責任鏈模式（Chain of Responsibility Pattern）：避免請求發(fā)送者與接收者耦合在一起，讓多個對象都有可能接收請求留储，將這些對象連接成一條鏈，并且沿著這條鏈傳遞請求，直到有對象處理它為止祟剔。
一限次、先來簡單的實現(xiàn)芒涡，理一下思路：
- 每個接收者應(yīng)該知道是否處理這個任務(wù)
- 每個接收者應(yīng)該持有下一個接收者，當自己不處理時卖漫，把任務(wù)向下傳遞
向上抽取出BaseReceiver：
public abstract class BaseReceiver {
/**
* 是否處理任務(wù)
*/
private boolean isExecute;
/**
* 下一個任務(wù)接收者
*/
private BaseReceiver nextReceiver;
public BaseReceiver(boolean isExecute) {
this.isExecute = isExecute;
}
/**
* 綁定下一個任務(wù)接收者
* @param receiver
*/
public void addNextReceiver(BaseReceiver receiver) {
nextReceiver = receiver;
}
/**
* 處理任務(wù)
*/
public abstract void execute();
/**
* 任務(wù)流费尽，每個任務(wù)判斷自己是否執(zhí)行，不執(zhí)行就傳遞給下一個任務(wù)
*/
public void run() {
if (isExecute) {
execute();
}else if (nextReceiver != null) {
nextReceiver.run();
}
}
}
創(chuàng)建出三個接收者：Receiver1羊始、Receiver3旱幼、Receiver3
public class Receiver1 extends BaseReceiver {
public Receiver1(boolean isExecute) {
super(isExecute);
}
@Override
public void execute() {
System.out.println("Receiver1執(zhí)行了");
}
}
測試調(diào)用：
public static void main(String[] args) {
Receiver1 receiver1 = new Receiver1(false);
Receiver2 receiver2 = new Receiver2(true);
Receiver3 receiver3 = new Receiver3(false);
receiver1.addNextReceiver(receiver2);
receiver2.addNextReceiver(receiver3);
receiver1.run();
}
輸出結(jié)果：
Receiver2執(zhí)行了
揍是這么簡單。
二突委、再來一種實現(xiàn)柏卤，其實還是一樣的，只是封裝了一下匀油，上面那種addNextReceiver()感覺有點不爽缘缚，這次用一個manager管理一下。
先看完代碼再解釋敌蚜，首先還是抽取的一個接收者接口：
public interface IBaseReceiver {
/**
*
* @param condition 判斷任務(wù)是否執(zhí)行的條件
* @param receiverManager 接受者管理器桥滨，也實現(xiàn)了IBaseReceiver
*/
public void execute(String condition, IBaseReceiver receiverManager);
}
condition就是第一種實現(xiàn)里的是否執(zhí)行的條件，這里用一個String表示钝侠。
然后是Receiver1该园、Receiver3、Receiver3
public class Receiver1 implements IBaseReceiver {
@Override
public void execute(String condition, IBaseReceiver receiverManager) {
if (condition == "1") {
System.out.println("Receiver1執(zhí)行了任務(wù)");
}else {
receiverManager.execute(condition, receiverManager);
}
}
}
這里是否處理的條件帅韧，就是判斷String的值里初，具體業(yè)務(wù)中這里的判斷條件靈活修改。
看到上面一直在傳遞一個也實現(xiàn)了IBaseReceiver的receiverManager忽舟，肯定是不理解為什么双妨，這里看一下這個manager的實現(xiàn)：
public class ReceiverManager implements IBaseReceiver {
/**
* 接收者集合
*/
private List<IBaseReceiver> receivers = new ArrayList<>();
/**
* 添加接收者
* @param receiver
*/
public void addReceiver(IBaseReceiver receiver) {
receivers.add(receiver);
}
/**
* 當前接收者角標
*/
private int index = 0;
/**
* 每次調(diào)用一次就會進行index++操作，用這種方式實現(xiàn)了接收者的向下傳遞
* @param condition 判斷任務(wù)是否執(zhí)行的條件
* @param receiverManager 接受者管理器叮阅，也實現(xiàn)了IBaseReceiver
*/
@Override
public void execute(String condition, IBaseReceiver receiverManager) {
if (receivers.isEmpty()) return;
if (index >= receivers.size()) return;
IBaseReceiver receiver = receivers.get(index);
index++;
receiver.execute(condition, receiverManager);
}
}
看完調(diào)用再解釋上面的函數(shù)刁品，調(diào)用：
ReceiverManager receiverManager = new ReceiverManager();
receiverManager.addReceiver(new Receiver1());
receiverManager.addReceiver(new Receiver2());
receiverManager.addReceiver(new Receiver3());
receiverManager.execute("2", receiverManager);
運行結(jié)果：
Receiver2執(zhí)行了任務(wù)
理一下上面的流程，這里的調(diào)用有點繞浩姥，但是很巧妙：
調(diào)用的時候receiverManager執(zhí)行execute()時挑随，參數(shù)直接傳入了他自己，那直接進入到ReceiverManager的execute ()方法：
public void execute(String condition, IBaseReceiver receiverManager) {
...
//此時index為0勒叠，receiver為Receiver1的實例對象
IBaseReceiver receiver = receivers.get(index);
index++;
receiver.execute(condition, receiverManager);
}
index的初始值是0兜挨，那直接拿到集合中的第一個元素膏孟，也就是Receiver1的一個實例，執(zhí)行Receiver1的execute()拌汇，并且還是把這個receiverManager傳遞了過去柒桑，注意在這之前進行了index++，也就是傳遞過去的這個receiverManager中的index已經(jīng)等于1了噪舀。
然后來到Receiver1中：
public class Receiver1 implements IBaseReceiver {
@Override
public void execute(String condition, IBaseReceiver receiverManager) {
if (condition == "1") {
System.out.println("Receiver1執(zhí)行了任務(wù)");
}else {
receiverManager.execute(condition, receiverManager);
}
}
}
因為傳遞過來的condition為2魁淳，不滿足執(zhí)行條件，所以走了else的流程与倡，用傳遞過來的receiverManager繼續(xù)執(zhí)行execute()界逛，還是要注意，這個receiverManager中的index已經(jīng)是等于1的蒸走，那么就又回到了ReceiverManager的代碼中：
public void execute(String condition, IBaseReceiver receiverManager) {
...
//此時index為1仇奶，receiver為Receiver2的實例對象
IBaseReceiver receiver = receivers.get(index);
index++;
receiver.execute(condition, receiverManager);
}
因為receiverManager一直是同一個對象貌嫡，只是傳遞來傳遞去比驻，沒有new，所以這里的index為1岛抄，拿到的receiver為Receiver2的實例對象别惦，那么就進入了Receiver2的execute()，這里邏輯就不再貼了夫椭，跟進入Receiver1的是一樣的掸掸，只是判斷條件不同，因為條件滿足蹭秋，Receiver2直接處理了任務(wù)扰付，不再繼續(xù)進行，如果條件還是不滿足仁讨，繼續(xù)Receiver3羽莺，這么一直循環(huán)下去。
還是亂的話洞豁，跟著代碼理一下盐固，其實很簡單很清晰，也有點妙丈挟。
這種設(shè)計模式的使用也很常見刁卜，Android源碼中的事件傳遞，Okhttp中的攔截器曙咽，好多好多蛔趴，都是使用到。
