A simple form using Spring
The class tree and diagram looks like this:
The UserManagementController at the beginning consists of two private properties userDatabase, userIdSequence and a synchronized private method getNextUserId() which yields another user ID by incrementing userIdSequence. There is also a request handler method displayUsers(map) that retrieves a map of users from userDatabase property, saves it into a model map employing a "userList" string as id and returns the name of the proper view "user/list" as a string.
@Controller
public class UserManagementController
{
private final Map<Long, User> userDatabase = new Hashtable<>();
private volatile long userIdSequence = 1L;
@RequestMapping(value = "user/list", method = RequestMethod.GET)
public String displayUsers(Map<String, Object> model)
{
model.put("userList", this.userDatabase.values());
return "user/list";
}
...
private synchronized long getNextUserId()
{
return this.userIdSequence++;
}
}The User as a simple POJO has three private fields userId, username, name and the relevant mutators and accessors.
The WEB-INF/jsp/view/user/list.jsp does two things. First it enables adding new user using <c:url> tag to fill a value of href property inside a HTML link. Second it provides viewing the existing users (if exist any), utilizing <c:forEach> tag to iterate through a map of users "${userList}".
<%--@elvariable id="userList" type="java.util.Collection<klm.pstryk.site.User>"--%>
<!DOCTYPE html>
<html>
<head>
<title>User List</title>
</head>
<body>
<h2>Users</h2>
[<a href="<c:url value="/user/add" />">new user</a>]<br />
<br />
<c:forEach items="${userList}" var="user">
${user.name} (${user.username})
[<a href="<c:url value="/user/edit/${user.userId}"/>">edit</a>]<br/>
</c:forEach>
</body>
</html>Following we have another request handler method createUser(map) that constructs a new UserForm object, saves it into a model map as a "userForm", returns the user/add view name.
@RequestMapping(value = "user/add", method = RequestMethod.GET)
public String createUser(Map<String, Object> model)
{
model.put("userForm", new UserForm());
return "user/add";
}Next we have a similar request handler method editUser(map model, long userId). It captures the User being edited from userDatabase map using userId, constructs and populates a new UserForm object, exposes to the model and returns the appropriate view name - user/edit.
@RequestMapping(value = "user/edit/{userId}", method = RequestMethod.GET)
public String editUser(Map<String, Object> model,
@PathVariable("userId") long userId)
{
User user = this.userDatabase.get(userId);
UserForm form = new UserForm();
form.setUsername(user.getUsername());
form.setName(user.getName());
model.put("userForm", form);
return "user/edit";
}
Instead of the UserForm object I could easily use User object but I would like to distinguish form objects and business objects.
The views /WEB_INF/jsp/view/user/add.jsp and /WEB_INF/jsp/view/user/edit.jsp set the title Expression Language variable and include the /WEB_INF/jsp/view/user/form.jspf that is a template for the form.
<c:set var="title" value="Add User" />
<%@ include file="form.jspf" %><c:set var="title" value="Edit User" />
<%@ include file="form.jspf" %><%--@elvariable id="userForm" type="klm.pstryk.site.UserForm"--%>
<!DOCTYPE html>
<html>
<head>
<title>${title}</title>
</head>
<body>
<h1>${title}</h1>
<form:form method="post" modelAttribute="userForm">
<form:label path="username">Username</form:label><br />
<form:input path="username" /><br />
<br />
<form:label path="name">Name:</form:label><br />
<form:input path="name" /><br />
<br />
<input type="submit" value="Save" />
</form:form>
</body>
</html>To pick up the form submission data I need to employ HTTP POST method this is RequestMethod.POST in my case. The Spring converter called FormHttpMessageConverter (path ..) renders automatically the UserForm object from request parameters and the request handler methods createUser(UserForm), editUser(UserForm, long) make use of it.
@RequestMapping(value = "user/add", method = RequestMethod.POST)
public View createUser(UserForm form)
{
User user = new User();
user.setUserId(this.getNextUserId());
user.setUsername(form.getUsername());
user.setName(form.getName());
this.userDatabase.put(user.getUserId(), user);
return new RedirectView("/user/list", true, false);
} @RequestMapping(value = "user/edit/{userId}", method = RequestMethod.POST)
public View editUser(UserForm form, @PathVariable("userId") long userId)
{
User user = this.userDatabase.get(userId);
user.setUsername(form.getUsername());
user.setName(form.getName());
return new RedirectView("/user/list", true, false);
}The Spring automatically bounds the UserForm object on the model to the form fields in the view. When editing an existing user, the values from the form <form:form method="post" modelAttribute="userForm"> from the model attribute "userForm" are automtically copied into the relevant form fields.