Java设计模式之构建者模式

• 1.构建者模式概述
• 2. 构建者模式实现

1.构建者模式概述

构建器模式：将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示。
构建者模式其实就是我们常用的构建器，lombok的Builder注解就是构建器模式，effective中也比较推荐这种方式，相比于构造器中容易误差参数，构造器参数更清晰。

通过构造函数创建对象
通过创建空对象然后set属性
自定义不同参数的构造函数
lombok提供的注解@Builder链式调用

使用场景
当一个类的构造函数参数个数超过4个，而且这些参数有些是可选的参数，考虑使用构造者模式。

2. 构建者模式实现

/**
 * Car对象
 * 通过lombok的@Builder方式创建
 *
 * @author 20023262
 * @date 2020/12/10
 * @since 1.0
 */
@Setter
@Getter
@ToString
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Car {
    private Integer number;
    private String name;
    private String brand;
}

/**
 * Person对象
 * 通过不同参数自定义构造函数方式创建对象
 *
 * @author 20023262
 * @date 2020/12/10
 * @since 1.0
 */
@Setter
@Getter
@ToString
@NoArgsConstructor
public class Person {
    //必要参数
    private int id;
    private String name;
    //可选参数
    private int age;
    private String sex;
    private String phone;
    private String address;
    private String desc;

    /**
     * 各个参数构造函数
     */
    public Person(int id, String name) {
        this(id, name, 0);
    }

    public Person(int id, String name, int age) {
        this(id, name, age, "");
    }

    public Person(int id, String name, int age, String sex) {
        this(id, name, age, sex, "");
    }

    public Person(int id, String name, int age, String sex, String phone) {
        this(id, name, age, sex, phone, "");
    }

    public Person(int id, String name, int age, String sex, String phone, String address) {
        this(id, name, age, sex, phone, address, "");
    }

    public Person(int id, String name, int age, String sex, String phone, String address, String desc) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.sex = sex;
        this.phone = phone;
        this.address = address;
        this.desc = desc;
    }

}

/**
 * 自定义构建者模式对象
 *
 * @author 20023262
 * @date 2020/12/10
 * @since 1.0
 */
@Getter
@Setter
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class PersonOne {
    //必要参数
    private int id;
    private String name;
    //可选参数
    private int age;
    private String sex;
    private String phone;
    private String address;
    private String desc;

    /**
     * 通过builder将值设置到PersonOne对象
     */
    private PersonOne(Builder builder) {
        this.id = builder.id;
        this.name = builder.name;
        this.age = builder.age;
        this.sex = builder.sex;
        this.phone = builder.phone;
        this.address = builder.address;
        this.desc = builder.desc;
    }

    public static class Builder {
        //必要参数
        private final int id;
        private final String name;
        //可选参数
        private int age;
        private String sex;
        private String phone;
        private String address;
        private String desc;

        /**
         * 设置必须参数
         */
        public Builder(int id, String name) {
            this.id = id;
            this.name = name;
        }

        /**
         * 以下设置可选参数
         */
        public Builder age(int val) {
            this.age = val;
            return this;
        }

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

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

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

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

        /**
         * 通过builder方法创建PersonOne对象
         */
        public PersonOne build() {
            return new PersonOne(this);
        }
    }
}

/**
 * 构建者模式
 *
 * @author 20023262
 * @date 2020/12/10
 * @since 1.0
 */
public class BuilderTest {

    /**
     * 方式一
     * 通过lombok的Builder方式链式创建对象
     */
    @Test
    public void builderCarTest() {
        Car car = Car.builder().number(1001).name("帕梅拉").brand("Porsche").build();
    }

    /**
     * 构建对象
     */
    @Test
    public void builderPersonTest() {

        /**
         * 通过创建空对象，依次set属性
         */
        Person person = new Person();
        person.setId(1);
        person.setName("王小二");
        person.setAge(18);
        person.setSex("男");
        person.setPhone("15765481256");
        person.setAddress("成都");
        person.setDesc("产品");

        /**
         * 通过构造函数
         */
        Person person1 = new Person(3, "张三");
        Person person2 = new Person(3, "李四", 32);
        Person person3 = new Person(1, "赵柳", 21, "女", "123123", "sc", "ceshi");

        /**
         * 自定义Builder
         */
        PersonOne personOne = new PersonOne.Builder(1, "大疆").age(19).sex("nan").phone("123").address("bj").desc("air").build();
        System.out.println("自定义Builder创建PersonOne:"+personOne);


    }

}