Spring mvc build a simple rest api

Trong bài viết này chúng ta sẽ build 1 restful api đơn giản sử dụng spring mvc. Dưới đây là các api

• GET request to /api/user/ returns a list of users
• GET request to /api/user/1 returns the user with ID 1
• POST request to /api/user/ with a user object as JSON creates a new user
• PUT request to /api/user/3 with a user object as JSON updates the user with ID 3
• DELETE request to /api/user/4 deletes the user with ID 4
• DELETE request to /api/user/ deletes all the users

Step1: Tạo maven project sau đó khai báo các dependencies trong file pom.xml như dưới đây:

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.websystique.springmvc</groupId>
  <artifactId>Spring4MVCCRUDRestService</artifactId>
  <packaging>war</packaging>
  <version>1.0.0</version>
  <name>Spring4MVCCRUDRestService Maven Webapp</name>
 
    <properties>
        <springframework.version>4.2.0.RELEASE</springframework.version>
        <jackson.version>2.5.3</jackson.version>
    </properties>
 
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>${springframework.version}</version>
        </dependency>
 
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
        </dependency>
             
    </dependencies>
 
 
    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.2</version>
                    <configuration>
                        <source>1.7</source>
                        <target>1.7</target>
                    </configuration>
                </plugin>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-war-plugin</artifactId>
                    <version>2.4</version>
                    <configuration>
                        <warSourceDirectory>src/main/webapp</warSourceDirectory>
                        <warName>Spring4MVCCRUDRestService</warName>
                        <failOnMissingWebXml>false</failOnMissingWebXml>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>
 
        <finalName>Spring4MVCCRUDRestService</finalName>
    </build>
</project>

Step2: Tạo User service

• Tạo User service interface

package com.websystique.springmvc.service;
 
import java.util.List;
 
import com.websystique.springmvc.model.User;
 
 
 
public interface UserService {
     
    User findById(long id);
     
    User findByName(String name);
     
    void saveUser(User user);
     
    void updateUser(User user);
     
    void deleteUserById(long id);
 
    List<User> findAllUsers(); 
     
    void deleteAllUsers();
     
    public boolean isUserExist(User user);
     
}

• Implement User service

package com.websystique.springmvc.service;
 
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;
 
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
 
import com.websystique.springmvc.model.User;
 
@Service("userService")
@Transactional
public class UserServiceImpl implements UserService{
     
    private static final AtomicLong counter = new AtomicLong();
     
    private static List<User> users;
     
    static{
        users= populateDummyUsers();
    }
 
    public List<User> findAllUsers() {
        return users;
    }
     
    public User findById(long id) {
        for(User user : users){
            if(user.getId() == id){
                return user;
            }
        }
        return null;
    }
     
    public User findByName(String name) {
        for(User user : users){
            if(user.getName().equalsIgnoreCase(name)){
                return user;
            }
        }
        return null;
    }
     
    public void saveUser(User user) {
        user.setId(counter.incrementAndGet());
        users.add(user);
    }
 
    public void updateUser(User user) {
        int index = users.indexOf(user);
        users.set(index, user);
    }
 
    public void deleteUserById(long id) {
         
        for (Iterator<User> iterator = users.iterator(); iterator.hasNext(); ) {
            User user = iterator.next();
            if (user.getId() == id) {
                iterator.remove();
            }
        }
    }
 
    public boolean isUserExist(User user) {
        return findByName(user.getName())!=null;
    }
 
    private static List<User> populateDummyUsers(){
        List<User> users = new ArrayList<User>();
        users.add(new User(counter.incrementAndGet(),"Sam",30, 70000));
        users.add(new User(counter.incrementAndGet(),"Tom",40, 50000));
        users.add(new User(counter.incrementAndGet(),"Jerome",45, 30000));
        users.add(new User(counter.incrementAndGet(),"Silvia",50, 40000));
        return users;
    }
 
    public void deleteAllUsers() {
        users.clear();
    }
 
}

Step 3: Tạo model class:

package com.websystique.springmvc.model;
 
public class User {
 
    private long id;
     
    private String name;
     
    private int age;
     
    private double salary;
 
    public User(){
        id=0;
    }
     
    public User(long id, String name, int age, double salary){
        this.id = id;
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
     
    public long getId() {
        return id;
    }
 
    public void setId(long id) {
        this.id = id;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public double getSalary() {
        return salary;
    }
 
    public void setSalary(double salary) {
        this.salary = salary;
    }
 
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + (int) (id ^ (id >>> 32));
        return result;
    }
 
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        User other = (User) obj;
        if (id != other.id)
            return false;
        return true;
    }
 
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age
                + ", salary=" + salary + "]";
    }
 
 
}

Step 4: Tạo các configuration class

• Configuration class

package com.websystique.springmvc.configuration;
 
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
 
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.websystique.springmvc")
public class HelloWorldConfiguration {
     
 
}

• Initialization Class

package com.websystique.springmvc.configuration;
 
import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;
 
public class HelloWorldInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
  
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] { HelloWorldConfiguration.class };
    }
   
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return null;
    }
   
    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }
  
}

Step 5: Tạo Rest Controller

package com.websystique.springmvc.controller;
 
import java.util.List;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
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 org.springframework.web.util.UriComponentsBuilder;
 
import com.websystique.springmvc.model.User;
import com.websystique.springmvc.service.UserService;
 
@RestController
public class HelloWorldRestController {
 
    @Autowired
    UserService userService;  //Service which will do all data retrieval/manipulation work
 
     
    //-------------------Retrieve All Users--------------------------------------------------------
     
    @RequestMapping(value = "/user/", method = RequestMethod.GET)
    public ResponseEntity<List<User>> listAllUsers() {
        List<User> users = userService.findAllUsers();
        if(users.isEmpty()){
            return new ResponseEntity<List<User>>(HttpStatus.NO_CONTENT);//You many decide to return HttpStatus.NOT_FOUND
        }
        return new ResponseEntity<List<User>>(users, HttpStatus.OK);
    }
 
 
    //-------------------Retrieve Single User--------------------------------------------------------
     
    @RequestMapping(value = "/user/{id}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<User> getUser(@PathVariable("id") long id) {
        System.out.println("Fetching User with id " + id);
        User user = userService.findById(id);
        if (user == null) {
            System.out.println("User with id " + id + " not found");
            return new ResponseEntity<User>(HttpStatus.NOT_FOUND);
        }
        return new ResponseEntity<User>(user, HttpStatus.OK);
    }
 
     
     
    //-------------------Create a User--------------------------------------------------------
     
    @RequestMapping(value = "/user/", method = RequestMethod.POST)
    public ResponseEntity<Void> createUser(@RequestBody User user,    UriComponentsBuilder ucBuilder) {
        System.out.println("Creating User " + user.getName());