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(lèi)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(méi)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(lèi)

@Datapublic class Receipt { /** * 回執(zhí)信息 */ String message; /** * 回執(zhí)類(lèi)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; }}

復(fù)制

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(lèi)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(lèi)型，就需要修改或添加if-else分支，違反了開(kāi)閉原則（對(duì)擴(kuò)展開(kāi)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(hù)端而獨(dú)立變化，客戶(hù)端僅僅依賴(lài)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(hù)端寫(xiě)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(chǎng)類(lèi)中去，這就是策略模式+簡(jiǎn)單工廠(chǎng)，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(lèi)，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(lèi)(策略接口的持有者)

/** * @Description: 上下文類(lèi)，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(chǎng)

/** * @Description: 策略工廠(chǎng) * @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(hù)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(chǎng)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(chǎng) * @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(chǎng)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(kāi)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(lèi)，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(hù)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(hù)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(lèi)

/** * @Description: 責(zé)任鏈實(shí)現(xiàn)類(lèi) * @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(lài)注入的方式獲取到IReceiptHandler的子類(lèi)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(hù)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(lèi)并修改ReceiptHandlerContainer處理者容器即可，如果要使得程序符合開(kāi)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(lèi)。Java知音公眾號(hào)內(nèi)回復(fù)“后端面試”，送你一份面試寶典

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

/** * @Description: 反射工具類(lèi) * @Auther: wuzhazha */public class ReflectionUtil { /** * 定義類(lèi)集合（用于存放所有加載的類(lèi)） */ private static final Set CLASS_SET; static { //指定加載包路徑 CLASS_SET = getClassSet(“com.yaolong”); } /** * 獲取類(lèi)加載器 * @return */ public static ClassLoader getClassLoader(){ return Thread.currentThread().getContextClassLoader(); } /** * 加載類(lèi) * @param className 類(lèi)全限定名稱(chēng) * @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(lèi) * @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(lèi)（或接口）的所有子類(lèi)（或?qū)崿F(xiàn)類(lèi)） * @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(lèi) * @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(lèi) 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(kāi)閉原則，如果新增一個(gè)回執(zhí)類(lèi)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(méi)有太大異同，為了能符合開(kāi)閉原則，通過(guò)自定義注解的方式，標(biāo)記處理者類(lèi)，然后反射獲取到該類(lèi)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(guān)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?，?huì)讓代碼更加清晰，容易維護(hù)，但同時(shí)類(lèi)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)！