org.apache.xml.utils
Class FastStringBuffer
java.lang.Object
org.apache.xml.utils.FastStringBuffer
public class FastStringBuffer
extends java.lang.Object
Bare-bones, unsafe, fast string buffer. No thread-safety, no
parameter range checking, exposed fields. Note that in typical
applications, thread-safety of a StringBuffer is a somewhat
dubious concept in any case.
Note that Stree and DTM used a single FastStringBuffer as a string pool,
by recording start and length indices within this single buffer. This
minimizes heap overhead, but of course requires more work when retrieving
the data.
FastStringBuffer operates as a "chunked buffer". Doing so
reduces the need to recopy existing information when an append
exceeds the space available; we just allocate another chunk and
flow across to it. (The array of chunks may need to grow,
admittedly, but that's a much smaller object.) Some excess
recopying may arise when we extract Strings which cross chunk
boundaries; larger chunks make that less frequent.
The size values are parameterized, to allow tuning this code. In
theory, Result Tree Fragments might want to be tuned differently
from the main document's text.
%REVIEW% An experiment in self-tuning is
included in the code (using nested FastStringBuffers to achieve
variation in chunk sizes), but this implementation has proven to
be problematic when data may be being copied from the FSB into itself.
We should either re-architect that to make this safe (if possible)
or remove that code and clean up for performance/maintainability reasons.
FastStringBuffer() - Construct a FastStringBuffer, using a default allocation policy.
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FastStringBuffer(int initChunkBits) - Construct a FastStringBuffer, using default maxChunkBits and
rebundleBits values.
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FastStringBuffer(int initChunkBits, int maxChunkBits) - Construct a FastStringBuffer, using a default rebundleBits value.
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FastStringBuffer(int initChunkBits, int maxChunkBits, int rebundleBits) - Construct a FastStringBuffer, with allocation policy as per parameters.
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void | append(String value) - Append the contents of a String onto the FastStringBuffer,
growing the storage if necessary.
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void | append(StringBuffer value) - Append the contents of a StringBuffer onto the FastStringBuffer,
growing the storage if necessary.
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void | append(char value) - Append a single character onto the FastStringBuffer, growing the
storage if necessary.
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void | append(char[] chars, int start, int length) - Append part of the contents of a Character Array onto the
FastStringBuffer, growing the storage if necessary.
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void | append(FastStringBuffer value) - Append the contents of another FastStringBuffer onto
this FastStringBuffer, growing the storage if necessary.
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char | charAt(int pos) - Get a single character from the string buffer.
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String | getString(int start, int length)
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boolean | isWhitespace(int start, int length)
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int | length() - Get the length of the list.
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void | reset() - Discard the content of the FastStringBuffer, and most of the memory
that was allocated by it, restoring the initial state.
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static void | sendNormalizedSAXcharacters(ch[] , int start, int length, org.xml.sax.ContentHandler handler) - Directly normalize and dispatch the character array.
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int | sendNormalizedSAXcharacters(org.xml.sax.ContentHandler ch, int start, int length) - Sends the specified range of characters as one or more SAX characters()
events, normalizing the characters according to XSLT rules.
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void | sendSAXComment(org.xml.sax.ext.LexicalHandler ch, int start, int length) - Sends the specified range of characters as sax Comment.
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void | sendSAXcharacters(org.xml.sax.ContentHandler ch, int start, int length) - Sends the specified range of characters as one or more SAX characters()
events.
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void | setLength(int l) - Directly set how much of the FastStringBuffer's storage is to be
considered part of its content.
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int | size() - Get the length of the list.
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String | toString() - Note that this operation has been somewhat deoptimized by the shift to a
chunked array, as there is no factory method to produce a String object
directly from an array of arrays and hence a double copy is needed.
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SUPPRESS_BOTH
public static final int SUPPRESS_BOTH
Manifest constant: Suppress both leading and trailing whitespace.
This should be used when normalize-to-SAX is called for a complete string.
(I'm not wild about the name of this one. Ideas welcome.)
SUPPRESS_LEADING_WS
public static final int SUPPRESS_LEADING_WS
Manifest constant: Suppress leading whitespace.
This should be used when normalize-to-SAX is called for the first chunk of a
multi-chunk output, or one following unsuppressed whitespace in a previous
chunk.
SUPPRESS_TRAILING_WS
public static final int SUPPRESS_TRAILING_WS
Manifest constant: Suppress trailing whitespace.
This should be used when normalize-to-SAX is called for the last chunk of a
multi-chunk output; it may have to be or'ed with SUPPRESS_LEADING_WS.
FastStringBuffer
public FastStringBuffer()
Construct a FastStringBuffer, using a default allocation policy.
FastStringBuffer
public FastStringBuffer(int initChunkBits)
Construct a FastStringBuffer, using default maxChunkBits and
rebundleBits values.
ISSUE: Should this call assert initial size, or fixed size?
Now configured as initial, with a default for fixed.
NEEDSDOC @param initChunkBits
FastStringBuffer
public FastStringBuffer(int initChunkBits,
int maxChunkBits)
Construct a FastStringBuffer, using a default rebundleBits value.
NEEDSDOC @param initChunkBits
NEEDSDOC @param maxChunkBits
FastStringBuffer
public FastStringBuffer(int initChunkBits,
int maxChunkBits,
int rebundleBits)
Construct a FastStringBuffer, with allocation policy as per parameters.
For coding convenience, I've expressed both allocation sizes in terms of
a number of bits. That's needed for the final size of a chunk,
to permit fast and efficient shift-and-mask addressing. It's less critical
for the inital size, and may be reconsidered.
An alternative would be to accept integer sizes and round to powers of two;
that really doesn't seem to buy us much, if anything.
initChunkBits
- Length in characters of the initial allocation
of a chunk, expressed in log-base-2. (That is, 10 means allocate 1024
characters.) Later chunks will use larger allocation units, to trade off
allocation speed of large document against storage efficiency of small
ones.maxChunkBits
- Number of character-offset bits that should be used for
addressing within a chunk. Maximum length of a chunk is 2^chunkBits
characters.rebundleBits
- Number of character-offset bits that addressing should
advance before we attempt to take a step from initChunkBits to maxChunkBits
append
public final void append(String value)
Append the contents of a String onto the FastStringBuffer,
growing the storage if necessary.
NOTE THAT after calling append(), previously obtained
references to m_array[] may no longer be valid.
value
- String whose contents are to be appended.
append
public final void append(StringBuffer value)
Append the contents of a StringBuffer onto the FastStringBuffer,
growing the storage if necessary.
NOTE THAT after calling append(), previously obtained
references to m_array[] may no longer be valid.
value
- StringBuffer whose contents are to be appended.
append
public final void append(char value)
Append a single character onto the FastStringBuffer, growing the
storage if necessary.
NOTE THAT after calling append(), previously obtained
references to m_array[][] may no longer be valid....
though in fact they should be in this instance.
value
- character to be appended.
append
public final void append(char[] chars,
int start,
int length)
Append part of the contents of a Character Array onto the
FastStringBuffer, growing the storage if necessary.
NOTE THAT after calling append(), previously obtained
references to m_array[] may no longer be valid.
chars
- character array from which data is to be copiedstart
- offset in chars of first character to be copied,
zero-based.length
- number of characters to be copied
append
public final void append(FastStringBuffer value)
Append the contents of another FastStringBuffer onto
this FastStringBuffer, growing the storage if necessary.
NOTE THAT after calling append(), previously obtained
references to m_array[] may no longer be valid.
value
- FastStringBuffer whose contents are
to be appended.
charAt
public char charAt(int pos)
Get a single character from the string buffer.
pos
- character position requested.
- A character from the requested position.
getString
public String getString(int start,
int length)
start
- Offset of first character in the range.length
- Number of characters to send.
- a new String object initialized from the specified range of
characters.
isWhitespace
public boolean isWhitespace(int start,
int length)
start
- Offset of first character in the range.length
- Number of characters to send.
- true if the specified range of characters are all whitespace,
as defined by XMLCharacterRecognizer.
CURRENTLY DOES NOT CHECK FOR OUT-OF-RANGE.
length
public final int length()
Get the length of the list. Synonym for size().
- the number of characters in the FastStringBuffer's content.
reset
public final void reset()
Discard the content of the FastStringBuffer, and most of the memory
that was allocated by it, restoring the initial state. Note that this
may eventually be different from setLength(0), which see.
sendNormalizedSAXcharacters
public static void sendNormalizedSAXcharacters(ch[] ,
int start,
int length,
org.xml.sax.ContentHandler handler)
throws org.xml.sax.SAXException
Directly normalize and dispatch the character array.
start
- The start position in the array.length
- The number of characters to read from the array.handler
- SAX ContentHandler object to receive the event.
sendNormalizedSAXcharacters
public int sendNormalizedSAXcharacters(org.xml.sax.ContentHandler ch,
int start,
int length)
throws org.xml.sax.SAXException
Sends the specified range of characters as one or more SAX characters()
events, normalizing the characters according to XSLT rules.
ch
- SAX ContentHandler object to receive the event.start
- Offset of first character in the range.length
- Number of characters to send.
- normalization status to apply to next chunk (because we may
have been called recursively to process an inner FSB):
sendSAXComment
public void sendSAXComment(org.xml.sax.ext.LexicalHandler ch,
int start,
int length)
throws org.xml.sax.SAXException
Sends the specified range of characters as sax Comment.
Note that, unlike sendSAXcharacters, this has to be done as a single
call to LexicalHandler#comment.
ch
- SAX LexicalHandler object to receive the event.start
- Offset of first character in the range.length
- Number of characters to send.
sendSAXcharacters
public void sendSAXcharacters(org.xml.sax.ContentHandler ch,
int start,
int length)
throws org.xml.sax.SAXException
Sends the specified range of characters as one or more SAX characters()
events.
Note that the buffer reference passed to the ContentHandler may be
invalidated if the FastStringBuffer is edited; it's the user's
responsibility to manage access to the FastStringBuffer to prevent this
problem from arising.
Note too that there is no promise that the output will be sent as a
single call. As is always true in SAX, one logical string may be split
across multiple blocks of memory and hence delivered as several
successive events.
ch
- SAX ContentHandler object to receive the event.start
- Offset of first character in the range.length
- Number of characters to send.
setLength
public final void setLength(int l)
Directly set how much of the FastStringBuffer's storage is to be
considered part of its content. This is a fast but hazardous
operation. It is not protected against negative values, or values
greater than the amount of storage currently available... and even
if additional storage does exist, its contents are unpredictable.
The only safe use for our setLength() is to truncate the FastStringBuffer
to a shorter string.
l
- New length. If l<0 or l>=getLength(), this operation will
not report an error but future operations will almost certainly fail.
size
public final int size()
Get the length of the list. Synonym for length().
- the number of characters in the FastStringBuffer's content.
toString
public final String toString()
Note that this operation has been somewhat deoptimized by the shift to a
chunked array, as there is no factory method to produce a String object
directly from an array of arrays and hence a double copy is needed.
By using ensureCapacity we hope to minimize the heap overhead of building
the intermediate StringBuffer.
(It really is a pity that Java didn't design String as a final subclass
of MutableString, rather than having StringBuffer be a separate hierarchy.
We'd avoid a
lot of double-buffering.)
- the contents of the FastStringBuffer as a standard Java string.
Copyright © 2006 Apache XML Project. All Rights Reserved.