Servlet3.0——註冊web元件
一、Servlet容器啟動時會掃描當前應用中每一個jar包中的在META-INF/services/javax.servlet.ServletContainerInitializer檔案(該檔案沒有後綴名)中配置的ServletContainerInitializer的實現類，javax.servlet.ServletContainerInitializer檔案的內容就是ServletContainerInitializer實現類的全類名，啟動時會執行這些實現類的onStartUp方法，可以通過@HandlesTypes傳入一些感興趣的型別，在onStartUp方法中做一些操作。一個jar包中只能有一個javax.servlet.ServletContainerInitializer配置檔案，一個javax.servlet.ServletContainerInitializer配置檔案中只能配置一個ServletContainerInitializer實現類。
ServletContainerInitializer實現類：
@HandlesTypes({HelloServiceInterface.class}) public class MyServletContainerInitializer implements ServletContainerInitializer{ @Override public void onStartup(Set<Class<?>> set, ServletContext context) throws ServletException { System.out.println("感興趣的類:"); for (Class<?> clazz : set) { System.out.println(">>>>>>" + clazz); } } }
onStartUp方法的入參：
set是@HandlesTypes中傳入的介面或者類的所有子介面或者子類(不包含該介面或該類本身)；context是web專案的servlet上下文，一個web專案對應一個ServletContext，通過ServletContext可以來註冊web元件，比如第三方的filter元件(由於第三方的元件並不是我們寫的，我們無法通過@WebServlet、@WebFilter、@WebListener來標註使其攔截相應的請求，這個時候就需要在ServletContainerInitializer中通過ServletContext來註冊了)
javax.servlet.ServletContainerInitializer配置檔案內容:
com.bdm.servlet.MyServletContainerInitializerjavax.servlet.ServletContainerInitializer配置檔案的目錄：
此時在專案啟動時可以看到後臺日誌中打印出：
二、使用ServletContext註冊web元件
UserServlet.java:
public class UserServlet extends HttpServlet{
private static final long serialVersionUID = -5343785314009218808L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.getWriter().write("tomcat...");
}
}UserFilter.java:
public class UserFilter implements Filter{
@Override
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain chain)
throws IOException, ServletException {
System.out.println("UserFilter...doFilter...");
chain.doFilter(arg0, arg1);
}
@Override
public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub
}
}UserListener.java:只要實現了ServletContextListener介面就可以監聽到ServletContext(Servlet容器)的建立和銷燬
public class UserListener implements ServletContextListener {
@Override
public void contextDestroyed(ServletContextEvent event) {
System.out.println("UserListener...contextDestroyed...");
}
@Override
public void contextInitialized(ServletContextEvent event) {
System.out.println("UserListener...contextInitialized...");
}
}註冊web元件：
@HandlesTypes({HelloServiceInterface.class})
public class MyServletContainerInitializer implements ServletContainerInitializer{
@Override
public void onStartup(Set<Class<?>> set, ServletContext context) throws ServletException {
ServletRegistration.Dynamic userServlet = context.addServlet("userServlet", new UserServlet());
userServlet.addMapping("/user");
FilterRegistration.Dynamic filter = context.addFilter("userFilter", UserFilter.class);
filter.addMappingForServletNames(EnumSet.of(DispatcherType.REQUEST), true, "userServlet");
filter.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), true, "/*");
context.addListener(UserListener.class);
}
}context.addServlet()註冊servlet元件，context.addFilter()註冊filter元件，這兩個元件都需要配置對映路徑，其中filter還可以配置攔截哪些servlet；context.addListener()註冊listener，listener在tomcat啟動時就會呼叫其中的邏輯；
servlet、filter、listener這些元件的註冊必須在tomcat容器啟動的時候，有兩處可以進行這些元件的註冊，一個就是上面的例子(通過ServletContainerInitializer中的ServletContext來註冊)，還有一個地方可以註冊，就是在ServletContextListener的實現類中獲取到ServletContext，然後通過ServletContext註冊其他的listener、filter、servlet：
@WebListener
public class UserListener implements ServletContextListener {
@Override
public void contextDestroyed(ServletContextEvent event) {
System.out.println("UserListener...contextDestroyed...");
}
@Override
public void contextInitialized(ServletContextEvent event) {
ServletContext servletContext = event.getServletContext();
Dynamic addServlet = servletContext.addServlet("userServlet", UserServlet.class);
addServlet.addMapping("/user");
javax.servlet.FilterRegistration.Dynamic addFilter = servletContext.addFilter("userFilter", UserFilter.class);
addFilter.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), true, "/*");
}
}
public class UserListener implements ServletContextListener {
@Override
public void contextDestroyed(ServletContextEvent event) {
System.out.println("UserListener...contextDestroyed...");
}
@Override
public void contextInitialized(ServletContextEvent event) {
ServletContext servletContext = event.getServletContext();
Dynamic addServlet = servletContext.addServlet("userServlet", UserServlet.class);
addServlet.addMapping("/user");
javax.servlet.FilterRegistration.Dynamic addFilter = servletContext.addFilter("userFilter", UserFilter.class);
addFilter.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), true, "/*");
}
}
此處的UserLisener需要使用@WebListener註解的方式註冊，而不可以在ServletContainerInitializer中註冊，不知道什麼原因？