在springboot web工程中可以通过使用@ServletComponentScan注解会自动扫描装配带有@WebServlet、@WebFilter和@WebListener的类，分别实现注册servelt、添加servler过滤器、添加servlet监听器，如：ServletContextListener、ServletRequestListener、HttpSessionListener等
实例添加过滤器
@WebFilter(urlPatterns ="
@Override
public void requestInitialized (ServletRequestEvent sre) {
sre.getServletRequest().setAttribute("myName", "张三;");
}
}
添加Servlet处理请求
@WebServlet(urlPatterns ="/myServlet")
public class MyWebServlet extends HttpServlet {
private static final long serialVersionUID = 6586226767091889098L;
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException
{
val myName = req.getAttribute("myName");
resp.getWriter().write("myName is" + myName );
resp.getWriter().write(" 我已经处理请求了");
}
}
运行结果
首先引入@ServletComponentScan定义要扫描的的包或class ，同时注入ServletComponentScanRegistrar来获取要扫描的包或者类
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
//此配置类为关键
@Import(ServletComponentScanRegistrar.class)
public @interface ServletComponentScan {
@AliasFor("basePackages")
String[] value() default {};
@AliasFor("value")
String[] basePackages() default {};
Class[] basePackageClasses() default {};
}
ServletComponentScanRegistrar实现了ImportBeanDefinitionRegistrar接口，实现了registerBeanDefinitions接口方法注入了ServletComponentRegisteringPostProcessor工厂处理器，具体代码分析如下：
class ServletComponentScanRegistrar implements ImportBeanDefinitionRegistrar {
private static final String BEAN_NAME = "servletComponentRegisteringPostProcessor";
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
Set packagesToScan = getPackagesToScan(importingClassMetadata);
if (registry.containsBeanDefinition(BEAN_NAME)) {
updatePostProcessor(registry, packagesToScan);
}
else {
addPostProcessor(registry, packagesToScan);
}
}
private void updatePostProcessor(BeanDefinitionRegistry registry, Set packagesToScan) {
ServletComponentRegisteringPostProcessorBeanDefinition definition = (ServletComponentRegisteringPostProcessorBeanDefinition) registry
.getBeanDefinition(BEAN_NAME);
definition.addPackageNames(packagesToScan);
}
private void addPostProcessor(BeanDefinitionRegistry registry, Set packagesToScan) {
ServletComponentRegisteringPostProcessorBeanDefinition definition = new ServletComponentRegisteringPostProcessorBeanDefinition(
packagesToScan);
registry.registerBeanDefinition(BEAN_NAME, definition);
}
private Set getPackagesToScan(AnnotationMetadata metadata) {
//获取注解元数据
AnnotationAttributes attributes = AnnotationAttributes
.fromMap(metadata.getAnnotationAttributes(ServletComponentScan.class.getName()));
String[] basePackages = attributes.getStringArray("basePackages");
Class[] basePackageClasses = attributes.getClassArray("basePackageClasses");
Set packagesToScan = new LinkedHashSet<>(Arrays.asList(basePackages));
for (Class basePackageClass : basePackageClasses) {
packagesToScan.add(ClassUtils.getPackageName(basePackageClass));
}
//如果没有指定包路径，将使用指定类的包路径作为要扫码的包
if (packagesToScan.isEmpty()) {
packagesToScan.add(ClassUtils.getPackageName(metadata.getClassName()));
}
return packagesToScan;
}
//继承至GenericBeanDefinition，构造函数及getInstanceSupplier方法指定了真正要注入的beanDefinition即
// ServletComponentRegisteringPostProcessorBeanDefinition，同时传了了该beanDefinition的参数
static final class ServletComponentRegisteringPostProcessorBeanDefinition extends GenericBeanDefinition {
private Set packageNames = new LinkedHashSet<>();
ServletComponentRegisteringPostProcessorBeanDefinition(Collection packageNames) {
setBeanClass(ServletComponentRegisteringPostProcessor.class);
setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
addPackageNames(packageNames);
}
//此处为关键，在生产bean实例的时候会取调用该方法，可以参考
// AbstractAutowireCapableBeanFactory#createBeanInstance
@Override
public Supplier getInstanceSupplier() {
return () -> new ServletComponentRegisteringPostProcessor(this.packageNames);
}
private void addPackageNames(Collection additionalPackageNames) {
this.packageNames.addAll(additionalPackageNames);
}
}
}
ServletComponentRegisteringPostProcessor实现了BeanFactoryPostProcessor工厂处理器，并且实现了postProcessBeanFactory，该方法是实现处理@WebFilter等注解的核心的方法，具体分析如下：
class ServletComponentRegisteringPostProcessor implements BeanFactoryPostProcessor, ApplicationContextAware {
private static final List HANDLERS;
//初始化的扫描器注解过滤器，如WebServletHandler构造函数里包含WebServlet注解
static {
List servletComponentHandlers = new ArrayList<>();
servletComponentHandlers.add(new WebServletHandler());
servletComponentHandlers.add(new WebFilterHandler());
servletComponentHandlers.add(new WebListenerHandler());
HANDLERS = Collections.unmodifiableList(servletComponentHandlers);
}
private final Set packagesToScan;
private ApplicationContext applicationContext;
ServletComponentRegisteringPostProcessor(Set packagesToScan) {
this.packagesToScan = packagesToScan;
}
//执行工厂后置处理器方法，通过classPath遍历扫描器对应的路径
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
if (isRunningInEmbeddedWebServer()) {
ClassPathScanningCandidateComponentProvider componentProvider = createComponentProvider();
for (String packageToScan : this.packagesToScan) {
scanPackage(componentProvider, packageToScan);
}
}
}
//执行扫描并获取满足条件的beanDefinition（过滤条件是具有@WebFilter等三个注解）
private void scanPackage(ClassPathScanningCandidateComponentProvider componentProvider, String packageToScan) {
for (BeanDefinition candidate : componentProvider.findCandidateComponents(packageToScan)) {
if (candidate instanceof AnnotatedBeanDefinition) {
for (ServletComponentHandler handler : HANDLERS) {
//注入对应的beanDefinition到容器，下面具体会说明
handler.handle(((AnnotatedBeanDefinition) candidate),
(BeanDefinitionRegistry) this.applicationContext);
}
}
}
}
//判断当前容器是web容器且servlet上下文还未初始化（因为filter、listenr、sevelt是在初始化过程中进行条件的）
private boolean isRunningInEmbeddedWebServer() {
return this.applicationContext instanceof WebApplicationContext
&& ((WebApplicationContext) this.applicationContext).getServletContext() == null;
}
//构造扫描器器
private ClassPathScanningCandidateComponentProvider createComponentProvider() {
ClassPathScanningCandidateComponentProvider componentProvider = new ClassPathScanningCandidateComponentProvider(
false);
componentProvider.setEnvironment(this.applicationContext.getEnvironment());
//设置扫描器条件过滤器，在扫描的时候会作为判断，具有详看：ClassPathScanningCandidateComponentProvider#isCandidateComponent方法
componentProvider.setResourceLoader(this.applicationContext);
for (ServletComponentHandler handler : HANDLERS) {
componentProvider.addIncludeFilter(handler.getTypeFilter());
}
return componentProvider;
}
Set getPackagesToScan() {
return Collections.unmodifiableSet(this.packagesToScan);
}
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
}
ServletComponentHandler#handle处理beanDefinition的注入，具体如下：
一：WebServletHandler注入ServletRegistrationBean，，具体构造Servlet实例并添加到容器中的源码如下：
ServletContextInitializerBeans#addServletContextInitializerBean
private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory) {
//构造Servlet实例，并添加到servlet容器中
if (initializer instanceof ServletRegistrationBean) {
Servlet source = ((ServletRegistrationBean) initializer).getServlet();
addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
}
//构造filter并添加到servlet容器中
else if (initializer instanceof FilterRegistrationBean) {
Filter source = ((FilterRegistrationBean) initializer).getFilter();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
//构造ServletListener并添加到servlet容器中
else if (initializer instanceof ServletListenerRegistrationBean) {
EventListener source = ((ServletListenerRegistrationBean) initializer).getListener();
addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
}
else {
addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
initializer);
}
}
二、WebFilterHandler注入FilterRegistrationBean，并设置filter相关属性，在初始化servelt上下文的时候出创建具体的Filter实例，原理同上
二、WebListenerHandler注入ServletComponentWebListenerRegistrar，具体构造ServletListener实例添加在servelt容器原理同上，
