margus hanni, nortal as
TRANSCRIPT
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Margus Hanni, Nortal AS
Spring MVC
01.04.2013
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Viited varasematele materjalidele …
2012 – TÜ - Spring MVC – Roman Tekhov
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What is a Web Framework ?
A web framework is a software framework designed to simplify your web development life.Frameworks exist to save you from having to re-invent the wheel and help alleviate some of the overhead when you’re building a new site.
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What is a Web Framework ?
Typically frameworks provide libraries for accessing a database, managing sessions and cookies, creating templates to display your HTML and in general, promote the reuse of code.
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Spring Framework
Open source application framework.Inversion of Control container (IoC).Lots of utility API-s.
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Should I bother?
Spring framework is still extremely popular in Java (web) applications.If you’re going to build web applications in Java then chances are that you will meet Spring.
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Should I bother?
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IoC in Spring
@Service
public class UserService {
@Resource
private UserDao userDao;
public User getByUserName(String name) {
User user = userDao.getByUserName(name);
// additional actions
return user;
}
}
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IoC in Spring
@Service
public class UserService {
@Resource
private UserDao userDao;
public User getByUserName(String name) {
User user = userDao.getByUserName(name);
// additional actions
return user;
}
}
Declare bean, Spring will create it
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IoC in Spring
@Service
public class UserService {
@Resource
private UserDao userDao;
public User getByUserName(String name) {
User user = userDao.getByUserName(name);
// additional actions
return user;
}
}
Declare dependencies, Spring will inject them
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IoC in Spring
Spring handles the infrastructure (bean creation, dependency lookup and injection)Developer focus on application specific logic.
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Dependency injection
public interface UserDao {
User getByUserName(String name);
}
@Repository
public class JdbcUserDao implements UserDao {
public User getByUserName(String name) {
// load user from DB
}
}
@Resource
private UserDao userDao;
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Dependency injection
public interface UserDao {
User getByUserName(String name);
}
@Repository
public class JdbcUserDao implements UserDao {
public User getByUserName(String name) {
// load user from DB
}
}
@Resource
private UserDao userDao;
Universal abstraction
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Dependency injection
public interface UserDao {
User getByUserName(String name);
}
@Repository
public class JdbcUserDao implements UserDao {
public User getByUserName(String name) {
// load user from DB
}
}
@Resource
private UserDao userDao;
One possible implementation.
Spring will create and register it
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Dependency injection
public interface UserDao {
User getByUserName(String name);
}
@Repository
public class JdbcUserDao implements UserDao {
public User getByUserName(String name) {
// load user from DB
}
}
@Resource
private UserDao userDao;
Spring can inject as an abstraction type
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XML based configuration
Bean can also be defined and injected in XML.
<bean id="userDao" class="example.JdbcUserDao" />
<bean id="userService" class="example.UserService">
<property name="userDao" ref="userDao" />
</bean>
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Dependency injection
Your code depends on abstractions, Spring handles actualimplementations.You can switch implementations easily.
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What is MVC?
The Model View Controller (MVC) pattern is a way of organising an application (not necessarily a web application) so that different aspects of it are kept separate. This is a good thing because:
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What is MVC?
It is good software engineering practice to maintain separation of concerns.An application might have more than one user interfaceDifferent developers may be responsible for different aspects of the application.
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Spring MVC
Spring based web framework.Implements the Model-View-Controller design pattern.Very flexible (we’ll see how exactly).
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Spring MVC
IoC again – framework handles the infrastructure, you focus on application specific things.
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Should I bother?
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Should I bother?
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Architecture - DispatcherServlet
http://static.springsource.org/spring/docs/current/spring-framework-reference/html/mvc.html
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Recall: Model-View -Controller
Model - The model represents enterprise data and the business rules that govern access to and updates of this data.View - The view renders the contents of a model.Controller - The controller translates interactions with the view into actions to be performed by the model.
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Recall: Model-View -Controller
http://www.oracle.com/technetwork/java/mvc-detailed-136062.html
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Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
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Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
Declare controller
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Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
Inject Spring resources
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Method for handling requests
Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
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Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
What requests to serve?
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Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
Prepare model data
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Controller
@Controller
public class HelloController {
@Resource
private UserService userService;
@RequestMapping("/hello")
public String hello(Model model) {
User user = userService.getByUserName("Cartman");
model.addAttribute("user", user);
return "hello";
}
}
Logical view name
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Model
Set of attributes that Controller collects and passes to the View.
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Model
Spring’s Model object…
@RequestMapping(value="/hello")
public String hello(Model model) {
User user = userService.getByUserName(“cartman");
model.addAttribute("user", user);
...
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Model
Spring’s Model object…
@RequestMapping(value="/hello")
public String hello(Model model) {
User user = userService.getByUserName(“cartman");
model.addAttribute("user", user);
...
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Model
Or plain java.util.Map
@RequestMapping(value="/hello")
public String hello(Map<String, Object> model) {
User user = userService.getByUserName("cartman");
model.put("user", user);
...
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Model
Or plain java.util.Map
@RequestMapping(value="/hello")
public String hello(Map<String, Object> model) {
User user = userService.getByUserName("cartman");
model.put("user", user);
...
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View
Any representation of output, invoked after the Controller, uses data from the Model to render itself.
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View technologies
Usually Java Server Pages that generate HTML.Out-of-the-box there are also PDF, XML, JSON, Excel and other views.You can create your own.
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View
Controller is totally decoupled from actual view technology.
@RequestMapping("/hello")
public String hello() {
...
return "hello";
}
Just a logical view name to be invoked
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JSP view
<bean class="org.springframework...InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/" />
<property name="suffix" value=".jsp" />
</bean>
"hello” /WEB-INF/jsp/hello.jsp
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JSP view (hello.jsp)
Model attributes are accessible as EL(Expression Language) variables in JSP.
JSP: <p>Hello, ${user.fullName}!</p>
HTML: <p>Hello, Eric Cartman!</p>
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JSON view
JSON view transforms the whole model to JSON format.
<bean
class="org.springframework...ContentNegotiatingViewResolver">
<property name="defaultViews">
<list>
<bean
class="org.springframework...MappingJacksonJsonView" />
</list>
</property>
</bean>
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JSON view
Outputs the Model as JSON document.
{"user":{"fullName":"Eric Cartman"}}
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Request mapping@RequestMapping("/hello")
@RequestMapping(value="/hello",
method=RequestMethod.GET)
@RequestMapping(value="/hello", params=
{"param1", "param2"})
@RequestMapping(value="/hello",
consumes="application/json",
produces="application/json")
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Path variables
@RequestMapping(value="/hello/{username}")
public String hello(
@PathVariable String username,
Model model) {
...
http://[SERVER]/hello/cartman
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Path variables
@RequestMapping(value="/hello/{username}")
public String hello(
@PathVariable String username,
Model model) {
...
http://[SERVER]/hello/cartman
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Request parameters
@RequestMapping(value="/hello")
public String hello(
@RequestParam("username") String username,
Model model) {
...
http://[SERVER]/hello?username=cartman
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Type conversion
HttpServletRequest parameters, headers, paths etc are all Strings.Spring MVC allows you to convert to and from Strings automatically.
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Built-in conversion
There are some standard built-in converters.
@RequestMapping("/foo")
public String foo(
@RequestParam("param1") int intParam,
@RequestParam("param2") long longParam) {
...
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Type conversion
You can also define your own PropertyEditorsPropertyEditorSupport implementsPropertyEditor
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Custom types
public class DateRange {
private Date start;
private Date end;
public DateRange(Date start, Date end) {
this.start = start;
this.end = end;
}
public int getDayDifference() {
// calculate
}
}
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Custom type editor
public class DateRangeEditor extends PropertyEditorSupport {
private DateFormat dateFormat = new SimpleDateFormat("dd.MM.yyyy");
public void setAsText(String text) throws IllegalArgumentException {
String[] parts = text.split("-");
Date start = dateFormat.parse(parts[0]);
Date end = dateFormat.parse(parts[1]);
setValue(new DateRange(start, end));
}
public String getAsText() {
DateRange dateRange = (DateRange) getValue();
return dateFormat.format(dateRange.getStart()) + "-" +
dateFormat.format(dateRange.getEnd());
}
}
String to custom type
Custom type to String
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Register and use
@Controller
public class MyController {
@InitBinder
public void initBinder(WebDataBinder binder) {
binder.registerCustomEditor(DateRange.class,
new DateRangeEditor());
}
@RequestMapping(value="/dateRange")
public String dateRange(@RequestParam("range") DateRange range) {
...
}
}
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Method parameters
It all about IoC and Convention Over Configuration.Your code simply declares what it needs from the environment, Spring makes it happen.The order is not important, the type is.
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Method parameters
Model/Map – model
@RequestParam/@PathVariable annotated
HttpServletRequest, HttpServletResponse, HttpSession – it is all based on Servlet API!
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Method parameters
java.io.Writer / java.io.OutputStream –if you want to generate response directly in controller…
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Method parameters
For example
@RequestMapping(value="/hello")
public String hello(Model model,
Writer writer, HttpServletRequest request,
HttpSession session) {
...
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Return values
Same principle – you return what Spring awaits from you.
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Return value examples
String – logical view name.void
If you write the response in controller If you use default/content negotiating views (like JSON earlier)
…
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Non-intrusive
Very important feature of a framework is non-intrusiveness.Spring MVC normally lets you do stuff according to MVC pattern.But it doesn’t prevent you from violating MVC if you really want to.
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No view examples
@RequestMapping(value="/noView")
@ResponseBody
public String noView() {
return "Too simple for a view";
}
@RequestMapping(value="/noView")
public void noView(Writer writer) {
writer.write("Too simple for a view");
}
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Form
First you need to give Spring a new command object
@RequestMapping(value="/addUser")
public String add(Model model) {
model.addAttribute("user", new User());
return "add";
}
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Command object
public class User {
private String fullName;
private int age;
// getters/setters
...
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Form JSP
<%@ taglib prefix="form"
uri="http://www.springframework.org/tags/form"%>
<form:form commandName="user">
<form:input path="fullName" />
...
<form:input path="age" />
...
<input type="submit" value="Add" />
</form:form>
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Form
Spring will bind the data to our command object
@RequestMapping(value="/addUser", method=RequestMethod.POST)
public String save(User user) {
// save user
return "home";
}
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Validation
JSR-303 defines constraint annotations:
public class User {
@NotNull
@Size(max=20)
private String fullName;
@Min(10)
private int age;
...
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Validation
@RequestMapping(value="/addUser", method=RequestMethod.POST)
public String save(@Valid User user, BindingResult result,
Model model) {
if (result.hasErrors()) {
model.addAttribute("user", user);
return "add";
}
// save user
return "home";
}
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Validation
@RequestMapping(value="/addUser",
method=RequestMethod.POST)
public String save(@Valid User user, BindingResult result,
Model model) {
if (result.hasErrors()) {
model.addAttribute("user", user);
return "add";
}
// save user
return "home";
}
Check for validation errors.
Render the same view in case of errors
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Validation
<%@ taglib prefix="form"
uri="http://www.springframework.org/tags/form"%>
<form:form commandName="user">
<form:input path="fullName" />
<form:errors path="fullName" />
...
<form:input path="age" />
<form:errors path="age" />
...
<input type="submit" value="Add" />
</form:form>
Show validation errors
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Validation
It is of course possible to define your own constraints and validators.
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Sources of wisdomSpring has great documentation: http://www.springsource.org/spring-framework#documentationJava BluePrints - Model-View-Controllerhttp://www.oracle.com/technetwork/java/mvc-detailed-136062.htmlModel-View-Controllerhttp://www.oracle.com/technetwork/java/mvc-140477.htmlInversion of controlhttp://en.wikipedia.org/wiki/Inversion_of_control