spring boot 的相关404页面配置都是针对项目路径下的（如果配置了 context-path）
在context-path不为空的情况下，如果访问路径不带context-path，这时候会显示空白页面或者是tomcat默认404页面
这时候如何自定义内置tomcat的404页面呢？
查看tomcat错误页面的实现源码org.apache.catalina.valves.ErrorReportValue：
report方法中先查找是否注册了错误页面，默认情况未注册任何错误页面，然后通过sendErrorPage方法发送错误页面
private boolean sendErrorPage(String location, Response response) { File file = new File(location); if (!file.isAbsolute()) { file = new File(getContainer().getCatalinaBase(), location); } if (!file.isFile() || !file.canRead()) { getContainer().getLogger().warn( sm.getString("errorReportValve.errorPageNotFound", location)); return false; } // Hard coded for now. Consider making this optional. At Valve level or // page level? response.setContentType("text/html"); response.setCharacterEncoding("UTF-8"); try (OutputStream os = response.getOutputStream(); InputStream is = new FileInputStream(file);){ IOTools.flow(is, os); } catch (IOException e) { getContainer().getLogger().warn( sm.getString("errorReportValve.errorPageIOException", location), e); return false; } return true; } 由于spring boot 默认打成的jar包运行tomcat，所以必须要把404页面放到外部，这里先将404.html放到resource目录下，然后启动过程中将页面复制到tomcat临时目录，将404路径指向该页面就可以了。
这里有两种实现办法：
1、通过AOP修改默认注册的ErrorReportValue
import java.io.File;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.aspectj.lang.JoinPoint;import org.aspectj.lang.annotation.After;import org.aspectj.lang.annotation.Aspect;import org.aspectj.lang.annotation.Pointcut;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 com.bc.core.util.FileUtil;@Aspect@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class, TomcatWebServerFactoryCustomizer.class })@Componentpublic class TomcatCustomizerAspect { @Pointcut("execution(public void org.springframework.boot.autoconfigure.web.embedded.TomcatWebServerFactoryCustomizer.customize(*))") public void customize() { } @After(value = "customize()") public void doAfter(JoinPoint joinPoint) throws Throwable { if (!(joinPoint.getArgs()[0] instanceof ConfigurableTomcatWebServerFactory)) { return; } ConfigurableTomcatWebServerFactory factory = (ConfigurableTomcatWebServerFactory) joinPoint.getArgs()[0]; addTomcat404CodePage(factory); } private static void addTomcat404CodePage(ConfigurableTomcatWebServerFactory factory) { factory.addContextCustomizers((context) -> { String path = context.getCatalinaBase().getPath() + "/404.html"; ClassPathResource cr = new ClassPathResource("404.html"); if (cr.exists()) { File file404 = new File(path); if (!file404.exists()) { try { FileCopyUtils.copy(cr.getInputStream(), FileUtil.openOutputStream(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); }); }} 2、通过自定义BeanPostProcessor添加自定义的ErrorReportValve
import java.io.File;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 com.bc.core.util.FileUtil;import lombok.extern.slf4j.Slf4j;@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class, TomcatWebServerFactoryCustomizer.class })@Component@Slf4jpublic class TomcatCustomizerBeanPostProcessor implements BeanPostProcessor { @Override public 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(), FileUtil.openOutputStream(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); }); }}
上面两种办法，都就可以达到，如果项目访问带项目名，访问任意错误路径（非项目路径下的路径），指向自定义的404页面