Error while saving java file in IntelliJ.

I want to add code in Java file and save that file in background.
Below is the code that I am writing, But getting error "com.intellij.util.IncorrectOperationException: Must not change document outside command or undo-transparent action. See com.intellij.openapi.command.WriteCommandAction or com.intellij.openapi.command.CommandProcessor"

final String fieldSource = "public static final String abc = \"abc\";";
final String methodSource = "public static String getAbc() {return abc;}";
// add contents to class
PsiElementFactory elementFactory = PsiElementFactory.SERVICE.getInstance(project);
final PsiField newField = elementFactory.createFieldFromText(fieldSource, null);
final PsiMethod newMethod = elementFactory.createMethodFromText(methodSource, null); 

ApplicationManager.getApplication().runWriteAction(new Runnable() {

     @Override

    public void run() {
        try {
            javaFile.add(newField);
            javaFile.add(newMethod);
            CodeStyleManager.getInstance(project).reformat(javaFile);
            FileDocumentManager fileDocumentManager = FileDocumentManager.getInstance();
            Document document = fileDocumentManager.getDocument(javaFile.getVirtualFile());
            if (document != null) {
                fileDocumentManager.saveDocument(document);
            }
        }catch (Exception e)
        {
            sourceRootsList.append("error"+e.toString()).append("\n");
        }

    }
});

Kindly help how I can save Java file after adding code