Mybatis简介

Mybatis的前身是iBatis，iBatis原本就是apache的一个开源项目，2010年该项目有apache迁移到了google code，并改名为MyBatis。

1. 简介

MyBatis支持普通SQL查询，存储过程和高级映射的优秀持久层框架，消除了几乎所有的JDBC代码和参数的手动设置以及结果集的检索。MyBatis可以使用XML或者注解用于配置和映射，将接口和JavaBean映射成数据库的记录。

每一个MyBatis的应用程序都以一个SqlSessionFactory对象的实例为核心。SqlSessionFactory对象的实例可以通过SqlSessionFactoryBuilder对象来获得，SqlSessionFactoryBuilder对象可以从XML配置文件或从Configuration类获得。例如：

String resource ="com/alvinliang/mybatis/mybatis-config.xml";
InputStreamis= Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory =newSqlSessionFactoryBuilder().build(is);

XML配置文件包含了对MyBatis系统的核心设置，有获取数据库连接实例的数据源和决定事务范围和控制事务管理器。详细内容后面会讲，这里给出一个简单示例：

还有很多可以配置，上面指出了最关键的部分。environment元素体里包含对事务管理和连接池的环境配置。mapppers元素包含了所有mapper映射器，这些mapper的xml文件包含了SQL代码和映射定义信息。
详细配置，见Mybatis官网

2.总体流程

（1） 加载配置并初始化

触发条件：加载配置文件，将SQL配置文件加载成一个个MappedStatement对象。
关于MappedStatement是Mybatis的几个重要类，详细见

（2） 接受调用请求

触发条件：调用MyBatis提供的API

传入参数：为SQL的ID和传入参数对象

处理过程：将请求传递给下层的请求的处理层进行处理。

（3） 处理操作请求

触发条件：API接口层传递请求过来

传入参数：为SQL的ID和传入参数对象

处理过程：

(A)根据SQL的ID查找对应的MappedStatement对象。

(B)根据传入参数对象解析MappedStatement对象，得到最终要执行的SQL和执行传入参数。

(C)获取数据库连接，根据得到的最终SQL语句和执行传入参数到数据库执行，并得到执行结果。

(D)根据MappedStatement对象中的结果映射配置对得到的执行结果进行转换处理，并得到最终的处理结果。

(E)释放连接资源。

（4）返回处理结果将最终的处理结果返回。

3.功能框架

Mybatis可以分为三层：

（1） API接口层：提供给外部使用的接口API，开发人员可以通过本地API来操纵数据库。

（2） 数据处理层：负责具体的SQL查找、SQL解析、SQL执行和执行结果映射处理等。

（3） 基础支持层：负责最基本的功能支撑，包括连接管理、事务管理、配置加载和缓存处理等。

4.简单使用

先从SqlSessionFactory对象来获得SqlSession的实例，SqlSession对象包含了对数据库的所有执行SQL操作的方法。例如：

SqlSession session = sqlSessionFactory.openSession();
try {  
Blogblog = (Blog) session.selectOne("com.alvinliang.mybatis.BlogMapper.selectBlog", 1);
} finally {  
session.close();
}

下面给出映射的SQL语句：

  
    select * from Blog where id = #{id}
  

这里只是给出了一个简洁的例子，其中在命名空间“com.alvinliang.mybatis.BlogMapper”中定义了一个名为“selectBlog”的映射语句，这样它允许你使用完全限定名“com.alvinliang.mybatis.BlogMapper.selectBlog”来调用映射语句。

注意：现在命名空间是必须的，而且命名空间使得接口绑定成为可能，使用命名空间并将它放在合适的Java包空间下，将会使你的代码变得简洁，会在很长的时间内提高MyBatis的作用。

5. 范围和生命周期

SqlSessionFactoryBuilder

这个类可以被实例化，使用和丢弃。一旦你创建了SqlSessionFactory后，这个类就不需要了。因此SqlSessionFactoryBuilder实例的最佳范围就是方法范围（也就是本地方法变量）。你可以重用SqlSessionFactoryBuilder来创建多个SqlSessionFactory实例。

SqlSessionFactory

一旦被创建，SqlSessionFactory应该在你的应用执行期间都存在，没有理来处理或者重新创建它。使用SqlSessionFactory的最佳实践是在应用运行期间不要重复创建多次。因此SqlSessionFactory的生命周期是Application范围。很多方法可以做到，如单例模式或者静态单例模式。

SqlSession

每个线程都应该有它自己的SqlSession实例。SqlSession的实例不能被共享，也是线程不安全的。因此最佳范围应该是request或者method范围。绝对不能将SqlSession实例的引用放在一个类的静态字段甚至是实例字段中。也绝对不能将SqlSession实例引用放在任何类型的管理范围中，比如Servlet中的HttpSession。如果你正在使用Web框架，可以考虑将SqlSession放在一个和Http Request对象相似的范围内。下面的示例就是一个确保SqlSession关闭的基本模式：

SqlSession session = sqlSessionFactory.openSession();
try {
// do work
} finally {  
session.close();
}

在你的代码中一贯的使用这种模式，将会保证所有的数据库资源都正常的关闭。

完整的Example

**Step1: **Create a Maven project and configure MyBatis dependencies.

 4.0.0

 com.sivalabs
 mybatis-demo
 0.0.1-SNAPSHOT
 jar

 mybatis-demo
 http://maven.apache.org

 
  UTF-8
 

 
  
   
    org.apache.maven.plugins
    maven-compiler-plugin
    2.3.2
    
     1.6
     1.6
     ${project.build.sourceEncoding}
    
   
  
 

 
  
   junit
   junit
   4.10
   test
  

  
      org.mybatis
      mybatis
      3.1.1
  
  
             mysql
             mysql-connector-java
             5.1.21
             runtime
         
 

Step#2: Create the table USER and a Java domain Object User as follows:

CREATE TABLE  user (
  user_id int(10) unsigned NOT NULL auto_increment,
  email_id varchar(45) NOT NULL,
  password varchar(45) NOT NULL,
  first_name varchar(45) NOT NULL,
  last_name varchar(45) default NULL,
  PRIMARY KEY  (user_id),
  UNIQUE KEY Index_2_email_uniq (email_id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

package com.sivalabs.mybatisdemo.domain;
public class User 
{
 private Integer userId;
 private String emailId;
 private String password;
 private String firstName;
 private String lastName;

 @Override
 public String toString() {
  return 'User [userId=' + userId + ', emailId=' + emailId
    + ', password=' + password + ', firstName=' + firstName
    + ', lastName=' + lastName + ']';
 }
 //setters and getters 
}

Step#3: Create MyBatis configuration files.
a) Create jdbc.properties file in src/main/resources folder

jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis-demo
jdbc.username=root
jdbc.password=admin

b) Create mybatis-config.xml file in src/main/resources folder

Step#4: Create an interface UserMapper.java in src/main/java folder in com.sivalabs.mybatisdemo.mappers package.

package com.sivalabs.mybatisdemo.mappers;

import java.util.List;
import com.sivalabs.mybatisdemo.domain.User;

public interface UserMapper 
{

 public void insertUser(User user);

 public User getUserById(Integer userId);

 public List getAllUsers();

 public void updateUser(User user);

 public void deleteUser(Integer userId);

}

Step#5: Create UserMapper.xml file in src/main/resources folder in com.sivalabs.mybatisdemo.mappers package.

  
     SELECT 
      user_id as userId, 
      email_id as emailId , 
      password, 
      first_name as firstName, 
      last_name as lastName
     FROM USER 
     WHERE USER_ID = #{userId}
  
  
   
    
    
    
    
       
   

  
   SELECT * FROM USER
  

  
   INSERT INTO USER(email_id, password, first_name, last_name)
    VALUES(#{emailId}, #{password}, #{firstName}, #{lastName})
  

  
    UPDATE USER 
    SET
     PASSWORD= #{password},
     FIRST_NAME = #{firstName},
     LAST_NAME = #{lastName}
    WHERE USER_ID = #{userId}
  

  
    DELETE FROM USER WHERE USER_ID = #{userId}
  

Step#6: Create MyBatisUtil.java to instantiate SqlSessionFactory.

package com.sivalabs.mybatisdemo.service;

import java.io.IOException;
import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class MyBatisUtil 
{
 private static SqlSessionFactory factory;

 private MyBatisUtil() {
 }

 static
 {
  Reader reader = null;
  try {
   reader = Resources.getResourceAsReader('mybatis-config.xml');
  } catch (IOException e) {
   throw new RuntimeException(e.getMessage());
  }
  factory = new SqlSessionFactoryBuilder().build(reader);
 }

 public static SqlSessionFactory getSqlSessionFactory() 
 {
  return factory;
 }
}

Step#7: Create UserService.java in src/main/java folder.

package com.sivalabs.mybatisdemo.service;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import com.sivalabs.mybatisdemo.domain.User;
import com.sivalabs.mybatisdemo.mappers.UserMapper;

public class UserService
{

 public void insertUser(User user) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  userMapper.insertUser(user);
  sqlSession.commit();
  }finally{
   sqlSession.close();
  }
 }

 public User getUserById(Integer userId) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  return userMapper.getUserById(userId);
  }finally{
   sqlSession.close();
  }
 }

 public List getAllUsers() {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  return userMapper.getAllUsers();
  }finally{
   sqlSession.close();
  }
 }

 public void updateUser(User user) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  userMapper.updateUser(user);
  sqlSession.commit();
  }finally{
   sqlSession.close();
  }

 }

 public void deleteUser(Integer userId) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  userMapper.deleteUser(userId);
  sqlSession.commit();
  }finally{
   sqlSession.close();
  }

 }

}

Step#8: Create a JUnit Test class to test UserService methods.

package com.sivalabs.mybatisdemo;

import java.util.List;

import org.junit.AfterClass;
import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;

import com.sivalabs.mybatisdemo.domain.User;
import com.sivalabs.mybatisdemo.service.UserService;

public class UserServiceTest 
{
 private static UserService userService;

 @BeforeClass
    public static void setup() 
 {
  userService = new UserService();
 }

 @AfterClass
    public static void teardown() 
 {
  userService = null;
 }

    @Test
 public void testGetUserById() 
 {
  User user = userService.getUserById(1);
  Assert.assertNotNull(user);
  System.out.println(user);
 }

    @Test
    public void testGetAllUsers() 
    {
  List users = userService.getAllUsers();
  Assert.assertNotNull(users);
  for (User user : users) 
  {
   System.out.println(user);
  }

 }

    @Test
    public void testInsertUser() 
    {
     User user = new User();
     user.setEmailId('test_email_'+System.currentTimeMillis()+'@gmail.com');
     user.setPassword('secret');
     user.setFirstName('TestFirstName');
     user.setLastName('TestLastName');

     userService.insertUser(user);
  Assert.assertTrue(user.getUserId() != 0);
  User createdUser = userService.getUserById(user.getUserId());
  Assert.assertNotNull(createdUser);
  Assert.assertEquals(user.getEmailId(), createdUser.getEmailId());
  Assert.assertEquals(user.getPassword(), createdUser.getPassword());
  Assert.assertEquals(user.getFirstName(), createdUser.getFirstName());
  Assert.assertEquals(user.getLastName(), createdUser.getLastName());

 }

    @Test
    public void testUpdateUser() 
    {
     long timestamp = System.currentTimeMillis();
  User user = userService.getUserById(2);
  user.setFirstName('TestFirstName'+timestamp);
     user.setLastName('TestLastName'+timestamp);
     userService.updateUser(user);
  User updatedUser = userService.getUserById(2);
  Assert.assertEquals(user.getFirstName(), updatedUser.getFirstName());
  Assert.assertEquals(user.getLastName(), updatedUser.getLastName());
 }

   @Test
   public void testDeleteUser() 
   {
     User user = userService.getUserById(4);
     userService.deleteUser(user.getUserId());
  User deletedUser = userService.getUserById(4);
  Assert.assertNull(deletedUser);   

 }
}

Now, I will explain how to perform CRUD operations using MyBatis Annotation support without need of Queries configuration in XML mapper files.

Step#1: Create a table BLOG and a java domain Object Blog.

CREATE TABLE  blog (
  blog_id int(10) unsigned NOT NULL auto_increment,
  blog_name varchar(45) NOT NULL,
  created_on datetime NOT NULL,
  PRIMARY KEY  (blog_id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

package com.sivalabs.mybatisdemo.domain;

import java.util.Date;

public class Blog {

 private Integer blogId;
 private String blogName;
 private Date createdOn;

 @Override
 public String toString() {
  return 'Blog [blogId=' + blogId + ', blogName=' + blogName
    + ', createdOn=' + createdOn + ']';
 }
 //Seeters and getters
}

Step#2: Create UserMapper.java interface with SQL queries in Annotations.

package com.sivalabs.mybatisdemo.mappers;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Options;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.sivalabs.mybatisdemo.domain.Blog;

public interface BlogMapper 
{
 @Insert('INSERT INTO BLOG(BLOG_NAME, CREATED_ON) VALUES(#{blogName}, #{createdOn})')
 @Options(useGeneratedKeys=true, keyProperty='blogId')
 public void insertBlog(Blog blog);

 @Select('SELECT BLOG_ID AS blogId, BLOG_NAME as blogName, CREATED_ON as createdOn FROM BLOG WHERE BLOG_ID=#{blogId}')
 public Blog getBlogById(Integer blogId);

 @Select('SELECT * FROM BLOG ')
 @Results({
  @Result(id=true, property='blogId', column='BLOG_ID'),
  @Result(property='blogName', column='BLOG_NAME'),
  @Result(property='createdOn', column='CREATED_ON')  
 })
 public List getAllBlogs();

 @Update('UPDATE BLOG SET BLOG_NAME=#{blogName}, CREATED_ON=#{createdOn} WHERE BLOG_ID=#{blogId}')
 public void updateBlog(Blog blog);

 @Delete('DELETE FROM BLOG WHERE BLOG_ID=#{blogId}')
 public void deleteBlog(Integer blogId);

}

Step#3: Configure BlogMapper in mybatis-config.xml

Step#4: Create BlogService.java

package com.sivalabs.mybatisdemo.service;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.sivalabs.mybatisdemo.domain.Blog;
import com.sivalabs.mybatisdemo.mappers.BlogMapper;

public class BlogService
{

 public void insertBlog(Blog blog) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
  blogMapper.insertBlog(blog);
  sqlSession.commit();
  }finally{
   sqlSession.close();
  }
 }

 public Blog getBlogById(Integer blogId) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
  return blogMapper.getBlogById(blogId);
  }finally{
   sqlSession.close();
  }
 }

 public List getAllBlogs() {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
  return blogMapper.getAllBlogs();
  }finally{
   sqlSession.close();
  }
 }

 public void updateBlog(Blog blog) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
  blogMapper.updateBlog(blog);
  sqlSession.commit();
  }finally{
   sqlSession.close();
  }  
 }

 public void deleteBlog(Integer blogId) {
  SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
  try{
  BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
  blogMapper.deleteBlog(blogId);
  sqlSession.commit();
  }finally{
   sqlSession.close();
  }

 }

}

Step#5: Create JUnit Test for BlogService methods

package com.sivalabs.mybatisdemo;

import java.util.Date;
import java.util.List;

import org.junit.AfterClass;
import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;

import com.sivalabs.mybatisdemo.domain.Blog;
import com.sivalabs.mybatisdemo.service.BlogService;

public class BlogServiceTest 
{
 private static BlogService blogService;

 @BeforeClass
    public static void setup() 
 {
  blogService = new BlogService();
 }

 @AfterClass
    public static void teardown() 
 {
  blogService = null;
 }

    @Test
 public void testGetBlogById() 
 {
  Blog blog = blogService.getBlogById(1);
  Assert.assertNotNull(blog);
  System.out.println(blog);
 }

    @Test
    public void testGetAllBlogs() 
    {
  List blogs = blogService.getAllBlogs();
  Assert.assertNotNull(blogs);
  for (Blog blog : blogs) 
  {
   System.out.println(blog);
  }

 }

    @Test
    public void testInsertBlog() 
    {
     Blog blog = new Blog();
     blog.setBlogName('test_blog_'+System.currentTimeMillis());
     blog.setCreatedOn(new Date());

     blogService.insertBlog(blog);
  Assert.assertTrue(blog.getBlogId() != 0);
  Blog createdBlog = blogService.getBlogById(blog.getBlogId());
  Assert.assertNotNull(createdBlog);
  Assert.assertEquals(blog.getBlogName(), createdBlog.getBlogName());

 }

    @Test
    public void testUpdateBlog() 
    {
     long timestamp = System.currentTimeMillis();
  Blog blog = blogService.getBlogById(2);
  blog.setBlogName('TestBlogName'+timestamp);
     blogService.updateBlog(blog);
  Blog updatedBlog = blogService.getBlogById(2);
  Assert.assertEquals(blog.getBlogName(), updatedBlog.getBlogName());
 }

   @Test
   public void testDeleteBlog() 
   {
     Blog blog = blogService.getBlogById(4);
     blogService.deleteBlog(blog.getBlogId());
  Blog deletedBlog = blogService.getBlogById(4);
  Assert.assertNull(deletedBlog);
 }
}