46.SpringBoot學習筆記--註冊 Servlet 三大組件

註冊 Servlet 三大組件【Servlet、Filter、Listener】

由於 Spring Boot 默認是以 jar 包的方式啓動嵌入式 Servlet 容器來啓動 Spring Boot 的 Web 應用，沒有 web.xml 文件。

註冊三大組件用以下方式：

Servlet——ServletRegistrationBean

demo.yangxu.springboot.servlet.MyServlet

package demo.yangxu.springboot.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class MyServlet extends HttpServlet {
    //處理get請求
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    //處理post請求
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("Hello MyServlet");
    }
}

demo.yangxu.springboot.config.MyServerConfig#myServlet

@Bean
public ServletRegistrationBean myServlet(){
    ServletRegistrationBean registrationBean = new ServletRegistrationBean(new MyServlet(),"/myServlet");
    //設置啓動順序
    registrationBean.setLoadOnStartup(1);
    return registrationBean;
}

Filter——FilterRegistrationBean

demo.yangxu.springboot.filter.MyFilter

package demo.yangxu.springboot.filter;

import javax.servlet.*;
import java.io.IOException;

public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("MyFilter process...");
        chain.doFilter(request,response);
    }

    @Override
    public void destroy() {

    }
}

demo.yangxu.springboot.config.MyServerConfig#myFilter

@Bean
public FilterRegistrationBean myFilter(){
    FilterRegistrationBean registrationBean = new FilterRegistrationBean();
    registrationBean.setFilter(new MyFilter());
    registrationBean.setUrlPatterns(Arrays.asList("/hello","/myServlet"));
    return registrationBean;
}

Listener——ServletListenerRegistrationBean

demo.yangxu.springboot.listener.MyListener

package demo.yangxu.springboot.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("contextInitialized...web應用啓動");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("contextDestroyed...當前web項目銷燬");
    }
}

org.springframework.boot.web.servlet.ServletListenerRegistrationBean

@Bean
public ServletListenerRegistrationBean myListener(){
    ServletListenerRegistrationBean<MyListener> registrationBean = new ServletListenerRegistrationBean<>(new MyListener());
    return registrationBean;
}

測試項目銷燬：

http://localhost:8083/crud/myServlet
http://localhost:8083/crud/hello

自動配置

Spring Boot 自動配置 SpringMVC 的時候，會自動註冊 SpringMVC 的前端控制器——DIspatcherServlet。

org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration.DispatcherServletRegistrationConfiguration#dispatcherServletRegistration

@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
        WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
    DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
            webMvcProperties.getServlet().getPath());
    
    //默認攔截： /  所有請求；包括靜態資源，但是不攔截jsp請求；   /*會攔截jsp
    //可以通過spring.mvc.pathmatch.use-suffix-pattern=true 與
    //server.servlet.path
    //來修改 SpringMVC 前端控制器默認攔截的請求路徑
    registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
    registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
    multipartConfig.ifAvailable(registration::setMultipartConfig);
    return registration;
}

org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties.Servlet#path

/**
 * Path of the dispatcher servlet.
 */
private String path = "/";