartA("A部分").buildPartB("B部分").build();
        System.out.println(house.toString());
    }
    public static void test02(){
        //调用方不可见创建算法
        House house = Director.build(new ConcreteBuilder());
        System.out.println(house.toString());
    }
}