Explanation
MyBatis Version: 3.5.1
Relevant historical articles ( Before reading this article, you may need to look at before the next series )
Spring Boot MyBatis most complete tutorial: you deserve
MyBatis can do outside of the Spring a diagram of an overview of works MyBatis from source to see MyBatis, is much easier MyBatis Mapper is what the `` garbage
Handwritten MyBatis, hand-built open-source framework (first post: revival)
Handwritten MyBatis, hand-built open-source framework (Second: Harborside)
Handwritten MyBatis, hand-built open-source framework (Title III: strategizing)
Foreword
Devised strategies, winning thousands of miles away, which is to be settled, and you guys can pull out the bayonet.
Previous SqlSession have been able to return results using a query. This one we are joined Swiss Army Knife Mapper.
First, analysis
In getMapper SqlSession provides a method, in DefaultSqlSession use of a Proxy instance MapperProxy agent, the agent obtains the MapperProxy SqlSession, where Sql operation, and then the result.
Second, coding
2.1 MapperProxy
MapperProxy is the core mapper final execution of:
package com.kfit.mybatis.session.impl;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Collection;
import com.kfit.mybatis.session.SqlSession;
public class MapperProxy implements InvocationHandler{
private SqlSession sqlSession;
public MapperProxy(SqlSession sqlSession) {
this.sqlSession = sqlSession;
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String statement = method.getDeclaringClass().getName()+"."+method.getName();
//isAssignableFrom方法是判断是否为某个类的父类
if(Collection.class.isAssignableFrom(method.getReturnType())) {
//返回值是集合的话，那么是调用selectList
return sqlSession.selectList(statement,null==args?null:args[0]);
}else {
return sqlSession.selectOne(statement,null==args?null:args[0]);
}
}
}
说明：
（1）由于MapperProxy是一个代理类，所以需要实现接口InvocationHandler的Invoke方法。
（2）在Invoke方法中直接使用SqlSession进行执行，那么主要的核心就是要判断具体执行什么方法，这里现在通过返回值是否是集合来判断是否是执行selectOne还是SelectList。
2.2 SqlSession
在SqlSession中添加getMapper方法：
public interface SqlSession {
<T> T selectOne(String statement, Object parameter);
<E> List<E> selectList(String statement);
<E> List<E> selectList(String statement, Object parameter);
<T> T getMapper(Class<T> type);
}
在DefaultSqlSession中进行实现getMapper方法：
@SuppressWarnings("unchecked")
public <T> T getMapper(Class<T> type) {
T newProxyInstance = (T) Proxy.newProxyInstance(type.getClassLoader(),new Class[]{type},new MapperProxy(this));
return newProxyInstance;
}
2.3 测试下
好了写段代码测试下吧：
public static void main(String[] args) {
String resource = "mybatis-config.xml";
InputStream inputStream = App.class.getClassLoader().getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
System.out.println(sqlSessionFactory);
System.out.println(sqlSessionFactory.getConfiguration().getJdbcProperties().getUrl());
SqlSession sqlSession = sqlSessionFactory.openSession();
Demo demo = null;
List<Demo> demos = null;
//使用Mapper
DemoMapper demoMapper = sqlSession.getMapper(DemoMapper.class);
demo = demoMapper.getById(1);
System.out.println(demo);
demos = demoMapper.getAll();
System.out.println(demos);
}
运行看下结果：
Demo [id=1,name=张三1]
[Demo [id=1, name=张三1], Demo [id=9, name=张三], Demo [id=10, name=张三], Demo [id=11, name=张三], Demo [id=12, name=张三], Demo [id=13, name=张三]]
很明显执行的结果和直接使用SqlSession调用的结果是一样的。
好了有关手写MyBatis的文章就先到此告一段落了，通过手写mybatis，想必大家对于MyBatis的认知又高了一个等级了。
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