Spring MVC with JPA databinding

Question

My problem is with having Spring bind the data I get from a form to a JPA entity. The wierd part is, it works just fine if I do not look at the BindingResults. The BindingResults says there were binding errors when an empty string is passed in for the field graduation, but I know it does bind them correctly because when I don't check Hibernate updates the database perfectly. Is there a way to not have to write logic to circumnavigate the wrongly fired binding errors?

    @Entity
    @Table(name="child")
    public class Child {

        @Id
        @Column(name="id")
        private Integer childId;

        @ManyToOne(fetch=FetchType.EAGER )
        @JoinColumn(name="house", referencedColumnName="house")
        private House house;

        @NotNull()
        @Past()
        @Column(name="birthday")
        private Date birthday;

        @Column(name="graduation_date")
        private Date graduationDay;

    }

I have tried the following lines in a property editor to no avail

    SimpleDateFormat dateFormat = new SimpleDateFormat("MMM dd, yyyy");
    registry.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, true));

Here is the method signature for the controller method Handling the request

    @Controller
    @SessionAttributes(value="child")
    @RequestMapping(value="child")
    public class ChildModController {

    @RequestMapping(value="save-child.do", params="update", method = RequestMethod.POST)
    public @ResponseBody Map<String,?> updateChild(

        HttpServletRequest request,
        @Valid @ModelAttribute(value="child")Child child,
        BindingResult results)
    }

This is what I get from the BindingResult class as a message

    09:01:36.006 [http-thread-pool-28081(5)] INFO  simple - Found fieldError: graduationDay, 
    Failed to convert property value of type java.lang.String to required type java.util.Date for property graduationDay; 
    nested exception is org.springframework.core.convert.ConversionFailedException: 
    Failed to convert from type java.lang.String to type @javax.persistence.Column java.util.Date for value '; 
    nested exception is java.lang.IllegalArgumentException

Answer 1

Spring automatically binds simple object types like String and Number, but for complex objects like java.util.Date or your own defined types, you will need to use what is called a PropertyEditors or Converters , both could solve your problem.

Spring already has a predefiend PropertyEditors and Converters like @NumberFormat and @DateTimeFormat

You can use them directly on your fields like this

public class Child {

  @DateTimeFormat(pattern="dd/MM/yyyy")
  private Date birthday;

  @DateTimeFormat(iso=ISO.DATE)
  private Date graduationDay;

  @NumberFormat(style = Style.CURRENCY)
  private Integer myNumber1;

  @NumberFormat(pattern = "###,###")
  private Double myNumber2;

}

Spring also allows you to define your own type converters which you must use it combined with Spring ConversionService

For example if you have a Color class like this

public class Color {
  private String colorString;

  public Color(String color){
     this.colorString = color;
  }
}

You would define the color converter for example like this

public class StringToColor implements Converter<String, Color> {
  public Color convert(String source) {
    if(source.equal("red") {
       return new Color("red");
    }

    if(source.equal("green") {
       return new Color("green");
    }

    if(source.equal("blue") {
       return new Color("blue");
    }

    // etc

    return null;
  }
}

To check more about converters check this , also check this to know the difference between Converters and PropertyEditors