{"id":18848,"date":"2013-11-11T16:00:31","date_gmt":"2013-11-11T14:00:31","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=18848"},"modified":"2013-11-11T13:02:09","modified_gmt":"2013-11-11T11:02:09","slug":"type-conversion-in-spring-2","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2013\/11\/type-conversion-in-spring-2.html","title":{"rendered":"Type Conversion in Spring"},"content":{"rendered":"

Here are few straight cases where we need type conversion:
\nCase #1.<\/strong> To help simplifying bean configurations, Spring supports conversion of property values to and from text values. Each property editor is designed for a property of certain type only. And to put them in use, we have to register them with Spring container.
\nCase #2.<\/strong> Also when using Spring MVC, controllers binds the form field values to properties of an object. Suppose the object is composed with another object, then the MVC controller cannot automatically assign values to the internal custom type object as all the values in the form are inputted as text values. Spring container will take of conversion of text values to primitive types but not to custom type objects. For this to be taken care, we have to initialize custom editors in the MVC flow.<\/p>\n

This article will discuss the various ways of implementing the converters for custom type objects. To elaborate more on these, let us consider the following use case. In the example, I would like to simulate play ground reservation system. So here are my domain objects:<\/p>\n

public class Reservation {\r\n\r\n\tpublic String playGround;\r\n\tpublic Date dateToReserve;\r\n\tpublic int hour;\r\n\tpublic Player captain;\r\n\tpublic SportType sportType;\r\n\r\n\tpublic Reservation(String playGround, Date date, int hour, Player captain, SportType sportType) {\r\n\t\tthis.playGround = playGround;\r\n\t\tthis.dateToReserve = date;\r\n\t\tthis.hour = hour;\r\n\t\tthis.captain = captain;\r\n\t\tthis.sportType = sportType;\r\n\t}\r\n\r\n\t\/**\r\n\t * Getters and Setters\r\n\t *\/\r\n}\r\n\r\npublic class Player {\r\n\r\n\tprivate String name;\r\n\tprivate String phone;\r\n\t\/**\r\n\t * Getters and Setters\r\n\t *\/\r\n\r\n}\r\n\r\npublic class SportType {\r\n\r\n\tpublic static final SportType TENNIS = new SportType(1, \"Tennis\");\r\n\tpublic static final SportType SOCCER = new SportType(2, \"Soccer\");\r\n\r\n\tprivate int id;\r\n\tprivate String name;\r\n\r\n\tpublic SportType(int id, String name) {\r\n\t\tthis.id = id;\r\n\t\tthis.name = name;\r\n\t}\r\n\r\n\tpublic static Iterable<SportType> list(){\r\n\t\treturn Arrays.asList(TENNIS, SOCCER);\r\n\t}\r\n\r\n\tpublic static SportType getSport(int id){\r\n\t\tfor(SportType sportType : list()){\r\n\t\t\tif(sportType.getId() == id){\r\n\t\t\t\treturn sportType;\r\n\t\t\t}\r\n\t\t}\r\n\t\treturn null;\r\n\t}\r\n\r\n\t\/**\r\n\t * Getters and Setters\r\n\t *\/\r\n}<\/pre>\n
Here is an example of Case #1:<\/strong> Suppose we want to define a reservation bean, here is how we do it:<\/p>\n
<bean id=\"dummyReservation\" class=\"com.pramati.model.Reservation\">\r\n\t<property name=\"playGround\" value=\"Soccer Court #1\"\/>\r\n\t<property name=\"dateToReserve\" value=\"11-11-2011\"\/>\r\n\t<property name=\"hour\" value=\"15\"\/>\r\n\t<property name=\"captain\">\r\n\t\t<bean class=\"com.pramati.model.Player\">\r\n\t\t\t<property name=\"name\" value=\"Prasanth\"\/>\r\n\t\t\t<property name=\"phone\" value=\"92131233124\"\/>\r\n\t\t<\/bean>\r\n\t<\/property>\r\n\t<property name=\"sportType\">\r\n\t\t<property name=\"id\" value=\"1\"\/>\r\n\t\t<property name=\"name\" value=\"TENNIS\"\/>\r\n\t<\/property>\r\n<\/bean><\/pre>\n
This bean definition is pretty verbose. It could have been more presentable if the definition looks somewhat like this:<\/p>\n
<bean id=\"dummyReservation\" class=\"com.pramati.model.Reservation\">\r\n\t<property name=\"playGround\" value=\"Soccer Court #1\"\/>\r\n\t<property name=\"dateToReserve\" value=\"11-11-2011\"\/>\r\n\t<property name=\"hour\" value=\"15\"\/>\r\n\t<property name=\"captain\" value=\"Prasanth,92131233124\"\/>\r\n\t<property name=\"sportType\" value=\"1,TENNIS\"\/>\r\n<\/bean><\/pre>\n
For this to work, we should tell Spring to use the custom converters in the process of defining a bean.<\/p>\n
Here is an example of Case #2:<\/strong> Suppose I have a JSP in my application which allows user to reserve the playground for a particular time of a day.<\/p>\n
<%@ page language=\"java\" contentType=\"text\/html; charset=ISO-8859-1\" pageEncoding=\"ISO-8859-1\"%>\r\n<%@ taglib prefix=\"form\" uri=\"http:\/\/www.springframework.org\/tags\/form\"%>\r\n<!DOCTYPE html PUBLIC \"-\/\/W3C\/\/DTD HTML 4.01 Transitional\/\/EN\" \"http:\/\/www.w3.org\/TR\/html4\/loose.dtd\">\r\n<html>\r\n<head>\r\n<meta http-equiv=\"Content-Type\" content=\"text\/html; charset=ISO-8859-1\">\r\n<title>Reservation Form<\/title>\r\n<style type=\"text\/css\">\r\n.error {\r\n\tcolor: #ff0000;\r\n\tfont-weight: bold;\r\n}\r\n<\/style>\r\n<\/head>\r\n<body>\r\n\t<form:form method=\"post\" modelAttribute=\"reservation\">\r\n\t\t<table>\r\n\t\t\t<tr>\r\n\t\t\t\t<th>Court Name<\/th>\r\n\t\t\t\t<td><form:input path=\"courtName\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t\t<tr>\r\n\t\t\t\t<th>Reservation Date<\/th>\r\n\t\t\t\t<td><form:input path=\"date\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t\t<tr>\r\n\t\t\t\t<th>Hour<\/th>\r\n\t\t\t\t<td><form:input path=\"hour\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t\t<tr>\r\n\t\t\t\t<th>Player Name<\/th>\r\n\t\t\t\t<td><form:input path=\"player.name\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t\t<tr>\r\n\t\t\t\t<th>Player Contact Number<\/th>\r\n\t\t\t\t<td><form:input path=\"player.phone\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t\t<tr>\r\n\t\t\t\t<th>Sport Type<\/th>\r\n\t\t\t\t<td><form:select path=\"sportType\" items=\"${sportTypes}\"\r\n\t\t\t\t\t\titemLabel=\"name\" itemValue=\"id\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t\t<tr>\r\n\t\t\t\t<td colspan=\"3\"><input type=\"submit\" name=\"Submit\" \/><\/td>\r\n\t\t\t<\/tr>\r\n\t\t<\/table>\r\n\t<\/form:form>\r\n<\/body>\r\n<\/html><\/pre>\n
And here is the corresponding MVC controller:<\/p>\n
@Controller\r\n@RequestMapping\r\n@SessionAttributes(\"reservation\")\r\npublic class ReservationFormController {\r\n\r\n\t@Autowired\r\n\tprivate ReservationService reservationService;\r\n\r\n\t@ModelAttribute(\"sportTypes\")\r\n\tpublic Iterable<SportType> getSportTypes(){\r\n\t\treturn SportType.list();\r\n\t}\r\n\r\n\t@RequestMapping(value=\"\/reservationForm\/{captainName}\", method=RequestMethod.GET)\r\n\tpublic String initForm(Model model, @PathVariable String captainName){\r\n\t\tReservation reservation = new Reservation();\r\n\t\treservation.setPlayer(new Player(captainName, null));\r\n\t\treservation.setSportType(SportType.TENNIS);\r\n\t\tmodel.addAttribute(\"reservation\", reservation);\r\n\t\treturn \"reservationForm\";\r\n\t}\r\n\r\n\t@RequestMapping(value=\"\/reservationForm\/{captainName}\",method=RequestMethod.POST)\r\n\tpublic String reserve(@Valid Reservation reservation, BindingResult bindingResult, SessionStatus sessionStatus){\r\n\t\tvalidator.validate(reservation, bindingResult);\r\n\t\tif(bindingResult.hasErrors()){\r\n\t\t\treturn \"\/reservationForm\";\r\n\t\t} else{\r\n\t\t\treservationService.make(reservation);\r\n\t\t\tsessionStatus.setComplete();\r\n\t\t\treturn \"redirect:..\/reservationSuccess\";\r\n\t\t}\r\n\t}\r\n}<\/pre>\n
Now as you see, in the JSP we are tying the form fields to a Reservation object(modelAttribute=\u201dreservation\u201d). This object is kept in the model by the controller(in initForm() method) which gets passed to the view. Now when we submit the form, Spring throws a validation message saying that the field values can\u2019t be converted to types, Player and SportType. For this to work, we have to define the custom converters and inject them into the Spring MVC flow.
 
<\/div> <\/div><\/p>\n
Now the question is how to define the custom converters? Spring provides two ways of supporting these custom converters:<\/p>\n