How to attach a FileItem to a HTTP POST request?
<p>I have created a webpage (JSP &amp; AngularJS) that contains a form allowing the user to attach a file and send it to the server (Java Servlet). The server will then take that file and forward it to an API by attaching it to a HTTP POST request.</p>

<p>The code I have at the moment within the JSP File and the AngularJS Controller appears to be working correctly. Once the file is sent from the webpage to the server, I can then access some of the file details (field name and size but not content type or file name) in the Java Servlet and print them out via <code>System.out.println()</code>.</p>

<p>The problem I am facing at the moment is trying to find a way how to attach the FileItem (attachment) to the HttpPost (postRequest).</p>

<p>I have read a number of examples online on how files are uploaded, however these examples always assume the file will be stored on a disk on the server instead of being forwarded elsewhere.</p>

<p>This is my current code (the problem seems to be in the Java Servlet section):</p>

<p><strong>JSP File:</strong></p>

<pre><code>&lt;form name="issueForm"&gt;
    &lt;input id="attachment" class="form-control" type="file" data-ng-model="attachment"/&gt;
    &lt;button type="submit" data-ng-click="setAttachment()"&gt;Create Issue&lt;/button&gt;
&lt;/form&gt;
</code></pre>

<p><strong>AngularJS Controller:</strong></p>

<pre><code>app.directive('fileModel', ['$parse', function ($parse) {
    return {
        restrict: 'A',
        link: function(scope, element, attrs) {
            var model = $parse(attrs.fileModel);
            var modelSetter = model.assign;

            element.bind('change', function() {
                scope.$apply(function() {
                    modelSetter(scope, element[0].files[0]);
                });
            });
        }
    };
}]);

$scope.setAttachment = function()
{
    var attachment = $scope.attachment;
    var fd = new FormData();
    fd.append('attachment', attachment);

    $http({
        url: 'IssueAttachment',
        method: 'POST',
        transformRequest: function(data, headersGetterFunction) { return data; },
        headers: { 'Content-Type': undefined },
        data: fd
    })
    .success(function(data, status) { alert("Success: " + status); })
    .error(function(data, status) { alert("Error: " + status); });
}
</code></pre>

<p><strong>Java Servlet:</strong></p>

<pre><code>protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
FileItem attachment = null;
boolean isMultipart = ServletFileUpload.isMultipartContent(request);

if (!isMultipart) { System.out.println("Not Multipart Content!"); }
else {
    FileItemFactory factory = new DiskFileItemFactory();
    ServletFileUpload upload = new ServletFileUpload(factory);
    List items = null;
    try {
        items = upload.parseRequest(new ServletRequestContext(request));
    } catch (FileUploadException e) { e.printStackTrace(); }
    try {
        //Get attachment and print details
        //This section prints "attachment", 9, null, null in that order).
        attachment = (FileItem) items.get(0);
        System.out.println("Field Name: " + attachment.getFieldName());
        System.out.println("Size: " + attachment.getSize());
        System.out.println("Content Type: " + attachment.getContentType());
        System.out.println("File Name: " + attachment.getName());
    } catch (Exception e) { e.printStackTrace(); }

    //Create a HTTP POST and send the attachment.
    HttpClient httpClient = HttpClientBuilder.create().build();
    HttpPost postRequest = new HttpPost(API_URL);
    MultipartEntityBuilder entity = MultipartEntityBuilder.create();
    entity.addPart("attachment", new FileBody(attachment)); //THE ERROR OCCURS HERE.
    postRequest.setEntity(entity.build());
    try {
        HttpResponse response = httpClient.execute(postRequest);
    } catch (IOException e) { e.printStackTrace(); }
}
}
</code></pre>