https://tomcat.apache.org/: Tomcat Servlet Engine Core Classes and Standard implementations 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.catalina.valves;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Writer;
import java.util.Scanner;
import java.util.concurrent.atomic.AtomicBoolean;

import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletResponse;

import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.catalina.util.ErrorPageSupport;
import org.apache.catalina.util.IOTools;
import org.apache.catalina.util.ServerInfo;
import org.apache.catalina.util.TomcatCSS;
import org.apache.coyote.ActionCode;
import org.apache.tomcat.util.ExceptionUtils;
import org.apache.tomcat.util.descriptor.web.ErrorPage;
import org.apache.tomcat.util.res.StringManager;
import org.apache.tomcat.util.security.Escape;


Implementation of a Valve that outputs HTML error pages.


This Valve should be attached at the Host level, although it will work
if attached to a Context.


HTML code from the Cocoon 2 project.


Author:Remy Maucherat, Craig R. McClanahan, Nicola Ken Barozzi Aisa, Stefano Mazzocchi, Yoav Shapira
/**
 * <p>Implementation of a Valve that outputs HTML error pages.</p>
 *
 * <p>This Valve should be attached at the Host level, although it will work
 * if attached to a Context.</p>
 *
 * <p>HTML code from the Cocoon 2 project.</p>
 *
 * @author Remy Maucherat
 * @author Craig R. McClanahan
 * @author <a href="mailto:nicolaken@supereva.it">Nicola Ken Barozzi</a> Aisa
 * @author <a href="mailto:stefano@apache.org">Stefano Mazzocchi</a>
 * @author Yoav Shapira
 */
public class ErrorReportValve extends ValveBase {

    private boolean showReport = true;

    private boolean showServerInfo = true;

    private final ErrorPageSupport errorPageSupport = new ErrorPageSupport();


    //------------------------------------------------------ Constructor

    public ErrorReportValve() {
        super(true);
    }


    // --------------------------------------------------------- Public Methods

    
Invoke the next Valve in the sequence. When the invoke returns, check
the response state. If the status code is greater than or equal to 400
or an uncaught exception was thrown then the error handling will be
triggered.

Params:
  • request – The servlet request to be processed
  • response – The servlet response to be created
Throws:
/**
     * Invoke the next Valve in the sequence. When the invoke returns, check
     * the response state. If the status code is greater than or equal to 400
     * or an uncaught exception was thrown then the error handling will be
     * triggered.
     *
     * @param request The servlet request to be processed
     * @param response The servlet response to be created
     *
     * @exception IOException if an input/output error occurs
     * @exception ServletException if a servlet error occurs
     */
    @Override
    public void invoke(Request request, Response response) throws IOException, ServletException {

        // Perform the request
        getNext().invoke(request, response);

        if (response.isCommitted()) {
            if (response.setErrorReported()) {
                // Error wasn't previously reported but we can't write an error
                // page because the response has already been committed. Attempt
                // to flush any data that is still to be written to the client.
                try {
                    response.flushBuffer();
                } catch (Throwable t) {
                    ExceptionUtils.handleThrowable(t);
                }
                // Close immediately to signal to the client that something went
                // wrong
                response.getCoyoteResponse().action(ActionCode.CLOSE_NOW,
                        request.getAttribute(RequestDispatcher.ERROR_EXCEPTION));
            }
            return;
        }

        Throwable throwable = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);

        // If an async request is in progress and is not going to end once this
        // container thread finishes, do not process any error page here.
        if (request.isAsync() && !request.isAsyncCompleting()) {
            return;
        }

        if (throwable != null && !response.isError()) {
            // Make sure that the necessary methods have been called on the
            // response. (It is possible a component may just have set the
            // Throwable. Tomcat won't do that but other components might.)
            // These are safe to call at this point as we know that the response
            // has not been committed.
            response.reset();
            response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        }

        // One way or another, response.sendError() will have been called before
        // execution reaches this point and suspended the response. Need to
        // reverse that so this valve can write to the response.
        response.setSuspended(false);

        try {
            report(request, response, throwable);
        } catch (Throwable tt) {
            ExceptionUtils.handleThrowable(tt);
        }
    }


    // ------------------------------------------------------ Protected Methods


    
Prints out an error report.

Params:
  • request – The request being processed
  • response – The response being generated
  • throwable – The exception that occurred (which possibly wraps
 a root cause exception
/**
     * Prints out an error report.
     *
     * @param request The request being processed
     * @param response The response being generated
     * @param throwable The exception that occurred (which possibly wraps
     *  a root cause exception
     */
    protected void report(Request request, Response response, Throwable throwable) {

        int statusCode = response.getStatus();

        // Do nothing on a 1xx, 2xx and 3xx status
        // Do nothing if anything has been written already
        // Do nothing if the response hasn't been explicitly marked as in error
        //    and that error has not been reported.
        if (statusCode < 400 || response.getContentWritten() > 0 || !response.setErrorReported()) {
            return;
        }

        // If an error has occurred that prevents further I/O, don't waste time
        // producing an error report that will never be read
        AtomicBoolean result = new AtomicBoolean(false);
        response.getCoyoteResponse().action(ActionCode.IS_IO_ALLOWED, result);
        if (!result.get()) {
            return;
        }

        ErrorPage errorPage = null;
        if (throwable != null) {
            errorPage = errorPageSupport.find(throwable);
        }
        if (errorPage == null) {
            errorPage = errorPageSupport.find(statusCode);
        }
        if (errorPage == null) {
            // Default error page
            errorPage = errorPageSupport.find(0);
        }


        if (errorPage != null) {
            if (sendErrorPage(errorPage.getLocation(), response)) {
                // If the page was sent successfully, don't write the standard
                // error page.
                return;
            }
        }

        String message = Escape.htmlElementContent(response.getMessage());
        if (message == null) {
            if (throwable != null) {
                String exceptionMessage = throwable.getMessage();
                if (exceptionMessage != null && exceptionMessage.length() > 0) {
                    try (Scanner scanner = new Scanner(exceptionMessage)) {
                        message = Escape.htmlElementContent(scanner.nextLine());
                    }
                }
            }
            if (message == null) {
                message = "";
            }
        }

        // Do nothing if there is no reason phrase for the specified status code and
        // no error message provided
        String reason = null;
        String description = null;
        StringManager smClient = StringManager.getManager(
                Constants.Package, request.getLocales());
        response.setLocale(smClient.getLocale());
        try {
            reason = smClient.getString("http." + statusCode + ".reason");
            description = smClient.getString("http." + statusCode + ".desc");
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
        }
        if (reason == null || description == null) {
            if (message.isEmpty()) {
                return;
            } else {
                reason = smClient.getString("errorReportValve.unknownReason");
                description = smClient.getString("errorReportValve.noDescription");
            }
        }

        StringBuilder sb = new StringBuilder();

        sb.append("<!doctype html><html lang=\"");
        sb.append(smClient.getLocale().getLanguage()).append("\">");
        sb.append("<head>");
        sb.append("<title>");
        sb.append(smClient.getString("errorReportValve.statusHeader",
                String.valueOf(statusCode), reason));
        sb.append("</title>");
        sb.append("<style type=\"text/css\">");
        sb.append(TomcatCSS.TOMCAT_CSS);
        sb.append("</style>");
        sb.append("</head><body>");
        sb.append("<h1>");
        sb.append(smClient.getString("errorReportValve.statusHeader",
                String.valueOf(statusCode), reason)).append("</h1>");
        if (isShowReport()) {
            sb.append("<hr class=\"line\" />");
            sb.append("<p><b>");
            sb.append(smClient.getString("errorReportValve.type"));
            sb.append("</b> ");
            if (throwable != null) {
                sb.append(smClient.getString("errorReportValve.exceptionReport"));
            } else {
                sb.append(smClient.getString("errorReportValve.statusReport"));
            }
            sb.append("</p>");
            if (!message.isEmpty()) {
                sb.append("<p><b>");
                sb.append(smClient.getString("errorReportValve.message"));
                sb.append("</b> ");
                sb.append(message).append("</p>");
            }
            sb.append("<p><b>");
            sb.append(smClient.getString("errorReportValve.description"));
            sb.append("</b> ");
            sb.append(description);
            sb.append("</p>");
            if (throwable != null) {
                String stackTrace = getPartialServletStackTrace(throwable);
                sb.append("<p><b>");
                sb.append(smClient.getString("errorReportValve.exception"));
                sb.append("</b></p><pre>");
                sb.append(Escape.htmlElementContent(stackTrace));
                sb.append("</pre>");

                int loops = 0;
                Throwable rootCause = throwable.getCause();
                while (rootCause != null && (loops < 10)) {
                    stackTrace = getPartialServletStackTrace(rootCause);
                    sb.append("<p><b>");
                    sb.append(smClient.getString("errorReportValve.rootCause"));
                    sb.append("</b></p><pre>");
                    sb.append(Escape.htmlElementContent(stackTrace));
                    sb.append("</pre>");
                    // In case root cause is somehow heavily nested
                    rootCause = rootCause.getCause();
                    loops++;
                }

                sb.append("<p><b>");
                sb.append(smClient.getString("errorReportValve.note"));
                sb.append("</b> ");
                sb.append(smClient.getString("errorReportValve.rootCauseInLogs"));
                sb.append("</p>");

            }
            sb.append("<hr class=\"line\" />");
        }
        if (isShowServerInfo()) {
            sb.append("<h3>").append(ServerInfo.getServerInfo()).append("</h3>");
        }
        sb.append("</body></html>");

        try {
            try {
                response.setContentType("text/html");
                response.setCharacterEncoding("utf-8");
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                if (container.getLogger().isDebugEnabled()) {
                    container.getLogger().debug("status.setContentType", t);
                }
            }
            Writer writer = response.getReporter();
            if (writer != null) {
                // If writer is null, it's an indication that the response has
                // been hard committed already, which should never happen
                writer.write(sb.toString());
                response.finishResponse();
            }
        } catch (IOException e) {
            // Ignore
        } catch (IllegalStateException e) {
            // Ignore
        }

    }


    
Print out a partial servlet stack trace (truncating at the last
occurrence of jakarta.servlet.).

Params:
  • t – The stack trace to process
Returns:the stack trace relative to the application layer
/**
     * Print out a partial servlet stack trace (truncating at the last
     * occurrence of jakarta.servlet.).
     * @param t The stack trace to process
     * @return the stack trace relative to the application layer
     */
    protected String getPartialServletStackTrace(Throwable t) {
        StringBuilder trace = new StringBuilder();
        trace.append(t.toString()).append(System.lineSeparator());
        StackTraceElement[] elements = t.getStackTrace();
        int pos = elements.length;
        for (int i = elements.length - 1; i >= 0; i--) {
            if ((elements[i].getClassName().startsWith
                 ("org.apache.catalina.core.ApplicationFilterChain"))
                && (elements[i].getMethodName().equals("internalDoFilter"))) {
                pos = i;
                break;
            }
        }
        for (int i = 0; i < pos; i++) {
            if (!(elements[i].getClassName().startsWith
                  ("org.apache.catalina.core."))) {
                trace.append('\t').append(elements[i].toString()).append(System.lineSeparator());
            }
        }
        return trace.toString();
    }


    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;
    }


    
Enables/Disables full error reports

Params:
  • showReport – true to show full error data
/**
     * Enables/Disables full error reports
     *
     * @param showReport <code>true</code> to show full error data
     */
    public void setShowReport(boolean showReport) {
        this.showReport = showReport;
    }

    public boolean isShowReport() {
        return showReport;
    }

    
Enables/Disables server info on error pages

Params:
  • showServerInfo – true to show server info
/**
     * Enables/Disables server info on error pages
     *
     * @param showServerInfo <code>true</code> to show server info
     */
    public void setShowServerInfo(boolean showServerInfo) {
        this.showServerInfo = showServerInfo;
    }

    public boolean isShowServerInfo() {
        return showServerInfo;
    }


    public boolean setProperty(String name, String value) {
        if (name.startsWith("errorCode.")) {
            int code = Integer.parseInt(name.substring(10));
            ErrorPage ep = new ErrorPage();
            ep.setErrorCode(code);
            ep.setLocation(value);
            errorPageSupport.add(ep);
            return true;
        } else if (name.startsWith("exceptionType.")) {
            String className = name.substring(14);
            ErrorPage ep = new ErrorPage();
            ep.setExceptionType(className);
            ep.setLocation(value);
            errorPageSupport.add(ep);
            return true;
        }
        return false;
    }

    public String getProperty(String name) {
        String result;
        if (name.startsWith("errorCode.")) {
            int code = Integer.parseInt(name.substring(10));
            ErrorPage ep = errorPageSupport.find(code);
            if (ep == null) {
                result = null;
            } else {
                result = ep.getLocation();
            }
        } else if (name.startsWith("exceptionType.")) {
            String className = name.substring(14);
            ErrorPage ep = errorPageSupport.find(className);
            if (ep == null) {
                result = null;
            } else {
                result = ep.getLocation();
            }
        } else {
            result = null;
        }
        return result;
    }
}