<1>SqlMapConfig.xml：mysql全局配置文件,配置了数据源，事务，运行环境等信息

      mapper.xml:配置映射文件,sql语句

<2>SqlSessionFactory:会话工厂，用于创建SqlSession(会话)，(通过执行器executor)用于操作数据库，底层

通过mapped statement对数据库存储封装，包括sql语句，输入参数,输出结果类型

·Executor:基本执行器和缓存执行器

<3>paramaterType,resultType

    #{}：代表一个占位符,接受简单类型，可以为任意

   ${}：sql串，拼接符，接受简单类型只能写成${value},

    selectOne与selectList

<4>自增主键的返回:

属性说明:

keyProperty:将查询到的主键值设置到paramterType指定对象的属性中

order:   select LAST_INSERT_ID()相对于insert语句的执行顺序

resultType：指定select LAST_INSERT_ID()查询的结果类型

<selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">

   select LAST_INSERT_ID()

</selectKey>

insert语句中不需要写id字段

<5>非自增主键的返回(uuid())

<selectKey keyProperty="id" order="BEFORE" resultType="java.lang.String">

   select uuid()

</selectKey>

insert语句中必须写id字段

<6>mapper接口开发规范:

   1.mapper.xml中namespace等于mapper接口地址(全路径)

   2.mapper.java中的接口方法名和xml中的statement的id一致

   3.输入参数类型和输出参数类型一致

代理对象的获取:UserMapper mapper=sqlSession.getMapper(UserMapper.class);

mapper调用selectOne或者selectList是根据接口的返回类型来确定的

<7>源码解析:

DefaultSqlSession类：

 public <T> T getMapper(Class<T> type) {
    return configuration.<T>getMapper(type, this);
  }

 Configuration类：

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
 }
MapperRegistry类：

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}

MapperProxyFactory类:

public class MapperProxyFactory<T> {

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

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

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

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

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

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

}