Как загрузить новую версию файла с помощью WebScript?

Решение можно представить следующим образом:

public class CustomFileUploader extends DeclarativeWebScript {
    private static final String FIRM_DOC = "{http://www.firm.com/model/content/1.0}doc";
    private static final String FIRM_DOC_FOLDER = "workspace://SpacesStore/8caf07c3-6aa9-4a41-bd63-404cb3e3ef0f";

    private FileFolderService fileFolderService;
    private ContentService contentService;
    private NodeService nodeService;
    private SearchService searchService;

    protected Map<String, Object> executeImpl(WebScriptRequest req, Status status) {
        processUpload(req);
        return null;
    }

    private void writeContent(NodeRef node, FirmFile firmFile) {
        try {
            ContentWriter contentWriter = contentService.getWriter(node, ContentModel.PROP_CONTENT, true);
            contentWriter.setMimetype(firmFile.getFileMimetype());
            contentWriter.putContent(firmFile.getFileContent().getInputStream());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private NodeRef checkIfNodeExists(String fileName) {
        StoreRef storeRef = new StoreRef(StoreRef.PROTOCOL_WORKSPACE, "SpacesStore");
        ResultSet resultSet = searchService.query(storeRef, SearchService.LANGUAGE_LUCENE/*LANGUAGE_FTS_ALFRESCO*/, 
                "TYPE:\"firm:doc\" AND @cm\\:name:" + fileName.replaceAll(" ", "\\ ")+ "");

        int len = resultSet.length();
        if (len == 0) { 
            return null;
        }

        NodeRef node = resultSet.getNodeRef(0);
        return node;
    }

    private NodeRef createNewNode(FirmFile firmFile) {
        NodeRef parent = new NodeRef(FIRM_DOC_FOLDER);
        NodeRef node = createFileNode(parent, firmFile.getFileName());

        return node;
    }

    private void processUpload(WebScriptRequest req) {
        FormData formData = (FormData) req.parseContent();
        FormData.FormField[] fields = formData.getFields();

        for(FormData.FormField field : fields) {
            String fieldName = field.getName();
            if (fieldName.equalsIgnoreCase("firm_file") && field.getIsFile()) {
                String fileName = field.getFilename();
                Content fileContent = field.getContent();
                String fileMimetype = field.getMimetype();

                NodeRef node = checkIfNodeExists(fileName);

                // POJO
                FirmFile firm = new FirmFile(fileName, fileContent, fileMimetype, FIRM_DOC);
                if (node == null) {
                    node = createNewNode(firmFile);
                } 

                writeContent(node, firmFile);
            }
        }
    }

    private NodeRef createFileNode(NodeRef parentNode, String fileName) {
        try {
            QName contentQName = QName.createQName(FIRM_DOC);
            FileInfo fileInfo = fileFolderService.create(parentNode, fileName, contentQName);
            return fileInfo.getNodeRef();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public FileFolderService getFileFolderService() {
        return fileFolderService;
    }

    public void setFileFolderService(FileFolderService fileFolderService) {
        this.fileFolderService = fileFolderService;
    }

    public ContentService getContentService() {
        return contentService;
    }

    public void setContentService(ContentService contentService) {
        this.contentService = contentService;
    }

    public NodeService getNodeService() {
        return nodeService;
    }

    public void setNodeService(NodeService nodeService) {
        this.nodeService = nodeService;
    }

    public SearchService getSearchService() {
        return searchService;
    }

    public void setSearchService(SearchService searchService) {
        this.searchService = searchService;
    }
}

Модель контента должна иметь обязательный аспект cm:versionable:

<mandatory-aspects>
    <aspect>cm:versionable</aspect>
</mandatory-aspects>