Spring MVC Web应用上下文

     Spring MVC是建立在Spring IoC容器的基础上，然而Spring IoC是一个独立的模块，因此并不能直接在Web环境中发挥作用。为了在Web环境中使用Ioc，就需要Spring提供一个适合于Web环境的相关容器（WebApplicationContext），以及基于此容器的IoC启动过程，将IoC导入，这个启动过程应该与Web容器启动过程相集成。下面着重介绍Web应用上下文。

WebApplicationContext 类继承体系   ：



      可以看到，Web应用上下文的实现是基于基本Ioc容器ApplicatoionContext相关接口，并在此基础上加入了适用于Web环境的相关功能扩展。

1）WebApplicationContext接口实现

public interface WebApplicationContext extends ApplicationContext {

String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";
String SCOPE_REQUEST = "request";
String SCOPE_SESSION = "session";
...
...
ServletContext getServletContext();

}

在该接口中，定义了几个常量，比如ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE，这个常量用于索引在ServletContext中保存的根Web应用上下文。还有就是ServletContext getServletContext()方法，通过这个方法可以得到当前web容器的Servlet上下文。

2）ConfigurableWebApplicationContext实现

public interface ConfigurableWebApplicationContext extends WebApplicationContext, ConfigurableApplicationContext {
String APPLICATION_CONTEXT_ID_PREFIX = WebApplicationContext.class.getName() + ":";
String SERVLET_CONFIG_BEAN_NAME = "servletConfig";
//设置与该WebApplicationContext相关的ServletContext
void setServletContext(ServletContext servletContext);
//设置与该WebApplicationContext相关的Servlet的servletConfig
void setServletConfig(ServletConfig servletConfig);
ServletConfig getServletConfig();
//设置该WebApplicationContext依赖的bean定义资源配置路径
void setConfigLocation(String configLocation);

void setConfigLocations(String... configLocations);

String[] getConfigLocations();

}

  ConfigurableWebApplicationContext继承自WebApplicationContext接口，并且提供了设置ServletContext
以及上下文配置资源路径的相关函数。

3）AbstractRefreshableWebApplicationContext
类

public abstract class AbstractRefreshableWebApplicationContext extends AbstractRefreshableConfigApplicationContext
implements ConfigurableWebApplicationContext, ThemeSource {

/** Servlet context that this context runs in */
private ServletContext servletContext;

/** Servlet config that this context runs in, if any */
private ServletConfig servletConfig;

/** Namespace of this context, or {@code null} if root */
private String namespace;

/** the ThemeSource for this ApplicationContext */
private ThemeSource themeSource;

public AbstractRefreshableWebApplicationContext() {
setDisplayName("Root WebApplicationContext");
}

@Override
public void setServletContext(ServletContext servletContext) {
this.servletContext = servletContext;
}

@Override
public ServletContext getServletContext() {
return this.servletContext;
}

@Override
public void setServletConfig(ServletConfig servletConfig) {
this.servletConfig = servletConfig;
if (servletConfig != null && this.servletContext == null) {
setServletContext(servletConfig.getServletContext());
}
}

@Override
public ServletConfig getServletConfig() {
return this.servletConfig;
}

@Override
public void setNamespace(String namespace) {
this.namespace = namespace;
if (namespace != null) {
setDisplayName("WebApplicationContext for namespace '" + namespace + "'");
}
}

@Override
public String getNamespace() {
return this.namespace;
}

@Override
public String[] getConfigLocations() {
return super.getConfigLocations();
}

@Override
public String getApplicationName() {
return (this.servletContext != null ? this.servletContext.getContextPath() : "");
}

/**
* Create and return a new {@link StandardServletEnvironment}. Subclasses may override
* in order to configure the environment or specialize the environment type returned.
*/
@Override
protected ConfigurableEnvironment createEnvironment() {
return new StandardServletEnvironment();
}

/**
* Register request/session scopes, a {@link ServletContextAwareProcessor}, etc.
*/
@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
beanFactory.ignoreDependencyInterface(ServletConfigAware.class);

WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
}

/**
* This implementation supports file paths beneath the root of the Serv
4000
letContext.
* @see ServletContextResource
*/
@Override
protected Resource getResourceByPath(String path) {
return new ServletContextResource(this.servletContext, path);
}

/**
* This implementation supports pattern matching in unexpanded WARs too.
* @see ServletContextResourcePatternResolver
*/
@Override
protected ResourcePatternResolver getResourcePatternResolver() {
return new ServletContextResourcePatternResolver(this);
}

/**
* Initialize the theme capability.
*/
@Override
protected void onRefresh() {
this.themeSource = UiApplicationContextUtils.initThemeSource(this);
}

/**
* {@inheritDoc}
* <p>Replace {@code Servlet}-related property sources.
*/
@Override
protected void initPropertySources() {
ConfigurableEnvironment env = getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(this.servletContext, this.servletConfig);
}
}

@Override
public Theme getTheme(String themeName) {
return this.themeSource.getTheme(themeName);
}

}

4）Spring MVC使用的WebApplicationContext实现

   Spring MVC使用一个默认的WebApplicationContext来作为Ioc容器，这个Ioc容器就是XmlWebApplicationContext。通过类继承体系可以看到其实现继承于AbstractRefreshableWebApplicationContext抽象类，而AbstractRefreshableWebApplicationContext又继承自AbstractRefreshableConfigApplicationContext。

public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {

//设置的默认的BeanDefinition的地方，在/WEB-INF/applicationContext.xml文件中
public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";
//默认的bean配置文件目录前缀和文件后缀
public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";
public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";

//loadBeanDefinitions函数，在Ioc容器启动时，通过该函数加载、注册BeanDefinition
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//用XmlBeanDefinitionReader 类来对BeanDefinition信息进行解析
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.setEnvironment(getEnvironment());
//设置ResourceLoader资源导入器，因ApplicationContext是DefaultResource子类，因此这里传入this，使用该DefaultResourceLoader来定位BeanDefinition资源文件
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
initBeanDefinitionReader(beanDefinitionReader);
//通过定义好的XmlBeanDefinitionReader 来载入BeanDefinition。
loadBeanDefinitions(beanDefinitionReader);
}

protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) {
}
//对多个BeanDefinition定义文件，通过XmlBeanDefinitionReader 逐个载入
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
reader.loadBeanDefinitions(configLocation);
}
}
}
//获取默认资源位置，默认的位置是/WEB-INF/applicationContext.xml
@Override
protected String[] getDefaultConfigLocations() {
if (getNamespace() != null) {
return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};
}
else {
return new String[] {DEFAULT_CONFIG_LOCATION};
}
}

}

  XmlWebApplicationContext中基本的上下文功能都通过类继承来获得，需要处理的就是获取Bean定义信息。这里是获取web容器环境指定的资源如/WEB-INF/applicationContext.xml。在获取到bean定义后，就如同Spring基本Ioc上下文容器ApplicationContext一样通过XmlBeanDefinitionReader来载入bean定义信息，最终完成上下文初始化。