设计模式（第十五式：责任链模式）

概念：
　　责任链模式：Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receivering objects and pass the request along the chain until an object handles it.使用多个对象都有机会处理请求，从而避免了请求的发送者和接受者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递请求，知道有对象处理它为止。

实现：
　　年级抽象类

public abstract class Grade {
    private Grade grade;
    private String gradeName;
    private Integer score;

    public Grade getGrade() {
        return grade;
    }

    public void setGrade(Grade grade) {
        this.grade = grade;
    }

    public String getGradeName() {
        return gradeName;
    }

    public void setGradeName(String gradeName) {
        this.gradeName = gradeName;
    }

    public Integer getScore() {
        return score;
    }

    public void setScore(Integer score) {
        this.score = score;
    }

    public void upgrade() {
        System.out.println("上" + this.getGradeName());

        if (score < 60) {
            System.out.println("考试没通过，留级");
        } else {
            if (grade == null) {
                System.out.println("考试通过，毕业");
            } else {
                System.out.println("考试通过，升级");
                grade.upgrade();
            }

        }

    }
}

　　具体年级实现

public class FirstGrade extends Grade {
}

public class SecondGrade extends Grade {
}
...

测试及结果：

@Test
public void responsibilityChainTest(){
    Grade firstGrade = new FirstGrade();
    Grade secondGrade = new SecondGrade();
    firstGrade.setGrade(secondGrade);
    firstGrade.setGradeName("一年级");
    firstGrade.setScore(70);
    secondGrade.setScore(50);
    secondGrade.setGradeName("二年级");
    secondGrade.setGrade(null);

    firstGrade.upgrade();

}

　　上一年级
　　考试通过，升级
　　上二年级
　　考试没通过，留级

分析：
　　1.有点类似递归的方式，所以效率上会有所损失。
　　2.灵活性较高，可以比较方便的改变运行流程
　　3.最常见的就是Struts2 请求中的拦截器链，就采用了这种设计模式