Tutorial Step 2 Adding Client-side Validation in Java

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22 Tutorial Step 2 Adding Client-side Validation
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In this step of the tutorial, we use Dojo to provide basic client-side validationsWe look at a number of useful techniques within the context of making real enhancements to our form One by one, we examine the fields that these techniques are appropriate for
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22 Tutorial Step 2 Adding Client-side Validation
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221 Validate the First Name Field
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Let s look at the First Name field firstWhat are the validations that we need to apply The data on this form feeds into our billing system, so the customer s name is very important the field must be required Are there any other validations Not only do we want to get the data, but also we d like it to be in a consistent format Possibly the data should be stored in all capital letters Or maybe we want to ensure that the data is not in all capitals Let s choose the latter but we ll still want to make sure that at least the first letter is capitalized As in many of the issues related to validation, things are more complicated then they might first appear For example, are we allowing enough room to enter long names Will single-word names such as Bono be allowed For our purposes, we ll keep it simple We turn on validation by using special attribute values in the HTML markup for these fieldsThe following code will add validation to the fields
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<label for="firstName">First Name: </label> <input type="text" id="firstName" name="firstName" dojoType="dijitformValidationTextBox" required="true" propercase="true" promptMessage="Enter first name" invalidMessage="First name is required" trim="true" /><br>
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The code is formatted to be more readable by using line breaksTo summarize what has happened: All we ve done is add some new attributes to the <input> tag for the field Each of the new attributes affects the validation in some way Notice the following line of code from the preceding example:
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dojoType="dijitformValidationTextBox"
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This attribute is not a standard HTML <input> tag attribute Depending on which editor you are using to modify the file, it may even be highlighted as an errorThe dojoType attribute is only meaningful to the Dojo parser, which was referenced in step 1 Remember the code we needed to include the parser It is shown here:
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dojorequire("dojoparser");
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The parser reads through the HTML and looks for any tag that contains dojoType as one of its attributesThen the magic happensThe parser replaces the element with the Dojo widget specified by dojoType In this case, the widget dijitformValidationTextBox is substituted for the Document Object Model (DOM) element created from the <input> tag
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Using Dojo for Client-side Validation
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How does Dojo know what to replace the tag with That is determined by the specific widget Each widget behaves a little differently HTML markup and JavaScript code is associated with the widget in its definition, and that is how Dojo knows what to replace the original element with which brings us to the missing piece of the puzzle We need to tell Dojo to include the code for the widget by specifying the widget in JavaScriptTo do that, we include the following JavaScript code after the link to Dojo and after the reference to the Dojo parser
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dojorequire("dijitformValidationTextBox");
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Notice that the name of the widget specified as the value for the dojoType attribute is the same as the argument for the dojorequire callThis is the linkage that allows Dojo to associate the HTML markup with the JavaScript code for that widget To emphasize this process, let s review the HTML markup specified in the original page and then compare it to the HTML markup after the parser runsTo see the original markup, we merely have to view the source of the file formhtml Seeing the new markup is a bit harderThe browser converts the original HTML into a DOM tree representing the various tagsThe Dojo parser modifies the DOM elements using JavaScript, but the original source for the page is untouchedWe need some tool that will convert the DOM (the browser s internal representation of the page) back into HTML for our reviewThe Firefox browser provides a DOM Inspector to do just that An excellent add-on to Firefox, called Firebug, also allows the DOM to be inspected Firebug also provides a number of excellent tools for developing web pages such as its DOM inspection capabilities we can use to inspect the DOM after the Dojo parser has run so we can see exactly what it does But before we see how the DOM changes, let s first review the original <input> tag for the first name field
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<input type="text" id="firstName" size="20" dojoType="dijitformValidationTextBox" required="true" propercase="true" promptMessage="Enter first name" invalidMessage="First name is required" trim="true" />
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The code has been reformatted to make it more readable by adding some line breaks The attributes from dojoType through trim are not valid HTML attributesThey are meaningful only to the Dojo parser and drive some features of the Dojo widget they pertain to Now let s see what the HTML looks like after the parser runs
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