设计模式之建造者(Builder)模式

使用前提是：IDEA或eclipse要安装lombok插件

1.创建实体类，在类上面加上@Builder注解

对象构建的时候使用：

OrderBatching orderBatching = OrderBatching.builder()
      .batchingId(goodsBatching.getId())                    
      .batchingName(goodsBatching.getBatchingName())
      .price(goodsBatching.getModifyPrice())
      .quantity(orderItemDto.getQuantity())
      .totalAmount(batchingAmount.longValue())
      .createBy(currentUser.getUsername())
      .updateBy(currentUser.getUsername())
      .build();

如果不这样做的话就是set方法一个一个设置

如果不使用lombok插件的话可以这样：

package xiao.javase.designPattern.builder;



public class Student {

    private String name;

    private int age;

    private int num;

    private String email;

    // 提供一个静态builder方法
    public static Student.Builder builder() {
        return new Student.Builder();
    }

    // 外部调用builder类的属性接口进行设值。
    public static class Builder {
        private String name;

        private int age;

        private int num;

        private String email;

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

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

        public Builder num(int num) {
            this.num = num;
            return this;
        }

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

        public Student build() {
            // 将builder对象传入到学生构造函数
            return new Student(this);
        }
    }

    // 私有化构造器
    private Student(Builder builder){
        name = builder.name;
        age = builder.age;
        num = builder.num;
        email = builder.email;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + ''' +
                ", age=" + age +
                ", num=" + num +
                ", email='" + email + ''' +
                '}';
    }

    public static void main(String[] args) {
        Student student = Student.builder().name("小草").num(1).age(18).email("小草@163.com").build();
        System.out.println(student);
    }
}

Builder模式（建造者模式）
实现步骤：
1.在要构建的类内部创建一个静态内部类 Builder
2.静态内部类的参数与构建类一致
3.构建类的构造参数是 静态内部类，使用静态内部类的变量一一赋值给构建类
4.静态内部类提供参数的 setter 方法，并且返回值是当前 Builder 对象
5.最终提供一个 build 方法构建一个构建类的对象，参数是当前 Builder 对象