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在GoF 的《設(shè)計模式》一書中對責(zé)任鏈模定義的:將請求的發(fā)送和接收解耦,讓多個接收對象都有機會處理這個請求。將這些接收對象串成一條鏈,并沿著這條鏈傳遞這個請求,直到鏈上的某個接收對象能夠處理它為止或者所有接收對象處理一遍。

在網(wǎng)站制作、做網(wǎng)站過程中,需要針對客戶的行業(yè)特點、產(chǎn)品特性、目標受眾和市場情況進行定位分析,以確定網(wǎng)站的風(fēng)格、色彩、版式、交互等方面的設(shè)計方向。創(chuàng)新互聯(lián)公司還需要根據(jù)客戶的需求進行功能模塊的開發(fā)和設(shè)計,包括內(nèi)容管理、前臺展示、用戶權(quán)限管理、數(shù)據(jù)統(tǒng)計和安全保護等功能。
用通俗的話解釋在責(zé)任鏈模式中,多個處理器(接收對象)依次處理同一個請求。一個請求先經(jīng)過 A 處理器處理,然后再把請求傳遞給 B 處理器,B 處理器處理完后再傳遞給 C 處理器,以此類推,形成一個鏈條。鏈條上的每個處理器各自承擔(dān)各自的處理職責(zé),所以叫作責(zé)任鏈模式。
責(zé)任鏈模式有效地降低了發(fā)送和接收者之間的耦合度,增強了系統(tǒng)的可擴展性。在責(zé)任鏈的模式下不僅能夠針對單個處理器對象進行定制升級(每個處理器對象關(guān)注各自的任務(wù)),而且能夠?qū)φ麄€責(zé)任鏈的處理器對象的順序的調(diào)整以及增刪。
本文約定:責(zé)任鏈上的接收對象統(tǒng)一稱為處理器;本文中介紹的責(zé)任鏈屬于GOF定義中責(zé)任鏈的變種即責(zé)任鏈上的所有處理器都會參與任務(wù)的處理。
責(zé)任鏈模式有多種實現(xiàn)方式,從驅(qū)動責(zé)任鏈上處理器方式的角度可以分類兩類,即責(zé)任鏈驅(qū)動 和 責(zé)任鏈處理器自驅(qū)動。
// 1、定義抽象類
public abstract class AbstractHandler {
protected Handler next = null;
// 綁定處理器
public void setSuccessor(Handler next) {
this.next = next;
}
// 處理器執(zhí)行操作并驅(qū)動下一個處理器
public abstract void handle();
}
// 2、定義處理器A
public class HandlerA extends AbstractHandler {
@Override
public void handle() {
// do something
if (next != null) {
next.handle();
}
}
}
// 3、定義處理器B
public class HandlerB extends AbstractHandler {
@Override
public void handle() {
// do something
if (next != null) {
next.handle();
}
}
}
// 4、構(gòu)建責(zé)任鏈并添加處理器
public class HandlerChain {
// 通過鏈表的形式保存責(zé)任鏈
private AbstractHandler head = null;
private AbstractHandler tail = null;
public void addHandler(AbstractHandler handler) {
handler.setSuccessor(null);
if (head == null) {
head = handler;
tail = handler;
return;
}
tail.setSuccessor(handler);
tail = handler;
}
public void handle() {
if (head != null) {
head.handle();
}
}
}
// 5、整體構(gòu)建責(zé)任鏈添加處理器并進行驅(qū)動
public class Application {
public static void main(String[] args) {
// 構(gòu)建責(zé)任鏈并添加處理器
HandlerChain chain = new HandlerChain();
chain.addHandler(new HandlerA());
chain.addHandler(new HandlerB());
// 責(zé)任鏈負責(zé)觸發(fā)
chain.handle();
}
}說明:
// 1、定義抽象接口
public interface IHandler {
void doSomething();
}
// 2、定義處理器A
public class HandlerA implements IHandler {
@Override
public void doSomething() {
// do something
}
}
// 3、定義處理器B
public class HandlerB implements IHandler {
@Override
public void doSomething() {
// do something
}
}
// 4、構(gòu)建責(zé)任鏈并添加處理器
public class HandlerChain {
// 通過數(shù)組的形式保存處理器
private List handlers = new ArrayList<>();
public void addHandler(IHandler handler) {
handlers.add(handler);
}
// 由責(zé)任鏈負責(zé)遍歷所有的處理器并進行調(diào)用
public void handle() {
for (IHandler handler : handlers) {
handler.handle();
}
}
}
// 5、整體構(gòu)建責(zé)任鏈添加處理器并進行驅(qū)動
public class Application {
public static void main(String[] args) {
HandlerChain chain = new HandlerChain();
chain.addHandler(new HandlerA());
chain.addHandler(new HandlerB());
chain.handle();
}
} 說明:
責(zé)任鏈低耦合高擴展的特點讓它在很多開源的框架中被采用,本文選取了開源框架中的Spring Interceptor、Servlet Filter、Dubbo、Sentinel進行責(zé)任鏈的實現(xiàn)介紹,通過對常用框架中責(zé)任鏈應(yīng)用的了解能夠更好掌握責(zé)任鏈落地并在日常的開發(fā)中積極的使用。
3.1.1 Interceptor介紹
圖片
3.1.2 處理器介紹
public interface HandlerInterceptor {
boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception;
void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception;
}
@Component
public class TimeInterceptor extends HandlerInterceptorAdapter {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
// 前置處理
System.out.println("time interceptor preHandle");
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
// 后置處理
System.out.println("time interceptor postHandle");
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
System.out.println("time interceptor afterCompletion");
}
}說明:
3.1.3 責(zé)任鏈構(gòu)建
public class HandlerExecutionChain {
private final Object handler;
private HandlerInterceptor[] interceptors;
private List interceptorList;
private int interceptorIndex = -1;
public void addInterceptor(HandlerInterceptor interceptor) {
// 添加攔截器
initInterceptorList().add(interceptor);
}
public void addInterceptors(HandlerInterceptor... interceptors) {
if (!ObjectUtils.isEmpty(interceptors)) {
CollectionUtils.mergeArrayIntoCollection(interceptors, initInterceptorList());
}
}
private List initInterceptorList() {
if (this.interceptorList == null) {
this.interceptorList = new ArrayList();
if (this.interceptors != null) {
// An interceptor array specified through the constructor
CollectionUtils.mergeArrayIntoCollection(this.interceptors, this.interceptorList);
}
}
this.interceptors = null;
return this.interceptorList;
}
} 說明:
3.1.4 責(zé)任鏈執(zhí)行
public class DispatcherServlet extends FrameworkServlet {
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
try {
try {
// mappedHandler代表的是HandlerExecutionChain責(zé)任鏈 mappedHandler = getHandler(processedRequest);
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// 1、執(zhí)行mappedHandler的applyPreHandle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 2、執(zhí)行controller的執(zhí)行邏輯
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
// 執(zhí)行mappedHandler的applyPostHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
}
finally {
}
}
}
public class HandlerExecutionChain {
private final Object handler;
private HandlerInterceptor[] interceptors;
private List interceptorList;
private int interceptorIndex = -1;
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
// 責(zé)任鏈從前往后的順序執(zhí)行
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
// 責(zé)任鏈從后往前的順序執(zhí)行
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
} 說明:
3.2.1 Filter介紹
3.2.2 處理器介紹
public interface Filter {
public void init(FilterConfig filterConfig) throws ServletException;
public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException;
public void destroy();
}
public class TimeFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("time filter init");
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
// 1、執(zhí)行處理的邏輯
System.out.println("time filter doFilter");
// 2、執(zhí)行責(zé)任鏈當中的下一個 Filter 對象,等價于執(zhí)行 FilterChain 的internalDoFilter方法
filterChain.doFilter(servletRequest, servletResponse);
}
}說明:
3.2.3 責(zé)任鏈構(gòu)建
public final class ApplicationFilterChain implements FilterChain {
// 責(zé)任鏈上 Filter 的維護對象
private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
//責(zé)任鏈上待執(zhí)行的 Filter 對象
private int pos = 0;
// 責(zé)任鏈上擁有的 Filter 數(shù)量
private int n = 0;
void addFilter(ApplicationFilterConfig filterConfig) {
// 避免重復(fù)添加Filter
for(ApplicationFilterConfig filter:filters)
if(filter==filterConfig)
return;
// 按需進行擴容
if (n == filters.length) {
ApplicationFilterConfig[] newFilters =
new ApplicationFilterConfig[n + INCREMENT];
System.arraycopy(filters, 0, newFilters, 0, n);
filters = newFilters;
}
// 保存Filter 對象
filters[n++] = filterConfig;
}
}說明:
3.2.4 責(zé)任鏈執(zhí)行
public final class ApplicationFilterChain implements FilterChain {
// 責(zé)任鏈上 Filter 的維護對象
private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
//責(zé)任鏈上待執(zhí)行的 Filter 對象
private int pos = 0;
// 責(zé)任鏈上擁有的 Filter 數(shù)量
private int n = 0;
// 責(zé)任鏈的執(zhí)行
private void internalDoFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException {
// 在責(zé)任鏈未執(zhí)行完的情況下執(zhí)行責(zé)任鏈 if (pos < n) {
// 獲取當前待執(zhí)行的 Filter,同時遞增下一次待執(zhí)行責(zé)任鏈的下標
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();
if( Globals.IS_SECURITY_ENABLED ) {
// 省略相關(guān)代碼
} else {
filter.doFilter(request, response, this);
}
} catch (Throwable e) {
}
return;
}
try {
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse) &&
Globals.IS_SECURITY_ENABLED ) {
// 執(zhí)行正常的業(yè)務(wù)邏輯
} else {
servlet.service(request, response);
}
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
throw new ServletException(sm.getString("filterChain.servlet"), e);
}
}
}說明:
3.3.1 Dubbo Filter介紹
3.3.2 處理器介紹
@Activate(group = PROVIDER, value = ACCESS_LOG_KEY)
public class AccessLogFilter implements Filter {
@Override
public Result invoke(Invoker> invoker, Invocation inv) throws RpcException {
try {
if (ConfigUtils.isNotEmpty(accessLogKey)) {
AccessLogData logData = buildAccessLogData(invoker, inv);
log(accessLogKey, logData);
}
} catch (Throwable t) {
}
// 執(zhí)行下一個invoker
return invoker.invoke(inv);
}
}說明:
3.3.3 責(zé)任鏈構(gòu)建
public class ProtocolFilterWrapper implements Protocol {
private final Protocol protocol;
public ProtocolFilterWrapper(Protocol protocol) {
this.protocol = protocol;
}
private static Invoker buildInvokerChain(final Invoker invoker, String key, String group) {
// 最后的 Invoker 對象
Invoker last = invoker;
// 遍歷所有 Filter 對象,構(gòu)建責(zé)任鏈 List filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
if (!filters.isEmpty()) {
for (int i = filters.size() - 1; i >= 0; i--) {
// 每個 Filter 封裝成一個 Invoker 對象,通過 filter.invoke進行串聯(lián)
final Filter filter = filters.get(i);
final Invoker next = last;
last = new Invoker() {
@Override
public Result invoke(Invocation invocation) throws RpcException {
return filter.invoke(next, invocation);
}
};
}
}
return last;
}
}
// 封裝了Filter的invoker對象
static final class ProtocolFilterWrapper.1 implements Invoker < T > {
final Invoker val$invoker;
final Filter val$filter;
// 指向下一個Invoker的變量
final Invoker val$next;
public Result invoke(Invocation invocation) throws RpcException {
return this.val$filter.invoke(this.val$next, invocation);
}
ProtocolFilterWrapper.1(Invoker invoker, Filter filter, Invoker invoker2) {
this.val$invoker = invoker;
this.val$filter = filter;
this.val$next = invoker2;
}
} 說明:
3.3.4 責(zé)任鏈執(zhí)行
public class FailfastClusterInvoker extends AbstractClusterInvoker {
public FailfastClusterInvoker(Directory directory) {
super(directory);
}
@Override
public Result doInvoke(Invocation invocation, List> invokers, LoadBalance loadbalance) throws RpcException {
checkInvokers(invokers, invocation);
Invoker invoker = select(loadbalance, invocation, invokers, null);
try {
// 執(zhí)行封裝了Filter的invoker對象,驅(qū)動處理器的執(zhí)行
return invoker.invoke(invocation);
} catch (Throwable e) {
}
}
}
static final class ProtocolFilterWrapper.1 implements Invoker < T > {
final Invoker val$invoker;
final Filter val$filter;
final Invoker val$next;
public Result invoke(Invocation invocation) throws RpcException {
return this.val$filter.invoke(this.val$next, invocation);
}
ProtocolFilterWrapper.1(Invoker invoker, Filter filter, Invoker invoker2) {
this.val$invoker = invoker;
this.val$filter = filter;
this.val$next = invoker2;
} 說明:
3.4.1 Sentinel Slot介紹
3.4.2 處理器介紹
public interface ProcessorSlot {
void entry(Context context, ResourceWrapper resourceWrapper, T param, int count, boolean prioritized,Object... args) throws Throwable;
void fireEntry(Context context, ResourceWrapper resourceWrapper, Object obj, int count, boolean prioritized,Object... args) throws Throwable;
void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args);
void fireExit(Context context, ResourceWrapper resourceWrapper, int count, Object... args);
}
public abstract class AbstractLinkedProcessorSlot implements ProcessorSlot {
private AbstractLinkedProcessorSlot> next = null;
@Override
public void fireEntry(Context context, ResourceWrapper resourceWrapper, Object obj, int count, boolean prioritized, Object... args)
throws Throwable {
// 觸發(fā)下一個處理器對象的處理
if (next != null) {
next.transformEntry(context, resourceWrapper, obj, count, prioritized, args);
}
}
void transformEntry(Context context, ResourceWrapper resourceWrapper, Object o, int count, boolean prioritized, Object... args)
throws Throwable {
T t = (T)o;
// 執(zhí)行具體處理器的邏輯,由具體的處理器自行實現(xiàn)
entry(context, resourceWrapper, t, count, prioritized, args);
}
public void setNext(AbstractLinkedProcessorSlot> next) {
// 綁定下一個處理器的邏輯
this.next = next;
}
}
public class NodeSelectorSlot extends AbstractLinkedProcessorSlot 說明:
3.4.3 責(zé)任鏈構(gòu)建
public class DefaultSlotChainBuilder implements SlotChainBuilder {
@Override
public ProcessorSlotChain build() {
// 責(zé)任鏈的頭部對象ProcessorSlotChain
ProcessorSlotChain chain = new DefaultProcessorSlotChain();
// sortedSlotList獲取所有的處理器對象
List sortedSlotList = SpiLoader.of(ProcessorSlot.class).loadInstanceListSorted();
for (ProcessorSlot slot : sortedSlotList) {
if (!(slot instanceof AbstractLinkedProcessorSlot)) {
continue;
}
// 通過尾添法將職責(zé)slot添加到DefaultProcessorSlotChain當中
chain.addLast((AbstractLinkedProcessorSlot>) slot);
}
return chain;
}
}
public class DefaultProcessorSlotChain extends ProcessorSlotChain {
// 創(chuàng)建DefaultProcessorSlotChain的頭尾節(jié)點first和end
AbstractLinkedProcessorSlot> first = new AbstractLinkedProcessorSlot 說明:
3.4.4 責(zé)任鏈執(zhí)行
public class CtSph implements Sph {
private Entry entryWithPriority(ResourceWrapper resourceWrapper, int count, boolean prioritized, Object... args)
throws BlockException {
Context context = ContextUtil.getContext();
// 省略相關(guān)代碼
ProcessorSlot說明:
在日常項目實踐中,責(zé)任鏈的設(shè)計模式會在很多業(yè)務(wù)場景中落地。
譬如對于支持用戶生成內(nèi)容(UGC)的應(yīng)用來說,用戶生成的內(nèi)容可能包含一些敏感內(nèi)容如敏感言論或者圖片等。針對這種應(yīng)用場景,可以通過責(zé)任鏈模式設(shè)置多個處理器來處理不同的任務(wù),如文本過濾器處理敏感詞,圖片過濾器處理敏感圖片等等。
譬如對于電商服務(wù)中的下單流程來說,一個下單流程包含訂單拆合單,優(yōu)惠計算,訂單生成等多個步驟,我們可以通過責(zé)任鏈模式設(shè)置多個處理器來處理不同的任務(wù)等等。
責(zé)任鏈的應(yīng)用場景非常廣泛,在常見的開源框架中有豐富的落地場景,同樣在業(yè)務(wù)開發(fā)中也可以根據(jù)場景靈活使用。

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