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package org.apache.taglibs.standard.tlv;
import java.util.Set;
import java.util.Stack;
import javax.servlet.jsp.tagext.PageData;
import javax.servlet.jsp.tagext.ValidationMessage;
import org.apache.taglibs.standard.resources.Resources;
import org.xml.sax.Attributes;
import org.xml.sax.helpers.DefaultHandler;
/**
* <p>A SAX-based TagLibraryValidator for the core JSTL tag library.
* Currently implements the following checks:</p>
*
* <ul>
* <li>Expression syntax validation.
* <li>Choose / when / otherwise constraints</li>
* <li>Tag bodies that must either be empty or non-empty given
* particular attributes. (E.g., <set> cannot have a body when
* 'value' is specified; it *must* have a body otherwise.) For
* these purposes, "having a body" refers to non-whitespace
* content inside the tag.</li>
* <li>Other minor constraints.</li>
* </ul>
*
* @author Shawn Bayern
*/
public class JstlCoreTLV extends JstlBaseTLV {
//*********************************************************************
// Implementation Overview
/*
* We essentially just run the page through a SAX parser, handling
* the callbacks that interest us. We collapse <jsp:text> elements
* into the text they contain, since this simplifies processing
* somewhat. Even a quick glance at the implementation shows its
* necessary, tree-oriented nature: multiple Stacks, an understanding
* of 'depth', and so on all are important as we recover necessary
* state upon each callback. This TLV demonstrates various techniques,
* from the general "how do I use a SAX parser for a TLV?" to
* "how do I read my init parameters and then validate?" But also,
* the specific SAX methodology was kept as general as possible to
* allow for experimentation and flexibility.
*/
//*********************************************************************
// Constants
// tag names
private final String CHOOSE = "choose";
private final String WHEN = "when";
private final String OTHERWISE = "otherwise";
private final String EXPR = "out";
private final String SET = "set";
private final String IMPORT = "import";
private final String URL = "url";
private final String REDIRECT = "redirect";
private final String PARAM = "param";
// private final String EXPLANG = "expressionLanguage";
private final String TEXT = "text";
// attribute names
private final String VALUE = "value";
private final String DEFAULT = "default";
private final String VAR_READER = "varReader";
// alternative identifiers for tags
private final String IMPORT_WITH_READER = "import varReader=''";
private final String IMPORT_WITHOUT_READER = "import var=''";
//*********************************************************************
// set its type and delegate validation to super-class
public ValidationMessage[] validate(
String prefix, String uri, PageData page) {
return super.validate( TYPE_CORE, prefix, uri, page );
}
//*********************************************************************
// Contract fulfillment
protected DefaultHandler getHandler() {
return new Handler();
}
//*********************************************************************
// SAX event handler
/** The handler that provides the base of our implementation. */
private class Handler extends DefaultHandler {
// parser state
private int depth = 0;
private Stack chooseDepths = new Stack();
private Stack chooseHasOtherwise = new Stack();
private Stack chooseHasWhen = new Stack();
private Stack urlTags = new Stack();
private String lastElementName = null;
private boolean bodyNecessary = false;
private boolean bodyIllegal = false;
// process under the existing context (state), then modify it
public void startElement(
String ns, String ln, String qn, Attributes a) {
// substitute our own parsed 'ln' if it's not provided
if (ln == null)
ln = getLocalPart(qn);
// for simplicity, we can ignore <jsp:text> for our purposes
// (don't bother distinguishing between it and its characters)
if (isJspTag(ns, ln, TEXT))
return;
// check body-related constraint
if (bodyIllegal)
fail(Resources.getMessage("TLV_ILLEGAL_BODY", lastElementName));
// validate expression syntax if we need to
Set expAtts;
if (qn.startsWith(prefix + ":")
&& (expAtts = (Set) config.get(ln)) != null) {
for (int i = 0; i < a.getLength(); i++) {
String attName = a.getLocalName(i);
if (expAtts.contains(attName)) {
String vMsg =
validateExpression(
ln,
attName,
a.getValue(i));
if (vMsg != null)
fail(vMsg);
}
}
}
// validate attributes
if (qn.startsWith(prefix + ":") && !hasNoInvalidScope(a))
fail(Resources.getMessage("TLV_INVALID_ATTRIBUTE",
SCOPE, qn, a.getValue(SCOPE)));
if (qn.startsWith(prefix + ":") && hasEmptyVar(a))
fail(Resources.getMessage("TLV_EMPTY_VAR", qn));
if (qn.startsWith(prefix + ":") && hasDanglingScope(a))
fail(Resources.getMessage("TLV_DANGLING_SCOPE", qn));
// check invariants for <choose>
if (chooseChild()) {
// mark <choose> for the first the first <when>
if (isCoreTag(ns, ln, WHEN)) {
chooseHasWhen.pop();
chooseHasWhen.push(Boolean.TRUE);
}
// ensure <choose> has the right children
if(!isCoreTag(ns, ln, WHEN) && !isCoreTag(ns, ln, OTHERWISE)) {
fail(Resources.getMessage("TLV_ILLEGAL_CHILD_TAG",
prefix, CHOOSE, qn));
}
// make sure <otherwise> is the last tag
if (((Boolean) chooseHasOtherwise.peek()).booleanValue()) {
fail(Resources.getMessage("TLV_ILLEGAL_ORDER",
qn, prefix, OTHERWISE, CHOOSE));
}
if (isCoreTag(ns, ln, OTHERWISE)) {
chooseHasOtherwise.pop();
chooseHasOtherwise.push(Boolean.TRUE);
}
}
// check constraints for <param> vis-a-vis URL-related tags
if (isCoreTag(ns, ln, PARAM)) {
// no <param> outside URL tags.
if (urlTags.empty() || urlTags.peek().equals(PARAM))
fail(Resources.getMessage("TLV_ILLEGAL_ORPHAN", PARAM));
// no <param> where the most recent <import> has a reader
if (!urlTags.empty() &&
urlTags.peek().equals(IMPORT_WITH_READER))
fail(Resources.getMessage("TLV_ILLEGAL_PARAM",
prefix, PARAM, IMPORT, VAR_READER));
} else {
// tag ISN'T <param>, so it's illegal under non-reader <import>
if (!urlTags.empty()
&& urlTags.peek().equals(IMPORT_WITHOUT_READER))
fail(Resources.getMessage("TLV_ILLEGAL_CHILD_TAG",
prefix, IMPORT, qn));
}
// now, modify state
// we're a choose, so record new choose-specific state
if (isCoreTag(ns, ln, CHOOSE)) {
chooseDepths.push(Integer.valueOf(depth));
chooseHasWhen.push(Boolean.FALSE);
chooseHasOtherwise.push(Boolean.FALSE);
}
// if we're introducing a URL-related tag, record it
if (isCoreTag(ns, ln, IMPORT)) {
if (hasAttribute(a, VAR_READER))
urlTags.push(IMPORT_WITH_READER);
else
urlTags.push(IMPORT_WITHOUT_READER);
} else if (isCoreTag(ns, ln, PARAM))
urlTags.push(PARAM);
else if (isCoreTag(ns, ln, REDIRECT))
urlTags.push(REDIRECT);
else if (isCoreTag(ns, ln, URL))
urlTags.push(URL);
// set up a check against illegal attribute/body combinations
bodyIllegal = false;
bodyNecessary = false;
if (isCoreTag(ns, ln, EXPR)) {
if (hasAttribute(a, DEFAULT))
bodyIllegal = true;
} else if (isCoreTag(ns, ln, SET)) {
if (hasAttribute(a, VALUE))
bodyIllegal = true;
// else
// bodyNecessary = true;
}
// record the most recent tag (for error reporting)
lastElementName = qn;
lastElementId = a.getValue(JSP, "id");
// we're a new element, so increase depth
depth++;
}
public void characters(char[] ch, int start, int length) {
bodyNecessary = false; // body is no longer necessary!
// ignore strings that are just whitespace
String s = new String(ch, start, length).trim();
if (s.equals(""))
return;
// check and update body-related constraints
if (bodyIllegal)
fail(Resources.getMessage("TLV_ILLEGAL_BODY", lastElementName));
if (!urlTags.empty()
&& urlTags.peek().equals(IMPORT_WITHOUT_READER)) {
// we're in an <import> without a Reader; nothing but
// <param> is allowed
fail(Resources.getMessage("TLV_ILLEGAL_BODY",
prefix + ":" + IMPORT));
}
// make sure <choose> has no non-whitespace text
if (chooseChild()) {
String msg =
Resources.getMessage("TLV_ILLEGAL_TEXT_BODY",
prefix, CHOOSE,
(s.length() < 7 ? s : s.substring(0,7)));
fail(msg);
}
}
public void endElement(String ns, String ln, String qn) {
// consistently, we ignore JSP_TEXT
if (isJspTag(ns, ln, TEXT))
return;
// handle body-related invariant
if (bodyNecessary)
fail(Resources.getMessage("TLV_MISSING_BODY",
lastElementName));
bodyIllegal = false; // reset: we've left the tag
// update <choose>-related state
if (isCoreTag(ns, ln, CHOOSE)) {
Boolean b = (Boolean) chooseHasWhen.pop();
if (!b.booleanValue())
fail(Resources.getMessage("TLV_PARENT_WITHOUT_SUBTAG",
CHOOSE, WHEN));
chooseDepths.pop();
chooseHasOtherwise.pop();
}
// update state related to URL tags
if (isCoreTag(ns, ln, IMPORT)
|| isCoreTag(ns, ln, PARAM)
|| isCoreTag(ns, ln, REDIRECT)
|| isCoreTag(ns, ln, URL))
urlTags.pop();
// update our depth
depth--;
}
// are we directly under a <choose>?
private boolean chooseChild() {
return (!chooseDepths.empty()
&& (depth - 1) == ((Integer) chooseDepths.peek()).intValue());
}
}
}
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