如何在Spring Boot中注册一个servlet?

Question

这段代码无法正常工作

我有一个web.xml需要转换成Spring Boot格式

    <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>

并且这个类

@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);
}
}

我写了注册此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);
}
}

- AbrA

Answer 1

首先检查并验证所有资源是否保留在正确的目录中。对于spring-boot，jsp页面应该放置在目录src->main->webapp->WEB-INF->view->*.jsp中。

使用嵌入式tomcat编译jsp时，您应该在pom文件中添加以下依赖项：

<!-- 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文件的位置，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jsp文件所在的文件夹，并定义视图。

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，关于注册servlets（小程序）的问题：

ServletRegistrationBean用于在Servlet 3.0 +容器中注册Servlets。我们需要在JavaConfig中创建ServletRegistrationBean的一个bean。以下是一些方法，可用于配置ServletRegistrationBean。 setServlet():设置要注册的servlet addUrlMappings():为Servlet添加URL映射 setLoadOnStartup:设置以优先级加载Servlet启动。

假设我们有两个Servlets，分别是HelloCountryServlet和HelloStateServlet，然后我们将使用ServletRegistrationBean在Spring Boot中将它们注册，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，我们都需要创建一个ServletRegistrationBean bean。 而servlet类看起来应该是这样的：

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。

另一种方法在spring-boot中注册servlet的方式是使用注释：@ServletComponentScan和@WebServlet。Spring Boot中的@ServletComponentScan将扫描用@WebServlet注释的Servlet、用@WebFilter注释的Filters以及用@WebListener注释的Listeners。注释@ServletComponentScan在JavaConfig的类级别上使用。@ServletComponentScan仅在嵌入式web服务器中扫描Servlets、Filters和Listeners。查找带有@WebServlet注释的Servlets。

因此，之前的HelloCountryServlet Servlet可以提供如下：

@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>");  
    }
}

并提供类似于ServletComponentScan注释的注释：

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

- Ananthapadmanabhan

Answer 2

如果您不需要注册Servlet，则可以将转发添加到 ViewControllerRegistry 中

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/index.html").setViewName("forward:/index.jsp");
        registry.addViewController("/login").setViewName("forward:/index.jsp");
        registry.addViewController("/qmgr/**").setViewName("forward:/index.jsp");
    }
}

您可以使用AntPathMatcher模式将这三个addViewController合并为一个。

将视图控制器映射到给定的URL路径（或模式），以便使用预配置的状态代码和视图呈现响应。

像“/admin/**”或“/articles/{articlename:\w+}”这样的模式是允许的。有关语法的详细信息，请参见AntPathMatcher。

个人认为将它们分开更易读。

- Misantorp