Действительно ли безопасно ввести EJB в сервлет как переменная экземпляра?

• Используйте атрибут [required] для каждого элемента управления формы:
  

  <input type='text' required>
  

• Удалите атрибут onevent в <form>:
  

  <form onsubmit = "return false" ...>

• Делегировать событие отправки на <form> ]

  $("#fieldsForm").on('submit', function(e) {...
  

• Добавить event.preventDefault() в обработчик событий.

См. Демонстрация 1

По поводу вашего вопроса:

«Я все еще не понимаю, почему функция проверить значение элементов управления формы и добавить класс не работает. "

jQuery .each() проверяет фактические элементы управления формы, которые будут продолжаться независимо от возврата в результате состояние. Когда условие выполнено, и существует ссылка вне цикла на ссылку, цикл учитывает break или return.

В демонстрационной версии 2 логическое значение: var invalid = false;

Кроме того, часть, где таблица заполняется значениями, также устанавливается в условии.

if (!invalid) { table() }

См. Демонстрация 2

---

Кстати, атрибуты [disabled] и [hidden] были удалены из <select>, потому что все поля должны иметь состояние, когда они фактически пустой.

---

Демонстрация 1

$("#fieldsForm").on('submit', function(e) {
  e.preventDefault();

  var field_name = $("#customfield_name").val();
  var field_slug = $("#customfield_slug").val().toLowerCase().replace(/\s/g, "_");
  var field_type = $("#customfield_type").val();

  var markup = "<tr class='field_row'><td class='edit_col'><span class='js_edit edit_link'>Edit</span></td><td><span class='field_name'>" + field_name + "</span></td><td><span class='field_slug'>" + field_slug + "</span></td><td><span class='field_type'>" + field_type + "</span></td><td><div class='dropdown'><button class='dropbtn'><i class='icon-arrow'></i></button><div class='dropdown-content'><span class='delete_link js_delete'>Delete</span></div></div></td></tr></tr>";

  $("table tbody").append(markup);

  $(this).trigger('reset');
});

$(document).on("click", ".js_delete", function() {
  $(this).parents("tr").remove();
});

.formstuff {
  color: #000;
}

label {
  display: block;
}

.form-group {
  margin-bottom: 20px;
}

input.form-control {
  background-color: #f8f9f9;
  border: 1px solid #e7e7e7;
  border-radius: 2px;
  height: 23px;
  width: 120px;
}

.error_notice {
  color: red;
  display: none;
}

.error .error_notice {
  display: block;
}

.error_field,
.error .error_field {
  border-color: red;
}

.dropbtn {
  border: none;
  padding: 8px;
}

.dropdown {
  position: relative;
  display: inline-block;
}

.dropdown-content {
  background-color: #fff;
  border: 1px solid #D1D4D5;
  border-radius: 2px;
  box-shadow: 0px 1px 6px 1px rgba(0, 0, 0, 0.1);
  box-sizing: border- box;
  display: none;
  min-width: 160px;
  padding: 5px 0;
  position: absolute;
  z-index: 1;
}

.delete_link {
  display: block;
  padding: 5px 10px;
  width: 100%;
}

.delete_link:hover {
  background: #1498BE;
  color: #fff;
}

.dropdown:hover .dropdown-content {
  display: block;
}

table {
  border: 1px solid blue;
  width: 100%;
}

.table tr {
  border: 1px solid #ddd;
}

.table td,
.table th {
  text-align: left;
  position: relative;
}

.table>thead>tr>th {
  color: #8F8F8F;
  font-size: 14px;
}

.table>thead>tr>th,
.table>tbody>tr>td {
  border-color: #F2F5F6;
}

.table>tbody tr:first-child td {
  border: none;
}

.edit_col {
  position: relative;
  width: 60px;
}

.field_row:hover {
  background-color: #FBFDFE;
  cursor: pointer;
}

.field_row .edit_link {
  color: #1498BE;
  cursor: pointer;
  display: none;
  font-size: 11px;
  text-align: center;
}

.field_row:hover .edit_link {
  display: block;
}

.field_row .delete_link {
  cursor: pointer;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<section class="formstuff">
  <form id="fieldsForm" name="create_fields">
    <div class="error_notice">
      <p>All Fields are Required</p>
    </div>
    <div class="row">
      <div class="col-md-6">
        <div class="form-group">
          <label for="customfield_name">Name*</label>
          <input type="text" class="form-control" id="customfield_name" aria-describedby="custom field name" required>
        </div>
      </div>
    </div>

    <div class="row d-flex  align-items-center">
      <div class="col-md-6">
        <div class="form-group">
          <label for="customfield_slug">Slug*</label>
          <input type="text" class="form-control" id="customfield_slug" aria-describedby="custom field slug" name="customfield_slug" required>
        </div>
      </div>


    </div>




    <div class="row">
      <div class="col-md-2">
        <div class="form-group">
          <label for="customfield_type">Field type*</label>
          <select class="form-control" id="customfield_type" placeholder="Select Option" required>
            <option value="" selected disabled hidden>Select Option</option>
            <option value="Text">Text</option>
            <option value="Checkbox">Checkbox</option>
            <option value="Multiple Choice">Multiple Choice</option>
          </select>
        </div>
      </div>
    </div>
    <button type="submit" class="btn btn-primary" id="createField">Create Field</button>
  </form>
  <table class="table" id="fieldsList">
    <thead>
      <tr>
        <th scope="col" class="edit_col"></th>
        <th scope="col">Name</th>
        <th scope="col">Slug</th>
        <th scope="col">Type</th>
        <th scope="col"></th>
      </tr>
    </thead>
    <tbody>
      <tr class="field_row">
        <td class="edit_col"><span class="js_edit edit_link">Edit</span></td>
        <td><span class="field_name">This is a name</span></td>
        <td><span class="field_slug">ThisSlug</span></td>
        <td><span class="field_type">Text</span></td>
        <td>
          <div class="dropdown">
            <button class="dropbtn">X</button>
            <div class="dropdown-content">
              <span class="delete_link js_delete">Delete</span>
            </div>
          </div>

        </td>

      </tr>
      <tr class="field_row">
        <td class="edit_col"><span class="js_edit edit_link">Edit</span></td>
        <td><span class="field_name">This is a name 2</span></td>
        <td><span class="field_slug">ThisSlug2</span></td>
        <td><span class="field_type">Checkbox</span></td>
        <td>
          <div class="dropdown">
            <button class="dropbtn">X</button>
            <div class="dropdown-content">
              <span class="delete_link js_delete">Delete</span>
            </div>
          </div>
        </td>
      </tr>
    </tbody>
  </table>
</section>

---

Демо 2

$("#fieldsForm").on('submit', function(e) {
  e.preventDefault();
  var invalid = false;

  $('.form-control').filter(function(e) {
    if ($(this).val().trim() === '') {
      $(this).addClass("error_field");
      invalid = true;
      return false;
    } else {
      $(this).removeClass('error_field');
    }
  });

  if (!invalid) {
    table();
  }
});

function table() {
  var field_name = $("#customfield_name").val();
  var field_slug = $("#customfield_slug").val().toLowerCase().replace(/\s/g, "_");
  var field_type = $("#customfield_type").val();

  // HTML to append on form submit
  var markup = "<tr class='field_row'><td class='edit_col'><span class='js_edit edit_link'>Edit</span></td><td><span class='field_name'>" + field_name + "</span></td><td><span class='field_slug'>" + field_slug + "</span></td><td><span class='field_type'>" + field_type + "</span></td><td><div class='dropdown'><button class='dropbtn'><i class='icon-arrow'></i></button><div class='dropdown-content'><span class='delete_link js_delete'>Delete</span></div></div></td></tr></tr>";

  // On successful submit append the markup html to the table body (bottom)
  $("table tbody").append(markup);
  // In case of an error class, remove it on a successful submit
  $(this).trigger('reset');
}

.formstuff {
  color: #000;
}

label {
  display: block;
}

.form-group {
  margin-bottom: 20px;
}

input.form-control {
  background-color: #f8f9f9;
  border: 1px solid #e7e7e7;
  border-radius: 2px;
  height: 23px;
  width: 120px;
}

.error_notice {
  color: red;
  display: none;
}

.error .error_notice {
  display: block;
}

.error_field,
.error .error_field {
  outline: 3px dashed red;
}

.dropbtn {
  border: none;
  padding: 8px;
}

.dropdown {
  position: relative;
  display: inline-block;
}

.dropdown-content {
  background-color: #fff;
  border: 1px solid #D1D4D5;
  border-radius: 2px;
  box-shadow: 0px 1px 6px 1px rgba(0, 0, 0, 0.1);
  box-sizing: border- box;
  display: none;
  min-width: 160px;
  padding: 5px 0;
  position: absolute;
  z-index: 1;
}

.delete_link {
  display: block;
  padding: 5px 10px;
  width: 100%;
}

.delete_link:hover {
  background: #1498BE;
  color: #fff;
}

.dropdown:hover .dropdown-content {
  display: block;
}

table {
  border: 1px solid blue;
  width: 100%;
}

.table tr {
  border: 1px solid #ddd;
}

.table td,
.table th {
  text-align: left;
  position: relative;
}

.table>thead>tr>th {
  color: #8F8F8F;
  font-size: 14px;
}

.table>thead>tr>th,
.table>tbody>tr>td {
  border-color: #F2F5F6;
}

.table>tbody tr:first-child td {
  border: none;
}

.edit_col {
  position: relative;
  width: 60px;
}

.field_row:hover {
  background-color: #FBFDFE;
  cursor: pointer;
}

.field_row .edit_link {
  color: #1498BE;
  cursor: pointer;
  display: none;
  font-size: 11px;
  text-align: center;
}

.field_row:hover .edit_link {
  display: block;
}

.field_row .delete_link {
  cursor: pointer;
}

<section class="formstuff">
  <form id="fieldsForm" name="create_fields">
    <div class="error_notice">
      <p>All Fields are Required</p>
    </div>
    <div class="row">
      <div class="col-md-6">
        <div class="form-group">
          <label for="customfield_name">Name*</label>
          <input type="text" class="form-control" id="customfield_name" aria-describedby="custom field name">
        </div>
      </div>
    </div>

    <div class="row d-flex  align-items-center">
      <div class="col-md-6">
        <div class="form-group">
          <label for="customfield_slug">Slug*</label>
          <input type="text" class="form-control" id="customfield_slug" aria-describedby="custom field slug" name="customfield_slug" />
        </div>
      </div>


    </div>




    <div class="row">
      <div class="col-md-2">
        <div class="form-group">
          <label for="customfield_type">Field type*</label>
          <select class="form-control" id="customfield_type" placeholder="Select Option">
            <option value="" selected>Select Option</option>
            <option value="Text">Text</option>
            <option value="Checkbox">Checkbox</option>
            <option value="Multiple Choice">Multiple Choice</option>
          </select>
        </div>
      </div>
    </div>
    <button type="submit" class="btn btn-primary" id="createField">Create Field</button>
  </form>
  <table class="table" id="fieldsList">
    <thead>
      <tr>
        <th scope="col" class="edit_col"></th>
        <th scope="col">Name</th>
        <th scope="col">Slug</th>
        <th scope="col">Type</th>
        <th scope="col"></th>
      </tr>
    </thead>
    <tbody>
      <tr class="field_row">
        <td class="edit_col"><span class="js_edit edit_link">Edit</span></td>
        <td><span class="field_name">This is a name</span></td>
        <td><span class="field_slug">ThisSlug</span></td>
        <td><span class="field_type">Text</span></td>
        <td>
          <div class="dropdown">
            <button class="dropbtn">X</button>
            <div class="dropdown-content">
              <span class="delete_link js_delete">Delete</span>
            </div>
          </div>

        </td>

      </tr>
      <tr class="field_row">
        <td class="edit_col"><span class="js_edit edit_link">Edit</span></td>
        <td><span class="field_name">This is a name 2</span></td>
        <td><span class="field_slug">ThisSlug2</span></td>
        <td><span class="field_type">Checkbox</span></td>
        <td>
          <div class="dropdown">
            <button class="dropbtn">X</button>
            <div class="dropdown-content">
              <span class="delete_link js_delete">Delete</span>
            </div>
          </div>
        </td>
      </tr>
    </tbody>
  </table>
</section>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>