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Editorial Team
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Asked: 2026-06-16T16:57:00+00:00

I am using Spring to populate a item in a form, using object passing

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I am using Spring to populate a item in a form, using object passing between controller and views:

Domain Objects

public class Client {
private String name;
private int id;
private Bar bar;
// getters and setters omitted
}


public class Bar {
private Integer id;
private String name;
// getters and setters omitted

}

Controller

@RequestMapping(method = RequestMethod.GET, value = "/")
public String index(Model m) {
m.addAttribute("Client", new Client());
Bar o1 = new Bar();
o1.setName("n 1");
o1.setId(1);
Bar o2 = new Bar();
o2.setName("n 2");
o2.setId(2);
Bar o3 = new Bar();
o3.setName("n 3");
o3.setId(3);
Bar o4 = new Bar();
o4.setName("n 4");
o4.setId(4);
Bar o5 = new Bar();
o5.setName("n 5");
o5.setId(5);
List<Bar> orders = new ArrayList<Bar>();
orders.add(o1);
orders.add(o2);
orders.add(o3);
orders.add(o4);
orders.add(o5);
m.addAttribute("ordersList", orders);
return "index";
}

@RequestMapping(method = RequestMethod.POST, value = "/")
public String indexPost(@ModelAttribute("Client") Client g, BindingResult r) {
log.info(g.getId() + " " + g.getName());
log.info(g.getBar().getName());
return "index";
}

View (index.jsp)

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<html xmlns="http://www.w3.org/1999/xhtml">
<body>
<form:form method="POST" modelAttribute="Client">
<form:label path="name">Name</form:label>
<form:input path="name" />
<form:label path="id">Id</form:label>
<form:input path="id" />
<form:label path="orders">Order</form:label>
<form:select path="bar" items="${ordersList}" />    
<form:button>Insert</form:button>
</form:form>
</body>
</html>

Problem

When I fill out the form, and make the submit, the controller throw a NullPointerException on log.info(g.getBar().getName());
I assume it is because getBar() returns null.
Where am I wrong with this data binding?

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1 Answer

  1. Editorial Team

    You are setting a new Client object to the model, but that object is empty. Try first to create the full Client object and then set it to the model in the index() method.

    EDIT:
    So you need a property editor for that field. Adjust and add the method below to your controller:

    @InitBinder
protected void initBinder(WebDataBinder binder) {

    binder.registerCustomEditor(Bar.class, "bar", new PropertyEditorSupport(Bar.class) {
        @Override
        public String getAsText() {
            if(null != getValue()) {
                return ((Bar) getValue()).getId();
            } else {
                return StringUtils.EMPTY;
            }
        }
        @Override
        public void setAsText(String text) {
            if(!StringUtils.isEmpty(text)) {
                setValue(UtilityClassUtils.getBarById(text));
            }
        }
    });
}
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