For example, you can use an interceptor to add the request header before sending the request to the controller and add the response header before sending the response to the client.

To work with interceptor, you need to create @Component class that supports it and it should implement the HandlerInterceptor interface.

The following are the three methods you should know about while working on Interceptors −

preHandle() method − This is used to perform operations before sending the request to the controller. This method should return true to return the response to the client.
postHandle() method − This is used to perform operations before sending the response to the client.
afterCompletion() method − This is used to perform operations after completing the request and response.

Observe the following code for a better understanding −

@Componentpublic class ProductServiceInterceptor implements HandlerInterceptor { @Override public boolean preHandle( HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { return true; } @Override public void postHandle( HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {} @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception exception) throws Exception {}}

You will have to register this Interceptor with InterceptorRegistry by using WebMvcConfigurerAdapter as shown below −

@Componentpublic class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter { @Autowired ProductServiceInterceptor productServiceInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(productServiceInterceptor); }}

In the example given below, we are going to hit the GET products API which gives the output as given under −

The code for the Interceptor class ProductServiceInterceptor.java is given below −

package com.tecklearn.demo.interceptor; import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse; import org.springframework.stereotype.Component;import org.springframework.web.servlet.HandlerInterceptor;import org.springframework.web.servlet.ModelAndView; @Componentpublic class ProductServiceInterceptor implements HandlerInterceptor { @Override public boolean preHandle (HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { System.out.println(“Pre Handle method is Calling”); return true; } @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { System.out.println(“Post Handle method is Calling”); } @Override public void afterCompletion (HttpServletRequest request, HttpServletResponse response, Object handler, Exception exception) throws Exception { System.out.println(“Request and Response is completed”); }}

The code for Application Configuration class file to register the Interceptor into Interceptor Registry – ProductServiceInterceptorAppConfig.java is given below −

package com.tecklearn.demo.interceptor; import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Component;import org.springframework.web.servlet.config.annotation.InterceptorRegistry;import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter; @Componentpublic class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter { @Autowired ProductServiceInterceptor productServiceInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(productServiceInterceptor); }}

The code for Controller class file ProductServiceController.java is given below −

package com.tecklearn.demo.controller; import java.util.HashMap;import java.util.Map; import org.springframework.http.HttpStatus;import org.springframework.http.ResponseEntity;import org.springframework.web.bind.annotation.PathVariable;import org.springframework.web.bind.annotation.RequestBody;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestMethod;import org.springframework.web.bind.annotation.RestController;import com.tecklearn.demo.exception.ProductNotfoundException;import com.tecklearn.demo.model.Product; @RestControllerpublic class ProductServiceController { private static Map<String, Product> productRepo = new HashMap<>(); static { Product honey = new Product(); honey.setId(“1”); honey.setName(“Honey”); productRepo.put(honey.getId(), honey); Product almond = new Product(); almond.setId(“2”); almond.setName(“Almond”); productRepo.put(almond.getId(), almond); } @RequestMapping(value = “/products”) public ResponseEntity<Object> getProduct() { return new ResponseEntity<>(productRepo.values(), HttpStatus.OK); }}

The code for POJO class for Product.java is given below −

package com.tecklearn.demo.model; public class Product { private String id; private String name; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; }}

The code for main Spring Boot application class file DemoApplication.java is given below −

package com.tecklearn.demo; import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplicationpublic class DemoApplication { public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); }}

The code for Maven build – pom.xml is shown here −

<?xml version = “1.0” encoding = “UTF-8”?><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 http://maven.apache.org/xsd/maven-4.0.0.xsd”> <modelVersion>4.0.0</modelVersion> <groupId>com.tecklearn</groupId> <artifactId>demo</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>demo</name> <description>Demo project for Spring Boot</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.8.RELEASE</version> <relativePath/> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>

The code for Gradle Build build.gradle is shown here −

buildscript { ext { springBootVersion = ‘1.5.8.RELEASE’ } repositories { mavenCentral() } dependencies { classpath(“org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}”) }}apply plugin: ‘java’apply plugin: ‘eclipse’apply plugin: ‘org.springframework.boot’group = ‘com.tecklearn’version = ‘0.0.1-SNAPSHOT’sourceCompatibility = 1.8 repositories { mavenCentral()}dependencies { compile(‘org.springframework.boot:spring-boot-starter-web’) testCompile(‘org.springframework.boot:spring-boot-starter-test’)}

You can create an executable JAR file, and run the Spring Boot application by using the below Maven or Gradle commands.

For Maven, use the command as shown below −

mvn clean install

After “BUILD SUCCESS”, you can find the JAR file under the target directory.

For Gradle, use the command as shown below −

gradle clean build

After “BUILD SUCCESSFUL”, you can find the JAR file under the build/libs directory.

You can run the JAR file by using the following command −

java –jar <JARFILE>

Now, the application has started on the Tomcat port 8080 as shown below −

Now hit the below URL in POSTMAN application and you can see the output as shown under −

GET API: http://localhost:8080/products

In the console window, you can see the System.out.println statements added in the Interceptor as shown in the screenshot given below −

So, this brings us to the end of blog. This Tecklearn ‘Spring Boot – Interceptor’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Spring Boot and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

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