File-Based Indexes
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:
getIndexer()returns theDataIndexerimplementation actually responsible for building a set of key/value pairs based on file content.getKeyDescriptor()returns theKeyDescriptorresponsible for comparing keys and storing them in a serialized binary format. Probably the most commonly used implementation isEnumeratorStringDescriptor, which is designed for storing identifiers efficiently.getValueExternalizer()returns theDataExternalizerresponsible for storing values in a serialized binary format.getInputFilter()allows restricting the indexing only to a certain set of files. Consider usingDefaultFileTypeSpecificInputFilter.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.,com.example.myplugin.indexing.MyIndex.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 SingleEntryFileBasedIndexExtension.
Please see also Improving indexing performance.
Accessing a File-Based Index
Access to file-based indexes is performed through the FileBasedIndex class.
The following primary operations are supported:
getAllKeys()andprocessAllKeys()allow obtaining the list of all keys found in files, which are a part of the specified project. To optimize performance, consider returningtruefromFileBasedIndexExtension.traceKeyHashToVirtualFileMapping()(see 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.
Standard Indexes
The IntelliJ Platform contains several standard file-based indexes. The most useful indexes for plugin developers are:
Word Index
Generally, the word index should be accessed indirectly by using helper methods of the PsiSearchHelper class.
File Name Index
FilenameIndex provides a quick way to find all files matching a specific file name.
File Type Index
FileTypeIndex serves a similar goal: it allows to find all files of a particular FileType quickly.
Additional Index Roots
To add additional files/directories to be indexed, implement IndexableSetContributor and register in com.intellij.indexedRootsProvider extension point.