Uncaught SyntaxError: Unexpected token <

Question

I am using ajaxupload.js from here and I see the file doing the upload work alright. But I am getting <pre style="word-wrap: break-word; white-space: pre-wrap;">{"id":"006","path":"006.png"}</pre> in the response.

I think the response should be just {"id":"006","path":"006.png"} but for some reasons it got wrapped around <pre> and hence the Uncaught SyntaxError: Unexpected token <.

I am using spring mvc 3, tomcat. I am using java.io.Writer to write the response as writer.write(json.toString());

Could someone help me understand this error and how to resolve it?

Thanks.

UPDATE:

CODE:

<form id="app-form" class="cols" action="#" method="POST">
    <fieldset class="w50">                              
        <!--  set of form fields -->
    </fieldset>   
    <fieldset class="w50">                              
        <button id="uploadButton" class="csbutton-grey" >Upload</button>
        <ul id="locationImages"></ul>
    </fieldset>
<div style="float: left;">
    <button type="submit" class="cool-button">Submit</button>
</div>
</form>


$(document).ready(function(){
    var button = $('#uploadButton'), interval;

    new AjaxUpload(button, {
        action: 'uploadImage', 
        name: 'qqfile',
        responseType: "json",
        onSubmit : function(file, ext){
            this.disable();
            console.log("file - " + file);
            console.log("ext - " + ext);
            if (! (ext && /^(jpg|png|jpeg|gif)$/.test(ext))){
                alert('Error: invalid file extension');
                return false; 
            }
            else {
                $.ajax({
                    type:"GET",
                    url:"file",
                    data:'file='+file,
                    success:function(data, textStatus, jqXHR){
                        console.log(jqXHR.status);
                        console.log(data);
                    },
                    error:function(jqXHR, textStatus, errorThrown) {
                        console.log(jqXHR.status);
                    },
                });                 
            }
        },
        onComplete: function(file, response){
            this.enable();
            console.log("file - " + file);
            console.log("response.id - " + response.id + ", response.path - " + response.path);
            $('<li></li>').appendTo('#locationImages').text(file);                      
        }
    }); 
});

Answer 1

Have you set the responseType property as json in AjaxUpload?

Answer 2

If you want to send JSON to the client, use Jackson. Spring MVC had native support for it. Create a bean class like this:

public class Result{
private String id;
private String path;
public Result(String id, String path){
this.id=id;this.path=path;}
public Result(){}
// add getters and setters
}

Now create your controller method like this

@ResponseBody // this is important
@RequestMapping("/path/to/mapping")
public Result someMethodName(SomeParameter param1, SomeParameter param2){
    // do something here
    return new Result(id, path);
}

As long as you have Jackson on your classpath and have configured your Spring app through <mvc:annotation-config />, this will automatically serialize your response Object to correct JSON (including correct mime type)