自定义MyBatis框架，实现一些简单的基础功能

git代码地址：https://gitee.com/lv_guoliang/mybatis

实现思路：

　　使用端：

　　提供核心配置文件

      sqlMapConfig.xml: 存放数据源信息， 引入mapper.xml

　　Mapper.xml:   sql语句的配置文件信息

　　框架端：

　　1. 读取配置文件

　　读取完以后以流的形式存在，我们不能将读取到的配置信息以流的形式存放在内存中，创建javaBean来存储

　　(1) Configuration: 存放数据库基本信息、Map<唯一标识， Mapper>: namespace+"."+id

　　(2)MappedSatement: sql语句、statement类型、输入参数java类型、输出参数java类型

 

　　2.解析配置文件

　　创建SqlSessionFactoryBuilder类：

　　方法：SqlSessionFactoryBuild():

　　第一：使用dom4j解析配置文件，将解析出来的内容封装到Configuration和MappedStatement中

　　第二：创建SqlSessionFactory的实现类DefaultSQLSession

 

　　3.创建SqlSessionFactory

　　方法：openSession(): 获取sqlSession接口的实现类实例对象

 

　　4.创建SqlSession接口及实现类：主要封装CRUD方法

核心代码

测试类调用方法

 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("添加sql成功：" + result);

 

获取配置文件，构建Configuration对象

public class SqlSessionFactoryBuilder {

    public SqlSessionFactory build(InputStream in) throws PropertyVetoException, DocumentException {
        //第一；使用dom4j解析配置文件， 将解析出来的内容封装到Configuration中
        XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();
        Configuration configuration = xmlConfigBuilder.parseConfig(in);

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

 

获取代理对象，生成查询，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动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[] {mapperClass
        }, new InvocationHandler() {
            //底层还是去执行JDBC代码
            //准备参数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();

                /* 返回类型是否是集合 */
                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 {
        //将要去完成对simpleExcutor里的query方法的调用
        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("查询结果为空或者返回结果更多");
        }

    }

    @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);
    }
}

 

具体实现更新，查询方法 

public class simpleExecutor implements IExecutor {

    private PreparedStatement getParamsPreparedStatement(Configuration configuration, MappedStatement mappedStatement, Object... params) throws SQLException, ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        // 1. 注册驱动，获取链接
        Connection connection = configuration.getDataSource().getConnection();

        // 2. 获取sql语句
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        // 3.获取预处理对象
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4. 设置参数
        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);
            //暴力访问
            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. 执行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);

        ArrayList<Object> objects = new ArrayList<>();
        // 6. 封装返回结果集
        while (resultSet.next()) {
            Object o = resultTypeClass.newInstance();
            //元数据
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i < metaData.getColumnCount() ; i++) {
                //获取字段名
                String columnName = metaData.getColumnName(i);
                Object value = resultSet.getObject(columnName);
                //使用反射或者内省，根据数据库表和实体的对应关系，完成封装
                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);
        //执行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，将#{}解析成?,  2.解析出#{}的值进行存储
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        //标记处理类：配置标记解析器来完成对占位符的解析处理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);

        //解析出来的sql
        String parseSql = genericTokenParser.parse(sql);

        //#{}解析出来的参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(parseSql, parameterMappings);

        return boundSql;
    }
}