Rough Book

random musings of just another computer nerd

Indenting XML and HTML from vim

vim has an awesome feature, using which you can pipe a range through an external command. This is pretty useful if you’re opening up an un-indented or poorly-indented XML or HTML file. If you want to indent your entire file, simply do the following:

:%!tidy -i -xml -q

The -i option tells tidy that it needs to indent the content, -xml tells tidy that the content is well-formed XML, and -q puts tidy into “quiet mode” where extraneous information is suppressed. You can also specify ranges like so:

:40, 74!tidy -i -xml -q

This indents content between lines 40 and 74 (both lines inclusive). You can also do:

:., .+50!tidy -i -xml -q

This indents the current line and the next 50 lines. You can also do the same for HTML:

:%!tidy -i -xml -q

You can of course, supply additional parameters to tidy to customize the indenting.

:%!tidy -i -q

Popularity: 1% [?]

January 17, 2012 Posted by | Computers, Programming and Development | , , , , | Leave a Comment

Implementing pinch-zoom and pan/drag in an Android view on the canvas

I was trying to get pinch-zoom and panning working on an Android view today. Basically I was trying to implement the same behavior you see when you use Google Maps (for example). You can zoom in and pan around until the edge of the image, but no further. Also, if the image is fully zoomed out, you can’t pan the image. Implementing the pinch-zoom functionality was pretty easy. I found an example on StackOverflow. I then wanted to implement panning (or dragging) as well. However, I wasn’t able to easily find examples and tutorials for this functionality. I started with this example that comes from the third edition of the Hello, Android! book but I didn’t get too far. So I started playing around a little bit with the events and started writing some code from scratch (using the example from Hello, Android!) so that I could have a better idea of what was happening.

As I mentioned before, getting zoom to work was pretty easy. Implementing panning/dragging was the hard part. The major issues I encountered and subsequently fixed were the following:

  1. Panning continues indefinitely in all directions.
  2. When you zoom and then pan, stop, and then start again, the view jerks to a new position instead of panning from the existing position.
  3. Excessive panning towards the left and top can be constrained, but panning towards the right and bottom is not so easily constrained.

Once I fixed all the problems, I figured that it would be nice to document it for future reference, and I also think it would be a useful resource for others who have the same problem. Now a little disclaimer before I go any further: I’m not an Android expert and I’m really not that great with graphics; I just started it learning to program for Android this semester for one of my Masters electives. So there might be a better way of doing all this, and if there is, please let me know! Also, if you want to skip all the explanations and just see the code, you can skip to the last page.

Read more »

Popularity: 9% [?]

December 4, 2011 Posted by | Android, Java, Operating Systems, Programming and Development, Software | , , , , , , , , , , , | 4 Comments

Akṣi: Handwritten-digit-recognizing neural-network

I’ve always been interested in Neural Networks (ever since I first found out about them around 10 years ago). However, I never got a chance to learn about them or write one of my own; this is something I’ve wanted to do for some time. I got the opportunity this semester when my professor in my advanced data-structures class told us that we could pick any topic we liked, for a semester project. I thought that this would be the perfect time for me to learn about neural networks and create one of my own.

The end result was Akṣi, a neural network that recognizes hand-written digits. I’ve hosted it using Google’s App Engine. Please check it out!

Popularity: 1% [?]

November 24, 2011 Posted by | Java, Programming and Development, Science | , , , | Leave a Comment

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: 2% [?]

November 7, 2011 Posted by | Computers, Java, Nerdy Stuff, Software, Web | , , , , , , , , | Leave a Comment

Popularity Contest WordPress plugin breaks RSS feed

I’m using a somewhat old plugin (it hasn’t been updated since ’09) called Popularity Contest to show the popularity of my posts. However, I noticed that it was breaking my RSS feed. This is due to the fact that the plugin doesn’t properly escape the ampersand character inside an image URL. Instead of &#38; it uses just &. You can fix this by changind line number 2272 to:

$str .= '<img src="'.site_url('?ak_action=api_record_view&#38;id='.$post->ID.'&#38;type=feed').'" alt="" />';

Popularity: 2% [?]

October 23, 2011 Posted by | PHP, Programming and Development, Web | , , , | Leave a Comment

Fixing Maven 3.0.3′s dependency-resolution performance-regression

TL; DR; version: Maven 3.0.3 has a performance-regression while resolving dependencies. This is because it uses version 1.11 of aether. The problem has been fixed in version 1.12 of aether, but a version of maven with this library is not available. I built maven from source with the 1.12 version of aether, so use maven-3.0.3-with-aether-1.12.zip if you have the same problem.

The whole story: At work we use Maven to build our project. Over the last few months, we started noticing a disparity in build times between different developers even though the hardware they were using was similar to each other (Core i7′s with 6 Gb RAM). Initially we suspected that it might have to do with SSD performance-degradation. Some of us were using SSD’s that didn’t support TRIM and others didn’t have TRIM enabled. I was one of the few with the former problem. I secure-erased my drive but still saw no performance benefits. I even got a new drive and even with that I didn’t see much of an improvement either.

We finally realized that the build-time disparity was related to the version of maven some developers were using. On maven 3.0b1, build times are much faster compared to 3.0.3. In 3.0.3 there is a performance regression when maven tries to build the dependency graph. For example, using 3.0b1 our project built in 3 minutes and 30 seconds, whereas using 3.0.3, the build times were upwards of 9 minutes. Long build-times take away from the amount of productive coding-time a developer has.

I was determined to find the reason for this performance regression and did some investigation by looking at the source for 3.0b1 and 3.0.3. In 3.0b1, maven uses its own code to resolve dependencies and build the dependency graph, whereas in 3.0.3 it uses the aether library. For more background information on the matter, take a look at this post on the maven developer’s mailing list and this JIRA issue.

Long story short, to get better build times, maven needs to use version 1.12 of aether. I downloaded the maven source and edited the pom.xml file to use version 1.12 of aether. I then built maven from source and got a deployable version that uses the newer aether library. When I tested it out, the build times were comparable to 3.0b1.

I initially thought that version 3.0.4 of maven would include version 1.12 of aether. But it turns out that there were licensing changes and so the maven developers are discussing whether to include it. In the meantime, you can use this version of maven that I built from source, which includes version 1.12 of aether. It’s a zip file and you can install it like you would normally install maven.

Popularity: 3% [?]

July 20, 2011 Posted by | Computers, Java, Nerdy Stuff, Programming and Development | , , , , , , | Leave a Comment

Generating API Documentation from XML using XSLT

I work at Infusionsoft, and we offer our customers API access. Visibility and access to the various tables and their fields is controlled by an XML file on our end. Naturally, our customers require user-friendly documentation that tells them what tables and fields they can access and in what manner. Previously, a former developer had written a maven goal that would generate the API documentation from the XML file. Unfortunately this was something that he did on his own and the code wasn’t in our subversion repository. When that developer left, we decided to take a look at the code to see if we could continue generating the documentation using the maven goal. We determined that the original solution though helpful, involved a lot of work in Java simply to generate API documentation. This was when I suggested using XSLT as it would be a remarkably lightweight solution and it is also perfectly suited to this task. My colleagues agreed and so I decided to go ahead with the task. There was one slight problem though. I had very little experience with XSLT! But how hard could it be? I love learning new things anyway!
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Popularity: 4% [?]

July 9, 2011 Posted by | Computers, Nerdy Stuff, XML, XSLT | , , , , | 5 Comments

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.
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Popularity: 9% [?]

July 1, 2011 Posted by | Computers, Java, Nerdy Stuff, Programming and Development, Software, Web | , , , , , | 13 Comments

Integrating Regula with Spring 3.0.x MVC

A little less than a year ago, I released Regula, an annotation-based form-validation written in Javascript. The source and documentation are available on GitHub. I started working on the integration on and off throughout most of last year. At the end of the year, I had a pretty good integration going, where you could annotate fields with Hibernate Validator annotations, and the corresponding Regula validation-code would be generated on the client side. Of course, I wasn’t done yet because what I had was simply a demo project and I had to figure out a good way to distribute the whole thing; I was able to finish up the packaging and distribution today. With minimal setup, you should be able to get started with Regula and Spring. You don’t need to go through this post to figure out how to use the integration. This post is mostly about how I accomplished the integration (I don’t go into all the details; just the important bits). As far as actually using it, I will make a blog post about it later.

The source for the integration is also hosted on GitHub. My approach towards translating validation constraints from the server-side to the client-side was two-fold: gather validation constraints from the object and represent it in a canonical form. Using the canonical form, generate Javascript code that uses Regula for validation. To do this, I created a service that examines a domain object and gathers all information regarding its properties and validation constraints. The service returns this information in a canonical form, that I then inserted into the model. On the client-side, I had a tag that used the canonical form and outputted Javascript that uses the Regula framework. Initially, I was calling the service explicitly from an action in the controller. Later, in an effort to make the integration less-invasive and more seamless, I used an aspect-oriented approach with interceptors. In fact, that’s where I’d like to start.
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Popularity: 6% [?]

February 21, 2011 Posted by | Computers, Java, Programming and Development, Web | , , , , , , , , , , , , , , | 1 Comment

Packaging and distributing taglibs in a JAR

This is more of a “note to self” than a “how to”.

If you’re trying to distribute tag files in a JAR, you need to put them under /META-INF/tags. You then need to create a TLD file that you also put under /META-INF/tags. If you have tags or functions that you created in Java, and want to distribute them alongside the tag files, you need to reference them in the TLD and package them in the same JAR (goes without saying).

If you want to do the same thing in maven, the location for the tag files and the tld file is different; you need to put them in src/main/resources/META-INF/tags. Then you can run mvn package and maven will create a JAR with your tags.
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Popularity: 5% [?]

February 21, 2011 Posted by | Computers, Java, Programming and Development, Web | , , , , , , , , | Leave a Comment

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