Tomcat

Tomcat 職責(zé)鏈

• Tomcat 的職責(zé)鏈以數(shù)組的形式進(jìn)行維護(hù)，通過(guò)職責(zé)鏈的總長(zhǎng)度 n 和執(zhí)行位置 pos進(jìn)行維護(hù)。
• Tomcat 的職責(zé)鏈的執(zhí)行過(guò)程借助于每個(gè) Filter 本身

職責(zé)鏈的構(gòu)建

public final class ApplicationFilterChain implements FilterChain {

    // 職責(zé)鏈上 Filter 的維護(hù)對(duì)象
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    //職責(zé)鏈上待執(zhí)行的 Filter 對(duì)象
    private int pos = 0;
    // 職責(zé)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(jìn)行擴(kuò)容
        if (n == filters.length) {
            ApplicationFilterConfig[] newFilters =
                new ApplicationFilterConfig[n + INCREMENT];
            System.arraycopy(filters, 0, newFilters, 0, n);
            filters = newFilters;
        }
        // 保存Filter 對(duì)象
        filters[n++] = filterConfig;

    }
}

• 職責(zé)鏈通過(guò)ApplicationFilterConfig[] filters維護(hù)所有的 Filter 對(duì)象。
• 職責(zé)鏈添加 Filter 通過(guò)addFilter實(shí)現(xiàn)，本質(zhì)上是往數(shù)組filters添加元素并更改總數(shù) n 。

職責(zé)鏈的執(zhí)行

public final class ApplicationFilterChain implements FilterChain {

    // 職責(zé)鏈上 Filter 的維護(hù)對(duì)象
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    //職責(zé)鏈上待執(zhí)行的 Filter 對(duì)象
    private int pos = 0;
    // 職責(zé)鏈上擁有的 Filter 數(shù)量
    private int n = 0;

    // 職責(zé)鏈的執(zhí)行
    private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {

        // 在職責(zé)鏈未執(zhí)行完的情況下執(zhí)行職責(zé)鏈
        if (pos < n) {
            // 獲取當(dāng)前待執(zhí)行的 Filter，同時(shí)遞增下一次待執(zhí)行職責(zé)鏈的下標(biāo)
            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);
        } 
    }

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 {
        // 執(zhí)行職責(zé)鏈當(dāng)中的下一個(gè) Filter 對(duì)象，等價(jià)于執(zhí)行 FilterChain 的internalDoFilter方法
        filterChain.doFilter(servletRequest, servletResponse);
    }
}

• FilterChain 的執(zhí)行邏輯在internalDoFilter中，核心就是從職責(zé)鏈的數(shù)組filters當(dāng)中獲取當(dāng)前待執(zhí)行Filter 比國(guó)內(nèi)調(diào)用doFilter邏輯。
• 每個(gè) Filter 內(nèi)部如TimeFilter為例，優(yōu)先執(zhí)行本 Filter 的業(yè)務(wù)邏輯，然后通過(guò)filterChain.doFilter驅(qū)動(dòng)職責(zé)鏈上的下一個(gè) Filter 執(zhí)行。

Mybatis

Mybatis職責(zé)鏈

• Mybatis 的職責(zé)鏈以 鏈表的形式進(jìn)行維護(hù)，職責(zé)鏈元素是攔截器 Interceptor 對(duì)象proxy 封裝。
• Mybatis 的職責(zé)鏈的執(zhí)行過(guò)程借助于每個(gè)Proxy本身的自驅(qū)。

職責(zé)鏈的構(gòu)建

public class InterceptorChain {

  private final List<Interceptor> interceptors = new ArrayList<>();

  // 進(jìn)行攔截器的織入
  public Object pluginAll(Object target) {
    for (Interceptor interceptor : interceptors) {
      target = interceptor.plugin(target);
    }
    return target;
  }
}

---------------------------

public interface Interceptor {

  Object intercept(Invocation invocation) throws Throwable;

  default Object plugin(Object target) {
    return Plugin.wrap(target, this);
  }

  default void setProperties(Properties properties) {
  }
}

-------------------------

public class Plugin implements InvocationHandler {

  private final Object target;
  private final Interceptor interceptor;
  private final Map<Class<?>, Set<Method>> signatureMap;

  private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) {
    this.target = target;
    this.interceptor = interceptor;
    this.signatureMap = signatureMap;
  }

  public static Object wrap(Object target, Interceptor interceptor) {
    Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
    Class<?> type = target.getClass();
    Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
    if (interfaces.length > 0) {
      return Proxy.newProxyInstance(
          type.getClassLoader(),
          interfaces,
          new Plugin(target, interceptor, signatureMap));
    }
    return target;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      Set<Method> methods = signatureMap.get(method.getDeclaringClass());
      if (methods != null && methods.contains(method)) {
        return interceptor.intercept(new Invocation(target, method, args));
      }
      return method.invoke(target, args);
    } catch (Exception e) {
    }
  }
}

• InterceptorChain負(fù)責(zé)遍歷所有的攔截器 Interceptor 對(duì)象構(gòu)建職責(zé)鏈。
• 在 Plugin#wrap方法中將 target 和 Interceptor 對(duì)象封裝成Plugin對(duì)象然后以 動(dòng)態(tài)代理Proxy 的形式返回。
• 每個(gè)Proxy 對(duì)象會(huì)成為下一個(gè) Interceptor 的內(nèi)部的 target 對(duì)象，形式鏈?zhǔn)疥P(guān)系。

職責(zé)鏈的執(zhí)行

public class Plugin implements InvocationHandler {

  private final Object target;
  private final Interceptor interceptor;
  private final Map<Class<?>, Set<Method>> signatureMap;

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      Set<Method> methods = signatureMap.get(method.getDeclaringClass());
      if (methods != null && methods.contains(method)) {
        // 執(zhí)行攔截器的邏輯
        return interceptor.intercept(new Invocation(target, method, args));
      }
      return method.invoke(target, args);
    } catch (Exception e) {
    }
  }
}

-----------------------

@Intercepts({ @Signature(type = Executor.class, method = "update"
        , args = { MappedStatement.class, Object.class}) })
public class SelfDefinePlugin implements Interceptor {

    public Object intercept(Invocation invocation) throws Throwable {
        
        // 執(zhí)行攔截器相關(guān)的邏輯

        // 執(zhí)行下一個(gè)攔截器
        return invocation.proceed();
    }

    public Object plugin(Object target) {
        return Plugin.wrap(target,this);
    }

    public void setProperties(Properties properties) {

    }
}

-----------------------

public class Invocation {

  private final Object target;
  private final Method method;
  private final Object[] args;

  public Invocation(Object target, Method method, Object[] args) {
    this.target = target;
    this.method = method;
    this.args = args;
  }

  public Object proceed() throws InvocationTargetException, IllegalAccessException {
    return method.invoke(target, args);
  }
}

• Proxy對(duì)象執(zhí)行plugin的invoke方法，在invoke方法內(nèi)部會(huì)訪問(wèn)攔截器 interceptor 對(duì)象的intercept方法。
• interceptor對(duì)象實(shí)現(xiàn)了Interceptor接口并重寫(xiě)了intercept方法，改寫(xiě)的intercept內(nèi)部?jī)?yōu)先執(zhí)行攔截器本身的邏輯，再通過(guò)invocation.proceed觸發(fā)職責(zé)鏈上下一個(gè)攔截器對(duì)象的執(zhí)行。
• Invocation對(duì)象封裝下一個(gè)攔截器對(duì)象的 Proxy 對(duì)象即 target 對(duì)象，執(zhí)行方法即method對(duì)象。

Dubbo

Dubbo 職責(zé)鏈

• Dubbo 的職責(zé)鏈以 鏈表的形式進(jìn)行維護(hù)，職責(zé)鏈元素是ProtocolFilterWrapper的匿名類(lèi)，匿名類(lèi)對(duì)象包含了下一個(gè)職責(zé)鏈元素。
• Dubbo 的職責(zé)鏈的執(zhí)行過(guò)程借助于每個(gè)ProtocolFilterWrapper匿名類(lèi)對(duì)象的自驅(qū)。

職責(zé)鏈的構(gòu)建

public class ProtocolFilterWrapper implements Protocol {

    private final Protocol protocol;

    public ProtocolFilterWrapper(Protocol protocol) {
        this.protocol = protocol;
    }

    private static <T> Invoker<T> buildInvokerChain(final Invoker<T> invoker, String key, String group) {

        // 最后的 Invoker 對(duì)象
        Invoker<T> last = invoker;

        // 遍歷所有 Filter 對(duì)象，構(gòu)建職責(zé)鏈
        List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
        if (!filters.isEmpty()) {
            for (int i = filters.size() - 1; i >= 0; i--) {
                // 每個(gè) Filter 封裝成一個(gè) Invoker 對(duì)象，通過(guò) filter.invoke進(jìn)行串聯(lián)
                final Filter filter = filters.get(i);
                final Invoker<T> next = last;
                last = new Invoker<T>() {

                    @Override
                    public Class<T> getInterface() {
                        return invoker.getInterface();
                    }

                    @Override
                    public URL getUrl() {
                        return invoker.getUrl();
                    }

                    @Override
                    public boolean isAvailable() {
                        return invoker.isAvailable();
                    }

                    @Override
                    public Result invoke(Invocation invocation) throws RpcException {
                        return filter.invoke(next, invocation);
                    }
                };
            }
        }
        return last;
    }
}

• Dubbo的職責(zé)鏈通過(guò)遍歷所有的filters并依次創(chuàng)建ProtocolFilterWrapper的匿名類(lèi)對(duì)象進(jìn)行鏈?zhǔn)酱?lián)。
• new Invoker<T>()的操作會(huì)生成ProtocolFilterWrapper匿名類(lèi)對(duì)象。

static final class ProtocolFilterWrapper.1 implements Invoker < T > {
    final Invoker val$invoker;
    final Filter val$filter;
    final Invoker val$next;

 ProtocolFilterWrapper.1(Invoker invoker, Filter filter, Invoker invoker2) {
     this.val$invoker = invoker;
     this.val$filter = filter;
     this.val$next = invoker2;
 }
}

• ProtocolFilterWrapper.1作為內(nèi)部匿名類(lèi)包含了 filter 對(duì)象和下一個(gè)職責(zé)鏈元素 invoker2.

職責(zé)鏈的構(gòu)建

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;
    }
}

--------------------------

@Activate(group = {Constants.CONSUMER, Constants.PROVIDER}, value = Constants.CACHE_KEY)
public class CacheFilter implements Filter {

    private CacheFactory cacheFactory;

    public void setCacheFactory(CacheFactory cacheFactory) {
        this.cacheFactory = cacheFactory;
    }

    @Override
    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        if (cacheFactory != null && ConfigUtils.isNotEmpty(invoker.getUrl().getMethodParameter(invocation.getMethodName(), Constants.CACHE_KEY))) {
            Cache cache = cacheFactory.getCache(invoker.getUrl(), invocation);
            if (cache != null) {
                String key = StringUtils.toArgumentString(invocation.getArguments());
                Object value = cache.get(key);
                if (value != null) {
                    return new RpcResult(value);
                }

                // 執(zhí)行下一個(gè) Filter 的調(diào)用
                Result result = invoker.invoke(invocation);

                if (!result.hasException() && result.getValue() != null) {
                    cache.put(key, result.getValue());
                }
                return result;
            }
        }
        return invoker.invoke(invocation);
    }
}

• 職責(zé)鏈的執(zhí)行參考ProtocolFilterWrapper.1#invoke方法，調(diào)用當(dāng)前 Filter 對(duì)象的 invoke 方法（this.val$filter.invoke）。
• 每個(gè)具體的 Filter 如CacheFilter會(huì)執(zhí)行自生的邏輯，然后調(diào)用下一個(gè) Filter 對(duì)象的 invoke 方法來(lái)驅(qū)動(dòng)職責(zé)鏈的執(zhí)行。