死磕源码系列【springboot内嵌tomcat如何启用ServletContextInitializer的onStartup方法进行初始化Servlet\Filiter\EventListener

不念不忘少年蓝@ 2022-12-28 08:12 47阅读 0赞

参考:[死磕源码系列springboot之ServletContextInitializerBeans如何将Filter、Servlet、EventListener注册到ServletContext中源码解][springboot_ServletContextInitializerBeans_Filter_Servlet_EventListener_ServletContext]

在springboot的jar包中有一个TomcatStarter类，是ServletContainerInitializer的子类，会对ServletContextInitializer的相关实现类及包装类进行初始化；

##### TomcatStarter源码如下： #####

class TomcatStarter implements ServletContainerInitializer { 
    
    	private static final Log logger = LogFactory.getLog(TomcatStarter.class);
    	//ServletContextInitializer相关实现类及包装类
    	private final ServletContextInitializer[] initializers;
    
    	private volatile Exception startUpException;
    	//创建一个TomcatStarter实例对象
    	TomcatStarter(ServletContextInitializer[] initializers) { 
    		this.initializers = initializers;
    	}
    
    	@Override
    	public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException { 
    		try { 
          //通过循环的方式调用ServletContextInitializer的onStartup方法将Servlet\Filter\EventListener等注册到ServletContext上下文之中
    			for (ServletContextInitializer initializer : this.initializers) { 
    				initializer.onStartup(servletContext);
    			}
    		}
    		catch (Exception ex) { 
    			this.startUpException = ex;
    			// Prevent Tomcat from logging and re-throwing when we know we can
    			// deal with it in the main thread, but log for information here.
    			if (logger.isErrorEnabled()) { 
    				logger.error("Error starting Tomcat context. Exception: " + ex.getClass().getName() + ". Message: "
    						+ ex.getMessage());
    			}
    		}
    	}
    
    	Exception getStartUpException() { 
    		return this.startUpException;
    	}
    
    }

##### TomcatStarter在TomcatServletWebServerFactory\#configureContext方法中进行初始化，并且在org.apache.catalina.core.StandardContext\#startInternal方法中启用 #####

protected void configureContext(Context context, ServletContextInitializer[] initializers) { 
    		//实例化TomcatStarter对象
        TomcatStarter starter = new TomcatStarter(initializers);
    		if (context instanceof TomcatEmbeddedContext) { 
    			TomcatEmbeddedContext embeddedContext = (TomcatEmbeddedContext) context;
    			embeddedContext.setStarter(starter);
    			embeddedContext.setFailCtxIfServletStartFails(true);
    		}
        //将TomcatStarter对象初始化到context上下文的initializers变量
    		context.addServletContainerInitializer(starter, NO_CLASSES);
      }

##### ServletContext对象是在StandardContext\#getServletContext方法中进行初始化 #####

@Override
        public ServletContext getServletContext() { 
            if (context == null) { 
              //ApplicationContext是ServletContext的子类
                context = new ApplicationContext(this);
                if (altDDName != null)
                    context.setAttribute(Globals.ALT_DD_ATTR,altDDName);
            }
            return context.getFacade();
        }

GitHub地址：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[springboot_ServletContextInitializerBeans_Filter_Servlet_EventListener_ServletContext]: https://mingyang.blog.csdn.net/article/details/111059405
[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent