I'm using a custom GWT component that wraps around an existing textbox in my HTML page.
The page returns a list of information - so as larger sets of information are loaded - the GWT loading process takes longer and longer.
Looking at the source code of the wrap() method - it appears it iterates through the DOM looking for matching ids.
Isn't this unnecessary? Is there a way to make it just iterate to my component and then stop?
GWT does a bunch of DOM house keeping and you are just not going to get around it easily or at all.
It sounds like there's a point at which you have so many text inputs that you need to rethink how you're approaching this anyway. Dynamically creating inputs fields in a form panel in GWT is pretty easy and fast, and you can very simply and quickly download a json structure with the data you need for the input fields in your original html page load, convert it to a dictionary or simple array in GWT and , use it to populate your form.
Once done, you can clear the pointer to the data so it will GC'd if you don't need it any longer.
To access data in javascript look at creating a native method, its very easy to do. If it makes sense, you can format the json data as a dictionary and GWT's dictionary class will map directly to it.
I use these techniques all the time and they are robust and pretty much as fast as javascript can populate the DOM.
Related
I am preparing to embark on a large solo project at my place of employment. First let me describe the project. I have been asked to create a Java program that can take a CamT54 file (which is just a xml file) and have java display the information in table form. Then users should be given the ability to remove certain components from the table and have it go back to xml format with the changes.
I'm not well versed in dealing with XML in Java so this is going to be a learn and work task. Before I begin investing time I would like to know that my approach is the best approach.
My plan is to use DOM4J to do the parsing and handling of the xml. I will use a JTable to display the data and incorporate some buttons to the GUI that allow the modifications of the data through the use of some action listeners.
Would this be a plausible plan? Can DOM4J effectively allow xml data to be displayed in a table format and furthermore could that data be easily modified or deleted then resaved to a new xml?
I thought I would go ahead and answer this as I finished the program and wanted to post what I thought was the easiest solution in case anyone else needed help.
It turned out the easiest approach (for me at least) was to use the standard DOM parser, here are the steps I took.
Parsed the entire XML into String array lists. XPath was required for this, I also had to convert the elements into Strings and remove the extra tag information from the string using substrings since I only wanted the actual value.
I populated a JTable with these arrays.
Once users finished editing and clicked a save button then another Dom parser would take the original XML and change each and every attribute using the values from the Arrays (that were deleted and repopulated with the JTable cell values when the user clicked "save").
Heres what i want to do. Im quite a beginner with this so maybe a lame question, But, I want to implement gui application in java wich gets data from sports livescore pages
e.g
http://www.futbol24.com/Live/
http://livescore.com/
and parse it (somehow) in my app...and then i will be able to store it in for example jtable ,save full time results in database,playing sounds after goal is scored and so on
What is the best way to do this ?
It would be almost impossible to parse an HTML document from a live web page and get specific information from it. If you did manage to work out exactly where in the document the data is, the page structure could change at any time. The scores might not even be in the HTML - they could be fetched by Javascript in the page.
I suggest you find an RSS feed of the information you want. Then you'll only have a nice, small piece of XML to parse. That's what it's for.
I am trying to create a java program that an detect changes in HTML elements on a web page. For example: http://timer.onlineclock.net/
With each passing second, the HTML elements of the clock change the source of the image they display. Is there anyway, using java, that I can EFFICIENTLY open a connection to this page, and be able to see when these elements change?
I have used HTMLUnit, but I decided that takes to long to load a page to be considered efficient enough.
The only way I know how to do it with a URL is to use a BufferedReader to read the page, and then use Regular Expressions to parse an HTML element within the source, but this would require me to "reload" the page every time that I want to see the properties of an element. Can anybody give me an suggetions on how I can detect these changes in a matter of milliseconds, without using much network resources?
Your best bet is to learn and use javascript instead of server-side java. Javascript program runs on the client side (ie: the web browser) as opposed to the server side.
Typical HTML document consists of elements (eg: text, paragraph, list items etc). With javascript you can create timer, action user's event accordingly and manipulate those elements.
http://www.w3schools.com/js/default.asp is probably a good introduction to javascript, I suggest you spend some time on it
The page in question appears to be a...Javascript digital clock.
If you want the current time, try new Date();.
If you want code to be called at a constant rate, try the Timer class. You can set a task to be called every second, which is the same frequency you will get by polling the page.
If you want to use the page as an external source of time, try the Network Time Protocol. http://en.wikipedia.org/wiki/Network_Time_Protocol It will provide much lower latency and is actually designed for this purpose.
I have a array of data which was generated due to some Actions in my previous actions
On submitting that page, Control will be redirecting to the second page,
IN the second page, I need to populate the array data into the Tables
( I want to use Javascript to populate this, No other means)
Problems which i am facing now
1) I cant read the Java array in the Java script ? (I am not sure how to pass the Java array to Javascript function)
2) Thought of implementing the Java script objects similar to the java objects, but there will be lot of over head
Can any one help me to over come this situation
I am using the BTT framework which is similar to Struts, for Javascript I am not using any frameworks
Thanks in advance
JSON would be a format to make the java-array accessible in javascript.
https://github.com/douglascrockford/JSON-java/blob/master/JSONStringer.java
too broad to answer, since specifics are missing. here are some generic steps.
Collect your stuff in JavaScript array
Have a hidden form field
while posting to server, set the value of hidden field to your array (in string format)
Read the hidden field content in server (posted form data)
Parse them (JSON is appropriate here)
Use them while preparing next page content as JS Array
I'm using json to pass data between the browser and a java server.
I'm using Json-lib to convert between java objects and json.
I'd like to strip out susupicious looking stuff (i.e "doSomethingNasty().) from the user input while converting from json to java.
I can imagine several points at which I could do this:
I could examine the raw json string and strip out funny-looking stuff
I could look for a way to intercept every json value on its way into the java object, and look for funny stuff there.
I could traverse my new java objects immediately after reconstitution from json, look for any fields that are Strings, and stripp stuff out there.
What's the best approach? Are there any technologies built for this this task that I tack tack on to what I have already?
I suggest approach 3: traverse the reconstructed Java objects immediately upon arrival, and before any other logic can act on them. Build the most restrictive validation you can get away with (that is, do white-listing).
You can probably do this in a single depth-first traversal of the object hierarchy that you retrieve from Json-lib. In general, you will not want to accept any JSON functions in your objects, and you will want to make sure that all values (numbers, strings, depth of object tree, ...) are within expected ranges. Yes, it is a huge hassle to do this well, but believe me, the alternative to good user-input validation is much, much worse. It may be a good idea to add logging for whenever you chop things out, to diagnose any possible bugs in your validation code.
As I understand you need to validate the JSON data coming into your application.
If you want to do white listing ("You know the data you expect and nothing else is valid"), then it makes sense to validate your java objects once they are created ("make sure not to send the java object to DB or back to UI in some way before validation is done).
In case you want to black listing of characters (you know some of the threat characters which you want to avoid"), then you can directly look at the json string as this validation would not change much over a period of time and even if it does, you only need to enhance one common place. For while listing iot would depend on your business logic.