Using PSI in IntelliJ IDEA Plugin Development

Background – The previous article introduced basic knowledge of IDEA plugin development; this article focuses on using PSI (Program Structure Interface) in IDEA plugins.

What is PSI – PSI stands for Program Structure Interface, a layer in the IDEA platform that parses files and creates syntax and semantic models, enabling operations on project files.

PsiFile – The root of all file content structures; all file‑related operations are performed on a PsiFile.

There are five ways to obtain a PsiFile object in the official documentation:

From an event: e.getData(LangDataKeys.PSI_FILE);

From a virtual file: PsiManager.getInstance(project).findFile();

From a document: PsiDocumentManager.getInstance(project).getPsiFile();

From an element in the file: psiElement.getContainingFile();

By file name in the project: FilenameIndex.getFilesByName(project, name, scope);

Creating a file in an IDEA project results in a FileTest.java file, initially empty and marked as a non‑compilable Java file.

PsiJavaFile – If the PsiFile represents a Java file, it can be cast to a PsiJavaFile , which contains package statements, import lists, and classes.

PsiClass – Represents a class in a Java file; operations on the class (e.g., generating code, adding annotations) are performed via PsiClass. Right‑click → Generate shows many class‑related actions.

Adding an annotation to a class requires wrapping the write operation in WriteCommandAction.runWriteCommandAction() . After adding the annotation, the IDE may flag missing imports, which can be resolved by invoking the import‑assist feature.

PsiField – Used to manipulate class fields. Fields can be added, and annotations can be attached to them. Annotation parameters are set via PsiAnnotation.setDeclaredAttributeValue() .

Creating PSI expressions for annotation parameters can be done using the PSI factory methods (illustrated in the article).

PsiMethod – Similar to PsiField, methods are manipulated via PsiMethod objects (not detailed here).

PsiType – Handles the data types of fields, including primitive, array, collection, and reference types. For reference types, one must retrieve the class’s fields and their default values.

Conclusion – The article covered essential PSI components used in IDEA plugin development, providing code snippets and screenshots to illustrate each step.