定义

• 将一个复杂对象的构建与他的表示分离，使得同样的构建过程可以创建不同的表示
• 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

使用场景

• 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、建造类直接独立，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

代码

场景

创建一门视频课程，包含名称、视频、ppt、手记、问答

public class Course {

    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    private String courseQA;

    public String getCourseName() {
        return courseName;
    }

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

    public String getCoursePPT() {
        return coursePPT;
    }

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

    public String getCourseVideo() {
        return courseVideo;
    }

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

    public String getCourseArticle() {
        return courseArticle;
    }

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

    public String getCourseQA() {
        return courseQA;
    }

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

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

创建抽象类及子类实现

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);
    //最终建造这个课程 
    public  abstract Course makeCourse();

}

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;
    }
}

创建一个课程教练，用来对接课程

public class Coach {

    private CourseBuilder courseBuilder;

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

    public Course makeCourse(String courseName, String coursePPT, String courseVideo, String courseArticle, String courseQA) {
        this.courseBuilder.buildCourseName(courseName);
        this.courseBuilder.buildCoursePPT(coursePPT);
        this.courseBuilder.buildCourseVideo(courseVideo);
        this.courseBuilder.buildCourseArticle(courseArticle);
        this.courseBuilder.buildCourseQA(courseQA);
        return this.courseBuilder.makeCourse();
    }

}

测试

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",
                "Java设计模式PPT",
                "Java设计模式视频",
                "Java设计模式手记",
                "Java设计模式问答");
        System.out.println(course);
    }
}

结果

Course{courseName='Java设计模式', coursePPTc='Java设计模式PPT', courseVideo='Java设计模式视频', courseArticle='Java设计模式手记', courseQA='Java设计模式问答'}

UML

演进
不再使用课程教练，同时使用链式调用创建课程

public class Course {

    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    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;
        private String courseQA;

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

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

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

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

        public CourseBuilder buildCourseQA(String courseQA) {
            this.courseQA = courseQA;
            return this;
        }

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

    }

}

测试

public class Test {

    public static void main(String[] args) {
        Course course = new Course.CourseBuilder()
                .buildCourseName("Java设计模式")
                .buildCoursePPT("Java设计模式PPT")
                .buildCourseVideo("Java设计模式视频")
                .build();
        System.out.println(course);
    }
}

结果

Course{courseName='Java设计模式',
coursePPT='Java设计模式PPT',
courseVideo='Java设计模式视频',
courseArticle='null',
courseQA='null'}

UML