PreCompiledJSPConfiguration.java

package org.example.web.graal;

import org.apache.tomcat.util.descriptor.web.ServletDef;
import org.apache.tomcat.util.descriptor.web.WebXml;
import org.apache.tomcat.util.descriptor.web.WebXmlParser;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.web.servlet.ServletContextInitializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.Resource;
import org.xml.sax.InputSource;

import javax.servlet.ServletRegistration;
import java.io.IOException;
import java.io.InputStream;
import java.util.Map;

@Configuration
public class PreCompiledJSPConfiguration {

    // Mapping xml created by the bmuschko.tomcat plugin
    @Value("classpath:WEB-INF/web.xml")
    private Resource precompiledJspWebXml;

    @Bean
    public ServletContextInitializer registerPreCompiledJsps() {
        return servletContext -> {
            // Use Tomcat's web.xml parser (assume complete XML file and validate).
            WebXmlParser parser = new WebXmlParser(false, true, true);
            try (InputStream is = precompiledJspWebXml.getInputStream()) {
                WebXml webXml = new WebXml();
                boolean success = parser.parseWebXml(new InputSource(is), webXml, false);
                if (!success) {
                    System.out.println("Possible problem when parsing " + precompiledJspWebXml);
                }
                for (ServletDef def :  webXml.getServlets().values()) {
                    System.out.printf("Registering precompiled JSP: {%s} -> {%s}", def.getServletName(), def.getServletClass());
                    ServletRegistration.Dynamic reg = servletContext.addServlet(def.getServletName(), def.getServletClass());
                    reg.setLoadOnStartup(99);
                }

                for (Map.Entry<String, String> mapping : webXml.getServletMappings().entrySet()) {
                    System.out.printf("Mapping servlet: {%s} -> {%s}", mapping.getValue(), mapping.getKey());
                    servletContext.getServletRegistration(mapping.getValue()).addMapping(mapping.getKey());
                }
            } catch (IOException e) {
                throw new RuntimeException("Error registering precompiled JSPs", e);
            }
        };
    }

}