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The MarkupWriter interface allows the majority of component code to treat the generation of output as a stream. In reality, MarkupWriter is more like a cursor into the DOM tree, and the DOM may ultimately be operated upon in a random access manner (rather than the serial (or buffered) approach used in Tapestry 4).

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DOM Classes

The implementation of this DOM is part of Tapestry, despite the fact that several third-party alternatives exist. This represents a desire to limit dependencies for the framework, but also the Tapestry DOM is streamlined for initial creation, and a limited amount of subsequent modification. Most DOM implementations are more sophisticated than needed for Tapestry, with greater support for querying (often using XPath) and manipulation.

Once the Document object is created, you don't directly create new DOM objects; instead, each DOM object includes methods that create new sub-objects. This primarily applies to the Element class, which can be a container of text, comments and other elements.

Document

The Document Object object represents the an entire document, which is to say, an entire response to be sent to the client.

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The Document class also has methods for setting and getting the DTD, adding comments and text, and finding an element based on a path of element names.

Element

An Element Object object represents an element of the document. Elements may have attributes, and they may themselves contain other elements, as well as text and comments.

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Calls to element() create a new element within the tree, and may provide attributes for the new element as well. Calls to write(), writeln() and writef() write text nodes within the current element. Every call to element() should be matched with a call to end(), which is used to move the current node up one level.

  writer.element("img", "src", "icon.png", "width", 20, "height", 20, alt, "*");
  writer.end();

Note that end() must be called here, even though the <img> element is empty (has no body). If the call to end() is omitted, then later elements created by calls to element() will be nested inside the <img> element, which is not desired.

Again, every call to element() must be matched with a call to end():

  writer.element("select", "name", "choice");
  
  for (String name : optionsNames)
  {
    writer.element("option");
    writer.write(name);
    writer.end();
  }
  
  writer.end();

attributes()

Adds additional name/value pairs to the current element.

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The write() method writes text inside the current element. It scans the provided text for XML control characters ('<', '>', and '&') and converts them to their XML entity equivalents ('<&lt;', '>&gt;', and '&amp;'). The result is correct, safe, HTML/XML output even when the content (which may come from a template, or from an external source such as a database) contains such problematic characters.

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The writeRaw() method writes unfiltered text into the DOM. When the DOM is rendered to markup, the provided string is written to the output stream exactly as-is. Care should be taken, as this can easily result invalid markup, or even markup that is not well formed. It can also introduce XSS vulnerabilities if the text comes from end users without proper filtering.

comment()

Adds an XML comment. The comment delimiters will be supplied by Tapestry:

  writer.comment("Start of JS Menu code");