tomcat - Apache Tomcat : how to prevent 404 status during [re]deployment

Question

当我更改部署描述符(例如 apache-tomcat/conf/Catalina/localhost/myApp.xml)或用新版本替换 myApp.war 文件时我的 Web 应用程序停止并使用来自 myApp.xml 的更新配置或来自 myApp.war 的新应用程序版本再次启动。

进入上下文路径 /myApp 的请求将获得一个 404 状态错误页面，直到应用程序完全加载并能够为请求提供服务。

我想对此进行自定义并显示一个 503 temporary unavailable 错误页面。某处是否有配置指令？

到目前为止，我想到的解决方法包括:

• 编辑 apache-tomcat/conf/web.xml 并将 org.apache.catalina.servlets.DefaultServlet 替换为根据需要响应的自定义 Servlet 实现。
• 或者在 apache-tomcat/webapps/ROOT/ 中提供一个微型自定义 Web 应用程序以根据需要进行响应。

恕我直言，这些有点老套，我希望有人知道更轻量级的解决方案。我也知道部署相同上下文路径的多个版本的可能性(myApp##v001.xml、myApp##v002.xml、...)但是并行运行的多个应用程序实例还不是一个选项。

Answer 1

我最终写了一个部署为 ROOT.war 的小 servlet。并检查给定请求是否存在具有匹配上下文路径的不可用(=已停止)部署。如果是，则返回 503 状态，否则返回 404。

为了访问外部部署，该应用程序依赖于 tomcat-catalina除了 servlet api:

<dependencies>
    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-servlet-api</artifactId>
        <version>${tomcatVersion}</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-catalina</artifactId>
        <version>${tomcatVersion}</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

并且它必须通过 context.xml 获得特权:

<Context privileged="true"/>

这是映射到 <url-pattern>/</url-pattern> 的 servlet :

package my.pkg;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.catalina.Container;
import org.apache.catalina.ContainerServlet;
import org.apache.catalina.Context;
import org.apache.catalina.Host;
import org.apache.catalina.Wrapper;

public class DefaultErrorPageServlet extends HttpServlet implements ContainerServlet {

    private static final long serialVersionUID = 1L;
    private Host host;
    private Wrapper wrapper;

    @Override
    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp)
            throws ServletException, IOException {
        if (matchesForeignUnavailableContextPath(req)) {
            // 503 if there is an unavailabe deployment matching the request
            sendUnavailable(resp);
        } else {
            // 404 if there is no unavailabe deployment matching the request
            sendNotFound(resp);
        }
    }

    @Override
    protected void doPost(final HttpServletRequest req, final HttpServletResponse resp)
            throws ServletException, IOException {
        // Redirect to make the client GET the requested URL
        resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
        final String requestUrl = req.getRequestURL().toString();
        resp.addHeader("Location", requestUrl);
    }

    private boolean matchesForeignUnavailableContextPath(HttpServletRequest req) {
        if (null != host) {
            Container[] children = host.findChildren();
            for (Container container : children) {
                String contextName = container.getName();
                Context context = (Context) host.findChild(contextName);
                if (null != context && !contextName.isEmpty()) {
                    String contextPath = context.getPath();
                    boolean started = context.getState().isAvailable();
                    String requestUri = req.getRequestURI();
                    if (!started && requestUri.startsWith(contextPath)) {
                        return true;
                    }
                }
            }
        }
        return false;
    }

    private void sendNotFound(HttpServletResponse resp) throws IOException {
        resp.setStatus(HttpServletResponse.SC_NOT_FOUND);
        resp.getWriter().append(
            // HTML document to show on 404 not found
        );
    }

    private void sendUnavailable(HttpServletResponse resp) throws IOException {
        resp.setStatus(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
        resp.getWriter().append(
        // HTML document to show on 503 unavailable
        );
    }

    @Override
    public Wrapper getWrapper() {
        return wrapper;
    }

    @Override
    public void setWrapper(Wrapper wrapper) {
        // see also org.apache.catalina.manager.ManagerServlet.setWrapper(Wrapper)
        if (null == wrapper) {
            return;
        }
        this.wrapper = wrapper;
        final Context context = (Context) wrapper.getParent();
        this.host = (Host) context.getParent();
    }
}