Java Doc for IndexReader.java in  » Net » lucene-connector » org » apache » lucene » index » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Concrete subclasses of IndexReader are usually constructed with a call to one of the static open() methods, e.g. IndexReader.open(String) .

For efficiency, in this API documents are often referred to via document numbers, non-negative integers which each name a unique document in the index. These document numbers are ephemeral--they may change as documents are added to and deleted from an index. Clients should thus not rely on a given document having the same number between sessions.

An IndexReader can be opened on a directory for which an IndexWriter is opened already, but it cannot be used to delete documents from the index then.

NOTE: for backwards API compatibility, several methods are not listed as abstract, but have no useful implementations in this base class and instead always throw UnsupportedOperationException. Subclasses are strongly encouraged to override these methods, but in many cases may not need to.

This Constructor should not be used, it exists for backwards compatibility only to support legacy subclasses that did not "own" a specific directory, but needed to specify something to be returned by the directory() method.

For IndexReader implementations that use TermInfosReader to read terms, this returns the current indexDivisor.

For IndexReader implementations that use TermInfosReader to read terms, this sets the indexDivisor to subsample the number of indexed terms loaded into memory.

This Constructor should not be used, it exists for backwards compatibility only to support legacy subclasses that did not "own" a specific directory, but needed to specify something to be returned by the directory() method. Future subclasses should delegate to the no arg constructor and implement the directory() method as appropriate.
Parameters:
  directory - Directory to be returned by the directory() method
See Also:   IndexReader.directory()

For IndexReader implementations that use TermInfosReader to read terms, this returns the current indexDivisor.
See Also:   IndexReader.setTermInfosIndexDivisor
See Also:   

Not implemented in the IndexReader base class.

Opening an IndexReader is an expensive operation. This method can be used to refresh an existing IndexReader to reduce these costs. This method tries to only load segments that have changed or were created after the IndexReader was (re)opened.

If the index has not changed since this instance was (re)opened, then this call is a NOOP and returns this instance. Otherwise, a new instance is returned. The old instance is not closed and remains usable.
Note: The re-opened reader instance and the old instance might share the same resources. For this reason no index modification operations (e. g. IndexReader.deleteDocument(int) , IndexReader.setNorm(int,String,byte) ) should be performed using one of the readers until the old reader instance is closed. Otherwise, the behavior of the readers is undefined.

You can determine whether a reader was actually reopened by comparing the old instance with the instance returned by this method:

 IndexReader reader = ... 
 ...
 IndexReader new = r.reopen();
 if (new != reader) {
 ...     // reader was reopened
 reader.close(); 
 }
 reader = new;
 ...
 

For IndexReader implementations that use TermInfosReader to read terms, this sets the indexDivisor to subsample the number of indexed terms loaded into memory. This has the same effect as IndexWriter.setTermIndexInterval except that setting must be done at indexing time while this setting can be set per reader. When set to N, then one in every N*termIndexInterval terms in the index is loaded into memory. By setting this to a value > 1 you can reduce memory usage, at the expense of higher latency when loading a TermInfo. The default value is 1.

Term    =>    <docNum, freq>^*

The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.
throws:
  IOException - if there is a low-level IO error

Term    =>    <docNum, freq, <pos₁, pos₂, ... pos_freq-1> >^*

This positional information facilitates phrase and proximity searching.

The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.
throws:
  IOException - if there is a low-level IO error

Caution: this should only be used by failure recovery code, when it is known that no other process nor thread is in fact currently accessing this index.