创建模式

建造者模式

定义

将一个复杂对象的构建与它的表示进行分离，使得同样的构建过程可以创建不同的表示

 

特征

用户只需指定需要建造的类型就可以得到他们，建造过程及细节不需要知道

类型

创建型

适用场景

如果一个对象有非常复杂的内部结构（很多属性）

想把复杂对象的创建和使用分离

优点

封装性好，创建和使用分离

扩展性好、建造类之间独立、一定程度上解耦

缺点

产生多余的builder对象

产品内部发生变化，建造者都要修改，成本较大

 

和工厂模式的区别

建造者模式更注重方法的调用顺序，而工厂模式注重于创建产品

创建对象的粒度不同：建造者模式可以创建一些复杂的产品，由各种复杂的部件组成，工厂模式创建出来的都是一个样子

关注点不同：工厂模式只要把产品创建出来就ok了，而建造者模式不仅要创建出这个产品，我还要知道这个产品都是由哪些部件组成的

建造者模式在某些业务场景，比如说一定的顺序决定了产出的产品不一样的话，那么这里也要把顺序进行调整，工厂则不关心顺序。

 

实例

假设我们要创建一个课程

 

   课程实体类

public class Course {
    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    //question&answer
    private String courseQA;


    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }


    public void setCoursePPT(String coursePPT) {
        this.coursePPT = coursePPT;
    }


    public void setCourseVideo(String courseVideo) {
        this.courseVideo = courseVideo;
    }


    public void setCourseArticle(String courseArticle) {
        this.courseArticle = courseArticle;
    }


    public void setCourseQA(String courseQA) {
        this.courseQA = courseQA;
    }

    @Override
    public String toString() {
        return "Course{" +
                "courseName='" + courseName + '\'' +
                ", coursePPT='" + coursePPT + '\'' +
                ", courseVideo='" + courseVideo + '\'' +
                ", courseArticle='" + courseArticle + '\'' +
                ", courseQA='" + courseQA + '\'' +
                '}';
    }
}

抽象的建造者

public abstract class  CourseBuilder {
    public abstract void buildCourseName(String courseName);
    public abstract void buildCoursePPT(String coursePPT);
    public abstract void buildCourseVideo(String courseVideo);
    public abstract void buildCourseArticle(String courseArticle);
    public abstract void buildCourseQA(String courseQA);

    public abstract Course makeCourse();
}

实际的建造者

public class CourseActualBuilder extends CourseBuilder{
    private Course course = new Course();
    @Override
    public void buildCourseName(String courseName) {
        course.setCourseName(courseName);
    }

    @Override
    public void buildCoursePPT(String coursePPT) {
        course.setCoursePPT(coursePPT);
    }

    @Override
    public void buildCourseVideo(String courseVideo) {
        course.setCourseVideo(courseVideo);
    }

    @Override
    public void buildCourseArticle(String courseArticle) {
        course.setCourseArticle(courseArticle);
    }

    @Override
    public void buildCourseQA(String courseQA) {
        course.setCourseQA(courseQA);
    }

    @Override
    public Course makeCourse() {
        return course;
    }
}

产品经理来建造这个课程

public class Coach {
    CourseBuilder courseBuilder;

    public void setCourseBuilder(CourseBuilder courseBuilder) {
        this.courseBuilder = courseBuilder;
    }

    public Course makeCourse(String courseName,String coursePPT,String courseVideo,String courseArticle,String courseQA) {

       courseBuilder.buildCourseName(courseName);
       courseBuilder.buildCoursePPT(coursePPT);
       courseBuilder.buildCourseVideo(courseVideo);
       courseBuilder.buildCourseArticle(courseArticle);
       courseBuilder.buildCourseQA(courseQA);
       return courseBuilder.makeCourse();
    }
}

Test 测试类

public class Test {
    public static void main(String[] args) {
        CourseBuilder courseBuilder = new CourseActualBuilder();
        Coach coach = new Coach();
        coach.setCourseBuilder(courseBuilder);
        Course course = coach.makeCourse("java设计模式", "PPT"
                , "视频", "手记", "问答");
        System.out.println(course);
    }
}

输出：
Course{courseName='java设计模式', coursePPT='PPT', courseVideo='视频', courseArticle='手记', courseQA='问答'}

uml

 

通过静态内部类链式调用来进行改进

course

public class Course {
    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    //question&answer
    private String courseQA;

    public Course(CourseBuilder courseBuilder) {
        this.courseName = courseBuilder.courseName;
        this.coursePPT = courseBuilder.coursePPT;
        this.courseVideo = courseBuilder.courseVideo;
        this.courseArticle = courseBuilder.courseArticle;
        this.courseQA = courseBuilder.courseQA;
    }

    @Override
    public String toString() {
        return "Course{" +
                "courseName='" + courseName + '\'' +
                ", coursePPT='" + coursePPT + '\'' +
                ", courseVideo='" + courseVideo + '\'' +
                ", courseArticle='" + courseArticle + '\'' +
                ", courseQA='" + courseQA + '\'' +
                '}';
    }

    public static class CourseBuilder{
        private String courseName;
        private String coursePPT;
        private String courseVideo;
        private String courseArticle;
        //question&answer
        private String courseQA;

        public CourseBuilder setCourseName(String courseName) {
            this.courseName = courseName;
            return this;
        }


        public CourseBuilder setCoursePPT(String coursePPT) {
            this.coursePPT = coursePPT;
            return this;
        }


        public CourseBuilder setCourseVideo(String courseVideo) {
            this.courseVideo = courseVideo;
            return this;
        }


        public CourseBuilder setCourseArticle(String courseArticle) {
            this.courseArticle = courseArticle;
            return this;
        }


        public CourseBuilder setCourseQA(String courseQA) {
            this.courseQA = courseQA;
            return this;
        }
        public Course build(){
            return new Course(this);
        }
    }
}

Test类

public class Test {
    public static void main(String[] args) {
        Course course = new Course.CourseBuilder().setCourseName("java设计模式").
                setCoursePPT("PPT").setCourseArticle("手记").setCourseQA("问答").setCourseVideo("视频").build();
        System.out.println(course);
    }
}

输出：
Course{courseName='java设计模式', coursePPT='PPT', courseVideo='视频', courseArticle='手记', courseQA='问答'}