How to manually render Spring MVC view to html?

Question

Is it possible to render my view into html in my controller mapping method, so that i can return the rendered html as a part of my json object ?

Example of my usual controller method :

@RequestMapping(value={"/accounts/{accountId}"}, method=RequestMethod.GET)
public String viewAcc(final HttpServletRequest req, 
        final HttpServletResponse resp, final Model model,
        @PathVariable("accountId") final String docId) {

    // do usual processing ...

    // return only a STRING value, 
    //   which will be used by spring MVC to resolve into myview.jsp or myview.ftl
    //   and populate the model to the template to result in html
    return "myview";
}

What i expect :

@RequestMapping(value={"/accounts/{accountId}"}, method=RequestMethod.GET)
public String viewAcc(final HttpServletRequest req, 
        final HttpServletResponse resp, final Model model,
        @PathVariable("accountId") final String docId) {

    // do usual processing ...

    // manually create the view
    ModelAndView view = ... ? (how)

    // translate the view to the html
    //   and get the rendered html from the view
    String renderedHtml = view.render .. ? (how)

    // create a json containing the html
    String jsonString = "{ 'html' : " + escapeForJson(renderedHtml) + "}"

    try {
        out = response.getWriter();
        out.write(jsonString);
    } catch (IOException e) {
        // handle the exception somehow
    }

    return null;
}

I wonder what is the right way to create the view and render the view into html manually within the controller method.

Update

Here's the working example from the accepted answer's guidance :

View resolvedView = thiz.viewResolver.resolveViewName("myViewName", Locale.US);
MockHttpServletResponse mockResp = new MockHttpServletResponse();
resolvedView.render(model.asMap(), req, mockResp);
System.out.println("rendered html : " + mockResp.getContentAsString());

Answer 1

Try autowiring the ViewResolver then calling resolveViewName("myview", Locale.US) to get the View.

Then call render() on the view, passing it a "mock" HTTP response that has a ByteArrayOutputStream for its output, and get the HTML from the ByteArrayOutputStream.

Update

Here's the working example, copied from the question. (so the code is actually with the answer)

View resolvedView = thiz.viewResolver.resolveViewName("myViewName", Locale.US);
MockHttpServletResponse mockResp = new MockHttpServletResponse();
resolvedView.render(model.asMap(), req, mockResp);
System.out.println("rendered html : " + mockResp.getContentAsString());

Answer 2

If you want to render the view under the same locale as the DispatcherServlet would render it, try coping it's render-method:

/** LocaleResolver used by this servlet */
private LocaleResolver localeResolver;

/** List of ViewResolvers used by this servlet */
private List<ViewResolver> viewResolvers;

/**
 * Render the given ModelAndView.
 * <p>This is the last stage in handling a request. It may involve resolving the view by name.
 * @param mv the ModelAndView to render
 * @param request current HTTP servlet request
 * @param response current HTTP servlet response
 * @throws ServletException if view is missing or cannot be resolved
 * @throws Exception if there's a problem rendering the view
 */
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
    // Determine locale for request and apply it to the response.
    Locale locale = this.localeResolver.resolveLocale(request);
    response.setLocale(locale);

    View view;
    if (mv.isReference()) {
        // We need to resolve the view name.
        view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
        if (view == null) {
            throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
                    "' in servlet with name '" + getServletName() + "'");
        }
    }
    else {
        // No need to lookup: the ModelAndView object contains the actual View object.
        view = mv.getView();
        if (view == null) {
            throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
                    "View object in servlet with name '" + getServletName() + "'");
        }
    }

    // Delegate to the View object for rendering.
    if (logger.isDebugEnabled()) {
        logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
    }
    try {
        view.render(mv.getModelInternal(), request, response);
    }
    catch (Exception ex) {
        if (logger.isDebugEnabled()) {
            logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +
                    getServletName() + "'", ex);
        }
        throw ex;
    }
}

/**
 * Resolve the given view name into a View object (to be rendered).
 * <p>The default implementations asks all ViewResolvers of this dispatcher.
 * Can be overridden for custom resolution strategies, potentially based on
 * specific model attributes or request parameters.
 * @param viewName the name of the view to resolve
 * @param model the model to be passed to the view
 * @param locale the current locale
 * @param request current HTTP servlet request
 * @return the View object, or {@code null} if none found
 * @throws Exception if the view cannot be resolved
 * (typically in case of problems creating an actual View object)
 * @see ViewResolver#resolveViewName
 */
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
        HttpServletRequest request) throws Exception {

    for (ViewResolver viewResolver : this.viewResolvers) {
        View view = viewResolver.resolveViewName(viewName, locale);
        if (view != null) {
            return view;
        }
    }
    return null;
}

It should usually be sufficient to add @Autowired to the fields on top, but the DispatcherServlet also employs a fallback when autowiring would fail.

Answer 3

you can use templating library for creating html, Velocity for example. Then, you need to define return type as

public @ResponseBody SomeObject viewAcc(...) {...}

and the object itself can obtain the html, as well as some other variables