Spring boot REST: Add interceptor to REST APIs

Step 1: Create interceptor by implementing HandlerInterceptor interface.

public class PerformanceInterceptor implements HandlerInterceptor {

    private long startTime;

    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        startTime = System.nanoTime();
        return true;

    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            @Nullable ModelAndView modelAndView) throws Exception {
        long executionTime = System.nanoTime() - startTime;
        System.out.println(
                "Total execution time for " + request.getServletPath() + " is " + executionTime + " nano seconds");
    }
}

Step 2: Add the interceptor to specific path patterns.

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new PerformanceInterceptor()).addPathPatterns("/api/v1/employees");
    }

}

Find the below working application.

App.java

package com.sample.app;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App {
    public static void main(String[] args) {

        SpringApplication.run(App.class, args);

    }
}

InterceptorConfig.java

package com.sample.app.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import com.sample.app.interceptors.PerformanceInterceptor;

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new PerformanceInterceptor()).addPathPatterns("/api/v1/employees");
    }

}

EmployeeController.java

package com.sample.app.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.sample.app.model.Employee;
import com.sample.app.repository.EmployeeRepository;

@RestController
@RequestMapping("api/v1/")
public class EmployeeController {
    
    @Autowired
    EmployeeRepository empRepo;

    @RequestMapping(value = "employees", method = RequestMethod.GET)
    public ResponseEntity<List<Employee>> all(){
        return ResponseEntity.ok(empRepo.all());
    }
}

HomeController.java

package com.sample.app.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HomeController {

    @RequestMapping("/")
    public String home() {
        return "Welcome to spring boot REST App development";
    }

}

PerformanceInterceptor.java

package com.sample.app.interceptors;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.lang.Nullable;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class PerformanceInterceptor implements HandlerInterceptor {

    private long startTime;

    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        startTime = System.nanoTime();
        return true;

    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            @Nullable ModelAndView modelAndView) throws Exception {
        long executionTime = System.nanoTime() - startTime;
        System.out.println(
                "Total execution time for " + request.getServletPath() + " is " + executionTime + " nano seconds");
    }
}

Employee.java

package com.sample.app.model;

public class Employee {
    private int id;
    private String firstName;
    private String lastName;
    private String country;

    public Employee(int id, String firstName, String lastName, String country) {
        super();
        this.id = id;
        this.firstName = firstName;
        this.lastName = lastName;
        this.country = country;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }

}

EmployeeRepository.java

package com.sample.app.repository;

import java.util.ArrayList;
import java.util.List;

import org.springframework.stereotype.Repository;

import com.sample.app.model.Employee;

@Repository
public class EmployeeRepository {

    private static final List<Employee> emps = new ArrayList<>();

    static {
        Employee emp1 = new Employee(1, "Sunil", "Dayanand", "India");
        Employee emp2 = new Employee(2, "Keerthi", "Shetty", "India");
        Employee emp3 = new Employee(3, "Ram", "Anand", "United States Of America");

        emps.add(emp1);
        emps.add(emp2);
        emps.add(emp3);

    }

    public List<Employee> all() {
        return emps;
    }

}

pom.xml

<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>springRest</groupId>
    <artifactId>springRest</artifactId>
    <version>1</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
    </parent>

    <name>springbootApp</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
</project>

Total project structure looks like below.

Run App.java.

Open the url ‘http://localhost:8080/api/v1/employees’ in browser, you can see below kind of message in console.

Total execution time for /api/v1/employees is 138007646 nano seconds

You can download complete working application from this link.

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