基於SpringMVC自定義HandlerMapping擴展Handler&注冊自己的Servlet

    今天在研究Zuul 源碼的時候發現其是自定義HandlerMapping 與 自己的Handler，相當於在SpringMVC的org.springframework.web.servlet.DispatcherServlet#doDispatch 方法中通過HandlerMapping 選擇handler時，擴展自己的HandlerMapping 和 Handler。讓MVC優先走自己的handlerMapping 選擇自己的handler。

    下面貼出自己的測試代碼

1. 測試代碼

　　基於Servlet 實現自己的Handler。

1. MyServlet 

package cn.xm.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class MyServlet extends HttpServlet {

    public MyServlet() {
        System.out.println("======myServlet");
    }

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("cn.xm.servlet.MyServlet");
    }

}

　　相當於我們原來的Servlet，然后注入到下面的Controller，在容器啟動會自動創建。調用過程中，會通過Controller 然后調用到Servlet。

2. MyController

package cn.xm.servlet;

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.ServletWrappingController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyController extends ServletWrappingController {

    public MyController() {
        /**
         * 父類org.springframework.web.servlet.mvc.ServletWrappingController實現了InitializingBean 接口，在 afterPropertiesSet 方法中會反射創建 Servlet 對象
         */
        setServletClass(MyServlet.class);
    }

    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception {
        return super.handleRequestInternal(request, response);
    }
}

　　構造方法指明Servlet的class類型，容器啟動會自動創建。

　　handleRequestInternal 方法是org.springframework.web.servlet.mvc.Controller#handleRequest 接口定義的方法，在SpringMVC 獲取到Controller 之后會自動調用該方法。上面會調用到父類org.springframework.web.servlet.mvc.ServletWrappingController#handleRequestInternal：(也就是會調用到MyServlet.service() 方法)

    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        this.servletInstance.service(request, response);
        return null;
    }

3. MyHandlerMapping

　　自己的HandlerMapping，在獲取的時候第一次注冊相關的路由以及Controller。

package cn.xm.servlet;

import org.springframework.web.servlet.handler.AbstractUrlHandlerMapping;

import javax.servlet.http.HttpServletRequest;

public class MyHandlerMapping extends AbstractUrlHandlerMapping {

    private MyController myController;

    private volatile boolean dirty = true;

    public MyHandlerMapping(MyController myController) {
        this.myController = myController;
        /**
         * 設置順序，值越小越先匹配 (在SpringMVC 處理流程會優先調用)
         */
        setOrder(-200);
    }

    @Override
    protected Object lookupHandler(String urlPath, HttpServletRequest request)
            throws Exception {
        if (this.dirty) {
            synchronized (this) {
                if (this.dirty) {
                    registerHandlers();
                    this.dirty = false;
                }
            }
        }
        return super.lookupHandler(urlPath, request);
    }

    private void registerHandlers() {
        // 我們假設自己的請求路徑都從 /api/v1/my/ 開始
        registerHandler("/api/v1/my/**", this.myController);
    }

}

4. MyConfiguration

　　注冊相關的對象到Spring 容器

package cn.xm.servlet;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyConfiguration {

    @Bean
    public MyController myController() {
        return new MyController();
    }

    @Bean
    public MyHandlerMapping myHandlerMapping(MyController myController) {
        return new MyHandlerMapping(myController);
    }

 

5. 還有另一種注冊方式

package cn.xm.servlet;

import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyServletAutoconfiguration {

    /**
     * 注入servlet，這種注入方式不會走SpringMVC的中央處理器, 相當於tomcat 在選擇servlet的時候直接走該Servlet
     *
     * @return
     */
    @Bean
    @ConditionalOnMissingBean(name = "myServlet")
    public ServletRegistrationBean myServlet() {
        ServletRegistrationBean myServlet = new ServletRegistrationBean(new MyServlet(), "/my/*");
        return myServlet;
    }

}

　　這種方式注入進去的不走SpringMVC的DispatcherServlet 邏輯，相當於和SpringMVC的DispatcherServlet 是平級，供tomcat 處理時選擇。

 

　　上面的配置就實現了兩種方式。

　　第一種基於AbstractUrlHandlerMapping 與 ServletWrappingController 走SpringMVC 的機制，在Spring的中央處理器進行分發。

　　第二種基於MyServletAutoconfiguration 這種方式不走SpringMVC，相當於Tomcat 根據路由選擇servlet的時候直接選中滿足條件的servlet。

2. 相關原理

1. 基於SpringMVC AbstractUrlHandlerMapping 原理

1. cn.xm.servlet.MyServlet 初始化時機

斷點跟蹤如下：

可以看出是在org.springframework.web.servlet.mvc.ServletWrappingController#afterPropertiesSet 方法中反射創建的對象：

    @Override
    public void afterPropertiesSet() throws Exception {
        if (this.servletClass == null) {
            throw new IllegalArgumentException("'servletClass' is required");
        }
        if (this.servletName == null) {
            this.servletName = this.beanName;
        }
        this.servletInstance = this.servletClass.newInstance();
        this.servletInstance.init(new DelegatingServletConfig());
    }

2. 調用原理

訪問： /api/v1/my/t3

(1) org.apache.catalina.mapper.Mapper#internalMapWrapper 找servlet (tomcat流程)

    private final void internalMapWrapper(ContextVersion contextVersion,
                                          CharChunk path,
                                          MappingData mappingData) throws IOException {

        int pathOffset = path.getOffset();
        int pathEnd = path.getEnd();
        boolean noServletPath = false;

        int length = contextVersion.path.length();
        if (length == (pathEnd - pathOffset)) {
            noServletPath = true;
        }
        int servletPath = pathOffset + length;
        path.setOffset(servletPath);

        // Rule 1 -- Exact Match
        MappedWrapper[] exactWrappers = contextVersion.exactWrappers;
        internalMapExactWrapper(exactWrappers, path, mappingData);

        // Rule 2 -- Prefix Match
        boolean checkJspWelcomeFiles = false;
        MappedWrapper[] wildcardWrappers = contextVersion.wildcardWrappers;
        if (mappingData.wrapper == null) {
            internalMapWildcardWrapper(wildcardWrappers, contextVersion.nesting,
                                       path, mappingData);
            if (mappingData.wrapper != null && mappingData.jspWildCard) {
                char[] buf = path.getBuffer();
                if (buf[pathEnd - 1] == '/') {
                    /*
                     * Path ending in '/' was mapped to JSP servlet based on
                     * wildcard match (e.g., as specified in url-pattern of a
                     * jsp-property-group.
                     * Force the context's welcome files, which are interpreted
                     * as JSP files (since they match the url-pattern), to be
                     * considered. See Bugzilla 27664.
                     */
                    mappingData.wrapper = null;
                    checkJspWelcomeFiles = true;
                } else {
                    // See Bugzilla 27704
                    mappingData.wrapperPath.setChars(buf, path.getStart(),
                                                     path.getLength());
                    mappingData.pathInfo.recycle();
                }
            }
        }

        if(mappingData.wrapper == null && noServletPath &&
                contextVersion.object.getMapperContextRootRedirectEnabled()) {
            // The path is empty, redirect to "/"
            path.append('/');
            pathEnd = path.getEnd();
            mappingData.redirectPath.setChars
                (path.getBuffer(), pathOffset, pathEnd - pathOffset);
            path.setEnd(pathEnd - 1);
            return;
        }

        // Rule 3 -- Extension Match
        MappedWrapper[] extensionWrappers = contextVersion.extensionWrappers;
        if (mappingData.wrapper == null && !checkJspWelcomeFiles) {
            internalMapExtensionWrapper(extensionWrappers, path, mappingData,
                    true);
        }

        // Rule 4 -- Welcome resources processing for servlets
        if (mappingData.wrapper == null) {
            boolean checkWelcomeFiles = checkJspWelcomeFiles;
            if (!checkWelcomeFiles) {
                char[] buf = path.getBuffer();
                checkWelcomeFiles = (buf[pathEnd - 1] == '/');
            }
            if (checkWelcomeFiles) {
                for (int i = 0; (i < contextVersion.welcomeResources.length)
                         && (mappingData.wrapper == null); i++) {
                    path.setOffset(pathOffset);
                    path.setEnd(pathEnd);
                    path.append(contextVersion.welcomeResources[i], 0,
                            contextVersion.welcomeResources[i].length());
                    path.setOffset(servletPath);

                    // Rule 4a -- Welcome resources processing for exact macth
                    internalMapExactWrapper(exactWrappers, path, mappingData);

                    // Rule 4b -- Welcome resources processing for prefix match
                    if (mappingData.wrapper == null) {
                        internalMapWildcardWrapper
                            (wildcardWrappers, contextVersion.nesting,
                             path, mappingData);
                    }

                    // Rule 4c -- Welcome resources processing
                    //            for physical folder
                    if (mappingData.wrapper == null
                        && contextVersion.resources != null) {
                        String pathStr = path.toString();
                        WebResource file =
                                contextVersion.resources.getResource(pathStr);
                        if (file != null && file.isFile()) {
                            internalMapExtensionWrapper(extensionWrappers, path,
                                                        mappingData, true);
                            if (mappingData.wrapper == null
                                && contextVersion.defaultWrapper != null) {
                                mappingData.wrapper =
                                    contextVersion.defaultWrapper.object;
                                mappingData.requestPath.setChars
                                    (path.getBuffer(), path.getStart(),
                                     path.getLength());
                                mappingData.wrapperPath.setChars
                                    (path.getBuffer(), path.getStart(),
                                     path.getLength());
                                mappingData.requestPath.setString(pathStr);
                                mappingData.wrapperPath.setString(pathStr);
                            }
                        }
                    }
                }

                path.setOffset(servletPath);
                path.setEnd(pathEnd);
            }

        }

        /* welcome file processing - take 2
         * Now that we have looked for welcome files with a physical
         * backing, now look for an extension mapping listed
         * but may not have a physical backing to it. This is for
         * the case of index.jsf, index.do, etc.
         * A watered down version of rule 4
         */
        if (mappingData.wrapper == null) {
            boolean checkWelcomeFiles = checkJspWelcomeFiles;
            if (!checkWelcomeFiles) {
                char[] buf = path.getBuffer();
                checkWelcomeFiles = (buf[pathEnd - 1] == '/');
            }
            if (checkWelcomeFiles) {
                for (int i = 0; (i < contextVersion.welcomeResources.length)
                         && (mappingData.wrapper == null); i++) {
                    path.setOffset(pathOffset);
                    path.setEnd(pathEnd);
                    path.append(contextVersion.welcomeResources[i], 0,
                                contextVersion.welcomeResources[i].length());
                    path.setOffset(servletPath);
                    internalMapExtensionWrapper(extensionWrappers, path,
                                                mappingData, false);
                }

                path.setOffset(servletPath);
                path.setEnd(pathEnd);
            }
        }


        // Rule 7 -- Default servlet
        if (mappingData.wrapper == null && !checkJspWelcomeFiles) {
            if (contextVersion.defaultWrapper != null) {
                mappingData.wrapper = contextVersion.defaultWrapper.object;
                mappingData.requestPath.setChars
                    (path.getBuffer(), path.getStart(), path.getLength());
                mappingData.wrapperPath.setChars
                    (path.getBuffer(), path.getStart(), path.getLength());
                mappingData.matchType = MappingMatch.DEFAULT;
            }
            // Redirection to a folder
            char[] buf = path.getBuffer();
            if (contextVersion.resources != null && buf[pathEnd -1 ] != '/') {
                String pathStr = path.toString();
                WebResource file;
                // Handle context root
                if (pathStr.length() == 0) {
                    file = contextVersion.resources.getResource("/");
                } else {
                    file = contextVersion.resources.getResource(pathStr);
                }
                if (file != null && file.isDirectory() &&
                        contextVersion.object.getMapperDirectoryRedirectEnabled()) {
                    // Note: this mutates the path: do not do any processing
                    // after this (since we set the redirectPath, there
                    // shouldn't be any)
                    path.setOffset(pathOffset);
                    path.append('/');
                    mappingData.redirectPath.setChars
                        (path.getBuffer(), path.getStart(), path.getLength());
                } else {
                    mappingData.requestPath.setString(pathStr);
                    mappingData.wrapperPath.setString(pathStr);
                }
            }
        }

        path.setOffset(pathOffset);
        path.setEnd(pathEnd);
    }

        mappingData.wrapper 在Rule 7 -- Default servlet 找到SpringMVC 默認的DispatcherServlet

(2) org.apache.catalina.core.ApplicationFilterChain#internalDoFilter 經過一系列的filter之后進入DispatcherServlet 父類的相關方法

    private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {

        // Call the next filter if there is one
        if (pos < n) {
            ApplicationFilterConfig filterConfig = filters[pos++];
            try {
                Filter filter = filterConfig.getFilter();

                if (request.isAsyncSupported() && "false".equalsIgnoreCase(
                        filterConfig.getFilterDef().getAsyncSupported())) {
                    request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
                }
                if( Globals.IS_SECURITY_ENABLED ) {
                    final ServletRequest req = request;
                    final ServletResponse res = response;
                    Principal principal =
                        ((HttpServletRequest) req).getUserPrincipal();

                    Object[] args = new Object[]{req, res, this};
                    SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
                } else {
                    filter.doFilter(request, response, this);
                }
            } catch (IOException | ServletException | RuntimeException e) {
                throw e;
            } catch (Throwable e) {
                e = ExceptionUtils.unwrapInvocationTargetException(e);
                ExceptionUtils.handleThrowable(e);
                throw new ServletException(sm.getString("filterChain.filter"), e);
            }
            return;
        }

        // We fell off the end of the chain -- call the servlet instance
        try {
            if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
                lastServicedRequest.set(request);
                lastServicedResponse.set(response);
            }

            if (request.isAsyncSupported() && !servletSupportsAsync) {
                request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
                        Boolean.FALSE);
            }
            // Use potentially wrapped request from this point
            if ((request instanceof HttpServletRequest) &&
                    (response instanceof HttpServletResponse) &&
                    Globals.IS_SECURITY_ENABLED ) {
                final ServletRequest req = request;
                final ServletResponse res = response;
                Principal principal =
                    ((HttpServletRequest) req).getUserPrincipal();
                Object[] args = new Object[]{req, res};
                SecurityUtil.doAsPrivilege("service",
                                           servlet,
                                           classTypeUsedInService,
                                           args,
                                           principal);
            } else {
                servlet.service(request, response);
            }
        } catch (IOException | ServletException | RuntimeException e) {
            throw e;
        } catch (Throwable e) {
            e = ExceptionUtils.unwrapInvocationTargetException(e);
            ExceptionUtils.handleThrowable(e);
            throw new ServletException(sm.getString("filterChain.servlet"), e);
        } finally {
            if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
                lastServicedRequest.set(null);
                lastServicedResponse.set(null);
            }
        }
    }

調用鏈如下：

(2)org.springframework.web.servlet.DispatcherServlet#doDispatch 進入SpringMVC 流程

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (logger.isDebugEnabled()) {
                        logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                    }
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            catch (Throwable err) {
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", err));
        }
        finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                // Instead of postHandle and afterCompletion
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            }
            else {
                // Clean up any resources used by a multipart request.
                if (multipartRequestParsed) {
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

1》 org.springframework.web.servlet.DispatcherServlet#getHandler 找相關的Handler：

    protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        for (HandlerMapping hm : this.handlerMappings) {
            if (logger.isTraceEnabled()) {
                logger.trace(
                        "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
            }
            HandlerExecutionChain handler = hm.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
        return null;
    }

　　這里的handlerMappings 如下：

 　　然后調用hm.getHandler 找handler， 會調用到： cn.xm.servlet.MyHandlerMapping#lookupHandler 第一次初始化相關的handler。然后根據路徑進行匹配找到的handler 如下：

2》然后調用org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter#handle 進行執行：

    @Override
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        return ((Controller) handler).handleRequest(request, response);
    }

這里會調用到父類方法org.springframework.web.servlet.mvc.AbstractController#handleRequest：

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        if (HttpMethod.OPTIONS.matches(request.getMethod())) {
            response.setHeader("Allow", getAllowHeader());
            return null;
        }

        // Delegate to WebContentGenerator for checking and preparing.
        checkRequest(request);
        prepareResponse(response);

        // Execute handleRequestInternal in synchronized block if required.
        if (this.synchronizeOnSession) {
            HttpSession session = request.getSession(false);
            if (session != null) {
                Object mutex = WebUtils.getSessionMutex(session);
                synchronized (mutex) {
                    return handleRequestInternal(request, response);
                }
            }
        }

        return handleRequestInternal(request, response);
    }

繼續調用到cn.xm.servlet.MyController-》org.springframework.web.servlet.mvc.ServletWrappingController#handleRequestInternal：

    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        this.servletInstance.service(request, response);
        return null;
    }

　　到這里就從SpringMVC的流程進入到我們的Servlet開始調用方法 cn.xm.servlet.MyServlet#service。

2. 基於ServletRegistrationBean 方式原理

1. 創建時機

org.springframework.boot.web.servlet.ServletRegistrationBean#onStartup 方法如下：

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        Assert.notNull(this.servlet, "Servlet must not be null");
        String name = getServletName();
        if (!isEnabled()) {
            logger.info("Servlet " + name + " was not registered (disabled)");
            return;
        }
        logger.info("Mapping servlet: '" + name + "' to " + this.urlMappings);
        Dynamic added = servletContext.addServlet(name, this.servlet);
        if (added == null) {
            logger.info("Servlet " + name + " was not registered "
                    + "(possibly already registered?)");
            return;
        }
        configure(added);
    }

　　相當於調用javax.servlet.ServletContext#addServlet(java.lang.String, javax.servlet.Servlet) 方法動態的注冊Servlet， 這是ServletContext 提供的動態注冊Servlet 的API。

調用鏈如下：

　　 核心是在 org.springframework.boot.context.embedded.EmbeddedWebApplicationContext#selfInitialize 調用onStartUp 方法

    private void selfInitialize(ServletContext servletContext) throws ServletException {
        prepareEmbeddedWebApplicationContext(servletContext);
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        ExistingWebApplicationScopes existingScopes = new ExistingWebApplicationScopes(
                beanFactory);
        WebApplicationContextUtils.registerWebApplicationScopes(beanFactory,
                getServletContext());
        existingScopes.restore();
        WebApplicationContextUtils.registerEnvironmentBeans(beanFactory,
                getServletContext());
        for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
            beans.onStartup(servletContext);
        }
    }

2. 調用時機

訪問：/my/t3

(1) 上面org.apache.catalina.mapper.Mapper#internalMapWrapper 方法在執行過程中從規則 Rule 2 -- Prefix Match 找到對應的myServlet。

(2) org.apache.catalina.core.ApplicationFilterChain#internalDoFilter 經過一系列的filter之后進入myServlet.service() 方法