七、Spring Boot Servlet 使用

时间：2022-09-19 14:27:39

Web开发使用 Controller 基本上可以完成大部分需求，但是我们还可能会用到 Servlet、Filter、Listener、Interceptor 等等。

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。

通过代码注册Servlet示例代码：

SpringBootSampleApplication.Java

package org.springboot.sample;

import org.springboot.sample.servlet.MyServlet;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.boot.context.embedded.ServletRegistrationBean;

import org.springframework.boot.web.servlet.ServletComponentScan;

import org.springframework.context.annotation.Bean;

import org.springframework.web.servlet.DispatcherServlet;

@SpringBootApplication

public class SpringBootSampleApplication {

    /**

     * 使用代码注册Servlet（不需要@ServletComponentScan注解）

     *

     */

    @Bean

    public ServletRegistrationBean servletRegistrationBean() {

        return new ServletRegistrationBean(new MyServlet(), "/xs/*");// ServletName默认值为首字母小写，即myServlet

    }

    public static void main(String[] args) {

        SpringApplication.run(SpringBootSampleApplication.class, args);

    }

}

MyServlet.java

package org.springboot.sample.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;

/**

 * Servlet

 *

 */

//@WebServlet(urlPatterns="/xs/*", description="Servlet的说明")

public class MyServlet extends HttpServlet{

    private static final long serialVersionUID = -8685285401859800066L;

    @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");

        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>");

    }

}

使用注解注册Servlet示例代码

SpringBootSampleApplication.java

package org.springboot.sample;

import org.springboot.sample.servlet.MyServlet;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.boot.context.embedded.ServletRegistrationBean;

import org.springframework.boot.web.servlet.ServletComponentScan;

import org.springframework.context.annotation.Bean;

import org.springframework.web.servlet.DispatcherServlet;

@SpringBootApplication

@ServletComponentScan

public class SpringBootSampleApplication {

    public static void main(String[] args) {

        SpringApplication.run(SpringBootSampleApplication.class, args);

    }

}

MyServlet2.java

package org.springboot.sample.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;

/**

 * Servlet

 *

 */

@WebServlet(urlPatterns="/xs/myservlet", description="Servlet的说明") // 不指定name的情况下，name默认值为类全路径，即org.springboot.sample.servlet.MyServlet2

public class MyServlet2 extends HttpServlet{

    private static final long serialVersionUID = -8685285401859800066L;

    @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");

        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。

有个问题：DispatcherServlet 默认拦截“/”，MyServlet 拦截“/xs/*”，MyServlet2 拦截“/xs/myservlet”，那么在我们访问 http://localhost:8080/xs/myservlet 的时候系统会怎么处理呢？如果访问 http://localhost:8080/xs/abc 的时候又是什么结果呢？这里就不给大家卖关子了，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;

    }

当然，这里可以对DispatcherServlet做很多修改，并非只是UrlMappings。

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