spring - 如何使用 Spring Boot 注册 servlet？

Question

此代码不起作用

我有一个需要翻译成spring boot的web.xml

    <servlet>       
            <servlet-name>page-resolver</servlet-name>       
            <servlet-class>com.bk.ForwardServlet</servlet-class>         
            <init-param>
                <param-name>page</param-name>
                <param-value>/index.jsp</param-value>         
            </init-param>         
    </servlet>
    <servlet-mapping>                            
        <servlet-name>page-resolver</servlet-name>         
        <url-pattern>/index.html</url-pattern>
        <url-pattern>/login</url-pattern>
        <url-pattern>/qmgr/*</url-pattern>  
    </servlet-mapping>

和这堂课

@WebServlet
public class ForwardServlet extends HttpServlet {

private String page;

@Override
public void init(ServletConfig config) throws ServletException {
    super.init(config);
    page = config.getInitParameter("page");
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.getRequestDispatcher(page).forward(req, resp);
}
}

我编写了注册这个 bean 的代码，但它不起作用，我不明白为什么

@Configuration
public class ConfigureWeb implements ServletContextInitializer {

private void registerServlet(ServletContext servletContext) {
    ServletRegistrationBean serviceServlet =
            new ServletRegistrationBean(new ForwardServlet(), "/index.html","/login","/qmgr/*");

    serviceServlet.addUrlMappings("/index.jsp");
}

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
    registerServlet(servletContext);
}
}

标签： springspring-bootservlets

Answer 1

首先检查并确认所有资源都保存在正确的目录中。对于 spring-boot，jsp 页面将保存在目录中src->main->webapp->WEB-INF->view->*.jsp。

您应该在 pom 中添加以下依赖项，以便在使用嵌入式 tomcat 时正确编译 jsp：

<!-- JSTL -->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>jstl</artifactId>
</dependency>
<!-- To compile JSP files -->
<dependency>
    <groupId>org.apache.tomcat.embed</groupId>
    <artifactId>tomcat-embed-jasper</artifactId>
    <scope>provided</scope>
</dependency>

现在我们需要告诉 spring jsp 文件驻留在哪里，我们可以有两种方法：

在 application.properties 中添加条目

spring.mvc.view.prefix=/WEB-INF/view/
spring.mvc.view.suffix=.jsp

在这里，我们可以指定预期 jsp 文件所在的文件夹，以及定义视图。或者

配置 InternalResourceViewResolver 以提供 JSP 页面

@Configuration
@EnableWebMvc
@ComponentScan
public class MvcConfiguration extends WebMvcConfigurerAdapter
{
    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        InternalResourceViewResolver resolver = new InternalResourceViewResolver();
        resolver.setPrefix("/WEB-INF/view/");
        resolver.setSuffix(".jsp");
        resolver.setViewClass(JstlView.class);
        registry.viewResolver(resolver);
    }
}

现在注册 servlet ：

ServletRegistrationBean用于在Servlet 3.0 +容器中注册 Servlet。我们需要ServletRegistrationBean在我们的 JavaConfig 中创建一个 bean。找到一些用于配置 Servlet 的 ServletRegistrationBean 方法。 setServlet()：设置要注册的servlet。 addUrlMappings()：为 Servlet 添加 URL 映射。 setLoadOnStartup：设置启动时加载 Servlet 的优先级。

假设我们有两个 Servlet HelloCountryServlet，HelloStateServlet然后我们将使用 ServletRegistrationBean 在 Spring Boot 中注册它们，如下所示：

@Configuration
public class WebConfig {
   @Bean    
   public ServletRegistrationBean<HttpServlet> countryServlet() {
       ServletRegistrationBean<HttpServlet> servRegBean = new ServletRegistrationBean<>();
       servRegBean.setServlet(new HelloCountryServlet());
       servRegBean.addUrlMappings("/country/*");
       servRegBean.setLoadOnStartup(1);
       return servRegBean;
   }
   @Bean    
   public ServletRegistrationBean<HttpServlet> stateServlet() {
       ServletRegistrationBean<HttpServlet> servRegBean = new ServletRegistrationBean<>();
       servRegBean.setServlet(new HelloStateServlet());
       servRegBean.addUrlMappings("/state/*");
       servRegBean.setLoadOnStartup(1);
       return servRegBean;
   }   
}  

对于每个 Servlet，我们创建一个ServletRegistrationBean bean。servlet 类将如下所示：

public class HelloCountryServlet extends HttpServlet   {
    private static final long serialVersionUID = 1L;
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException{
        doGet(request,response);
    }
        public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
            response.setContentType("text/html");
            PrintWriter out = response.getWriter();
        out.println("<h3>Hello India!</h3>");   
    }
}

这是一种方法。

在 spring-boot 中注册 servlet 的另一种方法是使用注解：@ServletComponentScan和@WebServlet。@ServletComponentScan在 Spring Boot 中，将扫描带有 注释的 Servlet、带有注释的@WebServlet过滤器@WebFilter和带有注释的侦听器@WebListener。注释 @ServletComponentScan 在类级别的 JavaConfig 上使用。@ServletComponentScan仅使用嵌入式 Web 服务器扫描 Servlet、过滤器和侦听器。找到带有@WebServlet 注释的Servlet。

所以早期的HelloCountryServlet servlet 可以提供为：

@WebServlet(urlPatterns = "/country/*", loadOnStartup = 1)
public class HelloCountryServlet extends HttpServlet   {
    private static final long serialVersionUID = 1L;
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException{
         doGet(request,response);
    }
        public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
             response.setContentType("text/html");
             PrintWriter out = response.getWriter();
         out.println("<h3>Hello India!</h3>");  
    }
}

并提供 ServletComponentScan 注释，如：

@ServletComponentScan
@SpringBootApplication
public class SpringBootAppStarter {
    public static void main(String[] args) {
        SpringApplication.run(SpringBootAppStarter.class, args);
    }
}