public class FastStringBuffer extends Object
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.
Modifier and Type | Field and Description |
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static int |
SUPPRESS_BOTH
Manifest constant: Suppress both leading and trailing whitespace.
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static int |
SUPPRESS_LEADING_WS
Manifest constant: Suppress leading whitespace.
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static int |
SUPPRESS_TRAILING_WS
Manifest constant: Suppress trailing whitespace.
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Constructor and Description |
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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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Modifier and Type | Method and Description |
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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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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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char |
charAt(int pos)
Get a single character from the string buffer.
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protected String |
getOneChunkString(int startChunk,
int startColumn,
int length) |
String |
getString(int start,
int length) |
boolean |
isWhitespace(int start,
int length) |
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(char[] ch,
int start,
int length,
ContentHandler handler)
Directly normalize and dispatch the character array.
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int |
sendNormalizedSAXcharacters(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 |
sendSAXcharacters(ContentHandler ch,
int start,
int length)
Sends the specified range of characters as one or more SAX characters()
events.
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void |
sendSAXComment(LexicalHandler ch,
int start,
int length)
Sends the specified range of characters as sax Comment.
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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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public static final int SUPPRESS_LEADING_WS
public static final int SUPPRESS_TRAILING_WS
public static final int SUPPRESS_BOTH
public FastStringBuffer(int initChunkBits, int maxChunkBits, int rebundleBits)
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 maxChunkBitspublic FastStringBuffer(int initChunkBits, int maxChunkBits)
public FastStringBuffer(int initChunkBits)
ISSUE: Should this call assert initial size, or fixed size? Now configured as initial, with a default for fixed. NEEDSDOC @param initChunkBits
public FastStringBuffer()
public final int size()
public final int length()
public final void reset()
public final void setLength(int l)
l
- New length. If l<0 or l>=getLength(), this operation will
not report an error but future operations will almost certainly fail.public final String toString()
(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.)
public final void append(char value)
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.public final void append(String value)
NOTE THAT after calling append(), previously obtained references to m_array[] may no longer be valid.
value
- String whose contents are to be appended.public final void append(StringBuffer value)
NOTE THAT after calling append(), previously obtained references to m_array[] may no longer be valid.
value
- StringBuffer whose contents are to be appended.public final void append(char[] chars, int start, int length)
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 copiedpublic final void append(FastStringBuffer value)
NOTE THAT after calling append(), previously obtained references to m_array[] may no longer be valid.
value
- FastStringBuffer whose contents are
to be appended.public boolean isWhitespace(int start, int length)
start
- Offset of first character in the range.length
- Number of characters to send.CURRENTLY DOES NOT CHECK FOR OUT-OF-RANGE.
public String getString(int start, int length)
start
- Offset of first character in the range.length
- Number of characters to send.protected String getOneChunkString(int startChunk, int startColumn, int length)
public char charAt(int pos)
pos
- character position requested.public void sendSAXcharacters(ContentHandler ch, int start, int length) throws SAXException
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.SAXException
- may be thrown by handler's
characters() method.public int sendNormalizedSAXcharacters(ContentHandler ch, int start, int length) throws SAXException
ch
- SAX ContentHandler object to receive the event.start
- Offset of first character in the range.length
- Number of characters to send.SAXException
- may be thrown by handler's
characters() method.public static void sendNormalizedSAXcharacters(char[] ch, int start, int length, ContentHandler handler) throws SAXException
ch
- The characters from the XML document.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.SAXException
- Any SAX exception, possibly
wrapping another exception.public void sendSAXComment(LexicalHandler ch, int start, int length) throws SAXException
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.SAXException
- may be thrown by handler's
characters() method.Copyright © 2021 JBoss by Red Hat. All rights reserved.