Controller Vs RestController annotation in Spring

In this blog post, I will be explaining the Controller and RestController Spring annotations and also their differences.

MVC V/s REST

Before diving into the Controller and RestController annotations, it is important to understand the difference between a normal MVC web application and a REST application. An MVC Web application returns HTML which is rendered in a browser and displayed to end users.  A REST application, on the other hand, returns an XML or JSON response.

Edit

Controller Annotation

You can use the Controller annotation to designate a Controller class in an MVC application. Normally in such scenarios, the code maps each method in the controller to a URL specified via the RequestMappingannotation. When the UI requests a particular URL, the code invokes the appropriate method. This executes the business logic and then redirects the user to the appropriate JSP page.

Consider the following code:

@Controllerpublic class HelloWorldController {  @RequestMapping("/hello")  public ModelAndView helloWorld() {     System.out.println("In HelloWorldController");    String message = "<h1>Hello World</h1>";    return new ModelAndView("hello", "message", message);  }}

 

This specifies that the class HelloWorldControlleris a Controller class. The code executes the method helloWorld

when the UI requests the URL /hello. It returns a ModelAndView object which specifies that the jsp with name “hello” should be displayed to the UI with the message specified.

Using Controller for REST service

You can also use the Controller annotation to create a REST service. As you probably know, a REST service returns am XML or JSON response, it does not return HTML. So when you use the Controller annotation for a REST service, you need to also specify the ResponseBodyannotation. This directly writes the values returned by the method to the Response stream.

Consider the following code snippet:

@Controller@ResponseBodypublic class HelloWorldController {  @GetMapping("/hello")  public String sayHello() {    return "Hello World";  }}

The ResponseBodyannotation is specified along with the Controllerannotation. In this case, too, the code maps the URL /hello to the sayHellomethod. However, this method no longer returns a ModelAndViewobject and does not redirect the user to a JSP page. Instead, this method directly returns a String value. The ResponseBodyannotation converts the Java object returned by the method into the appropriate type (XML or JSON) based on the Content-Type specified in the HTTP request header and writes it to the Response stream.

Instead of using the ResponseBodyannotation on the Controller class, you can also use it along with each method in the Controller too.

RESTController annotation

As seen above, you can use the Controllerand ResponseBody annotations to create a REST service. Instead of using two annotations, Spring 4.0 introduced the RestController annotation. So the RestControllerannotation is a convenience controller which combines the behavior of the  Controllerand ResponseBodyannotations.

So the above code can be re-written as follows:

@RestControllerpublic class HelloWorldController {  @GetMapping("/hello")  public String sayHello() {    return "Hello World";  }  }

This specifies that the class HelloWorldControlleris a Rest Controller. The code behaves exactly the way it would have if a Controllerand ResponseBodyannotation was used. So the String value returned by the method is converted into the appropriate type (XML or JSON) and written to the Response stream.

Differences

Edit
ControllerRestController
Normally used for an MVC controller, ut can be used for a REST service in conjunction with the ResponseBody annotationUsed for a RestController i.e. a Controller for a REST service
Methods in a Controller return a ModelAndViewMethods in a RestController directly return Java Objects which are written to the Response stream
Methods in a controller look for a view to display HTML to the UIMethods in a RestController directly write the Java objects into the Response stream which is converted to JSON or XML format
Present in Spring right from the startAdded in Spring 4.0

Further Learning

Spring MasterClass
Spring Tutorial For Beginners
Step by Step Spring MVC Tutorial
Spring Framework in Easy Steps

Comments

Post a Comment

Popular posts from this blog

How to use logging in SpringBoot with code samples

Image
In this article, we will learn how to use logging in SpringBoot. Introduction There are several Java logging frameworks like logback, log4j, and so on. Spring Boot supports out-of-the-box support for logback. Let us learn how to use logging in SpringBoot with logback. Step 1 – Create a New Maven Project Create a new Maven project. (Refer to  this  blog post). This will create a project in Eclipse as follows:   Step 2 – Add the Spring Boot Dependencies Add the spring-boot-starter-web dependency to the pom.xml . So, the pom.xml should look as follows: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.learnjava</groupId> <artifactId>learnjava-springboot-logging-example</artifactId> <version>0.0.1-SNAPSHOT&
Read more

Python While Loop with code samples

Much like a Java while loop, you can use a Python while loop to repeatedly execute a block of code as long as a condition is true. In this article, we will learn more about the Python while loop. Python While loop Syntax A while loop in Python has the following syntax: while <condition>: loop body The while keyword is followed by a condition. If the condition evaluates to true, the body of the loop is executed. Once the body of the loop is completed, the condition is checked again and this is repeated until the condition evaluates to false at which point the loop is exited. While loop Sample Code The following code demonstrates how you can use the while loop: num=10counter=1total=0while counter<=num: total += counter counter+=1print("sum of first 10 numbers is",total) This code adds the numbers from 1 to 10 and prints the sum. It uses a while loop to iterate from 1 to 10. The while loop checks the condition counter <= num and if so adds the current value of count
Read more

How to convert a List to a Set

In this blog post ,I will be showing you how you can convert a List to a Set. Consider the following code snippet: public class ListToSetDemo {public static void main(String[] args) {List<Integer> list = Arrays.asList(5,3,11,15,9);//Method 1Set<Integer> set = new HashSet<Integer>(list);System.out.println("Set is "+set);//method 2Set<Integer> set2 = new HashSet<Integer>();set2.addAll(list);System.out.println("Set is "+set2);}} This code demonstrates two ways to convert a List to a Set. Method 1 Here, we are creating a new HashSet . We are invoking the constructor that accepts a Collection object. Here, we are passing in the input list to this constructor.   Method 2 Here again, we are creating a new HashSet . However, we are using the default constructor. We are then invoking the addAll method and passing in the input list.   When you run this code, it will print the following output: Set is [3, 5, 9, 11, 15]Set is [3, 5, 9, 11, 15] No
Read more