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Spring 源码解析二:上下文组件(WebApplicationContext)

转载 作者:知者 更新时间:2024-03-13 08:14:57 28 4
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上一篇解析了 DispatcherServletContextLoaderListener 这两个类,解析了应用初始化与请求处理的流程,但还有一些组件需要解析:

  • ConfigurableWebApplicationContext.refresh 刷新上下文
  • ApplicationContext.getBean 从上下文中获取 bean
  • DispatcherServlet.properties 文件中定义的策略处理
  • ContextLoader.properties 文件中定义的策略处理
  • View.render 视图渲染

这一章来看看 ContextLoader.properties 文件中定义的策略处理

ContextLoader.properties 文件中只定义了一个策略

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

默认使用 XmlWebApplicationContext(基于 XML 加载)作为应用上下文

spring-web 内部定义 5 个应用上下文类:

  • GenericWebApplicationContext
    WebApplicationContext的基础实现,但不能通过配置文件和注解加载应用配置与 bean,一般用于扩展实现(如 SpringBoot),很少直接使用
  • StaticWebApplicationContext
    :也是WebApplicationContext的基础实现,但不支持 i18n,主要用于测试,不用产品环境
  • XmlWebApplicationContext
    :基于 XML 加载应用配置与 bean 的WebApplicationContext实现,是 SpringMVC 的默认 Context
  • AnnotationConfigWebApplicationContext
    :基于注解如 @Configuration, @bean 等加载应用配置与 bean 的WebApplicationContext实现
  • GroovyWebApplicationContext
    :与XmlWebApplicationContext的实现差不多,但可以用 Groovy 代替 xml 做配置文件,目前用得不多

先来看看这 5 个应用上下文类各自的继承关系

- DefaultResourceLoader
  - AbstractApplicationContext
    - GenericApplicationContext
      - GenericWebApplicationContext

- DefaultResourceLoader
  - AbstractApplicationContext
    - GenericApplicationContext
      - StaticApplicationContext
        - StaticWebApplicationContext

- DefaultResourceLoader
  - AbstractApplicationContext
    - AbstractRefreshableApplicationContext
      - AbstractRefreshableConfigApplicationContext
        - AbstractRefreshableWebApplicationContext
          - XmlWebApplicationContext

- DefaultResourceLoader
  - AbstractApplicationContext
    - AbstractRefreshableApplicationContext
      - AbstractRefreshableConfigApplicationContext
        - AbstractRefreshableWebApplicationContext
          - AnnotationConfigWebApplicationContext

- DefaultResourceLoader
  - AbstractApplicationContext
    - AbstractRefreshableApplicationContext
      - AbstractRefreshableConfigApplicationContext
        - AbstractRefreshableWebApplicationContext
          - GroovyWebApplicationContext

我们可以发现每个类都继承 AbstractApplicationContext,而 XmlWebApplicationContext, AnnotationConfigWebApplicationContext,
GroovyWebApplicationContext 都继承 AbstractRefreshableWebApplicationContext

1. DefaultResourceLoader

DefaultResourceLoader
的主要功能是实现资源加载

public class DefaultResourceLoader implements ResourceLoader {}

先来看看接口ResourceLoader

public interface ResourceLoader {
    // 根据一个字符位置信息获取资源
    Resource getResource(String location);

    // 获取资源加载器
    ClassLoader getClassLoader();
}

DefaultResourceLoader
ResourceLoader 的默认实现

public class DefaultResourceLoader implements ResourceLoader {
    @Override
    public ClassLoader getClassLoader() {
        // 如果有指定的classLoader,则返回指定的,没有则返回默认的
        return (this.classLoader != null ? this.classLoader : ClassUtils.getDefaultClassLoader());
    }

    @Override
    public Resource getResource(String location) {
        // 自定义协议解析
        for (ProtocolResolver protocolResolver : getProtocolResolvers()) {
            Resource resource = protocolResolver.resolve(location, this);
            if (resource != null) {
                return resource;
            }
        }

        // 如果以/开头,则认为是classpath资源
        if (location.startsWith("/")) {
            return getResourceByPath(location);
        }
        // 如果以classpath:开头的classpath资源
        else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
            return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
        }
        else {
            try {
                // 尝试以文件或url对待
                URL url = new URL(location);
                return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
            }
            catch (MalformedURLException ex) {
                // 失败则默认是classpath资源
                return getResourceByPath(location);
            }
        }
    }
}

2. AbstractApplicationContext

AbstractApplicationContext
的主要功能是通过名字、类型或注解获取 bean 实例,获取上下文的环境对象与资源、刷新上下文数据

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {}

接口 ConfigurableApplicationContext
及其继承的接口主要定义以下的方法

public interface ConfigurableApplicationContext {
    // 获取bean
    Object getBean(String name) throws BeansException;
    <T> T getBean(String name, Class<T> requiredType) throws BeansException;
    Object getBean(String name, Object... args) throws BeansException;
    <T> T getBean(Class<T> requiredType) throws BeansException;
    <T> T getBean(Class<T> requiredType, Object... args) throws BeansException;

    // 通过类型或注解获取bean
    <T> Map<String, T> getBeansOfType(@Nullable Class<T> type) throws BeansException;
    <T> Map<String, T> getBeansOfType(@Nullable Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)
            throws BeansException;
    Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType) throws BeansException;

    // 获取环境
     ConfigurableEnvironment getEnvironment();

    // 刷新上下文数据
    void refresh() throws BeansException, IllegalStateException;

    // 根据locationPattern获取多个资源,如通配符*
    Resource[] getResources(String locationPattern) throws IOException;
}

2.1. AbstractApplicationContext.getEnvironment

AbstractApplicationContext.getEnvironment
获取环境

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    @Override
    public ConfigurableEnvironment getEnvironment() {
        if (this.environment == null) {
            this.environment = createEnvironment();
        }
        return this.environment;
    }

    protected ConfigurableEnvironment createEnvironment() {
        // 内置的标准环境(也可以通过setEnvironment方法自定义环境处理机制)
        // 这是可以使用 `application-dev.yml, application-test.yml, application-prod.yml, ...` 来根据环境加载不同的配置的底层实现
        // 是spring-boot的基本功能
        return new StandardEnvironment();
    }
}

2.2. AbstractApplicationContext.getBean

AbstractApplicationContext.getBean
获取 bean

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    @Override
    public Object getBean(String name) throws BeansException {
        return getBeanFactory().getBean(name);
    }

    @Override
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
        return getBeanFactory().getBean(name, requiredType);
    }

    @Override
    public Object getBean(String name, Object... args) throws BeansException {
        return getBeanFactory().getBean(name, args);
    }

    @Override
    public <T> T getBean(Class<T> requiredType) throws BeansException {
        return getBeanFactory().getBean(requiredType);
    }

    @Override
    public <T> T getBean(Class<T> requiredType, Object... args) throws BeansException {
        return getBeanFactory().getBean(requiredType, args);
    }

    // 留给子类实现
    public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;
}

因为不同的Context注册 bean 的方式不一样,所以getBeanFactory留给子类来实现

2.3. AbstractApplicationContext.getBeansOfType

AbstractApplicationContext.getBeansOfType
通过类型或注解获取 bean

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    @Override
    public <T> Map<String, T> getBeansOfType(@Nullable Class<T> type) throws BeansException {
        return getBeanFactory().getBeansOfType(type);
    }

    @Override
    public <T> Map<String, T> getBeansOfType(@Nullable Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)
            throws BeansException {
        return getBeanFactory().getBeansOfType(type, includeNonSingletons, allowEagerInit);
    }

    @Override
    public Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType)
            throws BeansException {
        return getBeanFactory().getBeansWithAnnotation(annotationType);
    }

    // 留给子类实现
    public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;
}

2.4. AbstractApplicationContext.refresh

AbstractApplicationContext.refresh
刷新上下文数据

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // ... 代码省略

            // 初始化事件容器与监听器,检查必须的属性配置,并载入必要的实例
            prepareRefresh();

            // 刷新上下文的bean,获取bean工厂
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // 预备bean工厂
            prepareBeanFactory(beanFactory);

            try {
                // 后置处理bean工厂
                postProcessBeanFactory(beanFactory);

                // ... 代码省略

                // 调用bean工厂的后置处理器,以使在所有bean实例化之前,可以自定义添加自己的BeanPostProcessor(bean实例化后置操作)
                invokeBeanFactoryPostProcessors(beanFactory);

                // 给bean工厂注册BeanPostProcessor(bean实例化后置操作)
                registerBeanPostProcessors(beanFactory);

                // ... 代码省略

                // 实例化applicationEventMulticaster bean,作为应用事件广播器
                initApplicationEventMulticaster();

                // 扩展实现,留给开发者,默认不实现
                onRefresh();

                // 注册应用事件监听器
                registerListeners();

                // 初始化所有单例的bean
                finishBeanFactoryInitialization(beanFactory);

                // 刷新上下文数据完成,做一些后续处理
                finishRefresh();
            }

            catch (BeansException ex) {
                // ... 代码省略
            }

            finally {
                // ... 代码省略
            }
        }
    }

    // 刷新上下文的bean,获取bean工厂
    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        // 刷新上下文的bean
        refreshBeanFactory();
        // 获取bean工厂
        return getBeanFactory();
    }

    // 刷新上下文的bean,由子类实现
    protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;

    // 获取bean工厂,由子类实现
    public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;

    // 扩展实现,留给开发者,默认不实现
    protected void onRefresh() throws BeansException {}

    // 初始化所有单例的bean
    protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        // ... 代码省略

        // 固化所有bean的配置,后面不再更改
        beanFactory.freezeConfiguration();

        // 初始化所有单例的bean
        beanFactory.preInstantiateSingletons();
    }

    // 刷新上下文数据完成,做一些后续处理
    protected void finishRefresh() {
        // 清除一些资源缓存
        clearResourceCaches();

        // 实例化lifecycleProcessor bean
        initLifecycleProcessor();

        // 实例化Lifecycle bean,并调用这些bean的start方法
        getLifecycleProcessor().onRefresh();

        // 派发事件
        publishEvent(new ContextRefreshedEvent(this));

        // ... 代码省略
    }
}
  • 因为不同的Context注册 bean 的方式不一样,所以refreshBeanFactory, postProcessBeanFactory留给子类来实现
  • ConfigurableListableBeanFactory如何加载、实例化 bean,后面再解析

2.5. AbstractApplicationContext.prepareBeanFactory

AbstractApplicationContext.prepareBeanFactory
预备 bean 工厂

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // ... 代码省略

        // 添加对 #{} SpEL Spring 表达式语言的支持
        if (!shouldIgnoreSpel) {
            beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        }

        // 添加属性编辑器,xml、yaml 中定义的值转换成对象就是依赖这里实现的
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        // 添加一个BeanPostProcessor,后置处理器
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

        // ... 代码省略

        // 注册几个可以autowirable自动载入的实例
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);

        // ... 代码省略

        // 注册几个单例bean
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
        if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {
            beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
        }
    }
}
  • ResourceEditorRegistrar如何注册属性编辑器、属性编辑器如何解析为对象,后面再解析

2.6. AbstractApplicationContext.getResources

AbstractApplicationContext.getResources
根据 locationPattern 获取多个资源,如通配符*

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    private ResourcePatternResolver resourcePatternResolver;

    public AbstractApplicationContext() {
        this.resourcePatternResolver = getResourcePatternResolver();
    }

    protected ResourcePatternResolver getResourcePatternResolver() {
        return new PathMatchingResourcePatternResolver(this);
    }

    @Override
    public Resource[] getResources(String locationPattern) throws IOException {
        return this.resourcePatternResolver.getResources(locationPattern);
    }
}
  • PathMatchingResourcePatternResolver如何解析、加载 locationPattern 指定的资源,后面再解析

2.7. 综述

总的来说,AbstractApplicationContext 类完成上下文环境的大部分功能,包括环境加载、bean 的加载与前置后置处理、事件派发、完成一些初始化工作等,
但扩展了几个接口给子类实现,如如何加载、注册、实例化 bean 等

3. GenericApplicationContext

GenericApplicationContext
的主要功能是注册、管理 bean 的定义与别名

public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {}

BeanDefinitionRegistry
这个接口主要定义了注册 bean 的定义及别名

public interface BeanDefinitionRegistry {
    // 注册bean定义
    void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException;

    // 删除bean定义
    void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

    // 获取bean定义
    BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

    // 检查bean定义
    boolean containsBeanDefinition(String beanName);

    // 注册bean别名
    void registerAlias(String name, String alias);

    // 删除bean别名
    void removeAlias(String alias);

    // 检查bean别名
    boolean isAlias(String name);

    // 获取bean别名
    String[] getAliases(String name);
}

来看看 GenericApplicationContext 如何实现这些接口的

public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {
    @Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        this.beanFactory.registerBeanDefinition(beanName, beanDefinition);
    }

    @Override
    public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
        this.beanFactory.removeBeanDefinition(beanName);
    }

    @Override
    public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
        return this.beanFactory.getBeanDefinition(beanName);
    }

    @Override
    public void registerAlias(String beanName, String alias) {
        this.beanFactory.registerAlias(beanName, alias);
    }

    @Override
    public void removeAlias(String alias) {
        this.beanFactory.removeAlias(alias);
    }

    @Override
    public boolean isAlias(String beanName) {
        return this.beanFactory.isAlias(beanName);
    }
}

最终还是落脚在 beanFactory

4. GenericWebApplicationContext

GenericWebApplicationContext
的主要功能是添加了设置 bean 配置文件来源,允许通过配置的方式实例化上下文环境

public class GenericWebApplicationContext extends GenericApplicationContext
        implements ConfigurableWebApplicationContext, ThemeSource {}

ConfigurableWebApplicationContext

public interface ConfigurableWebApplicationContext {
    // 设置bean配置文件来源
    void setConfigLocation(String configLocation);
    // 设置多个bean配置文件来源
    void setConfigLocations(String... configLocations);
    // 获取bean配置文件来源
    String[] getConfigLocations();
}

ConfigurableWebApplicationContext扩展了WebApplicationContext,定义了允许通过配置的方式实例化上下文环境

public class GenericWebApplicationContext extends GenericApplicationContext
        implements ConfigurableWebApplicationContext, ThemeSource {
    @Override
    protected ConfigurableEnvironment createEnvironment() {
        // StandardServletEnvironment扩展了StandardEnvironment
        // 增加了可以从Servlet context init parameters和Servlet config init parameters增加应用配置来源
        return new StandardServletEnvironment();
    }

    // 不可设置bean配置文件来源
    @Override
    public void setConfigLocation(String configLocation) {
        if (StringUtils.hasText(configLocation)) {
            throw new UnsupportedOperationException(
                    "GenericWebApplicationContext does not support setConfigLocation(). " +
                    "Do you still have an 'contextConfigLocations' init-param set?");
        }
    }

    @Override
    public void setConfigLocations(String... configLocations) {
        if (!ObjectUtils.isEmpty(configLocations)) {
            throw new UnsupportedOperationException(
                    "GenericWebApplicationContext does not support setConfigLocations(). " +
                    "Do you still have an 'contextConfigLocations' init-param set?");
        }
    }

    @Override
    public String[] getConfigLocations() {
        throw new UnsupportedOperationException(
                "GenericWebApplicationContext does not support getConfigLocations()");
    }
}

GenericWebApplicationContext 并未实现 ConfigurableWebApplicationContext 的核心方法,也就不能通过文件加载配置,
该类设计的目的不是在web.xml中进行声明式的安装,而是编程式的安装,例如使用WebApplicationInitializers来构建内嵌的上下文;一般很少用到

5. StaticWebApplicationContext

因为 StaticApplicationContext
实现功能比较少,放在这里一起解析

public class StaticApplicationContext extends GenericApplicationContext {
    private final StaticMessageSource staticMessageSource;

    public StaticApplicationContext(@Nullable ApplicationContext parent) throws BeansException {
        super(parent);

        // 上下文对象中有一个messageSource组件,实现了i18n功能
        // 而StaticMessageSource实现的是由程序载入文本,而非文件,便是去掉了i18n功能
        this.staticMessageSource = new StaticMessageSource();
        getBeanFactory().registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.staticMessageSource);
    }
}

StaticWebApplicationContext
实现功能也比较少

public class StaticWebApplicationContext extends StaticApplicationContext
        implements ConfigurableWebApplicationContext, ThemeSource {
    // 不可设置bean配置文件来源
    @Override
    public void setConfigLocation(String configLocation) {
        throw new UnsupportedOperationException("StaticWebApplicationContext does not support config locations");
    }

    @Override
    public void setConfigLocations(String... configLocations) {
        throw new UnsupportedOperationException("StaticWebApplicationContext does not support config locations");
    }

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

StaticWebApplicationContext 也并未实现 ConfigurableWebApplicationContext 的核心方法,也就不能通过文件加载配置,
该类设计的目的主要用于测试,不用于产品环境

6. AbstractRefreshableApplicationContext

AbstractRefreshableApplicationContext
的主要功能是创建 bean 工厂,刷新上下文数据

public abstract class AbstractRefreshableApplicationContext extends AbstractApplicationContext {
    @Override
    protected final void refreshBeanFactory() throws BeansException {
        // ... 代码省略
        try {
            // 创建bean工厂
            DefaultListableBeanFactory beanFactory = createBeanFactory();

            // ... 代码省略

            // 加载bean的定义
            loadBeanDefinitions(beanFactory);
            this.beanFactory = beanFactory;
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

    // 创建bean工厂
    protected DefaultListableBeanFactory createBeanFactory() {
        // 默认使用DefaultListableBeanFactory创建bean工厂
        return new DefaultListableBeanFactory(getInternalParentBeanFactory());
    }

    // 加载bean的定义,由子类实现
    protected abstract void loadBeanDefinitions(DefaultListableBeanFactory beanFactory)
                throws BeansException, IOException;
}

7. AbstractRefreshableConfigApplicationContext

AbstractRefreshableConfigApplicationContext
的主要功能是可以通过文件加载配置

public abstract class AbstractRefreshableConfigApplicationContext extends AbstractRefreshableApplicationContext
        implements BeanNameAware, InitializingBean {
    // 设置配置文件来源,以",; \t\n"分隔多个
    public void setConfigLocation(String location) {
        setConfigLocations(StringUtils.tokenizeToStringArray(location, CONFIG_LOCATION_DELIMITERS));
    }

    public void setConfigLocations(@Nullable String... locations) {
        if (locations != null) {
            this.configLocations = new String[locations.length];
            for (int i = 0; i < locations.length; i++) {
                // 解析路径,替换${}占位符
                this.configLocations[i] = resolvePath(locations[i]).trim();
            }
        }
        else {
            this.configLocations = null;
        }
    }

    // 获取配置文件来源集,如果没有,则返回默认的
    protected String[] getConfigLocations() {
        return (this.configLocations != null ? this.configLocations : getDefaultConfigLocations());
    }

    // 默认的配置文件来源集由子类实现
    protected String[] getDefaultConfigLocations() {
        return null;
    }

    // 解析路径,替换${}占位符,有PropertySourcesPropertyResolver.resolveRequiredPlaceholders实现此功能
    protected String resolvePath(String path) {
        return getEnvironment().resolveRequiredPlaceholders(path);
    }
}
  • AbstractRefreshableConfigApplicationContext 实现了 ConfigurableWebApplicationContext 的核心方法,也就是可以文件加载配置
  • PropertySourcesPropertyResolver如何是解析路径的,后面再解析

8. XmlWebApplicationContext

因为 AbstractRefreshableWebApplicationContext
实现功能比较少,放在这里一起解析

public abstract class AbstractRefreshableWebApplicationContext extends AbstractRefreshableConfigApplicationContext
        implements ConfigurableWebApplicationContext, ThemeSource {
    @Override
    protected ConfigurableEnvironment createEnvironment() {
        // StandardServletEnvironment扩展了StandardEnvironment
        // 增加了可以从Servlet context init parameters和Servlet config init parameters增加应用配置来源
        return new StandardServletEnvironment();
    }
}

XmlWebApplicationContext
的主要功能是定义了默认的配置文件,创建一个 bean 定义的 xml 解析器,并注册 bean 定义

public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {
    // 默认配置文件
    public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";

    // 默认配置文件前缀
    public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";

    // 默认配置文件后缀
    public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";

    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // 创建一个bean定义的xml解析器,用XmlBeanDefinitionReader实现
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

        // ... 代码省略

        // 载入bean定义
        loadBeanDefinitions(beanDefinitionReader);
    }

    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            for (String configLocation : configLocations) {
                // 通过配置文件载入bean定义
                reader.loadBeanDefinitions(configLocation);
            }
        }
    }

    @Override
    protected String[] getDefaultConfigLocations() {
        if (getNamespace() != null) {
            // 如果有servlet-name(如testapp),用前缀后缀包裹为"/WEB-INF/testapp-servlet.xml"
            return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};
        }
        else {
            // 如果没有,默认为"/WEB-INF/applicationContext.xml"文件
            return new String[] {DEFAULT_CONFIG_LOCATION};
        }
    }
}

XmlWebApplicationContext 主要解决了 2 个问题:

  1. 定义了默认的配置文件,有 servlet-name(如testapp),用前缀后缀包裹为/WEB-INF/testapp-servlet.xml,如果没有 servlet-name,则为/WEB-INF/applicationContext.xml
  2. 创建一个 bean 定义的 xml 解析器,并通过配置文件载入 bean 定义

SpringMVC 框架的默认加载机制便是使用XmlWebApplicationContext作为上下文环境,从 xml 文件加载配置与 bean 定义

至于XmlBeanDefinitionReader如何是解析 bean 定义的,后面再解析

9. AnnotationConfigWebApplicationContext

AnnotationConfigWebApplicationContext
的主要功能是可以通过注解载入配置和 bean 定义

public class AnnotationConfigWebApplicationContext extends AbstractRefreshableWebApplicationContext
        implements AnnotationConfigRegistry {}

先来看看 AnnotationConfigRegistry

public interface AnnotationConfigRegistry {
    // 根据类名注册组件
    void register(Class<?>... componentClasses);

    // 根据包名扫描组件
    void scan(String... basePackages);
}

这两个方法正好是通过注解如 @Configuration, @bean, @Component, @Controller, @Service 等注册 bean 的底层机制

来看看 AnnotationConfigWebApplicationContext 是如何实现的

public class AnnotationConfigWebApplicationContext extends AbstractRefreshableWebApplicationContext
        implements AnnotationConfigRegistry {
    // 组件类集合
    private final Set<Class<?>> componentClasses = new LinkedHashSet<>();
    // 扫描包名集合
    private final Set<String> basePackages = new LinkedHashSet<>();

    // 注册组件
    @Override
    public void register(Class<?>... componentClasses) {
        Collections.addAll(this.componentClasses, componentClasses);
    }

    // 添加扫描包名
    @Override
    public void scan(String... basePackages) {
        Collections.addAll(this.basePackages, basePackages);
    }

    // 加载bean定义
    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) {
        // 创建一个bean定义的注解解析器,用AnnotatedBeanDefinitionReader实现
        AnnotatedBeanDefinitionReader reader = getAnnotatedBeanDefinitionReader(beanFactory);
        // 创建一个基于包名的bean注解扫描器,用ClassPathBeanDefinitionScanner实现
        ClassPathBeanDefinitionScanner scanner = getClassPathBeanDefinitionScanner(beanFactory);

        // 创建一个bean命名生成器
        BeanNameGenerator beanNameGenerator = getBeanNameGenerator();
        if (beanNameGenerator != null) {
            reader.setBeanNameGenerator(beanNameGenerator);
            scanner.setBeanNameGenerator(beanNameGenerator);
            beanFactory.registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, beanNameGenerator);
        }

        // 创建一个bean作用域元信息解析器,判断注册的bean是原生类型(prototype)还是单例类型(singleton)
        ScopeMetadataResolver scopeMetadataResolver = getScopeMetadataResolver();
        if (scopeMetadataResolver != null) {
            reader.setScopeMetadataResolver(scopeMetadataResolver);
            scanner.setScopeMetadataResolver(scopeMetadataResolver);
        }

        // 注册组件类
        if (!this.componentClasses.isEmpty()) {
            reader.register(ClassUtils.toClassArray(this.componentClasses));
        }

        // 扫描包
        if (!this.basePackages.isEmpty()) {
            scanner.scan(StringUtils.toStringArray(this.basePackages));
        }

        // 通过定义的配置来源注册组件类或扫描包名
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            for (String configLocation : configLocations) {
                try {
                    Class<?> clazz = ClassUtils.forName(configLocation, getClassLoader());
                    reader.register(clazz);
                }
                catch (ClassNotFoundException ex) {
                    int count = scanner.scan(configLocation);
                    // ... 代码省略
                }
            }
        }
    }

    // 创建一个bean定义的注解解析器,用AnnotatedBeanDefinitionReader实现
    protected AnnotatedBeanDefinitionReader getAnnotatedBeanDefinitionReader(DefaultListableBeanFactory beanFactory) {
        return new AnnotatedBeanDefinitionReader(beanFactory, getEnvironment());
    }

    // 创建一个基于包名的bean注解扫描器,用ClassPathBeanDefinitionScanner实现
    protected ClassPathBeanDefinitionScanner getClassPathBeanDefinitionScanner(DefaultListableBeanFactory beanFactory) {
        return new ClassPathBeanDefinitionScanner(beanFactory, true, getEnvironment());
    }
}

实际上,注册 bean 是由AnnotatedBeanDefinitionReader完成,扫描包是由ClassPathBeanDefinitionScanner完成,这两个类后面再解析

10. GroovyWebApplicationContext

GroovyWebApplicationContext
的运行机制与 XmlWebApplicationContext 差不多,从 groovy 文件加载配置与 bean 定义

public class GroovyWebApplicationContext extends AbstractRefreshableWebApplicationContext implements GroovyObject {
    // 默认配置文件
    public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.groovy";

    // 默认配置文件前缀
    public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";

    // 默认配置文件后缀
    public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".groovy";

    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // 创建一个bean定义的Groovy解析器,用GroovyBeanDefinitionReader实现
        GroovyBeanDefinitionReader beanDefinitionReader = new GroovyBeanDefinitionReader(beanFactory);

        // ... 代码省略

        // 载入bean定义
        loadBeanDefinitions(beanDefinitionReader);
    }

    protected void loadBeanDefinitions(GroovyBeanDefinitionReader reader) throws IOException {
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            for (String configLocation : configLocations) {
                // 通过配置文件载入bean定义
                reader.loadBeanDefinitions(configLocation);
            }
        }
    }

    @Override
    protected String[] getDefaultConfigLocations() {
        if (getNamespace() != null) {
            // 如果有servlet-name(如testapp),用前缀后缀包裹为"/WEB-INF/testapp-servlet.groovy"
            return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};
        }
        else {
            // 如果没有,默认为"/WEB-INF/applicationContext.groovy"文件
            return new String[] {DEFAULT_CONFIG_LOCATION};
        }
    }
}

11. 综述

WebApplicationContext
定义了 Web 应用初始化的基本流程,主要有 5 个实现类,常用的是:基于 Xml 加载的XmlWebApplicationContext
与基于注解加载的AnnotationConfigWebApplicationContext

12. 未完

这一节仍然有一些点留待下次解析:

  • ConfigurableListableBeanFactory如何加载、实例化 bean
  • ResourceEditorRegistrar如何注册属性编辑器、属性编辑器如何解析为对象
  • PathMatchingResourcePatternResolver如何解析、加载 locationPattern 指定的资源
  • PropertySourcesPropertyResolver如何是解析路径的
  • XmlBeanDefinitionReader如何是解析 bean 定义的
  • AnnotatedBeanDefinitionReader是如何注册 bean 的
  • ClassPathBeanDefinitionScanner是如何扫描包的

后续

更多博客,查看 https://github.com/senntyou/blogs

作者:深予之 (@senntyou)

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