Spring IOC容器详解

ゝ一世哀愁。 2023-06-16 04:00 20阅读 0赞

Spring版本: 5.0.5  
IOC : 控制反转， 把原先我们代码里需要实现的对象创建，依赖的代码， 反转给容器来实现。  
DI：dependency injection 依赖注入 就是指对象是被动接受依赖类， 而不是主动去找。 对象不是从容器中查找它依赖的类， 而是在容器实例化对象的时候， 主动将它依赖的类，注入给它。

Spring中对象和对象的关系如何表示？  
在传统的Spring开发中，是用xml或者properties文件来表示的

描述对象关系的文件存放在哪里？  
可以存放在classpath/network/filesystem/servletContext下  
用的最多的是classpath下.

既然描述对象关系的文件可以有如上的那么多， 那么如何来统一配置文件的标准？  
在Spring中有顶层的BeanDefinition进行标准的统一。

如何对不同的配置文件进行解析？  
采用策略模式， 针对不同的配置文件，进行解析， 最后都会变成BeanDefinition。

BeanFactory是容器中最顶层的接口。

例如在Spring中， 如果对象与对象直接是List集合关系， 那么就用ListableBeanFactory来保存。 如果是父子继承关系，那么就用HierarchicalBeanFactory来保存  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 1][]  
抽象工厂+ 模板方法模式 + 策略模式  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 2][]  
BeanFactory ： 定义容器  
BeanDefinition： 存储配置信息  
BeanDefinitionReader： 负责读取配置信息  
有了这三个类就可以完成IOC容器初始化的过程。

IOC容器初始化三部曲：

1.  定位： 定位配置文件和扫描相关的注解
2.  加载： 将配置信息载入到内存中
3.  注册： 根据载入的信息，将对象初始化到IOC容器中。

具体的17个步骤 :  
1、寻找入口  
2、获得配置路径  
3、开始启动  
4、创建容器  
5、载入配置路径  
6、分配路径处理策略  
7、解析配置文件路径  
8、开始读取配置内容  
9、准备文档对象  
10、分配解析策略  
11、将配置载入内存  
12、载入元素  
13、载入元素  
14、载入的子元素  
15、载入的子元素  
16、分配注册策略  
17、向容器注册

从org.springframework.web.servlet.DispatcherServlet 类入手.  
![在这里插入图片描述][20200503172611215.png]  
找到其父类org.springframework.web.servlet.FrameworkServlet  
![在这里插入图片描述][2020050317264562.png]  
再找到其父类 org.springframework.web.servlet.HttpServletBean  
![在这里插入图片描述][20200503172653215.png]  
在HttpServletBean 类中, 有如下的init()方法.  
其中包含了`initServletBean();`方法

@Override
    	public final void init() throws ServletException { 
    		if (logger.isDebugEnabled()) { 
    			logger.debug("Initializing servlet '" + getServletName() + "'");
    		}
    
    		// Set bean properties from init parameters.
    		PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
    		if (!pvs.isEmpty()) { 
    			try { 
    				BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
    				ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
    				bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
    				initBeanWrapper(bw);
    				bw.setPropertyValues(pvs, true);
    			}
    			catch (BeansException ex) { 
    				if (logger.isErrorEnabled()) { 
    					logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
    				}
    				throw ex;
    			}
    		}
    
    		// Let subclasses do whatever initialization they like.
    		initServletBean();
    
    		if (logger.isDebugEnabled()) { 
    			logger.debug("Servlet '" + getServletName() + "' configured successfully");
    		}
    	}

`initServletBean();`方法 在HttpServletBean 类中只是进行了申明.  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 3]  
在其子类 FrameworkServlet 中, 进行了重写.  
其中此方法中, 包含了`initWebApplicationContext();`方法, 该方法代表对web容器进行

/** * Overridden method of {@link HttpServletBean}, invoked after any bean properties * have been set. Creates this servlet's WebApplicationContext. */
    	@Override
    	protected final void initServletBean() throws ServletException { 
    		getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
    		if (this.logger.isInfoEnabled()) { 
    			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
    		}
    		long startTime = System.currentTimeMillis();
    
    		try { 
    			this.webApplicationContext = initWebApplicationContext();
    			initFrameworkServlet();
    		}
    		catch (ServletException | RuntimeException ex) { 
    			this.logger.error("Context initialization failed", ex);
    			throw ex;
    		}
    
    		if (this.logger.isInfoEnabled()) { 
    			long elapsedTime = System.currentTimeMillis() - startTime;
    			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
    					elapsedTime + " ms");
    		}
    	}

initWebApplicationContext() 方法具体内容如下 :

/** * Initialize and publish the WebApplicationContext for this servlet. * <p>Delegates to {@link #createWebApplicationContext} for actual creation * of the context. Can be overridden in subclasses. * @return the WebApplicationContext instance * @see #FrameworkServlet(WebApplicationContext) * @see #setContextClass * @see #setContextConfigLocation */
    	protected WebApplicationContext initWebApplicationContext() { 
    
    		//从父容器中, 获取根容器. 
    		WebApplicationContext rootContext =
    				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    		WebApplicationContext wac = null;
    
    		if (this.webApplicationContext != null) { 
    			// A context instance was injected at construction time -> use it
    			wac = this.webApplicationContext;
    			if (wac instanceof ConfigurableWebApplicationContext) { 
    				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
    				if (!cwac.isActive()) { 
    					// The context has not yet been refreshed -> provide services such as
    					// setting the parent context, setting the application context id, etc
    					if (cwac.getParent() == null) { 
    						// The context instance was injected without an explicit parent -> set
    						// the root application context (if any; may be null) as the parent
    						cwac.setParent(rootContext);
    					}
    					configureAndRefreshWebApplicationContext(cwac);
    				}
    			}
    		}
    		if (wac == null) { 
    			// No context instance was injected at construction time -> see if one
    			// has been registered in the servlet context. If one exists, it is assumed
    			// that the parent context (if any) has already been set and that the
    			// user has performed any initialization such as setting the context id
    			wac = findWebApplicationContext();
    		}
    		if (wac == null) { 
    			// No context instance is defined for this servlet -> create a local one
    			wac = createWebApplicationContext(rootContext);
    		}
    
    		if (!this.refreshEventReceived) { 
    			// Either the context is not a ConfigurableApplicationContext with refresh
    			// support or the context injected at construction time had already been
    			// refreshed -> trigger initial onRefresh manually here.
    			onRefresh(wac);
    		}
    
    		if (this.publishContext) { 
    			// Publish the context as a servlet context attribute.
    			String attrName = getServletContextAttributeName();
    			getServletContext().setAttribute(attrName, wac);
    			if (this.logger.isDebugEnabled()) { 
    				this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
    						"' as ServletContext attribute with name [" + attrName + "]");
    			}
    		}
    
    		return wac;
    	}

在上面的方法中, 有调用到configureAndRefreshWebApplicationContext(cwac);方法. 此方法的具体内容如下. 其中此方法中, 最后一步为 调用`wac.refresh();`

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) { 
    		if (ObjectUtils.identityToString(wac).equals(wac.getId())) { 
    			// The application context id is still set to its original default value
    			// -> assign a more useful id based on available information
    			if (this.contextId != null) { 
    				wac.setId(this.contextId);
    			}
    			else { 
    				// Generate default id...
    				wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
    						ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
    			}
    		}
    
    		wac.setServletContext(getServletContext());
    		wac.setServletConfig(getServletConfig());
    		wac.setNamespace(getNamespace());
    		wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
    
    		// The wac environment's #initPropertySources will be called in any case when the context
    		// is refreshed; do it eagerly here to ensure servlet property sources are in place for
    		// use in any post-processing or initialization that occurs below prior to #refresh
    		ConfigurableEnvironment env = wac.getEnvironment();
    		if (env instanceof ConfigurableWebEnvironment) { 
    			((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
    		}
    
    		postProcessWebApplicationContext(wac);
    		applyInitializers(wac);
    		wac.refresh();
    	}

refresh 方法为org.springframework.context.ConfigurableApplicationContext类的.

同样的, 在org.springframework.context.support.ClassPathXmlApplicationContext类中, 有如下的构造方法

/** * Create a new ClassPathXmlApplicationContext, loading the definitions * from the given XML files and automatically refreshing the context. * @param configLocations array of resource locations * @throws BeansException if context creation failed */
    	public ClassPathXmlApplicationContext(String... configLocations) throws BeansException { 
    		this(configLocations, true, null);
    	}

点击this方法, 可以看到是如下的方法. 在如下的方法中,可以看到有refresh();方法

/** * Create a new ClassPathXmlApplicationContext with the given parent, * loading the definitions from the given XML files. * @param configLocations array of resource locations * @param refresh whether to automatically refresh the context, * loading all bean definitions and creating all singletons. * Alternatively, call refresh manually after further configuring the context. * @param parent the parent context * @throws BeansException if context creation failed * @see #refresh() */
    	public ClassPathXmlApplicationContext(
    			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
    			throws BeansException { 
    
    		super(parent);
    		setConfigLocations(configLocations);
    		if (refresh) { 
    			refresh();
    		}
    	}

点击refresh();方法, 跳转到了org.springframework.context.support.AbstractApplicationContext  
类中的refresh方法.  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 4]  
可以看到 AbstractApplicationContext 类是实现了org.springframework.context.ConfigurableApplicationContext接口的.  
![在这里插入图片描述][20200503174511591.png]

在 org.springframework.web.servlet.FrameworkServlet 类中的initWebApplicationContext()中. 有  
`onRefresh(wac);`方法. 该方法以on开头, 代表事件的回调.

protected WebApplicationContext initWebApplicationContext() { 
    		WebApplicationContext rootContext =
    				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    		WebApplicationContext wac = null;
    
    		if (this.webApplicationContext != null) { 
    			// A context instance was injected at construction time -> use it
    			wac = this.webApplicationContext;
    			if (wac instanceof ConfigurableWebApplicationContext) { 
    				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
    				if (!cwac.isActive()) { 
    					// The context has not yet been refreshed -> provide services such as
    					// setting the parent context, setting the application context id, etc
    					if (cwac.getParent() == null) { 
    						// The context instance was injected without an explicit parent -> set
    						// the root application context (if any; may be null) as the parent
    						cwac.setParent(rootContext);
    					}
    					configureAndRefreshWebApplicationContext(cwac);
    				}
    			}
    		}
    		if (wac == null) { 
    			// No context instance was injected at construction time -> see if one
    			// has been registered in the servlet context. If one exists, it is assumed
    			// that the parent context (if any) has already been set and that the
    			// user has performed any initialization such as setting the context id
    			wac = findWebApplicationContext();
    		}
    		if (wac == null) { 
    			// No context instance is defined for this servlet -> create a local one
    			wac = createWebApplicationContext(rootContext);
    		}
    
    		if (!this.refreshEventReceived) { 
    			// Either the context is not a ConfigurableApplicationContext with refresh
    			// support or the context injected at construction time had already been
    			// refreshed -> trigger initial onRefresh manually here.
    			onRefresh(wac);
    		}
    
    		if (this.publishContext) { 
    			// Publish the context as a servlet context attribute.
    			String attrName = getServletContextAttributeName();
    			getServletContext().setAttribute(attrName, wac);
    			if (this.logger.isDebugEnabled()) { 
    				this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
    						"' as ServletContext attribute with name [" + attrName + "]");
    			}
    		}
    
    		return wac;
    	}

查看`onRefresh(wac);`实现的方法, 可以看到其实现类为org.springframework.web.servlet.DispatcherServlet. 其实现的方法如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 5]  
由上图可以看到 `onRefresh(wac);`调用的是initStrategies方法, 该方法,如下所示.

/** * Initialize the strategy objects that this servlet uses. * <p>May be overridden in subclasses in order to initialize further strategy objects. */
    	protected void initStrategies(ApplicationContext context) { 
    		//多文件上传的组件
    		initMultipartResolver(context);
    		
    		//初始化本地语言环境
    		initLocaleResolver(context);
    		//初始化模板处理器
    		initThemeResolver(context);
    		//初始化请求映射
    		initHandlerMappings(context);
    		//初始化参数适配器. 
    		initHandlerAdapters(context);
    		//初始化异常拦截器. 
    		initHandlerExceptionResolvers(context);
    		//初始化视图预处理器
    		initRequestToViewNameTranslator(context);
    		//初始化视图解析器
    		initViewResolvers(context);
    		initFlashMapManager(context);
    	}

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 6]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20191124150703896.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20191124150719846.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5,size_16,color_FFFFFF,t_70
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[20200503172611215.png]: https://img-blog.csdnimg.cn/20200503172611215.png
[2020050317264562.png]: https://img-blog.csdnimg.cn/2020050317264562.png
[20200503172653215.png]: https://img-blog.csdnimg.cn/20200503172653215.png
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[20200503174511591.png]: https://img-blog.csdnimg.cn/20200503174511591.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5_size_16_color_FFFFFF_t_70 6]: https://img-blog.csdnimg.cn/2020050320405672.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzMjI5NjY5,size_16,color_FFFFFF,t_70