遇到Unable to start embedded Tomcat或者自动停止如何查看具体报错信息

柔情只为你懂 2023-02-18 03:04 49阅读 0赞

*  本篇可以说是是上篇[spring boot项目打印banner后停止][spring boot_banner]的具体操作
 *  遇到`org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat`问题原因很多，网上说的一般情况不一样。
 *  所谓“授人以鱼不如授人以渔”，本篇要给大家带来的就是自己如何debug程序去找症结所在。
 *  首先找到spring boot创建web服务的地方`ServletWebServerApplicationContext#onRefresh`方法(当然这是web应用所以是这个类)

protected void onRefresh() { 
    		super.onRefresh();
    		try { 
        		 // 很明显就是这个方法
    			createWebServer();
    		}
    		catch (Throwable ex) { 
    			throw new ApplicationContextException("Unable to start web server", ex);
    		}
    	}

private void createWebServer() { 
    		WebServer webServer = this.webServer;
    		ServletContext servletContext = getServletContext();
    		if (webServer == null && servletContext == null) { 
    			ServletWebServerFactory factory = getWebServerFactory();
    			// 重点进入getWebServer方法
    			this.webServer = factory.getWebServer(getSelfInitializer());
    		}
    		else if (servletContext != null) { 
    			try { 
    				getSelfInitializer().onStartup(servletContext);
    			}
    			catch (ServletException ex) { 
    				throw new ApplicationContextException("Cannot initialize servlet context",
    						ex);
    			}
    		}
    		initPropertySources();
    	}

*  再进入`TomcatServletWebServerFactory#getWebServer`\->`getTomcatWebServer`\->`TomcatWebServer#TomcatWebServer(Tomcat tomcat, boolean autoStart)TomcatWebServer的构造方法`\->`initialize`

private void initialize() throws WebServerException { 
    		TomcatWebServer.logger
    				.info("Tomcat initialized with port(s): " + getPortsDescription(false));
    		synchronized (this.monitor) { 
    			try { 
    				addInstanceIdToEngineName();
    
    				Context context = findContext();
    				context.addLifecycleListener((event) -> { 
    					if (context.equals(event.getSource())
    							&& Lifecycle.START_EVENT.equals(event.getType())) { 
    						// Remove service connectors so that protocol binding doesn't
    						// happen when the service is started.
    						removeServiceConnectors();
    					}
    				});
    
    				// Start the server to trigger initialization listeners
    				this.tomcat.start();
    
    				// We can re-throw failure exception directly in the main thread
    				// 重点是这个，按照我的理解这个方法会收集启动时的异常并抛出
    				rethrowDeferredStartupExceptions();
    
    				try { 
    					ContextBindings.bindClassLoader(context, context.getNamingToken(),
    							getClass().getClassLoader());
    				}
    				catch (NamingException ex) { 
    					// Naming is not enabled. Continue
    				}
    
    				// Unlike Jetty, all Tomcat threads are daemon threads. We create a
    				// blocking non-daemon to stop immediate shutdown
    				startDaemonAwaitThread();
    			}
    			catch (Exception ex) { 
    				stopSilently();
    				throw new WebServerException("Unable to start embedded Tomcat", ex);
    			}
    		}
    	}

*  `TomcatWebServer#rethrowDeferredStartupExceptions` 重点是这个，按照我的理解这个方法会收集启动时的异常并抛出。
 *  我在这里debug下就明了了，具体异常就有了。  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70]  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 1]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 2]
 *  第一个阻塞点的异常我处理完了，遇到第二个问题依然是自动停止的情况，于是我又在`AbstractApplicationContext#refresh`打断点，看具体是什么异常  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 3]
 *  最后一个问题我发现居然还没有选择环境，只读取到默认的`default`，该断点在`ConfigFileApplicationListener#load`方法；目前看到该类是一个`EnvironmentPostProcessor`，主要功能就把它看成是处理处理文件的吧(环境事件的后处理器,不知道对不对，如果不对的话，请在评论下方指正，感谢您)  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 4]
 *  在外层debug的时候看到的确只读了`application.properties`配置文件，该断点位置在`SpringApplication#run`方法  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 5]
 *  于是我在`application.properties`(猜想他们可能是-D参数启动的吧)文件加入 `spring.profiles.active=dev`终于可以启动了。  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 6]  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 7]  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzE5NDczNTI5_size_16_color_FFFFFF_t_70 8]
 *  主要根据错误信息把错误一一解决了改改配置就能启动了
 *  本人水平有限，如果文章有误的地方，希望批评指正，感谢您的观看。

[spring boot_banner]: https://sample.blog.csdn.net/article/details/106763497
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