# File View Providers

> For the complete documentation index, see [llms.txt](https://plugins.jetbrains.com/docs/intellij/llms.txt).

A file view provider ([FileViewProvider](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/core-api/src/com/intellij/psi/FileViewProvider.java)) manages access to multiple PSI trees within a single file.

For example, a JSPX page has a separate PSI tree for the Java code in it (`PsiJavaFile`), a separate tree for the XML code (`XmlFile`), and a separate tree for JSP as a whole ([JspFile](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/java/jsp-openapi/src/com/intellij/psi/jsp/JspFile.java)).

Each of the PSI trees covers the entire contents of the file and contains special "outer language elements" in the places where contents in a different language can be found.

A `FileViewProvider` instance corresponds to a single `VirtualFile`, a single `Document`, and can retrieve multiple `PsiFile` instances.

##  How do I get a `FileViewProvider`? 

| Context | API |
| --- | --- |
| [PSI File](psi-files.html) | [PsiFile.getViewProvider()](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/core-api/src/com/intellij/psi/PsiFile.java) |
| [Virtual File](virtual-file.html) | [PsiManager.getInstance(project).findViewProvider()](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/core-api/src/com/intellij/psi/PsiManager.java) |

##  What can I do with a `FileViewProvider`? 

* To get the set of all languages for which PSI trees exist in a file: `fileViewProvider.getLanguages()`

* To get the PSI tree for a particular language: `fileViewProvider.getPsi(language)`. For example, to get the PSI tree for XML, use `fileViewProvider.getPsi(XMLLanguage.INSTANCE)`.

* To find an element of a particular language at the specified offset in the file: `fileViewProvider.findElementAt(offset, language)`

##  How do I extend the `FileViewProvider`? 

To create a file type that has multiple interspersing trees for different languages, a plugin must contain an extension to the [com.intellij.fileType.fileViewProviderFactory](https://jb.gg/ipe?extensions=com.intellij.fileType.fileViewProviderFactory) extension point .

Implement [FileViewProviderFactory](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/core-api/src/com/intellij/psi/FileViewProviderFactory.java) and return the custom `FileViewProvider` implementation from `createFileViewProvider()` method.

Register as follows in `[plugin.xml](plugin-configuration-file.html)`:

```XML
<extensions defaultExtensionNs="com.intellij">
  <fileType.fileViewProviderFactory
      filetype="$FILE_TYPE$"
      implementationClass="com.example.MyFileViewProviderFactory"/>
</extensions>
```

Where `$FILE_TYPE$` refers to the type of the file being created (for example, "JSF").