聊聊spring.mvc.servlet.load-on-startup

序

本文主要研究一下

WebMvcProperties$Servlet

org/springframework/boot/autoconfigure/web/servlet/WebMvcProperties.java

	public static class Servlet {

		/**
		 * Path of the dispatcher servlet.
		 */
		private String path = "/";

		/**
		 * Load on startup priority of the dispatcher servlet.
		 */
		private int loadOnStartup = -1;

		public String getPath() {
			return this.path;
		}

		public void setPath(String path) {
			Assert.notNull(path, "Path must not be null");
			Assert.isTrue(!path.contains("*"), "Path must not contain wildcards");
			this.path = path;
		}

		public int getLoadOnStartup() {
			return this.loadOnStartup;
		}

		public void setLoadOnStartup(int loadOnStartup) {
			this.loadOnStartup = loadOnStartup;
		}

		public String getServletMapping() {
			if (this.path.equals("") || this.path.equals("/")) {
				return "/";
			}
			if (this.path.endsWith("/")) {
				return this.path + "*";
			}
			return this.path + "/*";
		}

		public String getPath(String path) {
			String prefix = getServletPrefix();
			if (!path.startsWith("/")) {
				path = "/" + path;
			}
			return prefix + path;
		}

		public String getServletPrefix() {
			String result = this.path;
			int index = result.indexOf('*');
			if (index != -1) {
				result = result.substring(0, index);
			}
			if (result.endsWith("/")) {
				result = result.substring(0, result.length() - 1);
			}
			return result;
		}

	}

loadOnStartup默认为-1

DispatcherServletAutoConfiguration

org/springframework/boot/autoconfigure/web/servlet/DispatcherServletAutoConfiguration.java

	@Configuration(proxyBeanMethods = false)
	@Conditional(DispatcherServletRegistrationCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	@Import(DispatcherServletConfiguration.class)
	protected static class DispatcherServletRegistrationConfiguration {

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
		@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
				WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
			DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
					webMvcProperties.getServlet().getPath());
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}

	}

这里注册了dispatcherServlet，并设置loadOnStartup

ServletRegistrationBean

org/springframework/boot/web/servlet/ServletRegistrationBean.java

	protected void configure(ServletRegistration.Dynamic registration) {
		super.configure(registration);
		String[] urlMapping = StringUtils.toStringArray(this.urlMappings);
		if (urlMapping.length == 0 && this.alwaysMapUrl) {
			urlMapping = DEFAULT_MAPPINGS;
		}
		if (!ObjectUtils.isEmpty(urlMapping)) {
			registration.addMapping(urlMapping);
		}
		registration.setLoadOnStartup(this.loadOnStartup);
		if (this.multipartConfig != null) {
			registration.setMultipartConfig(this.multipartConfig);
		}
	}

configure最后设置到ServletRegistration.Dynamic

ApplicationServletRegistration

org/apache/catalina/core/ApplicationServletRegistration.java

    public void setLoadOnStartup(int loadOnStartup) {
        wrapper.setLoadOnStartup(loadOnStartup);
    }

最后是设置到tomcat的Wrapper.loadOnStartup

TomcatWebServer

org/springframework/boot/web/embedded/tomcat/TomcatWebServer.java

	public void start() throws WebServerException {
		synchronized (this.monitor) {
			if (this.started) {
				return;
			}
			try {
				addPreviouslyRemovedConnectors();
				Connector connector = this.tomcat.getConnector();
				if (connector != null && this.autoStart) {
					performDeferredLoadOnStartup();
				}
				checkThatConnectorsHaveStarted();
				this.started = true;
				logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"
						+ getContextPath() + "'");
			}
			catch (ConnectorStartFailedException ex) {
				stopSilently();
				throw ex;
			}
			catch (Exception ex) {
				PortInUseException.throwIfPortBindingException(ex, () -> this.tomcat.getConnector().getPort());
				throw new WebServerException("Unable to start embedded Tomcat server", ex);
			}
			finally {
				Context context = findContext();
				ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
			}
		}
	}

TomcatWebServer的start方法对于autoStart为true(默认)的会执行performDeferredLoadOnStartup

performDeferredLoadOnStartup

org/springframework/boot/web/embedded/tomcat/TomcatWebServer.java

	private void performDeferredLoadOnStartup() {
		try {
			for (Container child : this.tomcat.getHost().findChildren()) {
				if (child instanceof TomcatEmbeddedContext) {
					((TomcatEmbeddedContext) child).deferredLoadOnStartup();
				}
			}
		}
		catch (Exception ex) {
			if (ex instanceof WebServerException) {
				throw (WebServerException) ex;
			}
			throw new WebServerException("Unable to start embedded Tomcat connectors", ex);
		}
	}

performDeferredLoadOnStartup遍历child挨个执行deferredLoadOnStartup

deferredLoadOnStartup

org/springframework/boot/web/embedded/tomcat/TomcatEmbeddedContext.java

	void deferredLoadOnStartup() throws LifecycleException {
		doWithThreadContextClassLoader(getLoader().getClassLoader(),
				() -> getLoadOnStartupWrappers(findChildren()).forEach(this::load));
	}

	private Stream<Wrapper> getLoadOnStartupWrappers(Container[] children) {
		Map<Integer, List<Wrapper>> grouped = new TreeMap<>();
		for (Container child : children) {
			Wrapper wrapper = (Wrapper) child;
			int order = wrapper.getLoadOnStartup();
			if (order >= 0) {
				grouped.computeIfAbsent(order, (o) -> new ArrayList<>()).add(wrapper);
			}
		}
		return grouped.values().stream().flatMap(List::stream);
	}	

它通过getLoadOnStartupWrappers获取Wrapper，然后挨个执行其load方法

load

org/springframework/boot/web/embedded/tomcat/TomcatEmbeddedContext.java

	private void load(Wrapper wrapper) {
		try {
			wrapper.load();
		}
		catch (ServletException ex) {
			String message = sm.getString("standardContext.loadOnStartup.loadException", getName(), wrapper.getName());
			if (getComputedFailCtxIfServletStartFails()) {
				throw new WebServerException(message, ex);
			}
			getLogger().error(message, StandardWrapper.getRootCause(ex));
		}
	}

load方法即执行wrapper.load()

load

org/apache/catalina/core/StandardWrapper.java

    public synchronized void load() throws ServletException {
        instance = loadServlet();

        if (!instanceInitialized) {
            initServlet(instance);
        }

        if (isJspServlet) {
            StringBuilder oname = new StringBuilder(getDomain());

            oname.append(":type=JspMonitor");

            oname.append(getWebModuleKeyProperties());

            oname.append(",name=");
            oname.append(getName());

            oname.append(getJ2EEKeyProperties());

            try {
                jspMonitorON = new ObjectName(oname.toString());
                Registry.getRegistry(null, null).registerComponent(instance, jspMonitorON, null);
            } catch (Exception ex) {
                log.warn(sm.getString("standardWrapper.jspMonitorError", instance));
            }
        }
    }

tomcat的StandardWrapper的load是个同步方法，它加载和初始化servlet，如果已经加载或初始化不会重复加载

小结

springboot提供了spring.mvc.servlet.load-on-startup配置，可以设置未非负，这样子springboot启动时可以对servlet进行加载与初始化。