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Spring Boot 环境下的 Servlet 配置与使用

准备

新建 Spring Boot Starter Project

       
            
     
      org.springframework.boot
             
     
      spring-boot-starter-web
         
    
   

3. 新建一个 Servlet 类，位于 src/main/java/com/mk/servlet/HelloServlet.java，内容如下：

package com.mk.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 HelloServlet extends HttpServlet {    private static final long serialVersionUID = 1L;    public HelloServlet() {        System.out.println("HelloServlet.HelloServlet()");    }    @Override    public void init() throws ServletException {        System.out.println("HelloServlet.init()");    }    @Override    protected void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        System.out.println("HelloServlet.doGet()");        PrintWriter writer = response.getWriter();        writer.write("Hello, " + request.getRemoteAddr());        writer.flush();        writer.close();    }    @Override    public void destroy() {        System.out.println("HelloServlet.destroy()");    }}

配置类

创建一个配置类 ServletComponentConfiguration.java，位于 src/main/java/com/mk/configuration/ServletComponentConfiguration.java，内容如下：

package com.mk.configuration;import org.springframework.boot.web.servlet.ServletComponentScan;import org.springframework.context.annotation.Configuration;@Configuration@ServletComponentScan(basePackages = {"com.mk.servlet"})public class ServletComponentConfiguration {}

启动类

创建一个启动类 SpringBootServletApplication.java，位于 src/main/java/com/mk/SpringBootServletApplication.java，内容如下：

package com.mk;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class SpringBootServletApplication {    public static void main(String[] args) {        SpringApplication.run(SpringBootServletApplication.class, args);    }}

通过 Spring Bean 注册 Servlet

编辑 ServletComponentConfiguration.java，添加以下代码：

package com.mk.configuration;import java.util.Arrays;import javax.servlet.Servlet;import org.springframework.boot.web.servlet.ServletRegistrationBean;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import com.mk.servlet.HelloServlet;@Configurationpublic class ServletComponentConfiguration {        @Bean    public ServletRegistrationBean servletRegistration() {        ServletRegistrationBean registration = new ServletRegistrationBean();        registration.setServlet(new HelloServlet());        registration.setUrlMappings(Arrays.asList("/hello"));        return registration;    }}

启动应用后，控制台会输出：

HelloServlet.HelloServlet()HelloServlet.init()

表示 Servlet 已经成功注册到 Spring Boot 容器中。

使用类路劲扫描注册 Servlet

编辑 HelloServlet.java，添加 @WebServlet 注解：

package com.mk.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;@WebServlet(urlPatterns = "/hello")public class HelloServlet extends HttpServlet {    // ... 保持不变}

编辑 ServletComponentConfiguration.java，删除相关代码，并添加 @ServletComponentScan 注解：

package com.mk.configuration;import org.springframework.boot.web.servlet.ServletComponentScan;import org.springframework.context.annotation.Configuration;@Configuration@ServletComponentScan(basePackages = {"com.mk.servlet"})public class ServletComponentConfiguration {}

启动应用后，访问 /hello URL 应该能够正常工作。

注意事项

4. HelloServlet.init() 方法会在第一次访问时调用，后续不会重复调用
5. 使用 @WebServlet 注解可以直接定义 URL 映射路径

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