Recommended way to save uploaded files in a servlet application

I read here that one should not save the file in the server anyway as it is not portable, transactional and requires external parameters. However, given that I need a tmp solution for tomcat (7) and that I have (relative) control over the server machine I want to know :

Unfortunately the FileServlet by @BalusC concentrates on downloading files, while his answer on uploading files skips the part on where to save the file.

A solution easily convertible to use a DB or a JCR implementation (like jackrabbit) would be preferable.

Store it anywhere in an accessible location except of the IDE's project folder aka the server's deploy folder, for reasons mentioned in the answer to Uploaded image only available after refreshing the page:

It really doesn't matter to me or anyone else where exactly on the local disk file system it will be saved, as long as you do not ever use getRealPath() method. Using that method is in any case alarming.

The path to the storage location can in turn be definied in many ways. You have to do it all by yourself. Perhaps this is where your confusion is caused because you somehow expected that the server does that all automagically. Please note that @MultipartConfig(location) does not specify the final upload destination, but the temporary storage location for the case file size exceeds memory storage threshold.

So, the path to the final storage location can be definied in either of the following ways:

File uploads = new File("/path/to/uploads");

File uploads = new File(System.getenv("UPLOAD_LOCATION"));

File uploads = new File(System.getProperty("upload.location"));

File uploads = new File(properties.getProperty("upload.location"));

File uploads = new File(getServletContext().getInitParameter("upload.location"));

File uploads = new File(System.getProperty("jboss.server.data.dir"), "uploads");

Either way, you can easily reference and save the file as follows:

File file = new File(uploads, "somefilename.ext");

try (InputStream input = part.getInputStream()) {
    Files.copy(input, file.toPath());
}

Or, when you want to autogenerate an unique file name to prevent users from overwriting existing files with coincidentally the same name:

File file = File.createTempFile("somefilename-", ".ext", uploads);

try (InputStream input = part.getInputStream()) {
    Files.copy(input, file.toPath(), StandardCopyOption.REPLACE_EXISTING);
}

How to obtain part in JSP/Servlet is answered in How to upload files to server using JSP/Servlet? and how to obtain part in JSF is answered in How to upload file using JSF 2.2 <h:inputFile>? Where is the saved File?

Note: do not use Part#write() as it interprets the path relative to the temporary storage location defined in @MultipartConfig(location) .

See also:

I post my final way of doing it based on the accepted answer:

@SuppressWarnings("serial")
@WebServlet("/")
@MultipartConfig
public final class DataCollectionServlet extends Controller {

    private static final String UPLOAD_LOCATION_PROPERTY_KEY="upload.location";
    private String uploadsDirName;

    @Override
    public void init() throws ServletException {
        super.init();
        uploadsDirName = property(UPLOAD_LOCATION_PROPERTY_KEY);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // ...
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        Collection<Part> parts = req.getParts();
        for (Part part : parts) {
            File save = new File(uploadsDirName, getFilename(part) + "_"
                + System.currentTimeMillis());
            final String absolutePath = save.getAbsolutePath();
            log.debug(absolutePath);
            part.write(absolutePath);
            sc.getRequestDispatcher(DATA_COLLECTION_JSP).forward(req, resp);
        }
    }

    // helpers
    private static String getFilename(Part part) {
        // courtesy of BalusC : http://stackoverflow.com/a/2424824/281545
        for (String cd : part.getHeader("content-disposition").split(";")) {
            if (cd.trim().startsWith("filename")) {
                String filename = cd.substring(cd.indexOf('=') + 1).trim()
                        .replace(""", "");
                return filename.substring(filename.lastIndexOf('/') + 1)
                        .substring(filename.lastIndexOf('') + 1); // MSIE fix.
            }
        }
        return null;
    }
}

where :

@SuppressWarnings("serial")
class Controller extends HttpServlet {

    static final String DATA_COLLECTION_JSP="/WEB-INF/jsp/data_collection.jsp";
    static ServletContext sc;
    Logger log;
    // private
    // "/WEB-INF/app.properties" also works...
    private static final String PROPERTIES_PATH = "WEB-INF/app.properties";
    private Properties properties;

    @Override
    public void init() throws ServletException {
        super.init();
        // synchronize !
        if (sc == null) sc = getServletContext();
        log = LoggerFactory.getLogger(this.getClass());
        try {
            loadProperties();
        } catch (IOException e) {
            throw new RuntimeException("Can't load properties file", e);
        }
    }

    private void loadProperties() throws IOException {
        try(InputStream is= sc.getResourceAsStream(PROPERTIES_PATH)) {
                if (is == null)
                    throw new RuntimeException("Can't locate properties file");
                properties = new Properties();
                properties.load(is);
        }
    }

    String property(final String key) {
        return properties.getProperty(key);
    }
}

and the /WEB-INF/app.properties :

upload.location=C:/_/

HTH and if you find a bug let me know

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