读完源码，手写一个mybatis框架（使用mybatis设计模式和框架，内含手写源码）

public static void main(String[] args)
{

    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build("conf.properties");
    SqlSession session = factory.openSession();

    UserMapper userMapper = session.getMapper(UserMapper.class);
    User user = userMapper.getUser("1");
    System.out.println("******* " + user);
    System.out.println("*******all " + userMapper.getAll());
    
}

public SqlSessionFactory build(InputStream inputStream)
{
    try
    {
        Configuration.PROPS.load(inputStream);

    }
    catch (IOException e)
    {
        e.printStackTrace();
    }
    return new DefaultSqlSessionFactory(new Configuration());
}

public DefaultSqlSessionFactory(Configuration configuration)
{
    this.configuration = configuration;
    loadMappersInfo(Configuration.getProperty(Constant.MAPPER_LOCATION).replaceAll("\\.", "/"));
}

private void loadMappersInfo(String dirName)
{
    //...
    XmlUtil.readMapperXml(file, this.configuration);
    //...
}

/** XmlUtil类 **/
public static void readMapperXml(File fileName, Configuration configuration)
{
    //解析xml步骤省略
    //...
    //设置SQL的唯一ID
    String sqlId = namespace + "." + element.attributeValue(Constant.XML_ELEMENT_ID); 
    
    for (Iterator iterator = rootElement.elementIterator(); iterator.hasNext();)
    {
        //...
        statement.setSqlId(sqlId);
        statement.setNamespace(namespace);
        statement.setSql(CommonUtis.stringTrim(element.getStringValue()));
        statements.add(statement);
    
        System.out.println(statement);
        configuration.addMappedStatement(sqlId, statement);
    
        //这里其实是在MapperRegistry中生产一个mapper对应的代理工厂
        configuration.addMapper(Class.forName(namespace));
    }
}

/** MapperRegistry类 **/
public <T> void addMapper(Class<T> type)
{
    this.knownMappers.put(type, new MapperProxyFactory<T>(type)); //这里生成了代理工厂
}

public SqlSession openSession()
{
    SqlSession session = new DefaultSqlSession(this.configuration);
    return session;
}

public DefaultSqlSession(Configuration configuration)
{
    this.configuration = configuration;
    this.executor = new SimpleExecutor(configuration);

}

public SimpleExecutor(Configuration configuration)
{
    this.conf = configuration;
}

/** DefaultSqlSession类 **/
@Override
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 this.mapperRegistry.getMapper(type, sqlSession);
}

/** MapperRegistry类 **/
public <T> T getMapper(Class<T> type, SqlSession sqlSession)
{
    //前面解析xml做了addMapper操作，这里通过mapper类获取代理工厂
    MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>)this.knownMappers.get(type);
  
    return mapperProxyFactory.newInstance(sqlSession);
}

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

/**
 * 根据mapper代理返回实例
 * 
 * @param mapperProxy
 * @return 代理实例
 */
protected T newInstance(MapperProxy<T> mapperProxy)
{
    return (T)Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[] {this.mapperInterface}, mapperProxy);
}

public class MapperProxy<T> implements InvocationHandler, Serializable
｛
    //...
    public Object invoke(Object proxy, Method method, Object[] args)
    {
        //...
        return  this.execute(method, args);
    }

    private Object execute(Method method,  Object[] args)
    {
        String statementId = this.mapperInterface.getName() + "." + method.getName();
        MappedStatement ms = this.sqlSession.getConfiguration().getMappedStatement(statementId);
        
        Object result = null;
        switch (ms.getSqlCommandType())
        {
            case SELECT:
            {
                Class<?> returnType = method.getReturnType();
                
                // 如果返回的是list，应该调用查询多个结果的方法，否则只要查单条记录
                if (Collection.class.isAssignableFrom(returnType))
                {
                    //ID为mapper类全名+方法名
                    result = sqlSession.selectList(statementId, args);
                }
                else
                {
                    result = sqlSession.selectOne(statementId, args);
                }
                break;
            }
            //...
        }   
        return result;
    }
}

/**  DefaultSqlSession类 **/
public <T> T selectOne(String statementId, Object parameter)
{
    //这里跟源码保持一致，源码也是调用selectList，返回第一个结果的
    List<T> results = this.<T> selectList(statementId, parameter);
    return CommonUtis.isNotEmpty(results) ? results.get(0) : null;
}

public <E> List<E> selectList(String statementId, Object parameter)
{
    MappedStatement mappedStatement = this.configuration.getMappedStatement(statementId);
    return this.executor.<E> doQuery(mappedStatement, parameter); //调用执行器
}

/** SimpleExecutor类 **/
public <E> List<E> doQuery(MappedStatement ms, Object parameter)
{
    try
    {
        //1.获取数据库连接
        Connection connection = getConnect();
        
        //2.获取MappedStatement信息，里面有sql信息
        MappedStatement mappedStatement = conf.getMappedStatement(ms.getSqlId());
        
        //3.实例化StatementHandler对象，
        StatementHandler statementHandler = new SimpleStatementHandler(mappedStatement);
        
        //4.通过StatementHandler和connection获取PreparedStatement
        PreparedStatement preparedStatement = statementHandler.prepare(connection);
        
        //5.实例化ParameterHandler，将SQL语句中？参数化
        ParameterHandler parameterHandler = new DefaultParameterHandler(parameter);
        parameterHandler.setParameters(preparedStatement);
        
        //6.执行SQL，得到结果集ResultSet
        ResultSet resultSet = statementHandler.query(preparedStatement);
        
        //7.实例化ResultSetHandler，通过反射将ResultSet中结果设置到目标resultType对象中
        ResultSetHandler resultSetHandler = new DefaultResultSetHandler(mappedStatement);
        return resultSetHandler.handleResultSets(resultSet);
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    return null;
}