This class helps with parsing and rewriting an HTML document. The
source document is not changed; a new HTML document is built.
The user can sequentially examine and rewrite each token in the source
HTML document. As each token in the document is seen, the user has
two choices:
modify the current token.
don't modify the current token.
If the user modifies (or replaces, deletes, etc.) the current token,
then the resultant HTML document will contain that modification. On
the other hand, if the user doesn't do anything with the current token,
it will appear, unchanged, in the resultant HTML document.
Parsing is implemented lazily, meaning, for example, that unless the
user actually asks for attributes of an HTML tag, this parser
does not have to spend the time breaking up the attributes.
This class is used by HTML filters to maintain the state of the
document and allow the filters to perform arbitrary rewriting.
HtmlRewriter(LexHTML lex)
Creates a new HtmlRewriter from the given HTML parser.
HtmlRewriter(String str)
Creates a new HtmlRewriter that will operate on the given
string.
Method Summary
void
accumulate(boolean accumulate)
Turns on or off the automatic accumulation of each token.
void
append(String str)
Instead of modifying an existing token, this method allows the user
to completely replace the current token with arbitrary new content.
void
appendToken()
Appends the current token to the resultant HTML document.
Returns the "new" rewritten HTML document. This is normally called
once all of the tokens have been processed, and the user wants to
send on this rewritten document.
At any time, this method can be called to return the current state
of the HTML document. The return value is the result of
processing the source document up to this point in time; the
unprocessed remainder of the source document is not considered.
Due to the implementation, calling this method may be expensive.
Specifically, calling this method a second (or further) time for
a given HtmlRewriter may involve copying temporary
strings around. The pessimal case would be to call this method
every time a new token is appended.
The rewritten HTML document, up to this point in time.
nextToken
public boolean nextToken()
Advances to the next token in the source HTML document.
The other purpose of this function is to "do the right thing", which
is to append the token we just processed to the resultant HTML
document, unless the user has already appended something else.
A sample program follows. This program changes all
<img> tags to <form> tags,
deletes all <table> tags, capitalizes
and bolds each string token, and passes all other tokens through
unchanged, to illustrate how nextToken interacts with
some of the other methods in this class.
HtmlRewriter hr = new HtmlRewriter(str);
while (hr.nextToken()) {
switch (hr.getType()) {
case LexHTML.TAG:
if (hr.getTag().equals("img")) {
// Change the tag name w/o affecting the attributes.
hr.setTag("form");
} else if (hr.getTag().equals("table")) {
// Eliminate the entire "table" token.
hr.killToken();
}
break;
case LexHTML.STRING:
// Append a new sequence in place of the existing token.
hr.append("<b>" + hr.getToken().toUpperCase() + "</b>");
break;
}
// Any tokens we didn't modify get copied through unchanged.
}
Returns:
true if there are tokens left to process,
false otherwise.
nextTag
public boolean nextTag()
A convenence method built on top of nextToken.
Advances to the next HTML tag. All intervening strings and comments
between the last tag and the new current tag are copied through
unchanged. This method can be used when the caller wants to process
only HTML tags, without having to manually check the type of each
token to see if it is actually a tag.
Returns:
true if there are tokens left to process,
false otherwise.
Returns the value that the specified case-insensitive key maps
to in the attributes for the current tag. For keys that were
present in the tag's attributes without a value, the value returned
is the empty string. In other words, for the tag
<table border rows=2>:
get("border") returns the empty string "".
get("rows") returns 2.
Surrounding single and double quote marks that occur in the literal
tag are removed from the values reported. So, for the tag
<a href="/foo.html" target=_top onclick='alert("hello")'>:
get("href") returns /foo.html .
get("target") returns _top .
get("onclick") returns alert("hello") .
Parameters:
The - key to lookup in the current tag's attributes.
Returns:
The value to which the specified key is mapped, or
null if the key was not in the attributes.
Maps the given case-insensitive key to the specified value in the
current tag's attributes.
The value can be retrieved by calling get with a
key that is case-insensitive equal to the given key.
If the attributes already contained a mapping for the given key,
the old value is forgotten and the new specified value is used.
The case of the prior key is retained in that case. Otherwise
the case of the new key is used and a new mapping is made.
Removes the given case-insensitive key and its corresponding value
from the current tag's attributes. This method does nothing if the
key is not in the attributes.
Parameters:
key - The key that needs to be removed. Must not be
null.
Returns an enumeration of the keys in the current tag's attributes.
The elements of the enumeration are the string keys. The keys can
be passed to get to get the values of the attributes.
Instead of modifying an existing token, this method allows the user
to completely replace the current token with arbitrary new content.
This method may be called multiple times while processing the current
token to add more and more data to the resultant HTML document.
Before and/or after calling this method, the appendToken
method may also be called explicitly in order to add the current token
to the resultant HTML document.
Following is sample code illustrating how to use this method
to put bold tags around all the <a> tags.
HtmlRewriter hr = new HtmlRewriter(str);
while (hr.nextTag()) {
if (hr.getTag().equals("a")) {
hr.append("<b>");
hr.appendToken();
} else if (hr.getTag().equals("/a")) {
hr.appendToken();
hr.append("</b>");
}
}
The calls to appendToken are necessary. Otherwise,
the HtmlRewriter could not know where and when to
append the existing token in addition to the new content provided
by the user.
Parameters:
str - The new content to append. May be null,
in which case no new content is appended (the equivalent
of appending "").
Appends the current token to the resultant HTML document.
If the caller has changed the current token using the
setTag, set, or remove
methods, those changes will be reflected.
By default, this method is automatically called after each token is
processed unless the user has already appended something to the
resultant HTML document. Therefore, if the user appends something
and also wants to append the current token, or if the user wants
to append the current token a number of times, this method must
be called.
Tells this HtmlRewriter not to append the current token
to the resultant HTML document. Even if the user hasn't appended
anything else, the current token will be ignored rather than appended.
Turns on or off the automatic accumulation of each token.
After each token is processed, the current token is appended to
to the resultant HTML document unless the user has already appended
something else. By setting accumulate to
false, this behavior is turned off. The user must then
explicitly call appendToken to cause the current token
to be appended.
Turning off accumulation takes effect immediately, while turning
on accumulation takes effect on the next token. In other words,
whether the user turns this setting off or on, the current token
will not be added to the resultant HTML document unless the user
explicitly calls appendToken.
Following is sample code that illustrates how to use this method
to extract the contents of the <head> of the
source HTML document.
HtmlRewriter hr = new HtmlRewriter(str);
// Don't accumulate tokens until we see the <head> below.
hr.accumulate(false);
while (hr.nextTag()) {
if (hr.getTag().equals("head")) {
// Start remembering the contents of the HTML document,
// not including the <head> tag itself.
hr.accumulate(true);
} else if (hr.getTag().equals("/head")) {
// Return everything accumulated so far.
return hr.toString();
}
}
This method can be called any number of times while processing
the source HTML document.
Parameters:
accumulate - true to automatically accumulate tokens in the
resultant HTML document, false to require
that the user explicitly accumulate them.
Forgets all the tokens that have been appended to the resultant
HTML document so far, including the current token.
pushback
public void pushback()
Puts the current token back. The next time nextToken
is called, it will be the current token again, rather than
advancing to the next token in the source HTML document.
This is useful when a code fragment needs to read an indefinite
number of tokens, but that once some distinguished token is found,
needs to push that token back so that normal processing can occur
on that token.
Helper class to quote a attribute's value when the value is being
written to the resultant HTML document. Values set by the
put method are automatically quoted as needed. This
method is provided in case the user is dynamically constructing a new
tag to be appended with append and needs to quote some
arbitrary values.
The quoting algorithm is as follows:
If the string contains double-quotes, put single quotes around it.
If the string contains single-quotes or spaces, put double-quotes
around it.
This algorithm is, of course, insufficient for complicated
strings that include both single and double quotes. In that case,
it is the user's responsibility to escape the special characters
in the string using the HTML special symbols like
" or "
Returns:
The quoted string, or the original string if it did not
need to be quoted.
