來(lái)吧,用設(shè)計(jì)模式來(lái)干掉 if-else 啊~

來(lái)源：cnblogs.com/DiDi516/p/11787257.html

• 前言
• 傳統(tǒng)做法-if-else分支
• 策略模式+Map字典
• 責(zé)任鏈模式
• 策略模式+注解
• 小結(jié)

前言

物流行業(yè)中，通常會(huì)涉及到EDI報(bào)文(XML格式文件)傳輸和回執(zhí)接收，每發(fā)送一份EDI報(bào)文，后續(xù)都會(huì)收到與之關(guān)聯(lián)的回執(zhí)（標(biāo)識(shí)該數(shù)據(jù)在第三方系統(tǒng)中的流轉(zhuǎn)狀態(tài)）。

這里枚舉幾種回執(zhí)類型：MT1101、MT2101、MT4101、MT8104、MT8105、MT9999，系統(tǒng)在收到不同的回執(zhí)報(bào)文后，會(huì)執(zhí)行對(duì)應(yīng)的業(yè)務(wù)邏輯處理。當(dāng)然，實(shí)際業(yè)務(wù)場(chǎng)景并沒有那么籠統(tǒng)，這里以回執(zhí)處理為演示案例

模擬一個(gè)回執(zhí)類

@Data
public?class?Receipt?{

????/**
?????*?回執(zhí)信息
?????*/
????String?message;

????/**
?????*?回執(zhí)類型(`MT1101、MT2101、MT4101、MT8104、MT8105、MT9999`)
?????*/
????String?type;

}

模擬一個(gè)回執(zhí)生成器

public?class?ReceiptBuilder?{

????public?static?List?generateReceiptList(){
????????//直接模擬一堆回執(zhí)對(duì)象
????????List?receiptList?=?new?ArrayList<>();
????????receiptList.add(new?Receipt("我是MT2101回執(zhí)喔","MT2101"));
????????receiptList.add(new?Receipt("我是MT1101回執(zhí)喔","MT1101"));
????????receiptList.add(new?Receipt("我是MT8104回執(zhí)喔","MT8104"));
????????receiptList.add(new?Receipt("我是MT9999回執(zhí)喔","MT9999"));
????????//......
????????return?receiptList;
????}
}

傳統(tǒng)做法-if-else分支

List?receiptList?=?ReceiptBuilder.generateReceiptList();
//循環(huán)處理
for?(Receipt?receipt?:?receiptList)?{
????if?(StringUtils.equals("MT2101",receipt.getType()))?{
????????System.out.println("接收到MT2101回執(zhí)");
????????System.out.println("解析回執(zhí)內(nèi)容");
????????System.out.println("執(zhí)行業(yè)務(wù)邏輯");
????}?else?if?(StringUtils.equals("MT1101",receipt.getType()))?{
????????System.out.println("接收到MT1101回執(zhí)");
????????System.out.println("解析回執(zhí)內(nèi)容");
????????System.out.println("執(zhí)行業(yè)務(wù)邏輯");
????}?else?if?(StringUtils.equals("MT8104",receipt.getType()))?{
????????System.out.println("接收到MT8104回執(zhí)");
????????System.out.println("解析回執(zhí)內(nèi)容");
????????System.out.println("執(zhí)行業(yè)務(wù)邏輯");
????}?else?if?(StringUtils.equals("MT9999",receipt.getType()))?{
????????System.out.println("接收到MT9999回執(zhí)");
????????System.out.println("解析回執(zhí)內(nèi)容");
????????System.out.println("執(zhí)行業(yè)務(wù)邏輯");
????????System.out.println("推送郵件");
????}
????//?......未來(lái)可能還有好多個(gè)else?if
}

在遇到if-else的分支業(yè)務(wù)邏輯比較復(fù)雜時(shí)，我們都習(xí)慣于將其抽出一個(gè)方法或者封裝成一個(gè)對(duì)象去調(diào)用，這樣整個(gè)if-else結(jié)構(gòu)就不會(huì)顯得太臃腫。

就上面例子，當(dāng)回執(zhí)的類型越來(lái)越多時(shí)，分支else if 就會(huì)越來(lái)越多，每增加一個(gè)回執(zhí)類型，就需要修改或添加if-else分支，違反了開閉原則（對(duì)擴(kuò)展開放，對(duì)修改關(guān)閉）

策略模式+Map字典

我們知道， 策略模式的目的是封裝一系列的算法，它們具有共性，可以相互替換，也就是說(shuō)讓算法獨(dú)立于使用它的客戶端而獨(dú)立變化，客戶端僅僅依賴于策略接口 。

在上述場(chǎng)景中，我們可以把if-else分支的業(yè)務(wù)邏輯抽取為各種策略，但是不可避免的是依然需要客戶端寫一些if-else進(jìn)行策略選擇的邏輯，我們可以將這段邏輯抽取到工廠類中去，這就是策略模式+簡(jiǎn)單工廠，代碼如下

策略接口

/**
?*?@Description:?回執(zhí)處理策略接口
?*?@Auther:?wuzhazha
?*/
public?interface?IReceiptHandleStrategy?{

????void?handleReceipt(Receipt?receipt);

}

策略接口實(shí)現(xiàn)類，也就是具體的處理者

public?class?Mt2101ReceiptHandleStrategy?implements?IReceiptHandleStrategy?{

????@Override
????public?void?handleReceipt(Receipt?receipt)?{
????????System.out.println("解析報(bào)文MT2101:"?+?receipt.getMessage());
????}

}

public?class?Mt1101ReceiptHandleStrategy?implements?IReceiptHandleStrategy?{

????@Override
????public?void?handleReceipt(Receipt?receipt)?{
????????System.out.println("解析報(bào)文MT1101:"?+?receipt.getMessage());
????}

}

public?class?Mt8104ReceiptHandleStrategy?implements?IReceiptHandleStrategy?{

????@Override
????public?void?handleReceipt(Receipt?receipt)?{
????????System.out.println("解析報(bào)文MT8104:"?+?receipt.getMessage());
????}

}

public?class?Mt9999ReceiptHandleStrategy?implements?IReceiptHandleStrategy?{

????@Override
????public?void?handleReceipt(Receipt?receipt)?{
????????System.out.println("解析報(bào)文MT9999:"?+?receipt.getMessage());
????}

}

策略上下文類(策略接口的持有者)

/**
?*?@Description:?上下文類，持有策略接口
?*?@Auther:?wuzhazha
?*/
public?class?ReceiptStrategyContext?{

????private?IReceiptHandleStrategy?receiptHandleStrategy;

????/**
?????*?設(shè)置策略接口
?????*?@param?receiptHandleStrategy
?????*/
????public?void?setReceiptHandleStrategy(IReceiptHandleStrategy?receiptHandleStrategy)?{
????????this.receiptHandleStrategy?=?receiptHandleStrategy;
????}

????public?void?handleReceipt(Receipt?receipt){
????????if?(receiptHandleStrategy?!=?null)?{
?????????????receiptHandleStrategy.handleReceipt(receipt);
????????}
????}
}

策略工廠

/**
?*?@Description:?策略工廠
?*?@Auther:?wuzhazha
?*/
public?class?ReceiptHandleStrategyFactory?{

????private?ReceiptHandleStrategyFactory(){}

????public?static?IReceiptHandleStrategy?getReceiptHandleStrategy(String?receiptType){
????????IReceiptHandleStrategy?receiptHandleStrategy?=?null;
????????if?(StringUtils.equals("MT2101",receiptType))?{
????????????receiptHandleStrategy?=?new?Mt2101ReceiptHandleStrategy();
????????}?else?if?(StringUtils.equals("MT8104",receiptType))?{
????????????receiptHandleStrategy?=?new?Mt8104ReceiptHandleStrategy();
????????}
????????return?receiptHandleStrategy;
????}
}

客戶端

public?class?Client?{

????public?static?void?main(String[]?args)?{
????????//模擬回執(zhí)
????????List?receiptList?=?ReceiptBuilder.generateReceiptList();
????????//策略上下文
????????ReceiptStrategyContext?receiptStrategyContext?=?new?ReceiptStrategyContext();
????????for?(Receipt?receipt?:?receiptList)?{
????????????//獲取并設(shè)置策略
????????????IReceiptHandleStrategy?receiptHandleStrategy?=?ReceiptHandleStrategyFactory.getReceiptHandleStrategy(receipt.getType());
????????????receiptStrategyContext.setReceiptHandleStrategy(receiptHandleStrategy);
????????????//執(zhí)行策略
????????????receiptStrategyContext.handleReceipt(receipt);
????????}
????}
}

解析報(bào)文MT2101:我是MT2101回執(zhí)報(bào)文喔 解析報(bào)文MT8104:我是MT8104回執(zhí)報(bào)文喔

由于我們的目的是消除if-else，那么這里需要將ReceiptHandleStrategyFactory策略工廠進(jìn)行改造下，采用字典的方式存放我的策略，而Map具備key-value結(jié)構(gòu)，采用Map是個(gè)不錯(cuò)選擇。

稍微改造下，代碼如下

/**
?*?@Description:?策略工廠
?*?@Auther:?wuzhazha
?*/
public?class?ReceiptHandleStrategyFactory?{

????private?static?Map?receiptHandleStrategyMap;

????private?ReceiptHandleStrategyFactory(){
????????this.receiptHandleStrategyMap?=?new?HashMap<>();
????????this.receiptHandleStrategyMap.put("MT2101",new?Mt2101ReceiptHandleStrategy());
????????this.receiptHandleStrategyMap.put("MT8104",new?Mt8104ReceiptHandleStrategy());
????}

????public?static?IReceiptHandleStrategy?getReceiptHandleStrategy(String?receiptType){
????????return?receiptHandleStrategyMap.get(receiptType);
????}
}

經(jīng)過(guò)對(duì)策略模式+簡(jiǎn)單工廠方案的改造，我們已經(jīng)消除了if-else的結(jié)構(gòu)，每當(dāng)新來(lái)了一種回執(zhí)，只需要添加新的回執(zhí)處理策略，并修改ReceiptHandleStrategyFactory中的Map集合。

如果要使得程序符合開閉原則，則需要調(diào)整ReceiptHandleStrategyFactory中處理策略的獲取方式，通過(guò)反射的方式，獲取指定包下的所有IReceiptHandleStrategy實(shí)現(xiàn)類，然后放到字典Map中去。

責(zé)任鏈模式

責(zé)任鏈模式是一種對(duì)象的行為模式。在責(zé)任鏈模式里，很多對(duì)象由每一個(gè)對(duì)象對(duì)其下家的引用而連接起來(lái)形成一條鏈。請(qǐng)求在這個(gè)鏈上傳遞，直到鏈上的某一個(gè)對(duì)象決定處理此請(qǐng)求。

發(fā)出這個(gè)請(qǐng)求的客戶端并不知道鏈上的哪一個(gè)對(duì)象最終處理這個(gè)請(qǐng)求，這使得系統(tǒng)可以在不影響客戶端的情況下動(dòng)態(tài)地重新組織和分配責(zé)任

回執(zhí)處理者接口

/**
?*?@Description:?抽象回執(zhí)處理者接口
?*?@Auther:?wuzhazha
?*/
public?interface?IReceiptHandler?{

????void?handleReceipt(Receipt?receipt,IReceiptHandleChain?handleChain);

}

責(zé)任鏈接口

/**
?*?@Description:?責(zé)任鏈接口
?*?@Auther:?wuzhazha
?*/
public?interface?IReceiptHandleChain?{

????void?handleReceipt(Receipt?receipt);
}

責(zé)任鏈接口實(shí)現(xiàn)類

/**
?*?@Description:?責(zé)任鏈實(shí)現(xiàn)類
?*?@Auther:?wuzhazha
?*/
public?class?ReceiptHandleChain?implements?IReceiptHandleChain?{
????//記錄當(dāng)前處理者位置
????private?int?index?=?0;
????//處理者集合
????private?static?List?receiptHandlerList;

????static?{
????????//從容器中獲取處理器對(duì)象
????????receiptHandlerList?=?ReceiptHandlerContainer.getReceiptHandlerList();
????}

????@Override
????public?void?handleReceipt(Receipt?receipt)?{
????????if?(receiptHandlerList?!=null?&&?receiptHandlerList.size()?>?0)?{
????????????if?(index?!=?receiptHandlerList.size())?{
????????????????IReceiptHandler?receiptHandler?=?receiptHandlerList.get(index++);
????????????????receiptHandler.handleReceipt(receipt,this);
????????????}
????????}
????}
}

具體回執(zhí)處理者

public?class?Mt2101ReceiptHandler?implements?IReceiptHandler?{

????@Override
????public?void?handleReceipt(Receipt?receipt,?IReceiptHandleChain?handleChain)?{
????????if?(StringUtils.equals("MT2101",receipt.getType()))?{
????????????System.out.println("解析報(bào)文MT2101:"?+?receipt.getMessage());
????????}
????????//處理不了該回執(zhí)就往下傳遞
????????else?{
????????????handleChain.handleReceipt(receipt);
????????}
????}
}

public?class?Mt8104ReceiptHandler?implements?IReceiptHandler?{

????@Override
????public?void?handleReceipt(Receipt?receipt,?IReceiptHandleChain?handleChain)?{
????????if?(StringUtils.equals("MT8104",receipt.getType()))?{
????????????System.out.println("解析報(bào)文MT8104:"?+?receipt.getMessage());
????????}
????????//處理不了該回執(zhí)就往下傳遞
????????else?{
????????????handleChain.handleReceipt(receipt);
????????}
????}
}

責(zé)任鏈處理者容器(如果采用spring,則可以通過(guò)依賴注入的方式獲取到IReceiptHandler的子類對(duì)象)

/**
?*?@Description:?處理者容器
?*?@Auther:?wuzhazha
?*/
public?class?ReceiptHandlerContainer?{

????private?ReceiptHandlerContainer(){}

????public?static?List?getReceiptHandlerList(){
????????List?receiptHandlerList?=?new?ArrayList<>();
????????receiptHandlerList.add(new?Mt2101ReceiptHandler());
????????receiptHandlerList.add(new?Mt8104ReceiptHandler());
????????return?receiptHandlerList;
????}

}

客戶端

public?class?Client?{

????public?static?void?main(String[]?args)?{
????????//模擬回執(zhí)
????????List?receiptList?=?ReceiptBuilder.generateReceiptList();
????????for?(Receipt?receipt?:?receiptList)?{
????????????//回執(zhí)處理鏈對(duì)象
????????????ReceiptHandleChain?receiptHandleChain?=?new?ReceiptHandleChain();
????????????receiptHandleChain.handleReceipt(receipt);
????????}
????}
}

解析報(bào)文MT2101:我是MT2101回執(zhí)報(bào)文喔 解析報(bào)文MT8104:我是MT8104回執(zhí)報(bào)文喔

通過(guò)責(zé)任鏈的處理方式，if-else結(jié)構(gòu)也被我們消除了，每當(dāng)新來(lái)了一種回執(zhí)，只需要添加IReceiptHandler實(shí)現(xiàn)類并修改ReceiptHandlerContainer處理者容器即可，如果要使得程序符合開閉原則，則需要調(diào)整ReceiptHandlerContainer中處理者的獲取方式，通過(guò)反射的方式，獲取指定包下的所有IReceiptHandler實(shí)現(xiàn)類。

這里使用到了一個(gè)反射工具類，用于獲取指定接口的所有實(shí)現(xiàn)類

/**
?*?@Description:?反射工具類
?*?@Auther:?wuzhazha
?*/
public?class?ReflectionUtil?{

????/**
?????*?定義類集合（用于存放所有加載的類）
?????*/
????private?static?final?Set>?CLASS_SET;

????static?{
????????//指定加載包路徑
????????CLASS_SET?=?getClassSet("com.yaolong");
????}

????/**
?????*?獲取類加載器
?????*?@return
?????*/
????public?static?ClassLoader?getClassLoader(){
????????return?Thread.currentThread().getContextClassLoader();
????}

????/**
?????*?加載類
?????*?@param?className?類全限定名稱
?????*?@param?isInitialized?是否在加載完成后執(zhí)行靜態(tài)代碼塊
?????*?@return
?????*/
????public?static?Class?loadClass(String?className,boolean?isInitialized)?{
????????Class?cls;
????????try?{
????????????cls?=?Class.forName(className,isInitialized,getClassLoader());
????????}?catch?(ClassNotFoundException?e)?{
????????????throw?new?RuntimeException(e);
????????}
????????return?cls;
????}

????public?static?Class?loadClass(String?className)?{
????????return?loadClass(className,true);
????}

????/**
?????*?獲取指定包下所有類
?????*?@param?packageName
?????*?@return
?????*/
????public?static?Set>?getClassSet(String?packageName)?{
????????Set>?classSet?=?new?HashSet<>();
????????try?{
????????????Enumeration?urls?=?getClassLoader().getResources(packageName.replace(".","/"));
????????????while?(urls.hasMoreElements())?{
????????????????URL?url?=?urls.nextElement();
????????????????if?(url?!=?null)?{
????????????????????String?protocol?=?url.getProtocol();
????????????????????if?(protocol.equals("file"))?{
????????????????????????String?packagePath?=?url.getPath().replace("%20","");
????????????????????????addClass(classSet,packagePath,packageName);
????????????????????}?else?if?(protocol.equals("jar"))?{
????????????????????????JarURLConnection?jarURLConnection?=?(JarURLConnection)?url.openConnection();
????????????????????????if?(jarURLConnection?!=?null)?{
????????????????????????????JarFile?jarFile?=?jarURLConnection.getJarFile();
????????????????????????????if?(jarFile?!=?null)?{
????????????????????????????????Enumeration?jarEntries?=?jarFile.entries();
????????????????????????????????while?(jarEntries.hasMoreElements())?{
????????????????????????????????????JarEntry?jarEntry?=?jarEntries.nextElement();
????????????????????????????????????String?jarEntryName?=?jarEntry.getName();
????????????????????????????????????if?(jarEntryName.endsWith(".class"))?{
????????????????????????????????????????String?className?=?jarEntryName.substring(0,?jarEntryName.lastIndexOf(".")).replaceAll("/",?".");
????????????????????????????????????????doAddClass(classSet,className);
????????????????????????????????????}
????????????????????????????????}
????????????????????????????}
????????????????????????}
????????????????????}
????????????????}
????????????}


????????}?catch?(IOException?e)?{
????????????throw?new?RuntimeException(e);
????????}
????????return?classSet;
????}

????private?static?void?doAddClass(Set>?classSet,?String?className)?{
????????Class?cls?=?loadClass(className,false);
????????classSet.add(cls);
????}

????private?static?void?addClass(Set>?classSet,?String?packagePath,?String?packageName)?{
????????final?File[]?files?=?new?File(packagePath).listFiles(new?FileFilter()?{
????????????@Override
????????????public?boolean?accept(File?file)?{
????????????????return?(file.isFile()?&&?file.getName().endsWith(".class"))?||?file.isDirectory();
????????????}
????????});
????????for?(File?file?:?files)?{
????????????String?fileName?=?file.getName();
????????????if?(file.isFile())?{
????????????????String?className?=?fileName.substring(0,?fileName.lastIndexOf("."));
????????????????if?(StringUtils.isNotEmpty(packageName))?{
????????????????????className?=?packageName?+?"."?+?className;
????????????????}
????????????????doAddClass(classSet,className);
????????????}?else?{
????????????????String?subPackagePath?=?fileName;
????????????????if?(StringUtils.isNotEmpty(packagePath))?{
????????????????????subPackagePath?=?packagePath?+?"/"?+?subPackagePath;
????????????????}
????????????????String?subPackageName?=?fileName;
????????????????if?(StringUtils.isNotEmpty(packageName))?{
????????????????????subPackageName?=?packageName?+?"."?+?subPackageName;
????????????????}
????????????????addClass(classSet,subPackagePath,subPackageName);
????????????}
????????}
????}


????public?static?Set>?getClassSet()?{
????????return?CLASS_SET;
????}

????/**
?????*?獲取應(yīng)用包名下某父類（或接口）的所有子類（或?qū)崿F(xiàn)類）
?????*?@param?superClass
?????*?@return
?????*/
????public?static?Set>?getClassSetBySuper(Class?superClass)?{
????????Set>?classSet?=?new?HashSet<>();
????????for?(Class?cls?:?CLASS_SET)?{
????????????if?(superClass.isAssignableFrom(cls)?&&?!superClass.equals(cls))?{
????????????????classSet.add(cls);
????????????}
????????}
????????return?classSet;
????}

????/**
?????*?獲取應(yīng)用包名下帶有某注解的類
?????*?@param?annotationClass
?????*?@return
?????*/
????public?static?Set>?getClassSetByAnnotation(Class?annotationClass)?{
????????Set>?classSet?=?new?HashSet<>();
????????for?(Class?cls?:?CLASS_SET)?{
????????????if?(cls.isAnnotationPresent(annotationClass))?{
????????????????classSet.add(cls);
????????????}
????????}
????????return?classSet;
????}

}

接下來(lái)改造ReceiptHandlerContainer

public?class?ReceiptHandlerContainer?{

????private?ReceiptHandlerContainer(){}

????public?static?List?getReceiptHandlerList(){
????????List?receiptHandlerList?=?new?ArrayList<>();
????????//獲取IReceiptHandler接口的實(shí)現(xiàn)類
????????Set>?classList?=?ReflectionUtil.getClassSetBySuper(IReceiptHandler.class);
????????if?(classList?!=?null?&&?classList.size()?>?0)?{
????????????for?(Class?clazz?:?classList)?{
????????????????try?{
????????????????????receiptHandlerList.add((IReceiptHandler)clazz.newInstance());
????????????????}?catch?(?Exception?e)?{
????????????????????e.printStackTrace();
????????????????}
????????????}
????????}
????????return?receiptHandlerList;
????}

}

至此，該方案完美符合了開閉原則，如果新增一個(gè)回執(zhí)類型，只需要添加一個(gè)新的回執(zhí)處理器即可，無(wú)需做其它改動(dòng)。如新加了MT6666的回執(zhí)，代碼如下

public?class?Mt6666ReceiptHandler?implements?IReceiptHandler?{

????@Override
????public?void?handleReceipt(Receipt?receipt,?IReceiptHandleChain?handleChain)?{
????????if?(StringUtils.equals("MT6666",receipt.getType()))?{
????????????System.out.println("解析報(bào)文MT6666:"?+?receipt.getMessage());
????????}
????????//處理不了該回執(zhí)就往下傳遞
????????else?{
????????????handleChain.handleReceipt(receipt);
????????}
????}
}

策略模式+注解

此方案其實(shí)和上述沒有太大異同，為了能符合開閉原則，通過(guò)自定義注解的方式，標(biāo)記處理者類，然后反射獲取到該類集合，放到Map容器中，這里不再贅述

小結(jié)

if-else或switch case 這種分支判斷的方式對(duì)于分支邏輯不多的簡(jiǎn)單業(yè)務(wù)，還是直觀高效的。對(duì)于業(yè)務(wù)復(fù)雜，分支邏輯多，采用適當(dāng)?shù)哪Ｊ郊记桑瑫?huì)讓代碼更加清晰，容易維護(hù)，但同時(shí)類或方法數(shù)量也是倍增的。我們需要對(duì)業(yè)務(wù)做好充分分析，避免一上來(lái)就設(shè)計(jì)模式，避免過(guò)度設(shè)計(jì)！