Java : 在 servlet 中重新加载 webapp，然后重定向请求

Question

我的应用程序中有一个配置页面。当用户更改配置并提交时，我想用新的配置属性重新加载我的应用程序，然后重定向到某个页面。我能够使用我在此处找到的一些建议重新加载我的应用程序 Start / stop a web application from itself?

但我无法在应用程序重新加载后重定向到新页面。

更多详情。

public class ConfigurationServlet extends HttpServlet implements ContainerServlet{

    private static final long serialVersionUID = 1L;
    private SalsaEnvironment salsaEnv;
    protected Host host = null;
    protected Wrapper wrapper = null;
    protected Context context = null;

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        // update configuration properties
        .
        .
        . 

        // reload app once configuration is changed
        restartWebApp(resp.getWriter(), "/salsadb");

        // simple redirect/forward - does not work - gives following exception
        // java.lang.NullPointerException org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:610)
        //resp.sendRedirect("/salsadb/account");
        //req.getRequestDispatcher("/account");

        // invalid old session, create a new one and try to redirect - does not work
        req.getSession(false).invalidate();
        req.getSession(true);
        req.getRequestDispatcher("/account");
    }

    @Override
    public Wrapper getWrapper() {
        // TODO Auto-generated method stub
        return this.wrapper;
    }

    @Override
    public void setWrapper(Wrapper wrapper) {
        this.wrapper = wrapper;
        if (wrapper == null) {
            context = null;
            host = null;
        } else {
            context = (Context) wrapper.getParent();
            host = (Host) context.getParent();
            Engine engine = (Engine) host.getParent();
            try {
            } catch (Exception e) {
                // ?
            }
        }
    }

    private void restartWebApp(PrintWriter writer, String path){
        if ((path == null) || (!path.startsWith("/") && path.equals(""))) {
            System.out.println("invalid path");
            return;
        }
        String displayPath = path;
        if( path.equals("/") )
            path = "";

        try {
            Context context = (Context) host.findChild(path);
            if (context == null) {
                /*writer.println(sm.getString
                               ("managerServlet.noContext",
                                   RequestUtil.filter(displayPath)));*/
                System.out.println("no context");
                return;
            }

            context.reload();
            //writer.println(sm.getString("managerServlet.reloaded", displayPath));
            System.out.println("reloaded webapp");
        } catch (Throwable t) {
            log("ManagerServlet.reload[" + displayPath + "]", t);
            /*writer.println(sm.getString("managerServlet.exception",
                                        t.toString()));*/
            System.out.println("excpetion during reloading the webapp");
        }
    }

Answer 1

您可能无法执行此操作，因为您的 server-side 代码 刚刚 重新启动。

我推荐一种基于 AJAX 的 client-side 方法，在这种方法中，您不断地 ping 您的一些 servlet，直到应用程序 "back up" 并且然后通过 JavaScript.

移动到新页面

为此，您首先将重定向发送到 reload-checking 页面，然后然后（比如之后1s 允许浏览器获取重定向页面）启动重启：

    req.getSession(false).invalidate();
    req.getSession(true);
    resp.sendRedirect("check_restart_status.jsp");
    //Use a timer or whatever
    new Thread(() -> {
        try{
          Thread.sleep(5000);
        } catch(InterruptedException ie) {
          return;
        }
        restartWebApp("/salsadb");
    }).start();

Java : 在 servlet 中重新加载 webapp，然后重定向请求

Java : Reload webapp in the servlet and then redirect request

java

tomcat

servlets

http

httprequest