Android 責(zé)任鏈模式

源碼地址

介紹

它是一種行為型設(shè)計(jì)模式之一。它的每一個(gè)節(jié)點(diǎn)都可以看作是一個(gè)對(duì)象，每一個(gè)對(duì)象擁有不同的處理邏輯，將一個(gè)請(qǐng)求從鏈?zhǔn)降氖锥税l(fā)出，沿著鏈的路徑依次傳遞給每一個(gè)節(jié)點(diǎn)對(duì)象，直至有對(duì)象處理這個(gè)請(qǐng)求為止，這就是責(zé)任鏈模式。

使用場(chǎng)景

  1. 多個(gè)對(duì)象可以處理同一請(qǐng)求，但具體由哪個(gè)對(duì)象處理則在運(yùn)行時(shí)動(dòng)態(tài)決定。
  2. 在請(qǐng)求處理者不明確的情況下，向多個(gè)對(duì)象中的一個(gè)提交一個(gè)請(qǐng)求。
  3. 需要?jiǎng)討B(tài)指定一組對(duì)象處理請(qǐng)求。

示例一

說明：此為簡(jiǎn)化版代碼，分為抽象處理者，具體的處理者。代碼如下：

  1. 抽象處理者

    public abstract class Handler {
    protected Handler successor;    //下一節(jié)點(diǎn)的處理者

    /**
     * 請(qǐng)求處理
     * @param condition 請(qǐng)求條件
     */
    public abstract void handleRequest(String condition);
}

  2. 具體的處理者1

    public class ConcreteHandler1 extends Handler {
    @Override
    public void handleRequest(String condition) {
        if (condition.equals("ConcreteHandler1")) {
            System.out.println("ConcreteHandler1 handled");
        } else {
            successor.handleRequest(condition);
        }
    }
}

  3. 具體的處理者2

    public class ConcreteHandler2 extends Handler {
    @Override
    public void handleRequest(String condition) {
        if (condition.equals("ConcreteHandler2")) {
            System.out.println("ConcreteHandler2 handled");
        } else {
            successor.handleRequest(condition);
        }
    }
}

  4. 客戶類

    public class Client {
    public static void main(String[] args) {
        //構(gòu)造一個(gè)ConcreteHandler1對(duì)象
        ConcreteHandler1 handler1 = new ConcreteHandler1();
        //構(gòu)造一個(gè)ConcreteHandler2對(duì)象
        ConcreteHandler2 handler2 = new ConcreteHandler2();
        //設(shè)置handler1的下一個(gè)節(jié)點(diǎn)
        handler1.successor = handler2;
        //設(shè)置handler2的下一個(gè)節(jié)點(diǎn)
        handler2.successor = handler1;
        //處理請(qǐng)求
        handler1.handleRequest("ConcreteHandler2");
    }
}

示例二

說明：抽象處理者，抽象請(qǐng)求者，請(qǐng)求者，處理者。代碼如下：

  1. 抽象處理者

    public abstract class AbstractHandler {
    protected AbstractHandler nextHandler;    //下一節(jié)點(diǎn)的處理者對(duì)象

    /**
     * 請(qǐng)求處理
     * @param request 請(qǐng)求條件
     */
    public final void handleRequest(AbstractRequest request) {
        //判斷當(dāng)前處理者對(duì)象的處理級(jí)別是否與請(qǐng)求者的處理級(jí)別一致
        if (getHandleLevel() == request.getRequestLevel()) {
            //一致則由該處理對(duì)象處理
            handle(request);
        } else {
            //否則將該請(qǐng)求對(duì)象轉(zhuǎn)發(fā)給下一個(gè)節(jié)點(diǎn)上的請(qǐng)求對(duì)象
            if (nextHandler != null) {
                nextHandler.handleRequest(request);
            } else {
                //所有處理者對(duì)象均不能處理該請(qǐng)求時(shí)輸出
                System.out.println("All of handler can not handle the request");
            }
        }
    }

    /**
     * 獲取處理者對(duì)象的處理級(jí)別
     * @return  處理級(jí)別
     */
    protected abstract int getHandleLevel();

    /**
     * 每個(gè)處理者對(duì)象的具體處理方式
     * @param request   請(qǐng)求者對(duì)象
     */
    protected abstract void handle(AbstractRequest request);
}

  2. 抽象請(qǐng)求者

    public abstract class AbstractRequest {
    private Object obj; //處理對(duì)象

    public AbstractRequest(Object obj) {
        this.obj = obj;
    }

    public Object getContent() {
        return obj;
    }

    /**
     * 獲取請(qǐng)求級(jí)別
     * @return  請(qǐng)求級(jí)別
     */
    public abstract int getRequestLevel();
}

  3. 請(qǐng)求者

    public class Request1 extends AbstractRequest {
    public Request1(Object obj) {
        super(obj);
    }

    @Override
    public int getRequestLevel() {
        return 1;
    }
}

    public class Request2 extends AbstractRequest {
    public Request2(Object obj) {
        super(obj);
    }

    @Override
    public int getRequestLevel() {
        return 2;
    }
}

    public class Request3 extends AbstractRequest {
    public Request3(Object obj) {
        super(obj);
    }

    @Override
    public int getRequestLevel() {
        return 3;
    }
}

  4. 處理者

    public class Handler1 extends AbstractHandler {
    @Override
    protected int getHandleLevel() {
        return 1;
    }

    @Override
    protected void handle(AbstractRequest request) {
        System.out.println("Handler1 handle request:" + request.getRequestLevel());
    }
}

    public class Handler2 extends AbstractHandler {
    @Override
    protected int getHandleLevel() {
        return 2;
    }

    @Override
    protected void handle(AbstractRequest request) {
        System.out.println("Handler2 handle request:" + request.getRequestLevel());
    }
}

    public class Handler3 extends AbstractHandler {
    @Override
    protected int getHandleLevel() {
        return 3;
    }

    @Override
    protected void handle(AbstractRequest request) {
        System.out.println("Handler3 handle request:" + request.getRequestLevel());
    }
}

  5. 客戶類

    public class Client {
    public static void main(String[] args) {
        //構(gòu)造3個(gè)處理者對(duì)象
        AbstractHandler handler1 = new Handler1();
        AbstractHandler handler2 = new Handler2();
        AbstractHandler handler3 = new Handler3();

        //設(shè)置當(dāng)前處理者對(duì)象下一個(gè)節(jié)點(diǎn)的處理者對(duì)象
        handler1.nextHandler = handler2;
        handler2.nextHandler = handler3;

        //構(gòu)造3個(gè)請(qǐng)求者對(duì)象
        AbstractRequest request1 = new Request1("Request1");
        AbstractRequest request2 = new Request2("Request2");
        AbstractRequest request3 = new Request3("Request3");

        //總是從鏈?zhǔn)降氖锥税l(fā)起請(qǐng)求
        handler1.handleRequest(request1);
        handler1.handleRequest(request2);
        handler1.handleRequest(request3);
    }
}

示例三

說明：小明出差學(xué)些新技術(shù)，其中花費(fèi)了5w元，于是小明去找組長報(bào)銷費(fèi)用。。。代碼如下：

  1. 抽象領(lǐng)導(dǎo)者

    public abstract class Leader {
    //上一級(jí)領(lǐng)導(dǎo)處理者
    protected Leader nextHandler;

    /**
     * 處理報(bào)賬請(qǐng)求
     * @param money 能批復(fù)的報(bào)賬額度
     */
    public final void handleRequest(int money) {
        if (money <= limit()) {
            handle(money);
        } else {
            if (nextHandler != null) {
                nextHandler.handleRequest(money);
            }
        }
    }

    /**
     * 自身能夠批復(fù)的額度權(quán)限
     * @return  額度
     */
    protected abstract int limit();

    /**
     * 處理報(bào)賬行為
     * @param money 具體金額
     */
    protected abstract void handle(int money);
}

  2. 具體的領(lǐng)導(dǎo)者

    public class GroupLeader extends Leader {

    @Override
    protected int limit() {
        return 1000;
    }

    @Override
    protected void handle(int money) {
        System.out.println("組長批復(fù)報(bào)銷" + money + "元");
    }
}

    public class Director extends Leader {

    @Override
    protected int limit() {
        return 5000;
    }

    @Override
    protected void handle(int money) {
        System.out.println("主管批復(fù)報(bào)銷" + money + "元");
    }
}

    public class Manager extends Leader {

    @Override
    protected int limit() {
        return 10000;
    }

    @Override
    protected void handle(int money) {
        System.out.println("經(jīng)理批復(fù)報(bào)銷" + money + "元");
    }
}

    public class Boss extends Leader {

    @Override
    protected int limit() {
        return Integer.MAX_VALUE;
    }

    @Override
    protected void handle(int money) {
        System.out.println("老板批復(fù)報(bào)銷" + money + "元");
    }
}

  3. 客戶類小明

    public class XiaoMing {
    public static void main(String[] args) {
        //構(gòu)造各個(gè)領(lǐng)導(dǎo)對(duì)象
        GroupLeader groupLeader = new GroupLeader();
        Director director = new Director();
        Manager manager = new Manager();
        Boss boss = new Boss();

        //設(shè)置上一級(jí)領(lǐng)導(dǎo)處理者對(duì)象
        groupLeader.nextHandler = director;
        director.nextHandler = manager;
        manager.nextHandler = boss;

        //發(fā)起報(bào)賬申請(qǐng)
        groupLeader.handleRequest(50000);
    }
}

    小明先找組長報(bào)賬，然后組長找到主管，主管找到經(jīng)理，經(jīng)理最后找到老板解決。

    當(dāng)然也可以直接跳過某個(gè)人。

對(duì)于責(zé)任鏈中的一個(gè)處理者對(duì)象，其只有兩種行為，一是處理請(qǐng)求，二是將請(qǐng)求轉(zhuǎn)送給下一個(gè)節(jié)點(diǎn)，不允許某個(gè)處理者對(duì)象在處理了請(qǐng)求后又將請(qǐng)求轉(zhuǎn)送給上一個(gè)節(jié)點(diǎn)的情況。

對(duì)于一條責(zé)任鏈來說，一個(gè)請(qǐng)求最終只有兩種情況，一個(gè)唄某個(gè)處理對(duì)象所處理，另一個(gè)是所有對(duì)象均未對(duì)其處理，對(duì)于前一種情況我們稱該責(zé)任鏈為純的責(zé)任鏈，對(duì)于后一種情況我們稱為不純的責(zé)任鏈，在實(shí)際應(yīng)用中，我們所見到的責(zé)任鏈模式大多為不純的責(zé)任鏈。

Android 源碼中的實(shí)現(xiàn)

事件的分發(fā)處理。

責(zé)任鏈模式實(shí)戰(zhàn)

說明：有序廣播的處理。源碼地址

  1. 廣播接收者

    public class FirstReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        //獲取Intent中附加的限制值
        int limit = intent.getIntExtra("limit", -1001);
        //如果限制值等于1000，則處理，否則繼續(xù)轉(zhuǎn)發(fā)給下一個(gè)Receiver
        if (limit == 1000) {
            //獲取Intent中附加的字符串消息并Toast
            String msg = intent.getStringExtra("msg");
            Toast.makeText(context, msg, Toast.LENGTH_SHORT).show();

            //終止廣播
            abortBroadcast();
        } else {
            //添加信息發(fā)送給下一個(gè)Receiver
            Bundle bundle = new Bundle();
            bundle.putString("new", "Message from FirstReceiver");
            setResultExtras(bundle);
        }
    }
}

    public class SecondReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        //獲取Intent中附加的限制值
        int limit = intent.getIntExtra("limit", -1001);
        //如果限制值等于100，則處理，否則繼續(xù)轉(zhuǎn)發(fā)給下一個(gè)Receiver
        if (limit == 100) {
            //獲取Intent中附加的字符串消息并Toast
            String msg = intent.getStringExtra("msg");

            //獲取上一個(gè)Receiver增加的消息
            Bundle bundle = getResultExtras(true);
            String str = bundle.getString("new");
            Toast.makeText(context, msg + "-----" + str, Toast.LENGTH_SHORT).show();

            //終止廣播
            abortBroadcast();
        } else {
            //添加信息發(fā)送給下一個(gè)Receiver
            Bundle bundle = new Bundle();
            bundle.putString("new", "Message from SecondReceiver");
            setResultExtras(bundle);
        }
    }
}

    public class ThirdReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        //獲取Intent中附加的限制值
        int limit = intent.getIntExtra("limit", -1001);
        //如果限制值等于10，則處理，否則繼續(xù)轉(zhuǎn)發(fā)給下一個(gè)Receiver
        if (limit == 10) {
            //獲取Intent中附加的字符串消息并Toast
            String msg = intent.getStringExtra("msg");

            //獲取上一個(gè)Receiver增加的消息
            Bundle bundle = getResultExtras(true);
            String str = bundle.getString("new");
            Toast.makeText(context, msg + "-----" + str, Toast.LENGTH_SHORT).show();

            //終止廣播
            abortBroadcast();
        } else {
            //添加信息發(fā)送給下一個(gè)Receiver
            Bundle bundle = new Bundle();
            bundle.putString("new", "Message from ThirdReceiver");
            setResultExtras(bundle);
        }
    }
}

  2. 部分清單文件數(shù)據(jù)

    <receiver android:name="com.yan.iterator.FirstReceiver">
    <intent-filter android:priority="1000">
        <action android:name="com.yan.iterator.action.ORDER_BROADCAST"/>
    </intent-filter>
</receiver>
<receiver android:name="com.yan.iterator.SecondReceiver">
    <intent-filter android:priority="100">
        <action android:name="com.yan.iterator.action.ORDER_BROADCAST"/>
    </intent-filter>
</receiver>
<receiver android:name="com.yan.iterator.ThirdReceiver">
    <intent-filter android:priority="10">
        <action android:name="com.yan.iterator.action.ORDER_BROADCAST"/>
    </intent-filter>
</receiver>

  3. MainActivity

    public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setAction("com.yan.iterator.action.ORDER_BROADCAST");
                intent.putExtra("limit", 100);
                intent.putExtra("msg", "Message from MainActivity");
                sendOrderedBroadcast(intent, null);
            }
        });
    }
}

總結(jié)

  • 優(yōu)點(diǎn)

    可以對(duì)請(qǐng)求者和處理者關(guān)系解耦，提高代碼的靈活性。

  • 缺點(diǎn)

    對(duì)鏈中請(qǐng)求處理者的遍歷，如果處理者太多，那么遍歷必定會(huì)影響性能，特別是在一些遞歸調(diào)用中，要慎重。

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