I wanted to submit an html form to my Spring MVC Controller, but I wanted to do it with ajax. I had previously submitted a single value and returned a JSON object for use in jquery, but I had yet to do it with an entire form. I’m a java guy, so there may be better ways to do the html stuff, but this is how I did it and thought I would share some of what I learned along the way.
First, here’s my form.
<div id='newAnswerDialog'>
<form id='newAnswerForm' name='newAnswerForm' action='/admin/survey/answer/new' onsubmit='return false;' method='post'>
<label for='severity'><spring:message code='input.answer.severity' text='Severity' /></label>
<select id='answerSeverity' name='answerSeverity'>
<option value='MINIMAL'>MINIMAL</option>
<option value='MINOR'>MINOR</option>
<option value='MODERATE'>MODERATE</option>
<option value='SEVERE'>SEVERE</option>
<option value='URGENT'>URGENT</option>
</select><br/>
<label for='answerText'><spring:message code='input.answer.text' text='Answer Text' /></label>
<input type='text' id='answerText' name='answerText'/><br/>
<label for='requiresReason'><spring:message code='input.answer.requiresReason' text='Requires Reason?' /></label>
<input type='checkbox' id='requiresReason' name='requiresReason' onclick='toggleReasonControls(this)'/><br/>
<label for='answerReasons'><spring:message code='input.question.reasons' text='Reasons' /></label>
<select class='newReason' id='answerReasons' name='answerReasons' multiple='multiple'>
<c:forEach items='${reasons}' var='reason'>
<option value='${reason.key}'>${reason.text}</option>
</c:forEach>
</select><br/>
<input type='button' onclick='createNewAnswer()' value='<spring:message code='submit' />'/><input type='button' onclick='cancelNewAnswer()' value='<spring:message code='cancel' />' />
</form>
</div>
It’s JSP using the JSTL and the Spring tag libraries, but it’s all basically html. You can see that I have some javascript in the requriesReason checkbox that is called when it is clicked. The javascript function just enables everything with a css class of newReason based on the state of the requiresReason checkbox. This will come into play later.
When the user clicks the button labeled submit, it calls the javascript function called “createNewAnswer()” which looks like this
function createNewAnswer()
{
$.post( '<c:url value='/admin/survey/answer/new' />'
, $('#newAnswerForm').serialize()
, function( data )
{
// add the option to the list of answers, and select it.
var options = $('#'+data.severity.toLowerCase()+'Answer').attr( 'options' );
options[options.length] = new Option( data.text, data.key, true, true );
$('#newAnswerDialog').dialog( 'close' );
}
, 'json' );
}
This uses the jquery post function to submit the values to the server and read the response.
The first parameter is the URL to submit to. I’m using the JSTL c:url tag so that the web application context is added to the url. Your controller method must be configured to accept POST requests since we are submitting via POST, not GET. I’ll show the controller implementation later on.
The second parameter is the data you want to submit to the Controller. This is where I found it a bit tricky. Getting the form is simple with jquery. Getting the data is also simple using jquery’s serialize() method. The trick is in the fine print in the serialize method. You can find the documentation here. At the time of this writing, it says:
Note: Only “successful controls” are serialized to the string. No submit button value is serialized since the form was not submitted using a button. For a form element’s value to be included in the serialized string, the element must have a name attribute. Data from file select elements is not serialized.
It then links to this page that has an explanation of what a “successful control” is. The gist of it is that the control cannot be disabled. The control must have a name. Checkboxes that are not checked may not be submitted. At least, those are the parts that affected me when trying to get this to work.
So, knowing that, it affects how I create the controller method to handle the post. Here’s the implementation:
@RequestMapping( value='answer/new', method=RequestMethod.POST)
public ResponseEntity<String> newAnswer( @RequestParam(value='answerSeverity', required=true ) String severity
, @RequestParam( value='answerText', required=true ) String text
, @RequestParam( value='requiresReason', required=false, defaultValue='false' ) boolean requiresReason
, @RequestParam( value='answerReasons', required=false ) List<Long> reasonKeys
)
{
Severity sev = Severity.valueOf( severity );
SurveyAnswer answer = new SurveyAnswer( text, sev );
answer.setRequiresReason( requiresReason );
if ( requiresReason )
{
// add all the reasons
List<SurveyAnswerReason> reasons = surveyService.findReasonsByKey( reasonKeys );
for( SurveyAnswerReason reason : reasons )
{
answer.addReason( reason );
}
}
answer = surveyService.persist( answer );
return createJsonResponse( answer );
}
Notice that the requiresReason, and answerReasons are marked as optional. This is because they may or may not be passed. If you have a problem with your mapping here, you may get a 400 error with a message that says, “The request sent by the client was syntactically incorrect ()” if you look at it in the XHR response. That’s what I was getting from tomcat. Once I set the required to false on the optional attributes, things went through much better.
The rest of the code is just for creating our entity and saving it. You can do whatever you want with the data you post. The next critical part is in the createJsonResponse method. You’ll notice that the controller method doesn’t return a String for the view, and it doesn’t return a ModelAndView. It is returning a ResponseEntity, which I create in the createJsonResponse method, which is as follows:
private ResponseEntity<String> createJsonResponse( Object o )
{
HttpHeaders headers = new HttpHeaders();
headers.set( 'Content-Type', 'application/json' );
String json = gson.toJson( o );
return new ResponseEntity<String>( json, headers, HttpStatus.CREATED );
}
It’s a very simple method that just creates the ResponseEntity and sets the headers so the javascript receiving the response gets json as it is expecting (see the last parameter in the $.post method, it says we are expecting json in return.)
I am using Google’s JSON library to convert my entity object to a JSON object that I can return to the view. With that conversion, I can use the field names in the java object to reference the values in the returned JSON object. It’s really quite slick.
So, now we’ve done the work on the server and returned the response to the browser. The third argument to the $.post jquery method is a function that is called on successful return of the json object from the server. Here is my function again:
function( data )
{
// add the option to the list of answers, and select it.
var options = $('#'+data.severity.toLowerCase()+'Answer').attr( 'options' );
options[options.length] = new Option( data.text, data.key, true, true );
$('#newAnswerDialog').dialog( 'close' );
}
I’m taking the JSON object I receive and adding a new option to a select box further down in the page, and marking that option as selected. As I said above, I’m referencing the properties of the JSON object using the field names in the Java object.
There is a way to get a javascript method called when the request fails, but it’s not built into jquery’s post method, and I haven’t taken the time go through that part yet.
So, there you have it. A fair amount of time of trial and error all summed up in about 1000 words, including code.
