git程式碼地址：https://gitee.com/lv_guoliang/mybatis

實現思路：

　　使用端：

　　提供核心配置檔案

sqlMapConfig.xml: 存放資料來源資訊， 引入mapper.xml

　　Mapper.xml: sql語句的配置檔案資訊

　　框架端：

　　1. 讀取配置檔案

　　讀取完以後以流的形式存在，我們不能將讀取到的配置資訊以流的形式存放在記憶體中，建立javaBean來儲存

　　(1) Configuration: 存放資料庫基本資訊、Map<唯一標識， Mapper>: namespace+"."+id

　　(2)MappedSatement: sql語句、statement型別、輸入引數java型別、輸出引數java型別

　　2.解析配置檔案

　　建立SqlSessionFactoryBuilder類：

　　方法：SqlSessionFactoryBuild():

　　第一：使用dom4j解析配置檔案，將解析出來的內容封裝到Configuration和MappedStatement中

　　第二：建立SqlSessionFactory的實現類DefaultSQLSession

　　3.建立SqlSessionFactory

　　方法：openSession(): 獲取sqlSession介面的實現類例項物件

　　4.建立SqlSession介面及實現類：主要封裝CRUD方法

核心程式碼

測試類呼叫方法

 InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");
 SqlSessionFactory sqlSessionFactory 
 
= new SqlSessionFactoryBuilder().build(inputStream);
 ISqlSession sqlSession = sqlSessionFactory.openSession();
 userDao = sqlSession.getMapper(IUserDao.class);

 User user = new User();
 user.setId(4);
 user.setUsername("gxy");
 user.setPassword("111111");
 user.setBirthday("1990-01-01");
 int result = userDao.addUser(user);
 System.out.println("新增sql成功：" + result);

獲取配置檔案，構建Configuration物件

public class SqlSessionFactoryBuilder {

    public SqlSessionFactory build(InputStream in) throws PropertyVetoException, DocumentException {
        //第一；使用dom4j解析配置檔案， 將解析出來的內容封裝到Configuration中
        XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();
        Configuration configuration = xmlConfigBuilder.parseConfig(in);

        //第二： 建立sql
        IDefaultSqlSessionFactory defautlSqlSessionFactory = new IDefaultSqlSessionFactory(configuration);
        return  defautlSqlSessionFactory;
    }
}

獲取代理物件，生成查詢，更新方法

public class DefaultSqlSession implements ISqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用JDK動態代理來為Dao介面生成代理物件，並返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[] {mapperClass
        }, new InvocationHandler() {
            //底層還是去執行JDBC程式碼
            //準備引數1.statementId
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String statementId = className + "." + methodName;
                Type genericReturnType = method.getGenericReturnType();

                /* 返回型別是否是集合 */
                if (genericReturnType instanceof  ParameterizedType) {
                    List<Object> objects = selectList(statementId, args);
                    return  objects;
                } else {
                    Class<?> returnType = method.getReturnType();
                    String type = returnType.getTypeName();
                    if (type.equals("int")) {
                        return update(statementId, args);
                    } else {
                        Object object = selectOne(statementId, args);
                        return object;
                    }
                }
            }
        });

        return (T) proxyInstance;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws InvocationTargetException, SQLException, InstantiationException, IllegalAccessException, NoSuchFieldException, IntrospectionException, ClassNotFoundException {
        //將要去完成對simpleExcutor裡的query方法的呼叫
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> queryList = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) queryList;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws SQLException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchFieldException, IntrospectionException, ClassNotFoundException {
        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else  {
            throw new RuntimeException("查詢結果為空或者返回結果更多");
        }

    }

    @Override
    public int update(String statementId, Object... params) throws ClassNotFoundException, SQLException, NoSuchFieldException, IllegalAccessException {
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }
}

具體實現更新，查詢方法

public class simpleExecutor implements IExecutor {

    private PreparedStatement getParamsPreparedStatement(Configuration configuration, MappedStatement mappedStatement, Object... params) throws SQLException, ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        // 1. 註冊驅動，獲取連結
        Connection connection = configuration.getDataSource().getConnection();

        // 2. 獲取sql語句
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        // 3.獲取預處理物件
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4. 設定引數
        String paramterType = mappedStatement.getParamterType();
        Class<?> paramtertypeClass = getClassType(paramterType);
        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();

            //反射
            Field declaredField = paramtertypeClass.getDeclaredField(content);
            //暴力訪問
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);

            preparedStatement.setObject(i + 1, o);
        }

        return preparedStatement;
    }

    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws SQLException, IllegalAccessException, InstantiationException, InvocationTargetException, NoSuchFieldException, IntrospectionException, ClassNotFoundException {

        PreparedStatement preparedStatement = this.getParamsPreparedStatement(configuration, mappedStatement, params);
        // 5. 執行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);

        ArrayList<Object> objects = new ArrayList<>();
        // 6. 封裝返回結果集
        while (resultSet.next()) {
            Object o = resultTypeClass.newInstance();
            //元資料
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i < metaData.getColumnCount() ; i++) {
                //獲取欄位名
                String columnName = metaData.getColumnName(i);
                Object value = resultSet.getObject(columnName);
                //使用反射或者內省，根據資料庫表和實體的對應關係，完成封裝
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(o, value);
            }

            objects.add(o);
        }

        return (List<E>) objects;
    }

    @Override
    public int update(Configuration configuration, MappedStatement mappedStatement, Object... params) throws ClassNotFoundException, SQLException, IllegalAccessException, NoSuchFieldException {

        PreparedStatement preparedStatement = this.getParamsPreparedStatement(configuration, mappedStatement, params);
        //執行sql
        int i = preparedStatement.executeUpdate();
        return i;
    }

    private Class<?> getClassType(String paramterType) throws ClassNotFoundException {
        if (paramterType != null) {
            Class<?> aClass = Class.forName(paramterType);
            return aClass;
        }

        return null;
    }

    /**
     * 完成#{}的解析工作 1，將#{}解析成?,  2.解析出#{}的值進行儲存
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        //標記處理類：配置標記解析器來完成對佔位符的解析處理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);

        //解析出來的sql
        String parseSql = genericTokenParser.parse(sql);

        //#{}解析出來的引數名稱
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(parseSql, parameterMappings);

        return boundSql;
    }
}