Java建造者模式

建造者模式是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。用户只需指定需要建造的类型就可以得到它们，建造过程及细节不需要知道。属于创建型，也属于GOF23种设计模式。

适用范围

• 1.如果一个对象有非常复杂的内部结构（很多属性）。
• 2.想把复杂对象的创建和使用分离。

优缺点

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。

示例

Course.java 课程类，其中有个静态内部类 CourseBuilder ，用于创建课程。

package com.zaiae.design.pattern.creational.builder;

public class Course {
    private String courseName;
    private String coursePPT;
    private String courseVideo;
    private String courseArticle;
    private String courseQA;

    public Course() {
    }

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

    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);
        }

    }

}

Test.java 客户端（应用层）调用建造者，创建所需对象。

package com.zaiae.design.pattern.creational.builder;

public class Test {
    public static void main(String[] args) {
        Course course = new Course
                .CourseBuilder()
                .buildCourseName("Java设计模式精讲")
                .buildCoursePPT("Java设计模式精讲PPT")
                .buildCourseArticle("Java设计模式精讲文章")
                .buildCourseVideo("Java设计模式精讲视频")
                .buildCourseQA("Java设计模式精讲问答")
                .build();

        System.out.println(course);
    }
}

UML结构图：