Spring MVC 源码 分析

spring web

源码

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {

    /**
     * Delegate the {@code ServletContext} to any {@link WebApplicationInitializer}
     * implementations present on the application classpath.
     * <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)},
     * Servlet 3.0+ containers will automatically scan the classpath for implementations
     * of Spring's {@code WebApplicationInitializer} interface and provide the set of all
     * such types to the {@code webAppInitializerClasses} parameter of this method.
     * <p>If no {@code WebApplicationInitializer} implementations are found on the classpath,
     * this method is effectively a no-op. An INFO-level log message will be issued notifying
     * the user that the {@code ServletContainerInitializer} has indeed been invoked but that
     * no {@code WebApplicationInitializer} implementations were found.
     * <p>Assuming that one or more {@code WebApplicationInitializer} types are detected,
     * they will be instantiated (and <em>sorted</em> if the @{@link
     * org.springframework.core.annotation.Order @Order} annotation is present or
     * the {@link org.springframework.core.Ordered Ordered} interface has been
     * implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)}
     * method will be invoked on each instance, delegating the {@code ServletContext} such
     * that each instance may register and configure servlets such as Spring's
     * {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener},
     * or any other Servlet API componentry such as filters.
     * @param webAppInitializerClasses all implementations of
     * {@link WebApplicationInitializer} found on the application classpath
     * @param servletContext the servlet context to be initialized
     * @see WebApplicationInitializer#onStartup(ServletContext)
     * @see AnnotationAwareOrderComparator
     */
    @Override
    public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
            throws ServletException {

        List<WebApplicationInitializer> initializers = new LinkedList<>();

        if (webAppInitializerClasses != null) {
            for (Class<?> waiClass : webAppInitializerClasses) {
                // Be defensive: Some servlet containers provide us with invalid classes,
                // no matter what @HandlesTypes says...
                if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
                        WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
                    try {
                        initializers.add((WebApplicationInitializer)
                                ReflectionUtils.accessibleConstructor(waiClass).newInstance());
                    }
                    catch (Throwable ex) {
                        throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
                    }
                }
            }
        }

        if (initializers.isEmpty()) {
            servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
            return;
        }

        servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
        AnnotationAwareOrderComparator.sort(initializers);
        for (WebApplicationInitializer initializer : initializers) {
            initializer.onStartup(servletContext);
        }
    }

}

WebApplicationInitializer 有4个实现类 

1. AbstractContextLoaderInitializer

public abstract class AbstractContextLoaderInitializer implements WebApplicationInitializer {

    /** Logger available to subclasses */
    protected final Log logger = LogFactory.getLog(getClass());

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        registerContextLoaderListener(servletContext);    //注册 监听器
    }

    /**
     * Register a {@link ContextLoaderListener} against the given servlet context. The
     * {@code ContextLoaderListener} is initialized with the application context returned
     * from the {@link #createRootApplicationContext()} template method.
     * @param servletContext the servlet context to register the listener against
     */
    protected void registerContextLoaderListener(ServletContext servletContext) {
        WebApplicationContext rootAppContext = createRootApplicationContext();    //创建web根容器
        if (rootAppContext != null) {
            ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
            listener.setContextInitializers(getRootApplicationContextInitializers());
            servletContext.addListener(listener);          //添加监听器
        }
        else {
            logger.debug("No ContextLoaderListener registered, as " +
                    "createRootApplicationContext() did not return an application context");
        }
    }

    /**
     * Create the "<strong>root</strong>" application context to be provided to the
     * {@code ContextLoaderListener}.
     * <p>The returned context is delegated to
     * {@link ContextLoaderListener#ContextLoaderListener(WebApplicationContext)} and will
     * be established as the parent context for any {@code DispatcherServlet} application
     * contexts. As such, it typically contains middle-tier services, data sources, etc.
     * @return the root application context, or {@code null} if a root context is not
     * desired
     * @see org.springframework.web.servlet.support.AbstractDispatcherServletInitializer
     */
    @Nullable
    protected abstract WebApplicationContext createRootApplicationContext();

    /**
     * Specify application context initializers to be applied to the root application
     * context that the {@code ContextLoaderListener} is being created with.
     * @since 4.2
     * @see #createRootApplicationContext()
     * @see ContextLoaderListener#setContextInitializers
     */
    @Nullable
    protected ApplicationContextInitializer<?>[] getRootApplicationContextInitializers() {
        return null;
    }

}

2 .  AbstractDispatcherServletInitializer

public abstract class AbstractDispatcherServletInitializer extends AbstractContextLoaderInitializer {
    public static final String DEFAULT_SERVLET_NAME = "dispatcher";

    public AbstractDispatcherServletInitializer() {
    }

    public void onStartup(ServletContext servletContext) throws ServletException {
        super.onStartup(servletContext);
        this.registerDispatcherServlet(servletContext);
    }

    protected void registerDispatcherServlet(ServletContext servletContext) {
        String servletName = this.getServletName();
        Assert.hasLength(servletName, "getServletName() must not return null or empty");
        WebApplicationContext servletAppContext = this.createServletApplicationContext();
        Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");
        FrameworkServlet dispatcherServlet = this.createDispatcherServlet(servletAppContext);
        Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");
        dispatcherServlet.setContextInitializers(this.getServletApplicationContextInitializers());
        Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);    //添加servlet
        if (registration == null) {
            throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. Check if there is another servlet registered under the same name.");
        } else {
            registration.setLoadOnStartup(1);
            registration.addMapping(this.getServletMappings());  //添加mapping
            registration.setAsyncSupported(this.isAsyncSupported());
            Filter[] filters = this.getServletFilters();
            if (!ObjectUtils.isEmpty(filters)) {
                Filter[] var7 = filters;
                int var8 = filters.length;

                for(int var9 = 0; var9 < var8; ++var9) {
                    Filter filter = var7[var9];
                    this.registerServletFilter(servletContext, filter);
                }
            }

            this.customizeRegistration(registration);
        }
    }

    protected String getServletName() {
        return "dispatcher";
    }

    protected abstract WebApplicationContext createServletApplicationContext();

    protected FrameworkServlet createDispatcherServlet(WebApplicationContext servletAppContext) {
        return new DispatcherServlet(servletAppContext);
    }

    @Nullable
    protected ApplicationContextInitializer<?>[] getServletApplicationContextInitializers() {
        return null;
    }

    protected abstract String[] getServletMappings();

    @Nullable
    protected Filter[] getServletFilters() {
        return null;
    }

    protected javax.servlet.FilterRegistration.Dynamic registerServletFilter(ServletContext servletContext, Filter filter) {
        String filterName = Conventions.getVariableName(filter);
        javax.servlet.FilterRegistration.Dynamic registration = servletContext.addFilter(filterName, filter);
        if (registration == null) {
            for(int counter = 0; registration == null; ++counter) {
                if (counter == 100) {
                    throw new IllegalStateException("Failed to register filter with name '" + filterName + "'. Check if there is another filter registered under the same name.");
                }

                registration = servletContext.addFilter(filterName + "#" + counter, filter);   //添加filter
            }
        }

        registration.setAsyncSupported(this.isAsyncSupported());
        registration.addMappingForServletNames(this.getDispatcherTypes(), false, new String[]{this.getServletName()});
        return registration;
    }

    private EnumSet<DispatcherType> getDispatcherTypes() {
        return this.isAsyncSupported() ? EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE, DispatcherType.ASYNC) : EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE);
    }

    protected boolean isAsyncSupported() {
        return true;
    }

    protected void customizeRegistration(Dynamic registration) {
    }
}

3   AbstractAnnotationConfigDispatcherServletInitializer

public abstract class AbstractAnnotationConfigDispatcherServletInitializer extends AbstractDispatcherServletInitializer {
    public AbstractAnnotationConfigDispatcherServletInitializer() {
    }

    @Nullable
    protected WebApplicationContext createRootApplicationContext() {
        Class<?>[] configClasses = this.getRootConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();   //类似spring 中配置文件
            context.register(configClasses);
            return context;
        } else {
            return null;
        }
    }

    protected WebApplicationContext createServletApplicationContext() {
        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
        Class<?>[] configClasses = this.getServletConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            context.register(configClasses);
        }

        return context;
    }

    @Nullable
    protected abstract Class<?>[] getRootConfigClasses();

    @Nullable
    protected abstract Class<?>[] getServletConfigClasses();
}

public abstract class AbstractContextLoaderInitializer implements WebApplicationInitializer {

   /** Logger available to subclasses */
protected final Log logger = LogFactory.getLog(getClass());

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
      registerContextLoaderListener(servletContext);
}

   /**
    * Register a {@link ContextLoaderListener} against the given servlet context. The
    * {@code ContextLoaderListener} is initialized with the application context returned
    * from the {@link #createRootApplicationContext()} template method.
    * @param servletContext the servlet context to register the listener against
    */
protected void registerContextLoaderListener(ServletContext servletContext) {
      WebApplicationContext rootAppContext = createRootApplicationContext();
      if (rootAppContext != null) {
         ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
listener.setContextInitializers(getRootApplicationContextInitializers());
servletContext.addListener(listener);
}
      else {
         logger.debug("No ContextLoaderListener registered, as " +
               "createRootApplicationContext() did not return an application context");
}
   }

   /**
    * Create the "<strong>root</strong>" application context to be provided to the
    * {@code ContextLoaderListener}.
    * <p>The returned context is delegated to
    * {@link ContextLoaderListener#ContextLoaderListener(WebApplicationContext)} and will
    * be established as the parent context for any {@code DispatcherServlet} application
    * contexts. As such, it typically contains middle-tier services, data sources, etc.
    * @return the root application context, or {@code null} if a root context is not
    * desired
    * @see org.springframework.web.servlet.support.AbstractDispatcherServletInitializer
    */
@Nullable
protected abstract WebApplicationContext createRootApplicationContext();

/**
    * Specify application context initializers to be applied to the root application
    * context that the {@code ContextLoaderListener} is being created with.
    * @since 4.2
    * @see #createRootApplicationContext()
    * @see ContextLoaderListener#setContextInitializers
    */
@Nullable
protected ApplicationContextInitializer<?>[] getRootApplicationContextInitializers() {
      return null;
}

}