public class Sort extends Object
The fields used to determine sort order must be carefully chosen. Documents must contain a single term in such a field, and the value of the term should indicate the document's relative position in a given sort order. The field must be indexed, but should not be tokenized, and does not need to be stored (unless you happen to want it back with the rest of your document data). In other words:
document.add (new Field ("byNumber", Integer.toString(x), Field.Store.NO, Field.Index.NOT_ANALYZED));
There are four possible kinds of term values which may be put into
sorting fields: Integers, Longs, Floats, or Strings. Unless
SortField
objects are specified, the type of value
in the field is determined by parsing the first term in the field.
Integer term values should contain only digits and an optional
preceding negative sign. Values must be base 10 and in the range
Integer.MIN_VALUE
and Integer.MAX_VALUE
inclusive.
Documents which should appear first in the sort
should have low value integers, later documents high values
(i.e. the documents should be numbered 1..n
where
1
is the first and n
the last).
Long term values should contain only digits and an optional
preceding negative sign. Values must be base 10 and in the range
Long.MIN_VALUE
and Long.MAX_VALUE
inclusive.
Documents which should appear first in the sort
should have low value integers, later documents high values.
Float term values should conform to values accepted by
Float.valueOf(String)
(except that NaN
and Infinity
are not supported).
Documents which should appear first in the sort
should have low values, later documents high values.
String term values can contain any valid String, but should
not be tokenized. The values are sorted according to their
natural order
. Note that using this type
of term value has higher memory requirements than the other
two types.
One of these objects can be used multiple times and the sort order changed between usages.
This class is thread safe.
Sorting uses of caches of term values maintained by the
internal HitQueue(s). The cache is static and contains an integer
or float array of length IndexReader.maxDoc()
for each field
name for which a sort is performed. In other words, the size of the
cache in bytes is:
4 * IndexReader.maxDoc() * (# of different fields actually used to sort)
For String fields, the cache is larger: in addition to the above array, the value of every term in the field is kept in memory. If there are many unique terms in the field, this could be quite large.
Note that the size of the cache is not affected by how many fields are in the index and might be used to sort - only by the ones actually used to sort a result set.
Created: Feb 12, 2004 10:53:57 AM
Modifier and Type | Field and Description |
---|---|
static Sort |
INDEXORDER
Represents sorting by index order.
|
static Sort |
RELEVANCE
Represents sorting by computed relevance.
|
Constructor and Description |
---|
Sort()
Sorts by computed relevance.
|
Sort(SortField... fields)
Sets the sort to the given criteria in succession: the
first SortField is checked first, but if it produces a
tie, then the second SortField is used to break the tie,
etc.
|
Sort(SortField field)
Sorts by the criteria in the given SortField.
|
Modifier and Type | Method and Description |
---|---|
boolean |
equals(Object o)
Returns true if
o is equal to this. |
SortField[] |
getSort()
Representation of the sort criteria.
|
int |
hashCode()
Returns a hash code value for this object.
|
boolean |
needsScores()
Returns true if the relevance score is needed to sort documents.
|
Sort |
rewrite(IndexSearcher searcher)
Rewrites the SortFields in this Sort, returning a new Sort if any of the fields
changes during their rewriting.
|
void |
setSort(SortField... fields)
Sets the sort to the given criteria in succession: the
first SortField is checked first, but if it produces a
tie, then the second SortField is used to break the tie,
etc.
|
void |
setSort(SortField field)
Sets the sort to the given criteria.
|
String |
toString() |
public static final Sort RELEVANCE
IndexSearcher#search()
without a sort criteria,
only with slightly more overhead.public static final Sort INDEXORDER
public Sort()
IndexSearcher#search()
without a sort criteria,
only with slightly more overhead.public Sort(SortField field)
public Sort(SortField... fields)
public void setSort(SortField field)
public void setSort(SortField... fields)
public SortField[] getSort()
public Sort rewrite(IndexSearcher searcher) throws IOException
searcher
- IndexSearcher to use in the rewritingthis
if the Sort/Fields have not changed, or a new Sort if there
is a changeIOException
- Can be thrown by the rewritingpublic boolean equals(Object o)
o
is equal to this.public int hashCode()
public boolean needsScores()
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