Bookstore (1) Build a backend service using Springboot
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I built a bookstore website like Amazon last year. The backend is supported by Struts, Spring, and Hibernate (SSH). Recently, I am reconstructing the website using Springboot. Ideally, an enterprise-level information system. A series of articles will show the information system in detail. You can find the code here.
What is Struts, Spring, and Hibernate (SSH)?
- Struts: a framework of Web MVC (model, view, controller)
- Spring: manage the relationships between Java classes using DI (dependency injection) like a glue
- You are freed of considering memory allocation, life cycle of a object, and garbage collection.
- How to do: register a class as a Java bean, then spring will manage the bean. You just need to declare a object like the below then the object will be injected in democlass
public class democlass{
private TestClass tc;
}
- Hibernate: map a class and a table in a database
- You never ever bother writing a SQL sentence.
Springboot
SSH is an out-dated stuff which has been replaced by Springboot.
Springboot is amaming in that:
- You do not configure those xml files any more.
- You can use annotations to do a lot of things.
- You write less codes.
Backend demo
Our current goal:
- Map a RESTFUL url to an action in the backend
- Connect the backend and MYSQL database
- CRUD (create, read, update, delete) operations
Step 1: Create a springboot project
It seems simple in this step. Actually, this step may be very confusing. Many tutorials mislead readers and I’m a victim as well. Therefore, I decide to go into the details.
First, click on the button “Create New Project”. Note that clicking “Import Project” and “Open” differs in that “Import Project” will configure the project in some unexpected way while “Open” opens files like an editor. It is recommended to use “Open” then configure the dependencies. This is what painful experiences tell me.
Second, choose “Spring Initializr” like in the image. I got really despaired when first time saw this page.
Third, notice the “Package”, this will be the name of your main directory.
Fourth, choose “web”. If you wanna use other applications you can add the maven dependenies later.
Step 2: Organize the dictionary
Organize the dictionary like below:
It demonstrates the idea of layering.
- Controller: map a RESTFUL URL to a service
- Model: define objetcs
- Repository: CRUD operations to synchronize objects with databases
- Service: define business logic services by combining operations in Repository layer
Step 3: Coding
Before coding, you should know the meanings of anotations.
Springboot annotations:
- @SpringBootApplication
- A necessary configuration for springboot
- @SpringBootApplication = @Configuration + @EnableAutoConfiguration + @ComponentScan
- @Configuration：equals to the traditional xml files
- @AutoWired：auto inject a registered bean
- @RestController + @RequestMapping(“/test”)
- Always used together
- @RestController: methods in a class return a json
- @Component @Controller @Repository @Service
- Define beans的 (without these four annotations，a class cannot be registered as a bean and cannot be injected to other classes using @autowired)
- @Component: most general
- @Service, @Repository: is a type of @Component but with different meanings * For reading code conveniently * In the aspect of compiling, @Component, @Service, @Repository will not cause errors even if using @Service in Repository layer * @Service used in Service layer, @Repository used in Repository layer
- @Controller: cannot be replaced by @Component, @Repository, or @Service * @RestController includes @Controller
You also need to get familiar with JPA. JPA is for operating data in databases. Note that I just declare a function like in UserRepository.java and don’t implement it after extending JPA.
Take User services as an instance.
In UserController.java:
package com.zhengyu.bookstore.Controller;
import com.zhengyu.bookstore.model.User;
import com.zhengyu.bookstore.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import java.util.List;
@RestController
@RequestMapping("/users")
public class UserController {
@Autowired
private UserService userService;
@ResponseBody
@PostMapping("/addUser")
public User addUser(User user)
{
return userService.insert(user);
}
@ResponseBody
@GetMapping("/getAllUsers")
public List<User> getAllUser()
{
return userService.getAllUsers();
}
@ResponseBody
@PostMapping("/deleteByUserId")
public boolean deleteByUserId(int userId){
return userService.deleteUser(userId);
}
@ResponseBody
@PostMapping("/updateUser")
public void updateUser(User user)
{
userService.updateUser(user);
}
}
In User.java:
package com.zhengyu.bookstore.model;
import javax.persistence.*;
import java.util.Objects;
@Entity
@Table(name = "users")
public class User {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
@Column(nullable = false)
private String username;
@Column(nullable = false)
private String password;
@Column(nullable = false)
private String role;
@Column(nullable = false)
private String intro;
public User() {
}
public User(String username, String password, String role, String intro) {
this.username = username;
this.password = password;
this.role = role;
this.intro = intro;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getRole() {
return role;
}
public void setRole(String role) {
this.role = role;
}
public String getIntro() {
return intro;
}
public void setIntro(String intro) {
this.intro = intro;
}
}
In UserRepository.java:
package com.zhengyu.bookstore.repository;
import com.zhengyu.bookstore.model.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;
import java.util.List;
@Repository
public interface UserRepository extends JpaRepository<User,Integer> {
User findById(int userId);
}
In UserService interface:
package com.zhengyu.bookstore.service;
import com.zhengyu.bookstore.model.User;
import java.util.List;
public interface UserService {
User insert(User user);
boolean deleteUser(int id);
void updateUser(User user);
User getUserById(int id);
List<User> getAllUsers();
}
In UserServiceImpl.java:
package com.zhengyu.bookstore.service.impl;
import com.zhengyu.bookstore.model.User;
import com.zhengyu.bookstore.repository.UserRepository;
import com.zhengyu.bookstore.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserRepository userRepository;
public User insert(User user) {
try {
//插入前先看看这个id在数据库中是否存在
//存在则不在插入
User tmpUser=userRepository.findById(user.getId());
if(tmpUser!=null)
return null;
return userRepository.saveAndFlush(user);
}
catch (Exception e){
return null;
}
}
public boolean deleteUser(int id) {
try {
userRepository.deleteById(id);
return true;
}
catch (Exception e){
return false;
}
}
public void updateUser(User user) {
userRepository.updateById(user.getUsername(),user.getId());
}
public User getUserById(int id) {
return userRepository.findById(id);
}
public List<User> getAllUsers() {
return userRepository.findAll();
}
}
In application.properties (the only configuration file to connect to MYSQL database):
server.port=8080
# Hibernate
#hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
hibernate.show_sql=true
#hibernate.hbm2ddl.auto= update
spring.datasource.url=jdbc:mysql://localhost:3306/bookstore_test
spring.datasource.username=root
spring.datasource.password=000
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.jpa.properties.hibernate.hbm2ddl.auto=update
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
Finally, I highly recommend you to read the references.