Spring Boot 中的Servlet简单使用
当使用spring-Boot时,嵌入式Servlet容器通过扫描注解的方式注册Servlet、Filter和Servlet规范的所有监听器(如HttpSessionListener监听器)。
Spring boot 的主 Servlet 为 DispatcherServlet,其默认的url-pattern为“/”。也许我们在应用中还需要定义更多的Servlet,该如何使用SpringBoot来完成呢?
在spring boot中添加自己的Servlet有两种方法,代码注册Servlet和注解自动注册(Filter和Listener也是如此)。
一、代码注册通过ServletRegistrationBean、 FilterRegistrationBean 和 ServletListenerRegistrationBean 获得控制。
也可以通过实现 ServletContextInitializer 接口直接注册。
二、在 SpringBootApplication 上使用@ServletComponentScan 注解后,Servlet、Filter、Listener 可以直接通过 @WebServlet、@WebFilter、@WebListener 注解自动注册,无需其他代码。
1.通过代码注册Servlet示例代码
1).SpringBootSimpleApplication.Java类:
package com.example; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.web.servlet.ServletRegistrationBean; import org.springframework.context.annotation.Bean; import com.example.servlet.MyServlet; @SpringBootApplication public class SpringBootSimpleApplication { /** * 使用代码注册Servlet(不需要@ServletComponentScan注解) */ @Bean public ServletRegistrationBean servletRegistrationBean() { return new ServletRegistrationBean(new MyServlet(), "/st/*");// ServletName默认值为首字母小写,即myServlet } public static void main(String[] args) { SpringApplication.run(SpringBootSimpleApplication.class, args); } }
2).MyServlet.java类:
package com.example.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class MyServlet extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println(">>>>>>>>>>doGet()<<<<<<<<<<<"); doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println(">>>>>>>>>>doPost()<<<<<<<<<<<"); resp.setContentType("text/html"); resp.setCharacterEncoding("utf-8"); PrintWriter out = resp.getWriter(); out.println("<html>"); out.println("<head>"); out.println("<title>Hello World</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>大家好,我的名字叫Servlet</h1>"); out.println("</body>"); out.println("</html>"); } }
2.使用注解注册Servlet示例代码
1).SpringBootSimpleApplication.java类:
package com.example; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.web.servlet.ServletComponentScan; import org.springframework.boot.web.servlet.ServletRegistrationBean; import org.springframework.context.annotation.Bean; import com.example.servlet.MyServlet; @SpringBootApplication @ServletComponentScan public class SpringBootSimpleApplication { /** * 使用代码注册Servlet(不需要@ServletComponentScan注解) */ @Bean public ServletRegistrationBean servletRegistrationBean() { return new ServletRegistrationBean(new MyServlet(), "/st/*");// ServletName默认值为首字母小写,即myServlet } public static void main(String[] args) { SpringApplication.run(SpringBootSimpleApplication.class, args); } }
2).MyServlet2.java类:
package com.example.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; // 不指定name的情况下,name默认值为类全路径,即com.example.servlet.MyServlet2 @WebServlet(urlPatterns="/st/myservlet2", description="Servlet的说明") public class Myservlet2 extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println(">>>>>>>>>>doGet2()<<<<<<<<<<<"); doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println(">>>>>>>>>>doPost2()<<<<<<<<<<<"); resp.setContentType("text/html"); resp.setCharacterEncoding("utf-8"); PrintWriter out = resp.getWriter(); out.println("<html>"); out.println("<head>"); out.println("<title>Hello World</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>大家好,我的名字叫Servlet2</h1>"); out.println("</body>"); out.println("</html>"); } }
使用 @WebServlet 注解,其中可以设置一些属性。
3.访问结果
4.DispatcherServlet默认拦截
DispatcherServlet 默认拦截“/”,MyServlet 拦截“/st/*”,MyServlet2 拦截“/st/myservlet”,那么在我们访问 http://localhost:8080/st/myservlet2 的时候系统会怎么处理呢?如果访问 http://localhost:8080/st/abc的时候又是什么结果呢?其结果是“匹配的优先级是从精确到模糊,复合条件的Servlet并不会都执行”。
既然系统DispatcherServlet 默认拦截“/”,那么我们是否能做修改呢,答案是肯定的,我们在SpringBootSampleApplication中添加代码:
/** * 修改DispatcherServlet默认配置 */ @Bean public ServletRegistrationBean dispatcherRegistration(DispatcherServlet dispatcherServlet) { ServletRegistrationBean registration = new ServletRegistrationBean(dispatcherServlet); registration.getUrlMappings().clear(); registration.addUrlMappings("*.do"); registration.addUrlMappings("*.json"); return registration; }
可以通过注入DispatcherServlet 然后用ServletRegistrationBean包裹一层 动态的加上一些初始参数。