SpringBoot+Mytabis

什么是Mybatis

Mybatis是一款ORM（Object Relational Mapping）对象关系映射框架，其底层封装了jdbc并使用了jdk动态代理，需要一个interface、一个invocationHandler实现类、还有一个SqlSession

jdk动态代理

一、先准备一个接口与实现类

public interface MoveAble {

    public void move();
}

public class Car implements MoveAble{
	public Car(){}

    @Override
    public void move() {
        System.out.println("汽车开始运动");
    }
}

二、准备一个invocationHandler

/**   
 *    
 * JDK动态代理类   
 *    
 *   
 */  
public class JdkProxyHandler implements InvocationHandler {

    private Object target;//动态代理对象

    public Object bindProxy(Object target){//传入目标代理对象
        this.target = target;
        return Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(),this); //返回代理对象
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        System.out.println("jdk动态代理开始-------");
        Object object=method.invoke(target,args);
        System.out.println("jdk动态代理结束-------");
        return object;
    }
}

三、调用jdk动态代理过程

public class Test {
	public static void main(String[] args) {
    MoveAble subject=new Car();
    JdkProxyHandler handler = new JdkProxyHandler();
    MoveAble subjectProxy=(MoveAble) handler.bindProxy(subject);
    subjectProxy.move();
  }
}

cglib动态代理

实现原理是创建一个被代理类的子类，从而实现方法的增强。

一、先实现一个业务类，注意这个类并没有实现接口

public class HelloService {
 
    public HelloService() {
        System.out.println("HelloService构造");
    }
 
    /**
     * 该方法不能被子类覆盖,Cglib是无法代理final修饰的方法的
     */
    final public String sayOthers(String name) {
        System.out.println("HelloService:sayOthers>>"+name);
        return null;
    }
 
    public void sayHello() {
        System.out.println("HelloService:sayHello");
    }
}

二、实现一个MethodInterceptor

/**
 * 自定义MethodInterceptor
 */
public class MyMethodInterceptor implements MethodInterceptor{
	 
	 //被代理对象
	 private Object target;

	 public Object bindProxy(Object target){//传入目标代理对象
        this.target = target;
		// 通过CGLIB动态代理获取代理对象的过程
        Enhancer enhancer = new Enhancer();
        // 设置enhancer对象的父类
        enhancer.setSuperclass(target.getClass());
        // 设置enhancer的回调对象
        enhancer.setCallback(this);
        // 创建代理对象
        return enhancer.create();
    }
 
    /**
     * sub：cglib生成的代理对象
     * method：被代理对象方法
     * objects：方法入参
     * methodProxy: 代理方法
     */
    @Override
    public Object intercept(Object sub, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println("======插入前置通知======");
        Object object = methodProxy.invokeSuper(sub, objects);
        System.out.println("======插入后者通知======");
        return object;
    }
}

三、cglib测试类

  public class Test{
  		public static void main(String[] args){
  			HelloService service = new HelloService();
  			MyMethodInterceptor methodInterceptor = new MyMethodInterceptor();
  			HelloService proxy=(HelloService )methodInterceptor.bindProxy(sevice);
  			proxy.sayHello();
  		}
  }

jdk动态代理这便是Mybatis自动映射器Mapper的底层实现原理。

废话不多说，插曲结束，开始springboot与mybatis的整合

一、引入maven依赖

        <!--mybatis依赖-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.1.1</version>
        </dependency>

        <!-- MySQL连接对象 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>

二、配置application.yml

#数据库连接配置
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://10.212.130.05:3306/xxxDbNm?useUnicode=true&characterEncoding=utf8
spring.datasource.username=xxx
spring.datasource.password=xxx

#pojo扫描包路径
mybatis.type-aliases-package=com.bdcloud.bean
#mybaits配置文件目录
mybatis.mapper-locations=classpath:mapper/*Mapper.xml

三、定义用户bean与Mapper接口

public class User {

    private Integer id;
    private String user_id;
    private String user_name;
}
----------------------------------------------
import com.bdcloud.bean.User;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface UserMapper {
    public List<User> getAllUsers();
}

四、定义UserMapper.xml

<mapper namespace="com.bdcloud.mapper.UserMapper">
    <select id="getAllUsers" resultType="User">
        select * from login_user
    select>
mapper>

五、调用测试

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringbootMybatisApplicationTests {
    
    @Autowired
    UserMapper userMapper;

    @Test
    public void contextLoads() {
        List<User> allUsers = userMapper.getAllUsers();
        System.out.println(allUsers.toString());
    }

}

1.mybatis的核心代理类是MapperProxy代码如下

import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Map;
import org.apache.ibatis.reflection.ExceptionUtil;
import org.apache.ibatis.session.SqlSession;

public class MapperProxy<T> implements InvocationHandler, Serializable {
    private static final long serialVersionUID = -6424540398559729838L;
    private final SqlSession sqlSession;
    private final Class<T> mapperInterface;
    private final Map<Method, MapperMethod> methodCache;

    public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
        this.sqlSession = sqlSession;
        this.mapperInterface = mapperInterface;
        this.methodCache = methodCache;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (Object.class.equals(method.getDeclaringClass())) {
            try {
                return method.invoke(this, args);
            } catch (Throwable var5) {
                throw ExceptionUtil.unwrapThrowable(var5);
            }
        } else {
            MapperMethod mapperMethod = this.cachedMapperMethod(method);
            return mapperMethod.execute(this.sqlSession, args);
        }
    }

    private MapperMethod cachedMapperMethod(Method method) {
        MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method);
        if (mapperMethod == null) {
            mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration());
            this.methodCache.put(method, mapperMethod);
        }

        return mapperMethod;
    }
}

2.mybatis的核心代理工厂类是MapperProxyFactory代码如下

import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.ibatis.session.SqlSession;

public class MapperProxyFactory<T> {
    private final Class<T> mapperInterface;
    private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap();

    public MapperProxyFactory(Class<T> mapperInterface) {
        this.mapperInterface = mapperInterface;
    }

    public Class<T> getMapperInterface() {
        return this.mapperInterface;
    }

    public Map<Method, MapperMethod> getMethodCache() {
        return this.methodCache;
    }

    protected T newInstance(MapperProxy<T> mapperProxy) {
        return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
    }

    public T newInstance(SqlSession sqlSession) {
        MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
        return this.newInstance(mapperProxy);
    }
}

mybatis基础配置初始化以及执行过程

1.读取配置文件sqlMapperConfig.xml生成SqlSessionFactory

配置文件如下

<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="org/mybatis/example/BlogMapper.xml"/>
  mappers>
configuration>

创建sqlSessionFactory的代码如下：

String resource = "mybatis/sqlMapperConfig.xml";//或者路径字符串修改为"classpath:/mybatis/sqlMapperConfig.xml"
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

2.根据SqlSessionFactory对象获取SqlSession,通过调用session.getMapper()方法已经涉及到了上述jdk代理，获取到代理Mapper对象后，执行相应的sql语句并返回

SqlSession session = sqlSessionFactory.openSession();
try {
  BlogMapper mapper = session.getMapper(BlogMapper.class);
  Blog blog = mapper.selectBlog(101);
} finally {
  session.close();
}

3.构建数据返回结果集使用到了ObjectFactory封装返回结果

mybatis创建SqlSessionFactory的时序图

mybatis获取SqlSession的时序图