添加配置类

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.servlet.Servlet;
import org.apache.catalina.startup.Tomcat;
import org.apache.catalina.valves.ErrorReportValve;
import org.apache.coyote.UpgradeProtocol;
import org.springframework.beans.BeansException;
import  org.springframework.beans.factory.config.BeanPostProcessor;
import  org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import  org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer;
import  org.springframework.boot.web.embedded.tomcat.ConfigurableTomcatWebServerFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.stereotype.Component;
import org.springframework.util.FileCopyUtils;
import lombok.extern.slf4j.Slf4j;
@ConditionalOnClass({ Servlet.class, Tomcat.class,  UpgradeProtocol.class,  TomcatWebServerFactoryCustomizer.class })
@Component
@Slf4j
public class TomcatCustomizerBeanPostProcessor implements  BeanPostProcessor {@Overridepublic Object postProcessAfterInitialization(Object  bean, String beanName) throws BeansException {if (bean instanceof  ConfigurableTomcatWebServerFactory) {ConfigurableTomcatWebServerFactory  configurableTomcatWebServerFactory =  (ConfigurableTomcatWebServerFactory) bean;addTomcat404CodePage(configurableTomcatWebServerFactory);}return  BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);}private static void  addTomcat404CodePage(ConfigurableTomcatWebServerFactory  factory) {factory.addContextCustomizers((context) -> {String tomcatTempPath =  context.getCatalinaBase().getPath();log.info("tomcat目录：{}", tomcatTempPath);String path = tomcatTempPath + "/404.html";ClassPathResource cr = new  ClassPathResource("404.html");if (cr.exists()) {File file404 = new File(path);if (!file404.exists()) {try {FileCopyUtils.copy(cr.getInputStream(), new FileOutputStream(file404));} catch (IOException e) {e.printStackTrace();}}}ErrorReportValve valve = new  ErrorReportValve();valve.setProperty("errorCode.404", path);valve.setShowServerInfo(false);valve.setShowReport(false);valve.setAsyncSupported(true);context.getParent().getPipeline().addValve(valve);});}
}

在resources文件夹下直接添加404.html文件，再次启动测试，发现404页面已修改