Apache Tomcat:如何在[重新]部署期间防止404状态

最后我编写了一个小servlet,它被部署为 ROOT.war 并检查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状态。

为了访问该应用程序所依赖的国外部署 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>

而且必须通过 context.xml :

<Context privileged="true"/>

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

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();
    }
}