责任链模式

责任链模式定义:使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的耦合关系。

举个栗子:在公司OA系统中申请一个办公用品,可能需要项目经理或部门经理或总经理批准.

具体由谁来批准时办公用品的分类决定.以下用代码方式实现

代码清单-1 抽象的处理者

public abstract class Handler {
    private Handler nextHandler;
    private String handlerName;

    //处理者的名字
    public Handler(String handlerName) {
        this.handlerName = handlerName;
    }
    
    public final String HandleMesssage(OfficeSuppliesApply apply){
        String result = null;
        //判断处理者是否有处理权限
        if(this.getHandlerLevel() == apply.getApply_level()){
            result = this.handleApply(apply);
            System.out.println(handlerName+":"+result);
        }else{
            result = this.nextHandler.HandleMesssage(apply);
            //此处省略未匹配到处理等级的情况
        }
        return result;
    }
    //设置下一个处理者
    public void setNextHandler(Handler nextHandler) {
        this.nextHandler = nextHandler;
    }

    //每个处理者都有一个处理级别
    protected abstract int getHandlerLevel();
    //每个处理者必须实现处理任务
    protected abstract String handleApply(OfficeSuppliesApply apply);
}

代码清单-2  具体处理者

/**
 * 具体处理者 : 经理
 */
public class Manager extends Handler {
    private int handlerLevel ;

    public Manager(int handlerLevel, String handlerName) {
        super(handlerName);
        this.handlerLevel = handlerLevel;
    }

    @Override
    protected int getHandlerLevel() {
        return handlerLevel;
    }

    @Override
    protected String handleApply(OfficeSuppliesApply apply) {
        String result = "通过"+apply.getSupplies_name()+"的申请!";
        return result;
    }
}

代码清单-3  办公用品申请

/**
 * 办公用品申请
 */
public class OfficeSuppliesApply {
    //申请等级
    private int apply_level ;
    //办公用品名称
    private String supplies_name;

    public OfficeSuppliesApply(int apply_level , String supplies_name){
        this.apply_level = apply_level;
        this.supplies_name = supplies_name;
    }
    
    public int getApply_level() {
        return apply_level;
    }
    
    public String getSupplies_name() {
        return supplies_name;
    }
}

代码清单-4 场景类

public class Client {

    public static void main(String[] args) {
        Manager projectManger = new Manager(1,"项目经理");
        Manager departMange = new Manager(2,"部门经理");
        Manager topManager = new Manager(3,"总经理");
        //处理顺序:项目经理 => 部门经理 => 总经理
        projectManger.setNextHandler(departMange);
        departMange.setNextHandler(topManager);
        //申请一盒水笔
        OfficeSuppliesApply pensApply = new OfficeSuppliesApply(1,"请求一盒水笔");
        //申请一个台笔记本电脑
        OfficeSuppliesApply notbookPcApply = new OfficeSuppliesApply(2,"请求一台笔记本电脑");
        //申请一台投影仪
        OfficeSuppliesApply projectorsApply = new OfficeSuppliesApply(3,"请求一台投影仪");
        projectManger.HandleMesssage(pensApply);
        projectManger.HandleMesssage(notbookPcApply);
        projectManger.HandleMesssage(projectorsApply);
    }
}

执行结果

项目经理:通过请求一盒水笔的申请!
部门经理:通过请求一台笔记本电脑的申请!
总经理:通过请求一台投影仪的申请!

责任链模式总结

优点:处理者和请求分开,两者解耦，提高系统的灵活性。

缺点:性能问题,每个请求都是从链头遍历到链尾,类似递归的方式,调试逻辑时可能比较复杂.