Package com.intellij.util.gist

Interface VirtualFileGist<Data>

public interface VirtualFileGist<Data>

Calculates some data based on VirtualFile content, persists it between IDE restarts, and updates it when the content is changed. The data is calculated lazily, when needed, and can be different for different projects.

Obtained using GistManager.newVirtualFileGist(java.lang.String, int, com.intellij.util.io.DataExternalizer<Data>, com.intellij.util.gist.VirtualFileGist.GistCalculator<Data>).

Tracks VFS content only. Unsaved/uncommitted documents have no effect on the getFileData(com.intellij.openapi.project.Project, com.intellij.openapi.vfs.VirtualFile) results. Neither do any disk file changes, until VFS refresh has detected them. To work with PSI content, use PsiFileGist.

Please note that every call to getFileData(com.intellij.openapi.project.Project, com.intellij.openapi.vfs.VirtualFile) means a disk access. Clients that access gists frequently should take care of proper caching themselves. The data is calculated on demand when first requested, so if you need this data for a lot of files at once, this can take some amount of time on the first query. If that's unacceptable from the UX perspective, consider using FileBasedIndexExtension instead.

The differences to file-based index:

• Gists have simpler lifecycle and API, but don't provide a possibility for queries across multiple files.
• Gists are project-dependent.
• Gists are calculated on request for specific files, index processes all files in advance. Thus gists can be used to speed up the indexing phase and move the logic into later stages, when it's beneficial.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	VirtualFileGist.GistCalculator<Data> Used by VirtualFileGist to calculate the data when it's needed and to recalculate it after file changes.

Method Summary

Modifier and Type	Method and Description
Data	getFileData(Project project, VirtualFile file) Calculate or get the cached data by the current virtual file content in the given project (or null, if the data is project-independent).

Method Detail

getFileData

Data getFileData(Project project,
                 VirtualFile file)

Calculate or get the cached data by the current virtual file content in the given project (or null, if the data is project-independent).