public String doLayout(ILoggingEvent event) {

    // Reset working buffer. If the buffer is too large, then we need a new
    // one in order to avoid the penalty of creating a large array.
    if (buf.capacity() > UPPER_LIMIT) {
      buf = new StringBuilder(DEFAULT_SIZE);
    } else {
      buf.setLength(0);
    }

    // We yield to the \r\n heresy.

    buf.append("<log4j:event logger=\"");
    buf.append(Transform.escapeTags(event.getLoggerName()));
    buf.append("\"\r\n");
    buf.append("             timestamp=\"");
    buf.append(event.getTimeStamp());
    buf.append("\" level=\"");
    buf.append(event.getLevel());
    buf.append("\" thread=\"");
    buf.append(Transform.escapeTags(event.getThreadName()));
    buf.append("\">\r\n");

    buf.append("  <log4j:message>");
    buf.append(Transform.escapeTags(event.getFormattedMessage()));
    buf.append("</log4j:message>\r\n");

    // logback does not support NDC
    // String ndc = event.getNDC();


    IThrowableProxy tp = event.getThrowableProxy();
    if (tp != null) {
      StackTraceElementProxy[] stepArray = tp.getStackTraceElementProxyArray();
      buf.append("  <log4j:throwable><![CDATA[");
      for (StackTraceElementProxy step : stepArray) {
        buf.append(CoreConstants.TAB);
        buf.append(step.toString());
        buf.append("\r\n");
      }
      buf.append("]]></log4j:throwable>\r\n");
    }

    if (locationInfo) {
      StackTraceElement[] callerDataArray = event.getCallerData();
      if (callerDataArray != null && callerDataArray.length > 0) {
        StackTraceElement immediateCallerData = callerDataArray[0];
        buf.append("  <log4j:locationInfo class=\"");
        buf.append(immediateCallerData.getClassName());
        buf.append("\"\r\n");
        buf.append("                      method=\"");
        buf.append(Transform.escapeTags(immediateCallerData.getMethodName()));
        buf.append("\" file=\"");
        buf.append(Transform.escapeTags(immediateCallerData.getFileName()));
        buf.append("\" line=\"");
        buf.append(immediateCallerData.getLineNumber());
        buf.append("\"/>\r\n");
      }
    }

    /*
     * <log4j:properties> <log4j:data name="name" value="value"/>
     * </log4j:properties>
     */
    if (this.getProperties()) {
      Map<String, String> propertyMap = event.getMDCPropertyMap();

      if ((propertyMap != null) && (propertyMap.size() != 0)) {
        Set<Entry<String, String>> entrySet = propertyMap.entrySet();
        buf.append("  <log4j:properties>");
        for (Entry<String, String> entry : entrySet) {
          buf.append("\r\n    <log4j:data");
          buf.append(" name=\"" + Transform.escapeTags(entry.getKey()) + "\"");
          buf.append(" value=\"" + Transform.escapeTags(entry.getValue()) + "\"");
          buf.append(" />");
        }
        buf.append("\r\n  </log4j:properties>");
      }
    }

    buf.append("\r\n</log4j:event>\r\n\r\n");

    return buf.toString();
  }
@Test
    public void testDoLayout() throws Exception {
        ILoggingEvent le = createLoggingEvent();

        String result = DOCTYPE + "<log4j:eventSet xmlns:log4j='http://jakarta.apache.org/log4j/'>";
        if (layout.getFileHeader() != null) {
            result += layout.getFileHeader();
        }
        if (layout.getPresentationHeader() != null) {
            result += layout.getPresentationHeader();
        }
        result += layout.doLayout(le);
        if (layout.getPresentationFooter() != null) {
            result += layout.getPresentationFooter();
        }
        if (layout.getFileFooter() != null) {
            result += layout.getFileFooter();
        }
        result += "</log4j:eventSet>";

        Document document = parse(result);

        XPath xpath = this.newXPath();

        // Test log4j:event:
        NodeList eventNodes = (NodeList) xpath.compile("//log4j:event").evaluate(document, XPathConstants.NODESET);
        Assert.assertEquals(1, eventNodes.getLength());

        // Test log4g:message:
        Assert.assertEquals(MESSAGE, xpath.compile("//log4j:message").evaluate(document, XPathConstants.STRING));

        // Test log4j:data:
        NodeList dataNodes = (NodeList) xpath.compile("//log4j:data").evaluate(document, XPathConstants.NODESET);
        boolean foundMdc = false;
        for (int i = 0; i != dataNodes.getLength(); ++i) {
            Node dataNode = dataNodes.item(i);
            if (dataNode.getAttributes().getNamedItem("name").getNodeValue().equals(MDC_KEY)) {
                foundMdc = true;
                Assert.assertEquals(MDC_VALUE, dataNode.getAttributes().getNamedItem("value").getNodeValue());
                break;
            }
        }
        Assert.assertTrue(foundMdc);
    }