Show me my file first so it’s easier to explain.
1. Create a simple Spring Boot project.
What I created myself is a project of the user
public class User {
private Integer id;
private String name;
public User(Integer id, String name) {
this.id = id;
this.name = name;
}
}
2. Configure project dependencies, including Spring Boot and MySQL connection driver.
Be sure to write it in the big tag of
The code is as follows:
<dependency>
<groupId>com.mysql</groupId>
<artifactId>mysql-connector-j</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
3. Use JdbcTemplate to create a MySQL database and design an appropriate data table.
The data.sql in the db package of resources is created as follows:
drop table if exists user;
create table user(
id int(12) auto_increment primary key,
namevarchar(100)
)engine=InnoDB;
Insert the user name in schema.sql in the db package of resources:
insert into user(name) values ('Hex');
insert into user(name) values ('Master');
insert into user(name) values ('He Rensi');
insert into user(name) values ('Rongguisa');
insert into user(name) values ('Niu Feier');
insert into usSer(name) values ('Haoran');
4. Write the Spring Boot configuration file and configure the connection information between JdbcTemplate and MySQL.
Note: It is possible that your database is different from my database address and name, please modify it according to the situation.
5. Create a DAO class in the project and use JdbcTemplate to complete the addition, deletion, modification and query operations of the database.
Here is how your application to the database looks like
@Service
public class UserDao {
JdbcTemplate template;
@Autowired
public UserDao(JdbcTemplate template){
this.template=template;
}
public List<User> getAll(){
String sql="select * from user";
return template.query(sql,(rs,rowNum)->{
User entity=new User();
entity.setId(rs.getInt("id"));
entity.setName(rs.getString("name"));
return entity;
});
}
public User getById(Integer id){
String sql="select * from user where id=?";
return template.queryForObject(sql
,new Object[]{id}
,new BeanPropertyRowMapper<>(User.class));
}
public int add(User entity){
String sql="insert into user(name) values(?)";
return template.update(sql,entity.getName());
}
public int update(User entity){
String sql="update user set name=? where id=?";
return template.update(sql,entity.getName(),entity.getId());
}
public int delete(Integer id){
String sql="delete from user where id=?";
return template.update(sql,id);
}
}
6. Create a Controller class in the project and provide corresponding interfaces to access database operations.
@RestController
@RequestMapping("/user")
public class UserController {
UserDao dao;
@Autowired
public UserController(UserDao dao){
this.dao=dao;
}
@RequestMapping("/list")
public List<User> getAll(){
return dao.getAll();
}
@RequestMapping("/getById/{userId}")
public User findById(@PathVariable("userId") Integer id){
return dao.getById(id);
}
@RequestMapping("/insert")
public String insert(){
User entity=new User();
entity.setName("Test Username");
return dao.add(entity)>0?"Add successfully":"fail";
}
@RequestMapping("/edit")
public String edit(){
User entity=new User();
entity.setId(9);
entity.setName("Test username-update");
return dao.update(entity)>0?"Modification successful":"fail";
}
@RequestMapping("/delete/{userId}")
public String delete(@PathVariable("userId") Integer id){
return dao.delete(id)>0?"Delete successfully":"Data not found";
}
}
7. Implement the following functions:
– Insert a piece of data into the database. 
– Query all data in the database. 
– Query data in the database based on conditions. 
– Update data in the database.
Later I found that the above update data was a pitfall of the teacher. The update failed. Then I thought about what I had learned in class before, modified it and it worked. It can be solved in just a few sentences, just rewrite it, hahaha Ha ha
@PostMapping("/edit")
public String edit(@RequestBody User entity){
return dao.update(entity)>0?"Modification successful":"fail";
}
– Delete data from the database.
The first piece of data has been deleted
Final summary:
As long as you follow the step-by-step approach every time you write a project, it will be much faster. When a bug occurs, you can also use breakpoints to find it. If you really can’t find it, just use another method to write it.