File-based indexes are based on a Map/Reduce architecture. Each index has a specific type of key and a particular type of value.
The key is what's later used to retrieve data from the index.
Example: in the word index, the key is the word itself.
The value is arbitrary data, which is associated with the key in the index.
Example: in the word index, the value is a mask indicating in which context the word occurs (code, string literal, or comment).
In the simplest case, when one needs to know in what files some data is present, the value has type
Void and is not stored in the index.
When the index implementation indexes a file, it receives a file's content and returns a map from the keys found in the file to the associated values.
When accessing an index, specify the key you're interested in and get back the list of files in which the key occurs, and the value associated with each file.
Implementing a File-Based Index
Each specific index implementation is a class extending
FileBasedIndexExtension registered via
com.intellij.fileBasedIndex extension point.
An implementation of a file-based index consists of the following main parts:
DataIndexerimplementation actually responsible for building a set of key/value pairs based on file content.
KeyDescriptorresponsible for comparing keys and storing them in a serialized binary format. Probably the most commonly used implementation is
EnumeratorStringDescriptor, which is designed for storing identifiers efficiently.
DataExternalizerresponsible for storing values in a serialized binary format.
getInputFilter()allows restricting the indexing only to a certain set of files. Consider using
getName()returns a unique index ID. Consider using fully qualified index class name to not clash with other plugins defining index with the same ID, e.g.,
getVersion()returns the version of the index implementation. The index is automatically rebuilt if the current version differs from the version of the index implementation used to build it.
If there's no value to associate with the files (i.e., value type is
Void), simplify the implementation by extending
ScalarIndexExtension. In case of single value per file, extend from
Please see also Improving indexing performance.
Accessing a File-Based Index
Access to file-based indexes is performed through the
The following primary operations are supported:
processAllKeys()allow obtaining the list of all keys found in files, which are a part of the specified project. To optimize performance, consider returning
FileBasedIndexExtension.traceKeyHashToVirtualFileMapping()(see its Javadoc for details).
getValues()allows to get all values associated with a specific key but not the files in which they were found.
getContainingFiles()allows collecting all files in which a particular key was encountered.
processValues()allows iterating through all files in which a specific key was encountered and accessing the associated values simultaneously.
Nested Index Access
When accessing index data in nested calls (usually from multiple indexes), limitations might apply.
Nested index access is now possible.
The IntelliJ Platform contains several standard file-based indexes. The most useful indexes for plugin developers are:
Generally, the word index should be accessed indirectly by using helper methods of the
File Name Index
FilenameIndex provides a quick way to find all files matching a specific file name.