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Sping MVC, Thymeleaf, POST request, how to pass list of objects to controller

A "teacher" can have several assigned "subjects" to teach:
public class Teacher {
private int id;
private String firstName;
private String lastName;
...
private List<Subject> subjects;
}
In HTML view user can select one ore more subjects for the teacher and send POST request:
<select class="form-control" id="subjects" name="subjects" size="5" multiple required>
<option th:each="subject: ${allSubjects}"
th:value="${subject.id}"
th:text="${subject.name}"
th:selected="${teacher.subjects.contains(subject)}">
</option>
</select>
Controller to process this request:
#PostMapping("/update")
public String update(#ModelAttribute("teacher") Teacher teacher) {
logger.debug("Received update data: {}", teacher);
teacherService.update(teacher);
return "redirect:/teachers";
}
Here is the POST request that is being passed:
I expect Spring to take subject.id`s and inject them into teacher as list of subjects.
But I get exception:
BindException
org.springframework.validation.BeanPropertyBindingResult:
1 errors Field error in object 'teacher' on field 'subjects': rejected value [2,4]; codes [typeMismatch.teacher.subjects,typeMismatch.subjects,typeMismatch.java.util.List,typeMismatch];
arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [teacher.subjects,subjects];
arguments []; default message [subjects]]; default message [Failed to convert property value of type 'java.lang.String[]' to required type 'java.util.List' for property 'subjects'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'ua.com.foxminded.university.model.Subject' for property 'subjects[0]': no matching editors or conversion strategy found]
I carefully read first 50 google results for my question, code should work, but it doesn't. I must be missing something.

First of all wrong annotation - u dont use #ModelAttribute inside of the post but rather #RequestBody which is implicit in spring controllers for post.
Other than that what you are sending is not a teacher entity but rather teacherDTO which wont have all the fields (collections) that teacher entity that you showed has. That means you should be receiving a different class (TeacherDTO) and then convert it correctly to teacher entity which you then update in the database

i suppose this is an update form, so it take an object teacher as an input. try this
<form th:object="${teacher}" method="post">
<select class="form-control" th:field="*{subjects}" id="subjects" name="subjects" size="5" multiple required>
<option th:each="subject: ${allSubjects}"
th:value="${subject.id}"
th:text="${subject.name}"
th:selected="*{subjects.contains(subject)}">
</option>
</select>
</form>

Finally I found the solution while working on another part of my project.
I tried to pass Lecture object to controller, Lecture contains List of student groups. Each group has 2 fields: id and name.
First we implement a formatter
public class GroupFormatter implements Formatter<Group> {
#Override
public Group parse(String text, Locale locale) throws ParseException {
Group group=new Group();
if (text != null) {
String[] parts = text.split(",");
group.setId(Integer.parseInt(parts[0]));
if(parts.length>1) {
group.setName(parts[1]);
}
}
return group;
}
#Override
public String print(Group group, Locale locale) {
return group.toString();
}
}
Register formatter in MVCConfig
#Override
public void addFormatters(FormatterRegistry registry) {
GroupFormatter groupFormatter=new GroupFormatter();
registry.addFormatter(groupFormatter);
}
And we get the correct format from POST request:
groups=[4:VM-08, 5:QWE-123]

How to take LIST input in #RequestParam in Spring MVC?

Heyy,
I want to take a list of data in my request param,here "personIdCollection" is a set of list but when i am hitting through postman i am getting a bad request.
Here is my code.
controller
#PostMapping("/face-tag-data")
public String getFaceTaggedData(#RequestParam String projectId,#RequestParam List<String> personIdCollection) {
return null;
}
and here is my ajax
var data = {};
data.personIdCollection = personIdCollection;
data.projectId = $("#projectId").val();
$.ajax({
type:'POST',
url:contextPath+'/face-tag-data',
data:data,
success:function(resp){
console.log(resp);
},
failure:function(resp){
console.log(resp);
}
});

This is working for me. I do not use an ajax-request but instead submit my form directly but it should work either way.
My controller looks like:
#RequestMapping(value="addSingleArticles", method=RequestMethod.POST)
public #ResponseBody String addSingleArticles(
ArticleSubmitData pupilPackageData,
HttpServletRequest request) {
... // do something with the data
}
As you can see I have defined my own composite type which consists of three lists. So you obviously can use it with only one list directly.
public class ArticleSubmitData {
private List<Article> singleArticles;
private List<Article> packageArticle;
private List<Article> popupArticles;
... // getter & setter, inner classes etc.
}
In my server page oder faclet I use the following html-code to make this work
...
<input id="" class="" type="text" name="singleArticles[${line.index}].engraving" />
...
So the trick is to define the variables on your webpage as an array and use this in your controller as a list. As you can see in my example I also use an inner class in my composite class which has extra attributes.

JSF and type safety

As I struggled for hours I finally found where those annoying ClassCastExceptions came from, which I thought were produced by Hibernate and it's enum-mapping.
But they came from my JSF view, where I passed a List from
<h:selectManyCheckbox value="#{createUserManager.user.roles}" ... >
<f:selectItems value="#{createUserManager.roles}"/>
</h:selectManyCheckbox>
back into my backing bean.
My data simply consists of the values of an enum:
public Role[] getRoles()
{
return Role.values();
} .
I was really shocked when I tested the setter of roles in the User-class and got this:
public void setRoles(List<Role> paramRoles) {
System.out.println(paramRoles.get(0) instanceof Role); //output: false
for(Role role : paramRoles){ ...} //crashes with ClassCastException
}
Changing List<Role> paramRoles to List<String> paramRoles worked perfectly.
How is this possible? Shouldn't those generics be type safe or is type erasure in connection with JSF killing the whole type safety thing?
Also shouldn't the return value of h:selectManyCheckbox be List<Role>, like I passed in via the f:selectItems?

The behaviour you are experiencing is fully expected. Moreover, it is related to java generics in the same way as to how HTTP works.
The problem
The HTTP part
The problem is that you don't fully understand how HTTP works. When you submit data by pressing the submit button, parameters of your generated by JSF <h:selectManyCheckbox> tag, as a bunch of <input type="checkbox" name="..." value="userRoleAsString"> checkboxes, will be sent as strings and retrived ultimately as request.getParameter("checkboxName"); also as strings. Of course, JSF has no idea how to construct you model object class, Role.
The generics part
As you know due to the fact that java chose type erasure for generics to provide for backwards compatibility, information about generic types is basically a compile-type artifact and is lost at runtime. So at runtime your List<Role> erases to a plain, good old List. And as far as EL is a runtime language that uses Java Reflection API to deal with your expressions / call methods, at runtime no such information is available. Taking into account the HTTP part, JSF does its best and assigns string objects to your list, as it's all it can implicitly do. If you are willing to tell JSF to do otherwise, you need to do that explicitly, i.e. by specifying a converter to know what type of object to expect in an HTTP request.
The JSF part: aftermath
JSF has a provided javax.faces.Enum converter and in indeed works, if EL knew of the compile-time generic type of your list, that is Role. But it doesn't know of it. It would be not necessary to provide for a converter in case your multiple selection would be done on a Role[] userRoles object, or if you used the unique selection like in <h:selectOneMenu> with a value bound to Role userRole. In these examples the built-in enum converter will be called automatically.
So, to get it work as expected you need to provide for a Converter that will 'explain' JSF what type of values does this list hold, and how to do the transformations from Role to String, and vice versa.
It is worth noting that this will be the case with any bound List<...> values within the multiple choice JSF components.
Points of reference on Stack Overflow
After the problem was examined and resolved I was wondering if no one faced it in the past and searched for some previous answers here. Not surprisingly, it was asked before, and of course the problem was solved by BalusC. Below are two most valuable point of reference:
JSF 2.0 use enum in selectMany menu;
How to make a dropdown menu of a enum in JSF;
How to create and use a generic bean for enums in f:selectItems?.
The test case and two examples of working converters
Below I provide for a test case entirely for your understanding: everything works as expected apart from the third <h:selectManyCheckbox> component. It's up to you to trace it fully to eliminate the issue altogether.
The view:
<h:form>
Many with enum converter
<!-- will be mapped correctly with Role object -->
<h:selectManyCheckbox value="#{q16433250Bean.userRoles}" converter="roleEnumConverter">
<f:selectItems value="#{q16433250Bean.allRoles}" var="role" itemLabel="#{role.name}" />
</h:selectManyCheckbox>
<br/>
Many with plain converter
<!-- will be mapped correctly with Role object -->
<h:selectManyCheckbox value="#{q16433250Bean.userRoles2}" converter="roleConverter">
<f:selectItems value="#{q16433250Bean.allRoles2}" var="role" itemLabel="#{role.name}" />
</h:selectManyCheckbox>
<br/>
Without any converter
<!-- will NOT be mapped correctly with Role object, but with a default String instead -->
<h:selectManyCheckbox value="#{q16433250Bean.userRoles3}">
<f:selectItems value="#{q16433250Bean.allRoles}" var="role" itemLabel="#{role.name}" />
</h:selectManyCheckbox>
<br/>
Without any converter + array
<!-- will be mapped correctly with Role object -->
<h:selectManyCheckbox value="#{q16433250Bean.userRoles4}">
<f:selectItems value="#{q16433250Bean.allRoles}" var="role" itemLabel="#{role.name}" />
</h:selectManyCheckbox>
<br/>
<h:commandButton value="Submit" action="#{q16433250Bean.action}"/>
</h:form>
The bean:
#ManagedBean
#RequestScoped
public class Q16433250Bean {
private List<Role> userRoles = new ArrayList<Role>();//getter + setter
private List<Role> userRoles2 = new ArrayList<Role>();//getter + setter
private List<Role> userRoles3 = new ArrayList<Role>();//getter + setter
private Role[] userRoles4;//getter + setter
public enum Role {
ADMIN("Admin"),
SUPER_USER("Super user"),
USER("User");
private final String name;
private Role(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
}
public Role[] getAllRoles() {
return Role.values();
}
public String action() {
return null;
}
}
The converters:
#FacesConverter("roleEnumConverter")
public class RoleEnumConverter extends EnumConverter {
public RoleEnumConverter() {
super(Role.class);
}
}
and
#FacesConverter("roleConverter")
public class RoleConverter implements Converter {
public Object getAsObject(FacesContext context, UIComponent component, String value) {
if(value == null || value.equals("")) {
return null;
}
Role role = Role.valueOf(value);
return role;
}
public String getAsString(FacesContext context, UIComponent component, Object value) {
if (!(value instanceof Role) || (value == null)) {
return null;
}
return ((Role)value).toString();
}
}

Bind Collection to Form - why is it not working?

Could someone please help me find out why my attempt to bind Collection to the form in Spring MVC is not working?
Here is how my object looks like -
public class TestObj {
private Integer testNumber;
private String home;
private String destination;
}
Here is my form object that contains list of above object -
public class TestForm {
private List<TestObj> testList;
//contains getter and setter for testList
}
In my controller, I have implemented formBackingObject method -
public class MyController extends SimpleFormController {
public MyController() {
setCommandClass(TestForm.class);
setCommandName("testForm");
}
protected Object formBackingObject(HttpServletRequest request) throws Exception {
if (isFormSubmission(request)) {
testForm = (TestForm) super.formBackingObject(request);
//THIS ALWAYS RETURNS NULL ON FORM SUBMISSION
List<TestObj> testList = testForm.getTestList();
} else {
//load initial data using hibernate. TestObj is hibernate domain object.
List<TestObj> testList = myService.findTestList();
testForm = new TestForm(testList);
}
return testForm;
}
Here is my JSP snippet -
<form:form commandName="testForm" method="post">
<c:forEach items="${testForm.testList}" var="testvar" varStatus="testRow">
<tr>
<td>
<form:hidden path="testList[${testRow.index}].home" />
<c:out value="${testvar.home}" />
</td>
<td>
<form:input path="testList[${testRow.index}].destination" />
</td>
</tr>
</c:forEach>
<tr><td><input type="submit"></td></tr>
</form:form>
While the first time I load the data shows up fine on the form, when I press submit button the control goes to the formBackingObject method and the isFormSubmission returns true. However, when I get the command object using super.formBackingObject(request), it returns the form object with the testList value as null. I am unable to figure out why this simple case is not working?
I will really appreciate any help in getting this to work.

Are you using Spring 3? If so, you should take a look at this post.
With respect to list processing and object binding, take a look at this post.

Try using the following code. May be that can solve your problem.
private List<TestObj> operationParameterses = LazyList.decorate(new ArrayList<TestObj>(), FactoryUtils.instantiateFactory(TestObj.class));
It won't return you all null list.
Hope that helps you.
Cheers.

I guess my understanding of formBackingObject method must be wrong. I removed that method from the implementation, used referenceData for initial form load and onSubmit to process it on submit. This works fine and does get collection in the form back as expected.
Thanks all for the help though.

How to bind a Set<CustomObject> in spring mvc form

I have a command object associated with a spring form controller:
public class PluginInstance {
private Set<PluginParameter> pluginParameters = new HashSet<PluginParameter>();
... some other string/long properties and getter setters...
}
the PluginParameter also have a Set in it which contain the values
public class PluginParameter {
private String parmName;
private Set<PluginParmvalue> pluginParmvalues = new HashSet<PluginParmvalue>();
...some other string/long properties and getter setters...
}
(Normally the pluginParmvalues will contain only one value, a list have been used for future expandability)
In the spring form I binding the values as
<form:input path="pluginParameters[${itemsRow.index}].pluginParmvalues[0].parmValue" />
but the thing is that there can be a form:select(to present multiple predefined options to the user) or form:input (user can input any value). This has to be decided from another object
public class PluginConfigParm {
private String parmName;
private ArrayList<String> choices;
...getter setters and other properties
}
where I have to compare the name of PluginConfigParm.paramName with PluginParameter.paramName when they match and PluginConfigParm.choices.size() > 0 then form:select will be shown populated with the values from PluginConfigParm.choices otherwise form:input will be shown.
The question is simple: How can I do that.
Any help will be highly appreciated.

By using List<> instead of Set<> in controller. Problem solved. May be Set<> has no getter/setter that can be bind with spring form.
So <form:input path="pluginParameters[${itemsRow.index}].pluginParmvalues[0].parmValue" />
and List<> in controller makes my life easier.

The Set is not an indexed collection so I could not work by using this syntax
pluginParameters[${itemsRow.index}].pluginParmvalues[0].parmValue

eg:
class person{
set name<string> = new HashSet<String>()
}
<input type="hidden" path="person.name" name="person.name" value="<%=valueStr%>"/>
take valueStr = "hello, world"
by giving it as comma seperated values.. set works
Its working for me