1.注册Mapper接口

代码分支：01-regist-mapper

Mapper注册由MapperRegistry类实现，该类中用一个Map存储了mybatis中所有注册的Mapper，key为Mapper的接口，value为MapperProxyFactory的代理工厂类，核心代码如下

public class MapperRegistry {

    private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();

    public <T> void addMapper(Class<T> type) {
        knownMappers.put(type, new MapperProxyFactory<>(type));
    }

    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        MapperProxyFactory<?> mapperProxyFactory = knownMappers.get(type);
        if (Objects.isNull(mapperProxyFactory)) {
            throw new BindingException(type + " type is not exist");
        }
        return mapperProxyFactory.newInstance(sqlSession);
    }
}

单元测试：

public class MapperRegistryTest {

    @Test
    public void test() {
        Configuration configuration = new Configuration();
        configuration.addMapper(UserMapper.class);
        SqlSession sqlSession = new DefaultSqlSession(configuration);
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        Assert.assertNotNull(userMapper);
    }
}