Setting the content type to text/plain for a JSON response from a Spring controller
I was using a jQuery plugin called a ajaxfileupload to upload a file through AJAX. Technically what the plugin does isn’t AJAX. It creates a hidden form and an iframe, and then submits the form using the iframe as the target. The iframe will then end up with the response from the server. This response is then read-in by the plugin and handled appropriately. In my case I was using a controller action that would return JSON (using the .action extension). The action uses Spring’s MappingJacksonJSONView that returns JSON with a content type of application/json (as it should). This works perfectly in Chrome, however in both Firefox and IE, the user is presented with a dialog box that asks them to download the JSON response. This is obviously not what I wanted. The reason this is happening is because the response is being directly submitted to the iframe (and therefore, the page). That is, it’s not coming through via the XMLHttpRequest object. So IE and FF don’t know what to do with it and assume that it is something the user would want to download. The solution to this problem is to set the content-type to text/plain. This wasn’t as straightforward as I thought it would be.
Initially I was going to call the render(…) method of MappingJacksonJsonView but that didn’t work because the content-type had already been set to application/json. The solution I came up with was to duplicate some of the code (ugh) inside MappingJacksonJsonView to get the JSON as a string and to then write that to the response:
@RequestMapping
public void processFileUpload(HttpServletResponse response, Model model, ...) {
...
//Set the content-type and charset of the response
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
//I need to use another OutputStream here; I cannot use the response's OutputStream because that will cause errors
//later on when the JSP needs to render its content (recall that getOutputStream() can only be called exactly once
//on a response). Therefore I'm writing the data to a ByteArrayOutputStream and then writing the byte array from
//the ByteArrayOutputStream to the response manually.
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
ObjectMapper objectMapper = new ObjectMapper();
JsonGenerator generator = objectMapper.getJsonFactory().createJsonGenerator(byteArrayOutputStream, JsonEncoding.UTF8);
//Before I can convert the data into JSON, I will need to filter some attributes out of the model (namely BindingResult)
Map<String, Object> result = new HashMap<String, Object>();
for(Map.Entry<String, Object> entry : model.asMap().entrySet()) {
if(!(entry.getValue() instanceof BindingResult)) {
result.put(entry.getKey(), entry.getValue());
}
}
objectMapper.writeValue(generator, result);
response.getWriter().write(new String(byteArrayOutputStream.toByteArray(), "UTF8"));
}
This still seems a little hacky to me. A possible improvement is to annotate the action with @ResponseBody and return the JSON as a string without involving the response at all. If anyone has a better solution, I’m all ears!
Popularity: 3% [?]
Implementing JSONP in Spring MVC 3.0.x
In Spring 3, it’s very easy to get a view to return JSON. However, there is no built-in mechanism to return JSONP. I was able to find a pretty good tutorial That uses Spring’s DelegatingFilterProxy. I implemented this solution and I got it to work, but I didn’t like the fact that I had to create a separate filter and a bunch of other classes just for that. I also wanted to use a specific extension (.jsonp) for JSONP just to make it more explicit. Spring uses MappingJacksonJsonView to return JSON. I figured that I could extend this view and have it return JSONP instead of JSON.
Read more »
Popularity: 14% [?]
About Me and Projects
I finally got around to adding pages to my blog. I’ve added an “About Me” page and a “Projects” page. The “Projects” page is similar to the one I had on the old site. I’ve migrated one project (Sulekha) over. Will be moving the second one (FXCalendar) over soon and I’m also going to try and add another one to the list.
Popularity: unranked [?]
An update to running aterm (or any other X app) rootless, without a DOS console on Cygwin
A while ago, I wrote up a quick guide about running X/Windows applications (specifically, aterm) without root windows on Windows, using Cygwin. Recently I tried to set it up again and I realized that some of the information is slightly out of date. I’m also endeavoring to write a better guide. I’m assuming that you have, at the very least, a decent understanding of building things from source. The process under Cygwin is pretty much the same as under any other *nix, but there are a few quirks. On the whole, it’s a whole lot easier than it used to be. This guide is primarily geared towards running aterm with a transparent background on a windows machine so that you can have a decent client for the Cygwin commandline, instead of the crappy Windows one.
I’m assuming that you already have Cygwin installed. If you don’t, you can get it from here. In addition to whatever other packages you have selected to customize your install, you also need development packages (gcc and friends), Xorg packages (headers, includes, and libraries), and a few graphics libraries (for aterm):
- Devel
- gcc-core
- gcc-g++
- libXaw3d-devel (for xv)
- libjpeg-devel (for aterm)
- libpng12-devel (for aterm)
- Libs
- jpeg (for aterm)
- libXaw3d-devel
- libXaw3d-7
- libfreetype6
- libjpeg-devel
- libjpeg62 (for aterm)
- libjpeg6b (for aterm)
- libpng12 (for aterm)
- libpng12-devel (for aterm)
- libtiff5 (for aterm, xv)
- zlib-devel (for aterm)
- zlib0 (for aterm)
- Utils
- bzip2 (to handle .bz2 files)
- X11
- libX11-devel
- xinit
- xsetroot (if xv doesn’t work for you)
After Cygwin finishes installing those packages, grab the sources for libAfterImage, aterm, and xv. Unpack the sources perform the requisite steps to build and install from source (./configure, make, and make install should work if all goes well).
libAfterImage:
If you get “parse error before XErrorEvent” errors while building libAfterImage, make sure that you didn’t forget to select the X11 development package.
aterm:
gcc on Cygwin expects –rdynamic and not -rdynamic. If you’re seeing these errors, edit the Makefiles under src and src/graphics within the aterm source directory. Change the “-rdynamic” to “–rdynamic”. The changes should be on line 54 for both files.
xv:
Under the tiff directory within the xv sources, there is a file called RANLIB.csh. Edit this file and make sure that you ONLY have the following line in there:
ranlib $1 >& /dev/null
Otherwise the build process will fail. Additionally, you need to edit xv.h. This file lives right at the root of your xv source directory. If you do not perform the following change, you’ll get errors from gcc complaining that “sys_errlist has previously been defined”. Change line 119 of xv.h to:
/*extern char *sys_errlist[]; */ /* this too... */
What you’re doing is commenting out the definition for sys_errlist so that it doesn’t conflict with what has already been defined in the Cygwin header files. These changes should be the only ones you need to get xv compiling and running.
Now you need to set up two batch files. One to start up X rootlessly, and another to start up aterm. Before you do that, make sure you add C:\cygwin\usr\bin and C:\cygwin\X11R6\usr\bin to your PATH variable. You can do this by going to My Computer > Properties > Advanced > Environment Variables. If you don’t do this, you’ll get “cygwin1.dll not found” errors while trying to run these batch files. The X windows binaries used to live in C:\cygwin\usr\X11R6\bin, but have since been moved to C:\cygwin\usr\bin. Therefore, the start-up batch-file now looks like this:
xwin.bat:
C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\usr\bin\xwin.exe -multiwindow -clipboard -silent-dup-error C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\usr\local\bin\xv.exe -display :0 -root -quit -be -max /cygdrive/c/Documents\ and\ Settings/vivin/My\ Documents/My\ Pictures/Wallpapers/01707_spectrumofthesky_1920x1200.jpg
The first line starts up the X windowing system. The second line sets the wallpaper using aterm. You now need another batch file to run aterm, and that looks like this:
aterm.bat
C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\bin\bash.exe --login -i -c "aterm -sh 80 -tr -trsb -fade 20 -tint gray -sb -st -sr -sl 1000 -tn xterm"
This file starts aterm with the background image at 50% brightness, transparent background, transparent scrollbar, 20% fading on losing focus, gray tint, scrollbar, trough-less scrollbar, scrollbar on the right, 1000 scrollback lines, and with xterm terminal emulation. Like I mentioned in my original guide. xv will sometimes fail to start with xwin. If that is the case, you can modify aterm.bat to look like this:
aterm.bat:
C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\bin\bash.exe --login -i -c "xv -display :0 -root -quit -be -max /cygdrive/c/Documents\ and\ Settings/vivin/My\ Documents/My\ Pictures/Wallpapers/01707_spectrumofthesky_1920x1200.jpg &amp;amp;amp;&amp;amp;amp; aterm -sh 80 -tr -trsb -fade 20 -tint gray -sb -st -sr -sl 1000 -tn xterm"
Slightly inefficient, but it works. Now if you have a dual-monitor display, you’ll notice that the background image is stretched across both screens when you run aterm. This is probably not what you want. To fix this problem you need to change a few invocation options for xv. For this to work properly (meaning, not look crappy) both screens should be running at the same resolution:
xv -display :0 -root -quit -be -maxpect -rmode 1 /cygdrive/c/Documents\ and\ Settings/vivin/My\ Documents/My\ Pictures/Wallpapers/01707_spectrumofthesky_1920x1200.jpg
Notice the -maxpect and -rmode 1 options. -maxpect expands the image to fill the screen while maintaining the aspect ratio, while -rmode 1 sets the display mode on xv to tiled. So you should now have your wallpaper displaying on both screens now (under X) without being distorted.
Here’s what it looks like on my machine:
This is on a dual-monitor setup with both screens running at 1920×1200 resolution. I’ve set X’s background to be the same as my windows Wallpaper so that it looks cooler. Notice how the background image (inside aterm) is not stretched, but tiled across the two screens. That’s all there is to it. Seems like a bit of work, but I think it’s worth it. My main reason for going through all this trouble was to get a decent terminal running in windows. I guess I could have just used xterm, but aterm looks so much nicer, doesn’t it?
Popularity: 7% [?]
Running aterm (or any other X app) rootless, without a DOS console on Cygwin
This guide is outdated. Please check out the updated version of this guide here.
On any system that I plan to use for an extended period of time, I will always install Cygwin. This is mainly because I like have UNIX tools on Windows, and also so that I can use the console to do things that DOS is not able to do. I started using Cygwin in 2000, and I’ve continued using it since. One of the cool things you can do with Cygwin is run X, which means that you can have X applications running on the Windows desktop. When I was interning at Motorola, I used to run eXceed, with fvwm. This was where I first ran into aterm. What I liked most about aterm is the eye-candy. You can have transparent windows with shading effects and all sorts of other cool stuff. I tried to get aterm running on my machine at home by compiling it from source under Cygwin. I was eventually able to do this (install libjpeg, libpng, libAfterImage, zlib, and the X includes and libraries first), but what I didn’t like was the fact that you had to start up a Cygwin console to open up X, and then aterm. I wanted aterm to start up and run directly without that ugly DOS/Cygwin console window. Of course, you can’t simply run the aterm executable because it needs X and Cygwin to be running. I eventually figured it out (actually a few months before leaving on my “extended vacation”) by starting out with X running with a rootless window. Oh, and run.exe proved to be very helpful. Anyway, here is how you do it:
First you need to add C:\cygwin\bin to your PATH Environment Variable. You can do this from My Computer > Properties > Advanced > Environment Variables. You might also have to add C:\cygwin\usr\X11R6\bin to PATH.
Then you need to create two batch files. The first one is to start X, and the second one is to start aterm (or whatever X app you want to start). The example I’m going to show includes starting up X with a wallpaper (using xv), and then running aterm. I run aterm with a transparent background, using the X wallpaper. However, you can also load aterm with a background image of your choice.
The batch file to start X, which I call xwin.bat looks like this:
C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\usr\X11R6\bin\xwin.exe -multiwindow -clipboard -silent-dup-error C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\usr\local\bin\xv.exe -display :0 -root -quit -be -maxpect /cygdrive/c/Wallpapers/upper_limit_wp_dark_1600.jpg
This will start up X in a rootless window with upper_limit_wp_dark_1600.jpg as your X wallpaper. Next, you write a batch file (aterm.bat) that will load aterm:
C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\bin\bash.exe --login -i -c "aterm -sh 50 -tr -trsb -fade 20 -tint gray -bl -sb -st -sr -sl 1000 -tn xterm"
This batch file will load aterm with the background image at 50% brightness, transparent background, transparent scrollbar, 20% fading on losing focus, gray tint, borderless window (sometimes works), scrollbar, trough-less scrollbar, scrollbar on the right, 1000 scrollback lines, and with xterm terminal emulation. One issue I have had with this, is that aterm may load up with the default (checkered) X background. This is because the xv did not properly execute in xwin.bat. I have no idea why this happens, sometimes it works, and sometimes it doesn’t. If it doesn’t, you can modify aterm.bat:
C:\cygwin\usr\X11R6\bin\run.exe C:\cygwin\bin\bash.exe --login -i -c "xv -display :0 -root -quit -be -max /cygdrive/c/Wallpapers/upper_limit_wp_dark_1600.jpg && aterm -sh 50 -tr -trsb -fade 20 -tint gray -bl -sb -st -sr -sl 1000 -tn xterm"
This batch file will load xv every time you start aterm, so there is a slight performance hit on startup. However, it’s not that big of a deal because the xv instance quits right after it sets up the wallpaper, and so you’re not loading a new instance of xv into the memory every time.
Well, there you have it. I hope it was helpful!
Screenshot of my XP desktop, with aterm, xcalc, xclock, xeyes, and xterm running
Popularity: 28% [?]
Google Talk/Google IM
Google has come out with their instant messaging program. This seems to be unofficial; the only mentions I can see are on this Slashdot article, and the website I linked to.
You should be able to get it to work using any Jabber client. I’ve been trying to get it to work on Trillian, but I’ve been having some trouble. I’ve set my username as [my gmail id]@gmail.com and the server as talk.google.com. Trillian authenticates, but then quits after receiving “iq errors”:
[Tuesday, August 23, 2005 - 17:04:55] *** Creating connection "[my gmail id]@gmail.com/" [Tuesday, August 23, 2005 - 17:04:56] *** Server supports TLS encryption... [Tuesday, August 23, 2005 - 17:04:56] *** Negotiating XMPP SSL connection... [Tuesday, August 23, 2005 - 17:04:57] *** Connection established using EDH-RSA-DES-CBC3-SHA (TLSv1/SSLv3) [Tuesday, August 23, 2005 - 17:05:05] *** Attempting to authenticate using PLAIN [Tuesday, August 23, 2005 - 17:05:06] *** Authenticated. [Tuesday, August 23, 2005 - 17:05:15] *** You have successfully connected to Jabber. [Tuesday, August 23, 2005 - 17:05:15] *** ERROR: iq error 501 [Tuesday, August 23, 2005 - 17:05:15] *** Retrieved user roster from server. [Tuesday, August 23, 2005 - 17:05:16] *** ERROR: iq error 501 [Tuesday, August 23, 2005 - 17:05:16] *** ERROR: iq error 503 from gmail.com [Tuesday, August 23, 2005 - 17:05:16] *** ERROR: iq error 503 from gmail.com
If anyone has had anymore success, please let me know. I’m not sure how popular this is going to be; people usually tend to stay within a particular “IM clique” (with AIM, MSN Messenger, and Yahoo! Chat being the major players). I use Trillian so that I can talk people in any one of these “cliques”.
This ends months of speculation and rumours about Google’s foray into the IM arena. I wonder what’s next?
UPDATE #1
I tried it again, this time with “Trillian” in the “Resource” field, no luck – Trillian still loses connection to the server. It comes up with a bunch of “Connection lost to server” errors.
[Tuesday, August 23, 2005 - 17:44:00] *** Creating connection "[my gmail id]@gmail.com/Trillian" [Tuesday, August 23, 2005 - 17:44:01] *** Server supports TLS encryption... [Tuesday, August 23, 2005 - 17:44:01] *** Negotiating XMPP SSL connection... [Tuesday, August 23, 2005 - 17:44:02] *** Connection established using EDH-RSA-DES-CBC3-SHA (TLSv1/SSLv3) [Tuesday, August 23, 2005 - 17:44:10] *** Attempting to authenticate using PLAIN [Tuesday, August 23, 2005 - 17:44:16] *** Authenticated. [Tuesday, August 23, 2005 - 17:44:21] *** Connection lost to server. [Tuesday, August 23, 2005 - 17:44:21] *** Connection lost to server. [Tuesday, August 23, 2005 - 17:44:21] *** Connection lost to server. [Tuesday, August 23, 2005 - 17:44:21] *** Connection lost to server. [Tuesday, August 23, 2005 - 17:44:22] *** Connection lost to server. [Tuesday, August 23, 2005 - 17:44:22] *** Connection lost to server. [Tuesday, August 23, 2005 - 17:44:22] *** Connection lost to server.
UPDATE #2
I found this site that has instructions on getting Google IM to work through Jabber on Trillian. It has the same settings that I use, but they claim to have gotten it to work; although I see the same “Connection lost to server” errors on their status window as well. I also noticed that their status window shows the authentication being done with “username@talk.google.com” as oppsed to “username@gmail.com”, which is what I’m seeing.
UPDATE #3
Success (sort of)! It works now – I didn’t do anything different, I tried disconnecting and reconnecting, and now the connection seems to be stable. However, I’m unable to add anyone, or IM them. I tried adding myself, but was unable to do so. I’ll keep playing around anyway… Here are a few screenshots:
UPDATE #4
It looks like it’s working now – I still lose connection occasionally, but it seems much more stable than before. I have also been able to add people and IM them.
Popularity: 1% [?]
Firefox hits 50 million downloads!
Firefox, the Open Source browser has hit 50 million downloads! Absolutely amazing!
I remember when I used to use Internet Explorer because I didn’t think there were any good browsers out there. I also remember when I even flamed Mozilla (I knew this would bite me in the ass later), but that was because this guy I didn’t like, who I used to work with, used it and it was kinda like a “guilty by association” thing. But anyway, this right here, is really noteworthy. I don’t think any other Open Source project has even grabbed the attention of your every day computer user as much as Firefox has.
Ever since I downloaded Firefox I’ve had a markedly better browsing experience. No pop-ups, no browser hijacks, and tabbed browsing! I don’t even know how I got along without it! Firefox wins hands down over IE with its simplicity, speed, functionality and inuitive browsing experience. Why don’t you Open Source critics take a look at this? If they think Open Source can’t produce anything worthwhile, they should take a look at this. This is what Open Source can achieve. Firefox is well on its way to being a household name.
Congratulations to the Firefox team! Also, if you don’t have Firefox, go and get it now!
Popularity: 1% [?]