In-depth explanation of Mybatis series (1)---Getting started with Mybatis

In the past two years, the combination of springmvc + mybatis has been quite popular. As for the original poster, I have never really come into contact with mybatis. I will learn mybatis while I have some free time these days. This time, I plan to do a series of tutorials about mybatis based on my own learning progress, record my learning process, and also explore it for friends who have not yet come into contact with mybatis. This series of tutorials is intended to go from shallow (use) to deep (analyzing mybatis source code implementation), so it may take several days to complete the update. Okay, let’s start this mybatis learning journey. This is the first tutorial. Let’s simply write a demo and get to know mybatis together.​

For convenience, I use maven. As for how to use maven, I will not introduce it. If you have never used Maven, it will not affect your reading.

1. Mybatis environment setup and simple examples

1. Create a new web project and add dependency packages: mybatis package, database driver package (I use mysql), Log package (I use log4j), since I am a maven project, adding dependency packages is simple, just add dependencies directly in pom.xml.

pom.xml:

      
    
      junit
      junit
      4.11
      test
    
    
    
    
        log4j
      log4j
        1.2.16
    
    
    
    
        org.mybatis
      mybatis
        3.2.6
    
    
    
    
        mysql
        mysql-connector-java
        5.1.12
    
    
  

2. Configure log4j, configure mybatis

Create a configuration file on the classpath for configuring log4j log4j.properties, and then create a configuration file configuration.xml for configuring Mybatis (the file can be named arbitrarily). I won’t say much about the configuration of log4j. Here I will mainly talk about configuration.xml:

configuration.xml:

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 12      
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 19           
26          
27          
28          
29          
30          
31          
32          
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3. Start writing Demo

First, create a table user:

in mysql database test1 　

Then, start writing java code.

Take a look at my project structure:

First write an entity class User: The User class is used to correspond to the User table .

User:

 1 package com.dy.entity; 
 2  
 3 public class User { 
 4  
 5     private int id; 
 6     private String name; 
 7     private String password; 
 8     private int age; 
 9     private int deleteFlag;
 10     
 11     public int getId() {
 12         return id;
 13     }
 14     public void setId(int id) {
 15         this.id = id;
 16     }
 17     public String getName() {
 18         return name;
 19     }
 20     public void setName(String name) {
 21         this.name = name;
 22     }
 23     public String getPassword() {
 24         return password;
 25     }
 26     public void setPassword(String password) {
 27         this.password = password;
 28     }
 29     public int getAge() {
 30         return age;
 31     }
 32     public void setAge(int age) {
 33         this.age = age;
 34     }
 35     public int getDeleteFlag() {
 36         return deleteFlag;
 37     }
 38     public void setDeleteFlag(int deleteFlag) {
 39         this.deleteFlag = deleteFlag;
 40     }
 41     
 42 }

Write another UserDao interface:

UserDao:

 1 package com.dy.dao; 
 2  
 3 import java.util.List; 
 4  
 5 import com.dy.entity.User; 
 6  
 7 public interface UserDao { 
 8  
 9     public void insert(User user);
 10     
 11     public User findUserById (int userId);
 12     
 13     public List findAllUsers();
 14     
 15 }

Write another userDao-mapping.xml (you can name it whatever you want):

userDao-mapping.xml:

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 7     
 8       select * from user where id = #{id} 
 9    
 10 
 11 

userDao-mapping.xml相当于是UserDao的实现， 同时也将User实体类与数据表User成功关联起来。

4. 下面编写junit测试代码UserDaoTest：

　UserDaoTest:

 1 public class UserDaoTest { 
 2  
 3     @Test 
 4     public void findUserById() { 
 5         SqlSession sqlSession = getSessionFactory().openSession();  
 6         UserDao userMapper = sqlSession.getMapper(UserDao.class);  
 7         User user = userMapper.findUserById(2);  
 8         Assert.assertNotNull("没找到数据", user); 
 9     }
 10     
 11     //Mybatis 通过SqlSessionFactory获取SqlSession, 然后才能通过SqlSession与数据库进行交互12     private static SqlSessionFactory getSessionFactory() {  
13         SqlSessionFactory sessionFactory = null;  
14         String resource = "configuration.xml";  
15         try {  
16             sessionFactory = new SqlSessionFactoryBuilder().build(Resources  
17                     .getResourceAsReader(resource));
18         } catch (IOException e) {  
19             e.printStackTrace();  
20         }  
21         return sessionFactory;  
22     }  
23     
24 }

好啦，这样一个简单的mybatis 的demo就能成功运行啦。通过这个demo, 应该你就也能初步看出mybatis的运行机制，如果不清楚，也没关系。从下一篇文章开始，才开始正式讲解mybatis。

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