com.allanbank.mongodb.bson.io

Class StringDecoder

java.lang.Object

com.allanbank.mongodb.bson.io.StringDecoder

public class StringDecoder
extends Object

StringDecoder provides a decoder for byte arrays into strings that uses a trie data structure to cache recurring strings.

There are two controls on the amount of caching instances of this class will do:

1. getMaxCacheLength() limits the length of the encoded bytes this class will try and retrieve from the cache. Setting this value to zero disables the cache and limit any memory overhead.
2. getMaxCacheEntries() controls the number of cached strings in the trie. Each entry represents a single encoded strings so if you wanted to cache 100 strings of length 10 bytes each then you would set the value to 100 but there may be up to 1000 nodes in the trie.

This class is not thread safe.

API Warning:

This class is NOT part of the drivers API. This class may be mutated in incompatible ways between any two releases of the driver.

Copyright ©:

2013, Allanbank Consulting, Inc., All Rights Reserved

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	StringDecoder.Node Node provides a single node in the trie.

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_MAX_CACHE_ENTRIES The default maximum number of entries to keep in the trie cache.
static int	DEFAULT_MAX_CACHE_LENGTH The default maximum length byte array to cache.

Constructor Summary

Constructors

Constructor and Description
StringDecoder() Creates a new TrieStringCache.

Method Summary

Methods

Modifier and Type	Method and Description
String	decode(byte[] source, int offset, int length) Decode a string of a known length.
int	getMaxCacheEntries() Returns the maximum node count.
int	getMaxCacheLength() Returns the maximum depth of the nodes in the trie.
void	setMaxCacheEntries(int maxCacheEntries) Sets the value of maximum number of cached strings.
void	setMaxCacheLength(int maxlength) Sets the value of maximum depth of the nodes in the trie to the new value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_MAX_CACHE_ENTRIES

public static final int DEFAULT_MAX_CACHE_ENTRIES

The default maximum number of entries to keep in the trie cache.

See Also:

Constant Field Values

DEFAULT_MAX_CACHE_LENGTH

public static final int DEFAULT_MAX_CACHE_LENGTH

The default maximum length byte array to cache.

See Also:

Constant Field Values

Constructor Detail

StringDecoder

public StringDecoder()

Creates a new TrieStringCache.

Method Detail

decode

public String decode(byte[] source,
            int offset,
            int length)
              throws StreamCorruptedException,
                     EOFException

Decode a string of a known length. The last byte should be a zero byte and will not be included in the decoded string.

Parameters:

source - The source of the bytes in the string.

offset - The offset of the first byte to decode.

length - The length of the string to decode with a terminal zero byte.

Returns:

The decoded string.

Throws:

StreamCorruptedException - On the decoding of the string failing.

EOFException - On the array not containing enough bytes to decoded.

getMaxCacheEntries

public int getMaxCacheEntries()

Returns the maximum node count.

Returns:

The maximum node count.

getMaxCacheLength

public int getMaxCacheLength()

Returns the maximum depth of the nodes in the trie. This can be used to stop a single long string from pushing useful values out of the cache.

Returns:

The maximum depth of the nodes in the trie.

setMaxCacheEntries

public void setMaxCacheEntries(int maxCacheEntries)

Sets the value of maximum number of cached strings.

Parameters:

maxCacheEntries - The new value for the maximum number of cached strings.

setMaxCacheLength

public void setMaxCacheLength(int maxlength)

Sets the value of maximum depth of the nodes in the trie to the new value. This can be used to stop a single long string from pushing useful values out of the cache.

Parameters:

maxlength - The new value for the maximum depth of the nodes in the trie.