Mybatis简介
2017-06-28 本文已影响0人
默默无痕
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。
- 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：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/alvinliang/mybatis/BlogMapper.xml"/>
</mappers>
</configuration>
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：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.alvinliang.mybatis.BlogMapper">
<select id="selectBlog" resultType="Blog">
select * from Blog where id = #{id}
</select>
</mapper>
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。
- 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.
<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/xsd/maven-4.0.0.xsd'>
<modelVersion>4.0.0</modelVersion>
<groupId>com.sivalabs</groupId>
<artifactId>mybatis-demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>mybatis-demo</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.1.1</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.21</version>
<scope>runtime</scope>
</dependency>
</dependencies>
</project>
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
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE configuration
PUBLIC '-//mybatis.org//DTD Config 3.0//EN'
'http://mybatis.org/dtd/mybatis-3-config.dtd'>
<configuration>
<properties resource='jdbc.properties'/>
<typeAliases>
<typeAlias type='com.sivalabs.mybatisdemo.domain.User' alias='User'></typeAlias>
</typeAliases>
<environments default='development'>
<environment id='development'>
<transactionManager type='JDBC'/>
<dataSource type='POOLED'>
<property name='driver' value='${jdbc.driverClassName}'/>
<property name='url' value='${jdbc.url}'/>
<property name='username' value='${jdbc.username}'/>
<property name='password' value='${jdbc.password}'/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource='com/sivalabs/mybatisdemo/mappers/UserMapper.xml'/>
</mappers>
</configuration>
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<User> 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.
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE mapper PUBLIC '-//mybatis.org//DTD Mapper 3.0//EN'
'http://mybatis.org/dtd/mybatis-3-mapper.dtd'>
<mapper namespace='com.sivalabs.mybatisdemo.mappers.UserMapper'>
<select id='getUserById' parameterType='int' resultType='com.sivalabs.mybatisdemo.domain.User'>
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>
<!-- Instead of referencing Fully Qualified Class Names we can register Aliases in mybatis-config.xml and use Alias names. -->
<resultMap type='User' id='UserResult'>
<id property='userId' column='user_id'/>
<result property='emailId' column='email_id'/>
<result property='password' column='password'/>
<result property='firstName' column='first_name'/>
<result property='lastName' column='last_name'/>
</resultMap>
<select id='getAllUsers' resultMap='UserResult'>
SELECT * FROM USER
</select>
<insert id='insertUser' parameterType='User' useGeneratedKeys='true' keyProperty='userId'>
INSERT INTO USER(email_id, password, first_name, last_name)
VALUES(#{emailId}, #{password}, #{firstName}, #{lastName})
</insert>
<update id='updateUser' parameterType='User'>
UPDATE USER
SET
PASSWORD= #{password},
FIRST_NAME = #{firstName},
LAST_NAME = #{lastName}
WHERE USER_ID = #{userId}
</update>
<delete id='deleteUser' parameterType='int'>
DELETE FROM USER WHERE USER_ID = #{userId}
</delete>
</mapper>
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<User> 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<User> 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<Blog> 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
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE configuration
PUBLIC '-//mybatis.org//DTD Config 3.0//EN'
'http://mybatis.org/dtd/mybatis-3-config.dtd'>
<configuration>
<properties resource='jdbc.properties'/>
<environments default='development'>
<environment id='development'>
<transactionManager type='JDBC'/>
<dataSource type='POOLED'>
<!-- <property name='driver' value='com.mysql.jdbc.Driver'/>
<property name='url' value='jdbc:mysql://localhost:3306/mybatis-demo'/>
<property name='username' value='root'/>
<property name='password' value='admin'/> -->
<property name='driver' value='${jdbc.driverClassName}'/>
<property name='url' value='${jdbc.url}'/>
<property name='username' value='${jdbc.username}'/>
<property name='password' value='${jdbc.password}'/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper class='com.sivalabs.mybatisdemo.mappers.BlogMapper'/>
</mappers>
</configuration>
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<Blog> 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<Blog> 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);
}
}
