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 we only need 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 you access the index, you 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
A relatively simple file-based index implementation is the UI Designer bound forms index. Refer to it as an example to understand this topic better.
Each specific index implementation is a class extending
FileBasedIndexExtension. A file-based index should be registered in the
com.intellij.fileBasedIndex extension point.
An implementation of a file-based index consists of the following main parts:
getIndexer()returns the indexer class actually responsible for building a set of key/value pairs based on file content.
getKeyDescriptor()returns the key descriptor responsible for comparing keys and storing them in a serialized binary format.
getValueExternalizer()returns the value serializer responsible for storing values in a serialized binary format.
getInputFilter()allows restricting the indexing only to a certain set of files.
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 you don't need to associate any value with the files (i.e., your value type is
Void ), you can simplify the implementation by using
ScalarIndexExtension as the base class.
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.
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.
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.